Lightning and surge protection basics & Guide to surge protective devices (SPD)
We are a family company from Liushi, Wenzhou, China. Since 2010 we focus our efforts specializing in the development and production of AC & DC surge protective devices (SPDs). We offer a complete range of T1, T1+T2, T2, T3 surge protective devices (SPD) for low-voltage power systems according to EN 61643-11:2012 & IEC 61643-11:2011, T1+T2, T2 surge protection devices (SPD) for PV solar system according to EN 50539-11:2013 & IEC 61643-31:2018, PoE surge protector and signal surge protector according to EN/IEC 61643-21, LED lights surge protective device.
Our products provide protection against atmospheric and technological overvoltage and ensure safe and trouble-free operation of technological equipment, machinery and electrical appliances in the industry, transport, telecommunications, data centers, oil pipelines, gas pipelines, photovoltaics, power stations and railways office buildings as well as households.
We have our own research & development, production, technical support and testing laboratory as well. and have been supplying surge protection devices (SPD) over the world for more than 10 years.
We do not pretend that we can do everything, but if you ask questions about applications or the choice of proper surge protection, our team of skilled technicians will be happy to answer your questions and find the ideal solution for you.
We strive to serve our customers with highest quality products and services.
LSP’s values are pure and simple.
- SAFETY: our ambition and goal is to provide products that protect people, their property and their working environment.
- QUALITY: only through the quality & reliability of our products we can meet our promise.
- INNOVATION: continuous further development is the heartbeat of LSP. Cutting-edge products are the answer to our customers needs.
By means of these values, we at LSP want to keep track with the market, today and tomorrow.
Lightning and surge protection basics
We don’t just want to support you with excellent solutions, but also to be on hand with help and advice. This includes basic information about engineering and electronics topics. This brochure provides you with an overview of lightning and surge protection for electrical systems. Discover the most important facts in a nutshell. Have a look at the solutions available for the diverse challenges facing this sector. Or deepen your knowledge of the interrelationships and background; something only the specialists know.
We wish you – in the truest sense of the word – an electrifying read!
Questions and answers
You probably have a great deal of questions – ranging from basic queries as to how surge voltages even occur, to technical details about grid systems or individual components of a surge protection concept, right through to the device itself. Here you can find answers to questions such as:
What is a surge voltage? How does it occur?
What damage can surge voltages cause?
How does surge protection work?
What legal or standard requirements are there for surge protection?
What makes up a consistent surge protection concept?
How can the quality of surge protective devices be verified?
In which applications is surge protection particularly important?
Various types of surge voltages can occur in electrical and electronic systems. They differ mainly with respect to their duration and amplitude. Depending on the cause, a surge voltage can last a few hundred microseconds, hours or even days. The amplitude can range from a few millivolts to some ten thousand volts. Lightning strikes are a special cause of surge voltages. Direct and indirect strikes can result not only in high surge voltage amplitudes, but also particularly high and sometimes long current flows, which then have very serious effects.
1.1 The phenomenon of surge voltage
Every electrical device has a specific dielectric strength against surge voltages. If the level of a surge voltage exceeds this strength, malfunctions or damage can occur. Surge voltages with very high amplitudes in the kilovolt range are generally transient overvoltages, which means they have a comparatively short duration, ranging from a few microseconds to several hundred microseconds. The high amplitude and short duration, in turn, mean very abrupt voltage increases and high voltage differences, the effects of which can be protected against only with surge protection.
Although the operator of an electrical system can use corresponding insurance to fix material damage to the system, there is a separate risk for the time the system is down until it is repaired. This downtime is often not covered by insurance and, within a short period of time, can become a heavy financial burden, especially in comparison to the cost of a lightning and surge protection concept.
The typical duration and amplitude of a surge voltage varies depending on the cause.
Lightning strikes (lightning electromagnetic pulse, LEMP) have the greatest destructive potential out of all the causes of surge voltages. They cause transient overvoltages that can extend across great distances and are often associated with high-amplitude surge currents. Even the indirect effects of a lightning strike can lead to a surge voltage of several kilovolts and result in a surge current of tens of thousands of amperes. Despite its very brief duration, from a few microseconds to several hundred microseconds, such an event can lead to total failure or even the destruction of the affected installation. Switching operations Switching operations generate electromagnetic pulses (switching electromagnetic pulse, SEMP), which in turn can lead to induced surge voltages that can spread to electrical cables. The current flows that are extremely high for a brief period during a short-circuit or when activating consumers with high switch-on currents can induce transient overvoltages.
Electrostatic discharges (ESD) occur if exposed conductive parts with different electrostatic potential approach each other, resulting in a charge exchange. They may result in electrostatic charge generation in an exposed conductive part within electrical and electronic systems. Ultimately, the electrostatic charge reaches a level high enough to spark over to an exposed conductive part of a different potential. This sudden charge exchange leads to a brief surge voltage. This presents a hazard, especially for sensitive electronic components.
1.3 Coupling types
Surge voltages can reach a circuit in various ways. In reality, it is usually a case of an overlap between individual coupling types.
Two circuits that are connected to each other in an electrically conductive way can directly and mutually influence each other. A change in voltage or current in one circuit generates a corresponding reaction in another circuit.
A rapidly increasing flow of current through a conductor generates a magnetic field, with a level of strength around the conductor that quickly changes. If another conductor is located in this magnetic field, then according to the induction principle, a voltage difference occurs here due to the change in the magnetic field strength.
An electrical field occurs between two points with different potential. The charge carriers of exposed conductive parts within this field are arranged based on the field direction and strength according to the physical principle of influence. As such, a potential difference also occurs within the exposed conductive part, in other words, a voltage difference.
1.4 Direction of action
Normal-mode voltage (symmetrical voltage, differential mode voltage) Symmetrical surge voltages present a hazard primarily to equipment that is located between two active potentials. They can cause damage if the electric strength of the equipment is exceeded.
Common-mode voltage (asymmetrical voltage)
Common-mode surge voltages primarily present a hazard to equipment that is located between active potentials (phase conductors and neutral conductors) and the ground potential. They can cause damage if the dielectric strength of the equipment is exceeded.
1.5 Effects and damage
The German Insurance Association (GDV) regularly publishes statistics, allowing conclusions to be drawn on the total losses resulting from various causes. According to these statistics, after fires and storms, lightning strikes and surge voltages cause the most damage. In 2012, their share of damage to all insured items totaled 18%. In other words, almost a fifth of insured damage can be traced back to a surge voltage.
Device failure or defects caused by surge voltages are more frequent than expected. According to statistics from the GDV, surge voltages are in fact the most frequent cause of this damage. These figures only apply to damage that resulted in fire.
Fig. 6 shows that the amount of damage caused by lightning and surge voltages in 2013 as reported to the GDV has dropped by about 20% in comparison to the previous year. The financial payments by insurance providers, however, fell by just 10%. If the values from the comparable year of 2010 are taken as a basis, this amounts to a cost increase of approximately 20%. Insurers consider one of the causes to be that increasingly sensitive electronic devices are finding their way into households. On average, an individual lightning strike or damage from a surge voltage amounted to 800 euros in 2013. This is the highest amount since statistics began.
For commercial systems, however, the consequences of a failure (such as downtime or data loss) are generally much more serious. The failure of a device or a machine that is used in a professional environment often leads to costs that are many times higher than repairing the defective device.
For example, if a cell tower fails, the cost for the operator can lie in the range of several euros per second. Calculated over the course of a day, this corresponds to damages of more than 100,000 euros.
For this reason, a consistent surge protection concept is urgently required for industrial and business systems. It is not just a case of having effective protection for fire and personnel, but also about eliminating the possibility of large financial risks.
An additional factor that will underscore the need for lightning and surge protection in the future is the increase in the probability of lightning strikes, as shown by statistics. Various
studies have already shown that as part of global climate change, the frequency of storms is set to increase. This development is not limited only to regions that already have a high risk of strikes, but extends to all regions on Earth.
2. Surge protection: what should be considered?
Effective surge protection is not just simply installed. It has to be individually coordinated based on the system that is to be protected and the ambient conditions that are prevalent on site. For this reason, the design and concept must be consistent. This means that many details must be taken into account, for everything from standards and stipulations to creating a lightning protection zone concept.
2.1 How surge protection works
Surge protection should ensure that surge voltages do not cause damage to installations, equipment or end devices. As such, surge protective devices (SPDs) chiefly fulfill two tasks:
- Limit the surge voltage in terms of amplitude so that the dielectric strength of the devices is not exceeded.
- Discharge the surge currents associated with surge voltages to a distant ground.
The way in which the surge protection works can be easily explained by means of the equipment’s power supply diagram (Fig. 7). As described in Section 1.4, a surge voltage can arise either between the active conductors as normal-mode voltage (Fig. 8) or between active conductors and the protective conductor or ground potential as common-mode voltage (Fig. 9).
With this in mind, surge protective devices are installed either in parallel to the equipment, between the active conductors themselves (Fig. 10) or between the active conductors and the protective conductor (Fig. 11). A surge protective device functions in the same way as a switch that turns off for the brief time of the surge voltage. By doing so, a sort of short
circuit occurs; surge currents can flow to ground or to the supply network. This limits the difference in voltage (Fig. 12 and 13). This short circuit of sorts only lasts for the duration of the surge voltage event, typically a few microseconds. As such, the equipment to be protected is safeguarded and continues to work unaffected.
2.2 Lightning and surge protection standards
National and international standards provide a guide to establishing a lightning and surge protection concept as well as the design of the individual protective devices. A distinction is made between the following protective measures:
- Protective measures against lightning strike events: stipulated in lightning protection standard IEC 62305    . A key component of this is an extensive risk assessment regarding the necessity, scope, and cost-effectiveness of a protection concept.
- Protective measures against atmospheric influences or switching operations: stipulated in IEC 60364-4-44 . In comparison with IEC 62305, it is based on a shortened risk analysis and uses this as the basis for deriving corresponding measures. In addition to the standards mentioned, it may be necessary to observe other legal and country-specific stipulations, which often make the use of surge protection a compulsory requirement. The following sections do not address the individual particularities of standards in various countries. Normative references are made, to the extent possible, based on the international IEC documents.
2.2.1 Lightning protection in accordance with IEC 62305
Part 1: Characteristics of lightning strikes
In Part 1 of this standard , the characteristic properties of lightning strikes, the likelihood of occurrence, and the potential for hazard are taken into account.
Part 2: Risk analysis
The risk analysis according to Part 2 of this standard  describes a process with which, first of all, the need for lightning protection for a physical structure is analyzed. Various sources of damage, e.g., a direct lightning strike in the building, come into focus, as do the
types of damage resulting from this:
- Impact on health or loss of life
- Loss of technical services for the public
- Loss of irreplaceable objects of cultural significance
- Financial losses The financial benefits are determined as follows: how does the total annual
cost for a lightning protection system compare to the costs of potential damage without a protection system? The cost evaluation is based on the expenditures for the planning, assembly, and maintenance of the lightning protection system.
Parts 3 and 4: Planning aids and specifications
If the risk assessment determines that lightning protection is required and costeffective, then the type and scope of the specific measures for protection can be planned based on Parts 3  and 4  of this standard. The lightning protection level determined by risk management is decisive for determining the type and scope of the measures.
For physical structures that require an extremely high level of safety, almost all strikes must be captured and conducted away safely. For systems where a higher residual risk is acceptable, strikes with lower amplitudes are not captured. Fig. 14 shows the lowest current amplitudes of lightning strikes that can still be captured safely as well as the highest current amplitudes of lightning strikes that can be conducted away safely depending on the lightning protection level. This is described by means of lightning protection classes I to IV.
Furthermore, these describe the probability of capturing lightning strikes relative to the overall occurrences of lightning strikes. The highest class, lightning protection class I, corresponds to a 99% probability of capturing a strike.
2.2.2 Surge protection in accordance with IEC 60364-4-44
IEC 60364-4-44  includes a description of the requirements for protecting the electrical installation against transient overvoltages caused by atmospheric influences.
The standard’s area of application includes transient overvoltages that are transmitted by the power supply system. In addition to surge voltages (such as those arising from switching operations), this includes a direct lightning strike on the supply line. However, direct lightning strikes on or near a physical structure are not taken into consideration; in these cases, refer to IEC 62305 [1-4]. Likewise, the standard does not apply to installations if the consequences from surge voltages affect:
- Physical structures with a risk of explosion
- Physical structures that, if damaged, could impact the environment (such as chemical systems or nuclear power plants).
Surge protective devices must be used in accordance with IEC 60364-4-44 if transient overvoltages could have an impact on the following:
- Human life; for example, systems for safety purposes, medical areas
- Public and cultural institutions; for example, failure of public services, telecommunications centers, museums
Industrial or trade activities; for example, hotels, banks, industrial firms, trade markets, agricultural enterprises In all other cases, a risk assessment must be carried out in line with the international standard.
However, there are country-specific deviations in which the use of surge protection is generally obligatory, making a risk assessment unnecessary.
2.3 Basic protective measures and equipment
In order to ensure the total protection of a physical structure from the effects of lightning strikes and surge voltages, various protective measures or equipment that are tailored to
one another are required. A broad classification is shown below:
- External lightning protection
- Internal lightning protection
- Grounding and equipotential bonding
- Coordinated SPD system
2.3.1 External lightning protection
External lightning protection (Fig. 15) aims to divert strikes which come near to the object to be protected and to transmit the lightning current from the point where it hits to ground. Dangerous spark formation must be prevented. Damage due to thermal, magnetic or electrical effects must be prevented as well through proper design and dimensioning. External lightning protection is a system that consists of the air terminal, the arresters, and the grounding system.
Part 3 of standard IEC 62305  is essential for planning and erecting external lightning protection systems. Identifying and determining the lightning protection class is the basis for this. This is derived from the risk analysis. If there are no regulations or specifications for external lightning protection, a lightning protection class of at least class III is recommended.
The location of the air terminals on the building must also be determined. There are three methods of doing so:
- Rolling sphere method
- Protective angle method
- Mesh method
To insulate the external lightning protection system, a minimum distance between electrical lines and metal installations must be kept, referred to as the separation distance.
2.3.2 Internal lightning protection
The internal lightning protection system should prevent dangerous spark formation inside the system. Sparks can be caused by lightning induced surge voltages in the external lightning protection system or in other conductive parts of the physical structure. The internal lightning protection system consists of the equipotential bonding system and electrical insulation due to sufficient distances or suitable materials from the external lightning protection system. The lightning protection equipotential bonding is intended to prevent dangerous potential differences. For this purpose, the lightning protection system is primarily connected to metal installations, internal systems, as well as electrical and electronic systems within the system. This occurs by means of equipotential bonding lines, surge protective devices or isolating spark gaps.
2.3.3 Grounding and equipotential bonding
The grounding system aims to distribute and discharge the captured lightning current to ground. For this process, the geometry of the grounding system is crucial for effectively deriving lightning current (not the grounding resistance value). Effective equipotential bonding is also important. Equipotential bonding connects all electrically conductive parts with each other via cables. Active conductors are integrated into the equipotential bonding via surge protective devices.
2.3.4 Coordinated SPD system
A coordinated SPD system is understood to be a multi-level system of surge protective devices that are coordinated with each other.
The following points are recommended in order to achieve a high-performance SPD system:
- Divide the physical structure into lightning protection zones
- Incorporate all cables that cross between different zones into the local equipotential bonding using suitable SPDs
- Coordinate different types of SPDs: The devices must operate with each other in a coordinated manner to prevent individual SPDs from overloading
- Use short supply lines for connecting SPDs between active conductors and the equipotential bonding
- Lay protected and unprotected cables separately
For surge protection of signal transmission circuits, it is recommended to ground equipment only via the respective SPD
2.4 Lightning protection zones
The installation locations of surge protective devices within a physical structure are determined using the lightning protection zone concept from part 4 of lightning protection standard IEC 62305 .
It divides a physical structure into lightning protection zones (LPZ), and does so from outside to inside with decreasing lightning protection levels. In external zones only resistant equipment can be used. However, in internal zones, sensitive equipment can also be used. The individual zones are characterized and named as follows:
Unprotected zone outside of a building where direct lightning strikes are possible. The direct coupling of lightning currents in cables and the undamped magnetic field of the lightning strike can lead to danger and damage.
Zone outside the building that is protected from direct lightning strikes, for example, by an air terminal. The undamped magnetic field of the lightning strike and induced surge currents can cause hazards and damage.
Zone inside the building where highenergy surge voltages or surge currents and strong electromagnetic fields are still to be expected.
Zone inside a building where surge voltages or surge currents and electromagnetic fields that have already been significantly weakened are to be expected.
Zone inside the building where surge voltages or surge currents are expected to be only extremely low or entirely absent and electromagnetic fields are expected to be only very weak or nonexistent.
All cables that cross between zones must use coordinated surge protective devices (Fig. 16). Their discharge capacities are based on the lightning protection class to be achieved, which has been determined according to legal requirements and requirements from government agencies and insurance companies, or by a risk analysis. When it comes to selecting surge protective devices, use the standard as a basis, assuming that 50% of the lightning current will be discharged to ground. The other 50% of the lightning current is directed to the electrical installation via the main equipotential bonding and from there must be conducted away from the SPD system.
2.5 The protective circle principle
A clear depiction of the lightning protection zone concept is shown by the protective circle (Fig. 17). An imaginary circle should be drawn around the object to be protected. Surge protective devices should be installed at all points where cables intersect this circle. This secures the area inside the protective circle. Couplings of line-bound surge voltages are moderated to achieve effective protection. The protective circle must include all electrical and electronic transmission lines in the following areas:
- Power supply
- Measurement and control technology
- Information technology
- Transceiver systems
3. Classification and testing of surge protective devices
Surge protective devices must have defined protection functions and performance parameters to make them suitable for use in corresponding protection concepts. As such, they are developed, tested, and classified according to their own international series of product standards. Yet even during use at a later stage, proper operation and therefore adherence to the protective function must be checked at regular intervals, as is also required of other safety-related components in electrical installations and electronic systems.
3.1 Requirements in accordance with IEC 61643
Surge protective devices (SPDs) are generally classified according to their performance values, depending on the protection class and location of use; this classification is found in product standard IEC 61643. It contains definitions of terms, general requirements, and testing procedures for surge protective devices. Some of the standards in the series are:
- IEC 61643-11: Surge protective devices connected to low-voltage power systems – Requirements and test methods 
- IEC 61643-21: Surge protective devices connected to telecommunications and signaling networks – Performance requirements and test methods 
- IEC 61643-31: Surge protective devices connected to low-voltage power systems – Requirements and test methods for surge protective devices to be used in photovoltaic installations 
In the future, the following standard will be added to this series:
- IEC 61643-41: Surge protective devices connected to low-voltage DC systems – Requirements and test methods
3.2 Key characteristics for surge protective devices
Nominal voltage (UN)
The nominal value of the voltage of the current or signal circuit based on the use envisaged for the SPDs.
The nominal voltage stated for an SPD corresponds to the system voltage of the typical SPD installation site for a standard three-phase system, e.g., 230/400 V AC. Systems with lower system voltages can also be protected by the SPD. In the event of higher system voltages, it must be decided on a case-to-case basis as to whether the SPD can be used and if there are restrictions to observe.
Nominal load current (IL)
Maximum r.m.s. value of the nominal current, which allows a connected load to flow to one of the protected outputs of the SPD.
This maximum value is specified by the parts carrying operational current within the SPDs; these must be able to withstand the continuous thermal current load.
Short-circuit withstand capability (ISCCR)
Maximum prospective short-circuit current of the electrical network, for which the SPD is rated in conjunction with the upstream overcurrent protective device.
The short-circuit withstand capability indicates the maximum prospective short-circuit current at which the SPD can be used at the installation location. The corresponding tests to determine this value are carried out in connection with the maximum permissible upstream overcurrent protective device (OCPD). In the event that the special surge protective devices for photovoltaic systems correspond to the value ISCPV, this is the maximum direct current short-circuit current of a system at which the SPD may be used.
Maximum continuous voltage (UC)
Maximum r.m.s. value of the voltage that is allowed to be continuously applied to the terminals of the SPD.
The maximum continuous voltage must be at least 10% higher than the value of the nominal voltage. In systems with greater voltage deviations, SPDs with a greater difference between UC and UN must be used.
Voltage protection level (Up)
Maximum voltage that can occur on the connection terminal blocks of the SPD while loaded with a pulse of specific voltage steepness and a discharge surge current of specified amplitude and wave form.
This value characterizes the surge voltage protective effect of the SPD. In the event of a surge voltage or surge current within the performance parameters of the SPD, the voltage is safely limited to a maximum of this value at the protected connections of the SPD.
Lightning surge current (Iimp)
Peak value of the current flowing through the SPD with pulse shape (10/350 μs).
The pulse shape (10/350 μs) of a surge current is used for simulating the current flow of direct lightning strikes.The value of the lightning surge current is used for special testing of an SPD to demonstrate its load capacity with regard to high-energy lightning currents. Depending on the lightning protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this peak value.
Nominal discharge current (In)
Peak value of the current flowing through the SPD with pulse shape (8/20 μs).
The pulse shape (8/20 μs) of a surge current is characteristic of the effects of an indirect lightning strike or switching operation. The value of the nominal discharge current is used for a variety of tests on an SPD, including those used to determine the voltage protection level. Depending on the lightning protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this peak value.
Off-load voltage (UOC)
Off-load voltage of the hybrid generator at the terminal points of the SPD.
A hybrid generator creates a combined surge; e.g., in off-load. It supplies a voltage pulse with a defined pulse shape, generally (1.2/50 μs), and in a short circuit, a current pulse with a defined pulse shape, generally (8/20 μs). The combined surge is characteristic of the effects of an induced surge voltage. Depending on the protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this value.
Normative surge current and voltage surge pulses
The voltage-limiting function of the SPDs is tested, for example, using surge currents with a pulse shape of (8/20 μs) (Fig. 19), i.e., with a rise time of 8 μs and a decay time to half value of 20 μs. This pulse shape also provides information about the dynamic response behavior of the SPD. For voltage-switching SPDs, such as spark gaps or gas-filled surge protective devices, this response behavior is also tested using a very fast voltage surge pulse with the pulse shape of (1.2/50 μs) (Fig. 20).
SPDs that are designed to protect against direct lightning currents are additionally tested using surge currents with a pulse shape of (10/350 μs) (Fig. 21).
The amplitude is based on the lightning surge current specified by the manufacturer for the device. This pulse shape contains several times the electrical load in comparison to the (8/20 μs) pulse shape, at the same amplitude. Therefore, it places a considerably higher load on the SPD in terms of energy.
3.3 Maintenance and testing in accordance with IEC 62305
To achieve high system availability, system operators must regularly inspect and maintain their electrical system (Table 1). This is stipulated by legislators, supervisory authorities or professional associations based on the respective system type. Regular testing and maintenance of lightning protection systems (external and internal lightning protection) is also required in Appendix E.7 of the lightning protection standard IEC 62305-3 . Specialist knowledge is required in order to carry out professional testing of lightning protection systems. For this reason, this test must be carried out by a lightning protection expert. Inspecting the SPDs is also part of this. The standard also demands that maintenance is properly documented. The three following points are particularly important to note:
- “Comprehensive testing in critical situations” relates to physical structures that contain sensitive systems or systems with a large number of persons.
- Explosion-protected, physical structures should undergo a visual check every 6 months. The electrical test of the installations should be carried out once a year.
- For systems with strict requirements in terms of safety technology, for example, the legislator can prescribe a comprehensive check. This can be necessary if there has been a lightning strike within a certain radius of the respective system.
At this point the question arises as to what exactly should be covered by a comprehensive test. A visual check alone often cannot reliably provide an idea of the functional efficiency of an SPD. An electrical test, however, can clearly verify the performance capacity of the SPD. When an electrical test is carried out on SPDs and simulates a real surge voltage, the test voltage is selected such that the SPD “works”, that is, becomes conductive. The measurement results are then compared to reference values and evaluated.
3.4 Pulse and high-current testing technology
Surge protective devices are more effective the more precisely they are tailored to the requirements and special features of their area of application. Therefore, the development of surge protective devices requires laboratory simulation of the operating conditions or more specifically, of the electrical conditions and the surge voltage events to be anticipated.
Realistic simulation of surge voltage events
For the test-based technical certification of high-performance SPDs of all types, the short-circuit behavior of high performance, low-voltage power supply systems must be simulated. This is accomplished using an adjustable three-phase transformer with adjustable short-circuit behavior. This simulation is coupled with a surge current generator, which generates surge currents that are typically produced by transient surge voltage events. It is only with a test arrangement of this type that the performance of the protective devices can be determined, as well as their interactions with different power supply systems. The IEC 61643-11 standard  describes a testing procedure in this context that is referred to as an operating duty test. During this test, the surge protective device is subjected to surge pulse currents while it is simultaneously connected to a specifically parameterized power supply system. The basic structure of such a testing system, which generally consists of a surge current generator, surge protective device, and line-frequency power supply system, is depicted in Fig. 24.
Simulation of lightning surge currents
Surge current generators (Fig. 27) are key components of a high-current laboratory; they help to determine the discharge capacity, test components for external lightning protection, and also demonstrate the function of surge voltage protection concepts. They simulate lightning surge currents with amplitudes of up to 100 kA with a pulse shape of (10/350μs) and surge currents, for example, consisting of switching surge voltages with amplitudes of 160 kA or higher with a pulse shape of (8/20μs).
4. Quality features of surge protective devices
The quality and performance of surge protective devices are hard for a customer to assess. Correct functioning can only be tested in labs with appropriate equipment. Thus, aside from the external appearance and haptics, only the technical data provided by the manufacturer can provide any guidance. Even more important is a reliable statement from the manufacturer regarding the performance of the SPD and successful completion of the tests established in the respective part of the IEC 61643 standard series.
4.1 CE Declaration of Conformity
An initial statement of quality is the CE Declaration of Conformity. It certifies that the product complies with the 2014/35/EU Low-voltage Directive of the European Union. Fulfillment of the testing requirements in the EN 61643 standard series, which are based on the IEC 61643 series, serves as the primary basis for assessing surge protective devices.
Please note: The CE conformity assessment and declaration is issued by the manufacturer. It is therefore by no means a seal of approval by an independent institute or other attestation of an examination or evaluation of the product by a third party. The CE mark only means that the manufacturer has confirmed adherence to the relevant regulations with regard to its product. If non-adherence to the relevant regulations or misuse of the CE marking is proven, legal steps can be initiated that may even result in prohibition of market launch under the European Union’s supervision.
4.2 Independent product certifications
A true mark of quality is a product certification from an independent testing institute. These can confirm fulfillment of the respective testing requirements specified in standards. Furthermore, they can also document additional characteristics of the products, such as resistance to the effects of shocks and vibrations or safety requirements of specific domestic markets.
The regulatory requirements placed on SPDs sometimes require highly complex tests that only a few testing laboratories in the world are fully capable of carrying out. For increasingly more manufacturers and providers of SPDs, specifically in the lower pricing segment, the specifications regarding the performance of the devices are also to be taken into account. As such, the independent certification of SPDs, and therefore also the confirmation of performance specifications, is becoming increasingly more important.
These certification marks from independent testing institutes confirm, for example, that the current version of the respective testing requirements from the EN/IEC 61643-11 standard series has been fulfilled.
UL, CSA, EAC, and more
These certifications are examples of requirements for certain domestic markets.
What’s more, in their own standards, UL and CSA place safety requirements on the products for the North American markets or areas influenced by American markets. In contrast, EAC is primarily an administrative approval of the products for the Eurasian Economic Area. It is the same as the CE Declaration of Conformity and can also be obtained on this basis.
Independently verified quality
LSP has a large part of its surge protection product range certified by independent testing institutes. By doing so, compliance with standards and maximum product quality are verified for the user.
4.3 Expertise in surge protection
Understanding the application
Further development of electrical systems and system technology always leads to new technologies and, as a result, to completely innovative technical solutions that place very specific requirements on surge protection. One example is the system technology for using renewable energies (photovoltaics and wind power). For this reason, it is important to fully understand the system to be protected and its environment, in order to develop tailor-made surge protective devices.
Research and development
The basis for ongoing development is intensive commitment to fundamental research and technological development. The following tasks are part of this:
- Determine the precise requirements placed on surge protective devices (protection objectives)
- Research new, appropriate materials available for applications
- Develop and master innovative basic technologies
- Structure development processes
- Develop new protection concepts as well as devices with tailor-made properties
Testing and qualification
Testing systems that simulate real conditions are essential in order to develop surge protection concepts and devices. This also applies to technical laboratory trials.
Manufacturing and quality assurance
Manufacturing surge protective devices suitable for the market with the highest quality levels demands that aspects relating to processes and procedures are taken into account during the development phase of these products. This requires early interlinking of product development activities with process and procedure development.
Measures to ensure quality are critical and should be carried out in series manufacturing as part of routine testing. For surge protective devices it can be useful, for example, to perform destructive testing that records product characteristics right up to the performance limit and beyond. In this way, any possible deviations in manufacturing processes and consequently in product quality can be detected at an early stage.
6. Fields of application
The IEC 61643 series of standards divides the areas of application in which surge voltage protective devices are implemented into low-voltage systems, telecommunications and signal processing networks and photovoltaic installations. In general, all areas have very different individual system prerequisites. Correspondingly, the solutions or steps involved can vary greatly. It is worth examining these applications in closer detail.
6.1 Protection of AC systems
6.1.1 SPD types and technologies
The lightning protection zone concept provides coordinated surge protective devices for all cables that cross between zones. Their power values are based on the protection class to be achieved. As such, different SPDs are required based on the zone transition points (see Table 2). The requirements for the individual SPD types are defined in the standard IEC 61643- 11  for surge protective devices used in low-voltage systems. A multi-level protection concept is derived from this (Fig. 36).
The multi-level functionality limits the lightning protection level from zone to zone. The amplitudes and specific energy levels of the surge voltages or surge currents to be expected gradually decrease. The voltage value to which the individual SPDs must limit the surge voltages also decreases. This is achieved by correspondingly low voltage protection levels that are based on the dielectric strength of the equipment to be protected in the immediate vicinity. The dielectric strength is specified in accordance with IEC 60664-1  in the overvoltage categories I to IV (Table 3).
6.1.2 Type 1: Lightning current arrester/combination protective device
Lightning / surge protection for type I with varistors / spark gap technology: FLP12,5 and FLP25
LSP offers type I surge protection featuring varistor technology with a leakage current capacity of 12.5 kA to 25 kA (10/350 μs). The pluggable, self monitoring surge arresters of up to 25 kA are optionally available as 1-, 2-, 3- or 4-pole versions – with or without a remote signalling contact.
The advantages for you:
Remote signalling function
Suitable for various types of mains voltages (TN/TT)
Tested in compliance with IEC 61643-11 and EN 61643-11
Convenient installation in sub-distribution boards and electrical cabinets
Designed for use in buildings according to lightning protective level I/II for 12.5 kA and 25 kA
Very low residual voltage, thus also suitable as Type II surge protection
Lightning conductors with spark gap for lightning protection or equipotential bonding providing Surge protection type I
According to the requirements of Type I (DIN VDE 0675 part 6) and Type I according to IEC 61643-11: the lightning arrester should be used in the transition zone between protective zones (LP) 0 and 1 (acc. to IEC 1312-1) for lightning protection equipotential bonding. In combination with several lightning protectors, the surge protection is used in the mains forms TN, TT and IT. When lightning strikes, the triggered air gap protector provides the necessary equipotential bonding between the building lightning protection and the earthing system of the power supply.
Electrical connection for building installation
The type 1 FLP25 series lightning arrester is connected between the external conductors (L1, L2, L3) and N/PE. The N/PE spark gap (Fig. 37) is produced with the FLP25 N-PE 50 kA or 100 kA. Cables as short as possible should be used. The maximum permissible operating voltage UC is 320 V AC. Decoupling to downstream type II arresters is not necessary. Please note the installation instructions.
6.1.3 Type 2: Surge protective device
Type 2 surge protective devices are generally installed in sub-distributions or machine control cabinets. These SPDs must be able to discharge induced surge voltages from indirect lightning strikes or switching operations but not handle direct lightning currents. As such, the energy input to be managed is significantly lower. In any case, induced surge voltages caused by switching operations are often very dynamic. Here, discharge technology such as varistor technology with fast response behavior stands up to the test.
Varistors (variable resistor or metal oxide varistor, MOV) (Fig. 40) are semi conductor components made from metal oxide ceramics. They exhibit a non-linear current-voltage characteristic curve (Fig. 41). In low voltage ranges, the resistance of a varistor is very high. However, in higher voltage ranges, the resistance drops away rapidly to allow very high currents to be discharged without any problems.
For this reason, the characteristics of varistors are referred to as voltagelimiting. With a typical response time in the lower nanosecond range, varistors are very well suited even to limiting particularly dynamic surge voltage phenomena.
Varistors that carry lightning current
High-performance varistor ceramics can even exhibit a pulse discharge capacity of 12.5 kA (10/350 μs) in acceptable installation spaces. As a result, they are also suitable as type 1 SPDs for environments with low protection levels.
For a higher pulse discharge capacity of 25 kA to 50 kA (10/350 μs), multiple varistors generally need to be used in a parallel connection. As a result, surge protection manufacturers who have no spark gap technology often use varistors as type 1 SPDs to meet the requirements of lightning protection class I. This concept has serious defects, however. If the characteristics of the varistors connected in parallel do not match precisely, a requirement that is very hard to meet, the individual paths are placed under differing loads during the process. Correspondingly, they age very differently. The difference between loads becomes increasingly larger over time. This ultimately leads to varistor overload and consequently the failure of the entire SPD.
6.1.4 Type 3: Device protection
Type 3 surge protective devices are generally installed right in front of the end devices to be protected. Due to differing installation environments, type 3 SPDs are available in a wide range of designs. In addition to standard DIN rail mounting, there are devices for installation in sockets or for direct mounting on a PCB of the end device. Technologically, type 3 SPDs are most similar to type 2, which are based on varistors, but the requirements in terms of discharge capacity in comparison to type 2 are even lower.
It is often useful to combine the protection of the power supply to the protection of other interfaces in the end device, such as data or communication lines. There are combined devices for this purpose. They take on the surge protection for all corresponding (supply) cables.
6.1.5 Coordinating different SPD types
The lightning protection zone concept provides coordinated surge protective devices for all cables that cross between zones. Their power values are based on the protection class to be achieved.
Depending on the zone transition, different types are therefore required (see Table 2). The requirements for individual SPD types are defined in the product standard for surge protective devices, IEC 61643-11 .
A multi-level protection concept can be derived from this (Fig. 43).
Starting from the internal protection zones, a type 3 SPD and an upstream type 2 SPD are to be coordinated. It must be ensured that type 3 SPDs do not experience energy overload. As only surge voltages of low amplitudes are to be measured in lightning protection zone 2, coordination can be accomplished using just the response behavior of the SPDs. The type 3 SPD and the components used in this device must be designed so that they only react to higher voltage values than the type 2 SPD.
In the direction of the external lightning protection zones, the coordination between type 2 SPDs and upstream type 1 SPDs must once again be ensured. As the possibility of direct lightning strikes or partial lightning strikes must be considered here that can only be borne by type 1 SPDs, it is particularly important that the SPDs are addressed selectively. Otherwise, the type 2 SPD may be overloaded.
The technologies used for type 1 SPDs are very different, so there are no generally applicable conditions for coordination. Type 1 SPDs based on spark gaps provide a clear advantage in this area. Their comparatively low residual voltage of just a few hundred volts throughout most of the duration of the lightning current ensures that almost all of the current flow is absorbed.
6.1.6 Grid systems in accordance with IEC 60364
The design of a surge protection concept for three-phase current systems depends on the existing grid system, among other factors. These systems can vary depending on the design of the grounding of the transformer providing the supply, the consumer system, and their connection to one another.
The directive for establishing low-voltage power supply systems, IEC 60364-1 , lists the following system configurations:
In this grid system, a point of the transformer supplying the energy is grounded directly, usually the neutral point. The neutral conductor (N) and protective conductor (PE) are routed to the consumer system in separate conductors. A three-phase power supply consists of five conductors: L1, L2, L3, N, and PE (Fig. 44).
In this grid system, the neutral point of the transformer supplying the energy is directly grounded. The neutral conductor and protective conductor are routed to the consumer system in one conductor (PEN). A three-phase power supply consists of four conductors: L1, L2, L3, and PEN (Fig. 45).
In this grid system, the grounded point of the transformer is routed to the system solely as a neutral conductor. The parts of the electrical system are connected to a local grounding system that is separated from the grounded point of the transformer. The neutral conductor and the local protective conductor are routed to the consumer system in separate conductors. A three phase power supply consists of five conductors: L1, L2, L3, N, and local PE (Fig. 46).
In this grid system, the neutral point of the transformer supplying the energy is not grounded, or only grounded via a high impedance. The exposed conductive parts of the electrical system are connected to a local grounding system. If a neutral conductor is also routed from the neutral point of the transformer supplying the energy, it is routed separately from the local protective conductor. A three-phase power supply consists of four or five conductors: L1, L2, L3, if appropriate, N, and local PE (Fig. 47).
One peculiarity of the IT system is that an insulation fault to ground may occur for a limited period of time. The ground fault in a phase must be simply detected by insulation monitoring and reported so that it can be promptly rectified. Only in the event of a second ground fault would this lead to a short circuit between two phases and the relevant surge protection equipment would trip. Surge protective devices for use in IT systems must therefore be able to withstand the phase-to-phase voltage of the system as well as the tolerance. This is ensured by the normative requirement that only SPDs with a maximum continuous voltage of at least the phase-to-phase voltage plus tolerance may be used between the phase and PE in IT systems.
6.1.7 American grid systems
Other grid systems are used, especially in the North and Central American regions. The most important are:
- Wye system
- Delta system
- Split-phase system
These systems largely correspond to the TN systems. The neutral point of the supplying transformer is directly grounded, and from there, the protective conductor (grounding conductor, GND) is routed to the consumer system. Insulated Wye systems do exist, but there are comparatively few. Generally, a possible neutral conductor is first tapped within the consumer system. This then corresponds to a TN-C-S system. A three-phase power supply consists of four or five conductors: L1, L2, L3, if appropriate, N, and GND (Fig. 48).
Grounding in this system either takes place via one of the phases (corner-grounded) or via a center tap between two phases (high-leg). The GND is routed from the respective grounding point to the consumer system. Insulated delta systems do exist, but there are comparatively few.
The neutral conductor is, if required, usually first tapped within the consumer system, as well. A three-phase power supply consists of four or five conductors: L1, L2, L3, if appropriate, N, and GND (Fig. 49).
This widely used two-phase system is grounded by means of a center tap on the transformer winding and a neutral conductor is routed from there. A two-phase power supply consists of four conductors: L1, L2, N, and GND (Fig. 50).
6.1.8 Connection scheme
Surge protective devices are part of the equipotential bonding of a physical structure. In the event of a surge voltage, they connect the active conductors in electrical installations with the grounding.
Depending on the grid system of the consumer system, different SPDs can be used. They are combined in various connection schemes (CT) in order to establish this connection.
In the installation directive for surge protection, IEC 60364-5-53 , the following types are specified:
- CT1 connection scheme: a combination of SPDs that have a mode of protection between each active conductor (outer conductor and neutral conductor, if present) and PE conductor. This connection scheme is often designated as a x+0 circuit, where x represents the number of active conductors (Fig. 51).
- CT2 connection scheme: a combination of SPDs that have a mode of protection between each outer conductor and neutral conductor and a mode of protection between the neutral conductor and the PE conductor. This connection scheme is often designated as a x+1 circuit, where x represents the number of outer conductors (Fig. 52).
The possible uses of the connection schemes in the individual grid systems are listed in Table 4. When using SPDs between neutral and protective conductors in IT systems, note that the short-circuit withstand capability and, if applicable, the follow current interrupt rating of the SPD must at least match the expected short-circuit current at the installation location in the event of a two-phase ground fault.
6.1.9 Connection and over-current protection of SPDs
If transient over-voltages occur, an inductive voltage drop can result on the electrical conductors. This additional voltage drop in the connecting cables can weaken the protective effect, particularly when connecting surge protection. For this reason, the connecting cables of the SPDs are always to be routed as short as possible, avoiding small bending radii.
SPDs can essentially be connected in two different ways:
- Branch wiring (stub wiring), see Fig. 53
- V-wiring (V-shaped wiring, Kelvin connection), see Fig.54
In both cases, the total cable lengths of a, b and c must not exceed 0.5 m whenever possible, in accordance with IEC 60364 part 5, chapter 53, section 534 . This is particularly easy to ensure in the case of V-wiring, as only length c is relevant. In this way, the overall voltage protection level, consisting of the SPD voltage protection level and voltage drop along the connecting cables, can be minimized as much as possible. In the case of branch wiring, the SPD can and must be protected, depending on the nominal value of the F1 upstream overcurrent protective device, with a second additional overcurrent protective device, F2, of a lower nominal value. This wiring enables use in systems with nominal currents of any strength, provided the prospective short-circuit current on the SPD installation location does not exceed its short-circuit withstand capability.
The V-wiring can only be used up to a nominal value of the F1 upstream overcurrent protective device or a nominal current of the system that does not exceed the continuous current capacity of the connecting cables and the SPD connection terminal blocks.
CT2 connection scheme
For TN and TT systems, LSP mainly provides SPDs with the CT2 connection scheme. The advantages of this connection scheme are:
- Can be used universally in all countries worldwide
- Lower voltage protection level between outer and neutral conductor
- No leakage current to the protective conductor due to the use of spark gaps between the neutral and protective conductor
As part of the electrical installation, corresponding legal or regulatory requirements are to be fulfilled for the connection and overcurrent protection of surge protective devices. These predominantly aim to guarantee the operational reliability of the system. Furthermore, specific conditions regarding connection and fuse protection are to be taken into account for correct surge protection function.
The requirements are based on various parts of IEC 60364 for creating low-voltage systems: on the one hand, Part 5, Section 53, Main Section 534 , regarding the selection and setup of surge protective devices, and on the other, Part 4, Section 43 , regarding protective measures against overcurrent, as well as the product standard for surge protective devices, IEC 61643-11 .
Connection cross sections
If these requirements are combined, this results in the following conditions for dimensioning the connecting cables of SPDs (based on PVC-insulated copper cables):
- The minimum cross sections for the SPD connecting cables initially result from the requirements for installing surge protective devices, depending on the active conductor connection or the main grounding busbar/ protective conductor (PE(N)) as well as the type of the SPD:
– Connection cross section of the active conductor for type 1 SPDs: min. 6 mm2
– Connection cross section of the active conductor for type 2 SPDs: min. 2.5 mm2
– Connection cross section for the main grounding busbar or the protective conductor for type 1 SPDs: min. 16 mm2
– Connection cross section for the main grounding busbar or the protective conductor for type 2 SPDs: min. 6 mm2
- Over a specific nominal value of the upstream overcurrent protection, the minimum cross sections are determined by the connecting cables’ need for short-circuit withstand capability
- If the SPD connecting cables carry operating current, then the continuous current load can be used to determine the minimum cross section as of a certain current value
When designing the overcurrent protection of SPDs, the following elements must first be prioritized:
- Priority of the system supply: Branch wiring with separate F2 overcurrent protective device in the branch
- Priority of the system surge protection: V-wiring or branch wiring without separate F2 overcurrent protective device
In the first case, the F2 separate overcurrent protective device ensures that this is triggered in the event of an SPD failure, e.g. due to a short circuit. The F1 upstream overcurrent protective device is not triggered so that the supply of the equipment to be protected is not interrupted. In this case, however, the equipment is no longer protected from subsequent overvoltage events.
In the second case, the F1 upstream overcurrent protective device takes on the overcurrent protection in the event that the SPD fails. In this process, the failure of the supply is accepted so that no damage can arise from subsequent overvoltage events.
When dimensioning the overcurrent protection, the following points should be kept in mind:
- Selectivity of the respective overcurrent protective device to upstream overcurrent protective devices.
- The final overcurrent protective device before the SPD must not exceed the maximum nominal value of the upstream overcurrent protective device as specified by the SPD manufacturer.
- The upstream overcurrent protective device is intended to be able to carry the amplitudes of lightning and surge current required by the lightning protection class when possible. Especially with regard to high-energy lightning currents, under-dimensioned fuses can pose a risk, as they can be destroyed in a very short time due to high-energy inputs.
Adhering to the selectivity is therefore the top priority. In the simple case that the two overcurrent protective devices to be taken into account are gG fuses, then a nominal value of 1250 A applies, which must be F2 X 1.6 = F1. If one or both of the overcurrent protective devices is a circuit breaker or miniature circuit breaker, then their tripping characteristics must be compared with each other or with the fuse characteristics and, if applicable, tailored to each other. This is the case if the curves do not touch or overlap (Fig. 55 and 56). Furthermore, they must have a sufficient time interval in areas with short-circuit currents so that the respective downstream overcurrent protective device can address the other two devices and switch them off.
A similar scenario applies in the event that a miniature circuit breaker or circuit breaker is intended to provide the overcurrent protection for the SPD as F1, without a separate F2 overcurrent protective device. Then, the switching-off characteristics of the switch must be compared with the characteristics of the maximum overcurrent protection specified for the SPD by the manufacturer. This must not be exceeded in the range for shortcircuit currents.
It is difficult to make general statements on this point. Statements can only be made regarding comparatively low nominal currents of switches compared with the nominal currents of the maximum gG backup fuses that are typical for SPDs. If, for example, a maximum backup fuse of 315 A gG is specified, then in comparison only a 125 A miniature circuit breaker of the C characteristic can generally serve as a backup fuse for the SPD. Switches with higher nominal currents or other characteristics must be considered on an individual basis and checked if necessary (Fig. 56).
6.2 Protection of DC systems with linear voltage sources
The operating behavior of DC systems can deviate from one another significantly due to large differences in their source characteristics. It is therefore impossible to easily select surge protective devices without precise knowledge of the properties of the respective systems. This particularly applies to systems with limited or low short-circuit currents.
Direct current power supply systems with linear source characteristics are mainly used for the following:
- Consumers with low direct current supply voltage, e.g. programmable logic controllers or telecommunication systems
- Mobile consumers, e.g. fork-lift trucks or onboard power systems
- Battery storage in UPS systems
- Computer centers
- Rail vehicles
Typical power sources of direct current power supply systems with linear source characteristics include:
- Controlled and non-controlled rectifiers with or without smoothing
- Regulated power supply units
- Charging power supply units
- Battery sets
Selecting surge protective devices
Selecting SPDs for direct current systems is generally much more complex than for alternating current power supply systems.
In the case of AC power supply systems, there is often only one, strictly defined power source; for DC systems, however, there are often multiple power sources with different operating behaviors. This particularly applies to battery-operated DC systems.
In the majority of AC systems, the minimum short-circuit current is high enough to cause upstream overcurrent protective devices to trigger in a few milliseconds. This enables easy selection of fuses that reliably protect the system in the event of failure but also are able to carry surge currents with regard to their rating.
In the case of DC systems with limited or low short-circuit currents, however, it is very important that even minimal prospective shortcircuit currents at the SPD installation site are detected, in order to meet basic safety requirements. Ensuring that fuses are not triggered by surge current loads is then a secondary priority. Significant design criteria for the selection of SPDs and corresponding overcurrent protective devices in DC systems are:
- Nominal voltage of the DC power source(s)
- Number, type and operating behavior of DC power source(s)
- Maximum and minimum prospective short-circuit current at the SPD installation location
Protective circuits for grounded and non-grounded DC systems The preferred circuits for SPDs in DC systems conform to the CT1 connection scheme (see Fig. 51) and are designed with either one or two positions. A 2+0 circuit is also required for grounded TN systems if the installation location of the SPDs is far away from the system’s grounding point (Fig. 67).
6.3 Protection of DC systems in photovoltaic systems
The use of renewable energy sources has become increasingly important in recent years. In addition to wind turbine generators, hydroelectric plants or biomass systems, photovoltaic power generation systems (PV systems) supply a significant portion of renewable energy. PV systems are designed, for example, as rooftop systems on private homes and industrial buildings as well as free-standing systems. Due to their exposed location, these systems are susceptible to increased risk of damage by the effects of lightning. To prevent such damage and the associated loss of system availability, lightning and surge protection measures are to be considered during the design phase. Standards and directives tailored specifically to PV power supply systems make it easy to plan lightning and surge protection for these systems.
Requirements for SPDs for use in PV systems
The characteristics of PV sources impose specific requirements on SPDs for PV system protection for DC systems. Compared to conventional low-voltage power supply systems, PV systems feature the following characteristics:
- High DC system voltages up to 1500 V
- Source characteristics, which correspond to a non-linear current source
- Operating current at the optimum Maximum Power Point (MPP), which is only a few percent below the system’s short-circuit current
- Dependence of the short-circuit current on ambient conditions such as irradiation and temperature
With respect to only the overload failure behavior of DC devices and components, the results have significant implications: Due to the undefined short-circuit current, it is often difficult to achieve useful coordination of overcurrent protective devices or fuses for SPDs in these systems. In addition, the non-linear source characteristics for switching operations place very high demands on the performance of switching devices, fuses and other separators.
In light of this, special requirements have been defined for using SPDs in PV systems and for testing them to verify their function. These requirements have been published for the first time in the European standard EN 50539-11. A particular focus of these standards is on the overload and failure behavior of SPDs for DC system protection. In particular, options for laboratory simulation of the source characteristics of PV systems are described in these standards. IEC 61643-31  describes this topic in terms of international standardization.
These standards form the basis for certifying SPDs for use in PV systems on the DC side with respect to their performance and especially their reliability in the event of a failure.
Selecting and installing SPDs for protection of PV systems
Effective protection against lightning currents and surge voltages is relevant for both the DC and AC parts of PV systems. Implementing this protection requires taking into account not only the general regulations for installing photovoltaic systems (IEC 60364-7-712), but also particular guidelines for selecting and installing SPDs for DC system protection. These are CLC/TS 50539-12 or subsequently CLC/TS 61643-32 as a technical specification at the European level as well as IEC 61643-32  as an international counterpart.
6.3.1 PV systems on buildings
When designing and installing SPDs for protecting PV systems, it is essential to distinguish between physical structures (buildings) and free-standing systems. In the case of physical structures, the PV system is part of a building structure and is connected to the electrical installation. The following aspects are relevant for correctly designing and installing SPDs in these systems:
- Characteristic data for supply systems, such as the network configuration, nominal voltage and short-circuit current
- Lightning protection class (LPL) to be attained
- Presence of an external lightning protection system as well as the number of protective devices that system has
- Maintaining the separation distance
- Installation location of the inverter
- Cable lengths between devices to be protected
Based on the profile of properties of the PV system to be protected, which is characterized by the abovementioned aspects, IEC 61643-32  includes recommendations for the installation locations of SPDs as well as requirements for their performance.
A distinction is made here between building installations with and without an external lightning protection system. For physical structures without an external lightning protection system, protection of the PV system is generally sufficient with one type 2 SPD with a discharge capacity of at least 5 kA (8/20 μs) per mode of protection.
Advantages of the Y-circuit
For the DC-side protection of PV systems are based on the Y-circuit. This fault resistant circuit always has two varistors with properly coordinated disconnect devices switched in series between all potentials. This ensures that even in extreme cases, when one of the varistors fails, the flow of current can reliably continue through the second without being interrupted. This ensures maximum safety.
This applies to both the DC and the AC side of the system protection, insofar as the country-specific provisions do not define any higher requirements, such as the requirement of type 1 SPDs for protecting the AC side of the system.
In the case of buildings with PV systems and an external lightning protection system for which the required separation distance between all conductive parts of the building and of the electrical installation is maintained, a type 1 SPD is required for the AC-side system protection. Also in the case of DC-side system protection, it is sufficient to have one type 2 SPD with a discharge capacity of at least 5 kA (8/20 μs) per mode of protection.
However, if the required separation distance is not maintained, a type 1 SPD is required for the DC-side system protection. For this purpose, IEC 61643-32  defines the required discharge capacity for the SPDs to be used, depending on the lightning protection class and the SPD technology used.
The differentiation between the SPD technology used is based on the fact that the SPD itself influences the distribution of lightning current in the system and, as a result, has to discharge surge currents of different magnitudes based on the technology. IEC 61643-32  makes a distinction here between voltage-limiting SPDs based on varistors and voltage-switching SPDs based on spark gaps or gas-filled surge protective devices (gas discharge tube, GDT). Combinations of these basic elements are viewed as follows: The series connection consisting of varistor and GDT is also viewed as voltagelimiting, while the parallel connection is viewed as voltage-switching. For effective system protection, IEC 61643-32  also provides instructions on the number of SPDs to be installed and the optimum installation location. To protect the inverter, follow the recommendation to install the SPDs as close to it as possible.
If the cable length between PV panels and inverters exceeds 10 m, install an additional protective device at the other end of the cable in the area of the PV panels to protect these effectively, too. In systems with an external lightning protection system where the separation distance is not maintained, it is also necessary for the metal frames and carrier systems of the PV panels to be connected to the lightning protection system with connectors that are able to carry lightning current. In this case, regardless of the respective cable length, a type 1 SPD has to be installed at each installation site. The reason for this is that all cables of the PV system are considered parallel paths to the equipotential bonding lines and the building’s protective devices and, connected via the SPDs, must carry partial lightning currents.
6.3.2 Free-standing systems
Compared to physical structures, further aspects are relevant for properly designing lightning and surge protection systems for free-standing PV systems:
- Equipotential bonding mesh width
- Design of the grounding system
- Use of inverter types (string or central power inverters)
Free-standing systems are generally characterized by a high intermeshed equipotential bonding system, which is normally equipped with numerous ground connections. The module frames are also connected to the equipotential bonding system. The cable lengths between the PV panels and the feeding point can be several hundred meters in these systems.
If lightning strikes the external lightning protection system, partial lightning currents are coupled into the equipotential bonding system. Therefore, free-standing systems with central power inverters on the DC side are to be protected using type 1 SPDs, for which the required performance is specified in Table 8.
For free-standing systems with string inverters installed near the PV panels, the following applies:
To protect the AC side, choose SPDs with a discharge capacity analogous to the values in Table 8. To protect the DC side, it is sufficient to use type 2 SPDs with a discharge capacity of at least 5 kA (8/20 μs) per mode of protection.
The costs of a PV system can be significantly reduced by a high DC system voltage of up to 1500 V. Fewer string combiner boxes are needed, and material costs for cable installation are also reduced. With the FLP12,5-PV product range, LSP is setting new standards with high-performance SPDs for voltages up to 1500 V DC. It features a high total discharge capacity Itotal of 12.5 kA (10/350 μs) and thereby satisfies all standard requirements and conditions of the installation guideline for use in lightning protection class III and IV.
6.4 Protection of signal transmission circuits in MCR technology
Interference-free transmission of signals plays a central role in the field of measurement, control and regulation technology (MCR technology). Smooth operation of building services management, manufacturing or process technology demands a high level of quality and availability of the signals transmitted. However, these technologies are being exposed to an increasingly active electrical environment. This isespecially true for the rather weak signals emitted by sensors. Small voltages or electric currents that must be securely transmitted, carefully conditioned or evaluated are increasingly being subjected to electromagnetic and radio frequency interference. Reasons for this are:
- An increasing number of electrically operated components in all performance classes, especially motors operated via frequency inverters and other actuators.
- The increasing miniaturization and packing density of device components.
- A growing volume of wireless communication and control equipment.
- Digital systems that work with ever higher transmission frequencies.
Insufficient consideration of these disturbance variables, inadequate adjustments to remedy faults or other planning deficiencies can all affect interference-free signal transmission.
Surge voltages, such as those caused by the effects of lightning, can also have a negative impact on the function and availability of electronic modules in MCR technology. Interference and damage caused by surge voltages in MCR technology systems can, however, be effectively prevented by using tailor-made protective devices.
Depending on the potential for risk and the requirements of the protection level, surge protective devices with combined protective circuits or with individual components are used. These are installed directly upstream of the signal inputs to be protected. The circuits of the surge protective devices to be used are adapted to the various signal types.
6.4.1 Function of surge protective devices
A plethora of different applications and signal forms exist in MCR technology. For this reason, various protective devices specifically tailored to the respective application are necessary. Typical components for these protective devices include gas discharge tubes (GDT) and transient voltage suppressor diodes (TVS diode). Varistors are seldom used due to their “aging behavior” (increase of leakage current after heavy loading) and larger design.
GDTs consist of an electrode arrangement in a ceramic or glass tube. Inert gas, such as argon or neon, is located between the electrodes. When the strike voltage is reached, the component changes to a low resistance state as a result of the gas discharge used. The strike voltage is not a constant; rather, it is dependent on the rate of rise of the surge voltage. After igniting the discharge path, arc voltage between 10 and 30 V is typically generated, which can be measured as a voltage drop at the SPD. GDTs have a high surge current discharge capacity of more than ten thousand amperes (8/20 μs). With values starting at several hundred volts, however, the voltage protection level is relatively high. Suppressor diodes become conductive if a voltage threshold or the reverse voltage UR is exceeded. A current of 1 mA flows through the suppressor diode at the slightly higher breakdown voltage UBR. At this point, the suppressor diode starts limiting the surge voltage. The maximum limit voltage is the highest voltage that can occur at the suppressor diode in the event of surge voltage. The main advantages of TVS diodes are the reaction speed and the exceptional voltage limiting. The surge voltage discharge capacity is significantly lower than that of GDTs, however. Modern protective devices use GDTs and TVS diodes tailored to one another to make best use of their respective benefits. This way, the GDT offers a high discharge capacity and the TVS diode provides a lower voltage protection level and speedy response behavior. Achieving this requires coordinating the coupling elements between the GDT and TVS diode. The way a two-level circuit such as this works is explained in Figure 76. If a transient overvoltage occurs between the signal wires, the TVS diode assumes a low-resistance state after a short response time. This results in a flow of current over the diode and the decoupling elements found in the signal path Rtotal. The voltage drop is limited to the value of the maximum clamping voltage at the diode and to the value of the voltage protection level UP at the output terminal of the SPD. The optimal design for conducting current through the SPD features a voltage protection level UP that is only slightly higher than the maximum clamping voltage. In order to discharge surge currents that exceed the maximum surge current discharge capacity of the TVS diode, the GDT must conduct the portion of the surge current that would otherwise result in an overload of the TVS diode. The current is commutated abruptly in this process after the voltage on the GDT reaches its strike voltage UZ. When the flow of current is applied, the voltage present at the discharge path sinks to the value of the arc voltage (10 V – 30 V depending on the type). The commutation behavior at the protective devices being observed (Fig. 76) is determined mainly by the resistance of the decoupling elements, which is made clear from subsequent observation. The voltage drop UG at the GDT, which determines its ignition behavior, arises from the voltage drop along the decoupling elements (observation in terms of resistance) and the voltage drop US at the TVS diode. From the approximately linear relationship of the previously mentioned voltage drops, it becomes apparent that the voltage drop at the GDT and, moreover, its response behavior and power conversion in the TVS diode can be specifically controlled by varying the resistance value of the decoupling elements. These positive characteristics linked to the increase of Rtotal are in contrast with the increase of power losses in the decoupling elements (resistances). An upper limit for the rated current of the SPD is derived from the self-heating, connected with the need to comply with maximum temperatures.
Various protective circuits tailored to individual applications are available for MCR technology. First of all, a distinction is made between signal types that are designed as an independent closed circle (loop) and signals with a common reference potential or a shared return conductor. The independent closed circuits (loops) are often designed so that they are insulated from the ground potential for interference immunity. A frequently encountered application of this type is the 4 to 20 mA current loop for transmitting measured values. The SPDs are designed to ensure continued insulation in the application. Gas discharge tubes guarantee insulation between the signal wires and the ground potential during operation. In the event of surge voltage, the GDT effectively discharges the transients to ground and limits the voltage so that the dielectric strength of the end device is not exceeded. Typical dielectric strength of end devices is 1.5 kV. In addition to protecting the dielectric strength, protection between signal wires is especially important for MCR applications in order to prevent exceeding the electric strength. The end devices are often much more sensitive to potential differences of this nature, as sensitive semiconductor components in the end device are directly affected. Often, the corresponding electric strength of the devices is below 100 V. The protection level reached by the SPD therefore consists of a fast-response TVS diode that implements a correspondingly low voltage protection level.
In cases where the decoupling resistors in the common mode paths are not reliable, a version of the circuit without decoupling is needed. This can be the case with Pt 100 two-conductor measuring circuits in which the resistors can distort the measuring result. Even for actuator circuits with higher nominal currents, this type of protective circuit is used. A lower surge current discharge capacity between the signal wires nonetheless results if there is no decoupling present.
Applications with a common reference potential require a specially designed protective circuit, as the sensitive semiconductor components in the end devices can also be damaged by transient overvoltages between the signal wires and the reference potential. For this reason, in such cases the TVS diodes are switched between each wire and the reference potential. In cases where the reference potential is grounded, the SPD can be used, as shown in Fig. 79. In the majority of cases, a direct connection between the common reference potential (e.g. ground) and the ground potential is not permitted or desired. Circuit versions with an additional GDT between the reference potential and the ground are used for this application. (Fig. 80). This is referred to as indirect grounding.
6.4.2 Protection zone concept in MCR applications
The necessity for implementing surge protection is determined based on a risk analysis. SPDs are then selected using the test class prescribed by the zone transition (see Fig. 81). In order to attain the ideal optimal protective effect, the SPDs are each to be placed at the zone limits. All cables that lead into or out of the building are to be integrated into the common equipotential bonding by the corresponding SPDs. In particular, the zone concept is to be applied if there is an external lightning protection system. For example, the first protection level (j, I) primarily offers protection against destruction for installation directly at the entrance to the building. The SPDs used are to be rated according to the expected level of threat. Subsequent SPDs (k,n and m,o) then only need to reduce the interference voltages and surge currents to a value acceptable for the end device. In contrast to the SPD installation for power supply systems, an SPD must be installed at every zone transition for MCR signals (see IEC 61643-22, ).
In practice, the choice is made to not separate the signal cables from the field at each zone transition. This keeps the cost of installation low. Multiple protection levels are therefore combined in one MCR SPD. As a practical solution, this protective module can be installed upstream of the device to be protected, such as the inputs of a controller. Compared to SPDs for power supply in accordance with IEC 61643-11, the distinction here is not made according to T1, T2, T3; rather, the SPDs are classified according to discharge capacity. D1 for lightning signals at the LPZ 0/1 zone limit, C2 for reduced noise pulses at LPZ 1/2 and C1 at LPZ 2/3. The selection list (Table 9) from DIN CLC/TS 61643-22  provides information about the location at which each SPD type must be installed.
Surge protection for current loops
Measured values are usually transmitted using standardized processes in the field. The 4 to 20 mA signal is used especially often for applications where longer cables are in use. The measured value at the sensor is converted into a current value that runs between
both transmission devices. The ohmic resistance of the cable has no influence here on the current of the measured value transmission. For current loops, two signal wires are often used which do not require an additional reference potential and are routed in an insulated state from the ground potential. In order to protect an application of this kind from transients, an SPD is needed at both end points. The respective SPD is equipped with a multi-stage protective circuit. Transient normal-mode voltages between signal wires and common-mode voltages to ground are effectively limited at both end points as a result (see Fig. 82).
Surge protection for binary signals
In control technology, modules are often used that feature a higher number of signal inputs and outputs (digital in/ digital out). Furthermore, there is a common reference potential that is often simultaneously used as a common return conductor from the field. The protective circuit suitable for this type of application is designed with two protection levels between each wire and the common reference potential. Between two neighboring” signal wires, there is always protection through series connection of two suppressor diodes. Moreover, there is protection to the ground via a GDT so that, together, all conceivable transients are limited (see Fig. 83).
Surge protection for temperature measurements
If a temperature measurement is taken using a temperature-dependent resistor, like Pt 100, the ohmic portion of the additional cables as well as the decoupling resistors of surge protective devices specifically need to be taken into account. In the case of two-wire measurement, the resistance value of the SPD can distort the measured result. If the sum of the decoupling resistances in the measured circuit is, for example, 4 ohms, there is then a measuring error of 4% for a measurement of 0°C, as instead of 100 ohms, 104 ohms is detected. For this reason, the two-stage protective circuits are available as a version without decoupling resistors in order to minimize the influence of the SPD in this application (see Fig. 84).
Surge protection in explosion protected areas
Explosive atmospheres can frequently occur in the chemical and petrochemical industries due to industrial processes. They are caused, for example, by gases, fumes or vapors. Explosive atmospheres are also likely to occur in mills, silos, and sugar and fodder factories due to the dust present there. Therefore, electrical devices in potentially explosive areas are subject to special directives. This also applies to SPDs that are used in these types of applications.
Potentially explosive areas are divided into standardized zones. Classification for explosive dust and gas zones is found in the standard IEC/EN 60079-11 . Zones are classified based on the probability that an explosive atmosphere will arise.
The Ex i intrinsic safety type of protection is used often in the field of MCR technology. Intrinsic safety protection, as opposed to other types of protection (such as increased safety), refers not only to individual items of equipment but to the entire circuit. A circuit is described as intrinsically safe if the current and voltage are limited to such an extent that no spark or thermal effect can cause an explosive atmosphere to ignite. The voltage is limited in order to keep the energy of the spark below the ignition energy of the surrounding gas. A thermal effect, such as a surface that is too hot, is prevented by limiting the current. Energy may also be stored in the form of capacitances or inductances within the intrinsically safe circuit. This must also be taken into consideration when examining the intrinsically safe circuit. Safety level ia, ib or ic defines whether protection is maintained with two faults or one fault in the protective circuit, or whether no protection is provided in the event of a fault. Intrinsic safety is based on fault monitoring in order to rule out an explosion hazard. In relation to the surge protection of intrinsically safe circuits, it is important to ensure that a corresponding Ex i approval is present. Furthermore, the SPD must be able to discharge at least 10 signals of a surge current of 10 kA (8/20 μs) safely. The comprehensive description of explosion protection measures in connection with the intrinsic safety type of protection can be found in the standard IEC/EN 60079-11 .
Area in which a hazardous explosive gas atmosphere is present for continuous, frequent or long periods. These conditions are usually found inside containers, pipelines, equipment and tanks.
Area in which a hazardous explosive gas atmosphere is to be expected only occasionally during normal operation. This includes the immediate area surrounding zone 0, as well as areas close to filling and emptying equipment.
Area in which a hazardous explosive gas atmosphere is not expected during normal operation; however if it does occur, it is only for a short time. Zone 2 includes areas that are used exclusively for storage, areas around pipe connections that can be disconnected and generally the intermediate area surrounding zone 1.
6.5 Protection of signal transmission circuits in information technology
Communication via data networks is a part of daily life in all areas of business.
The interfaces operate with low signal levels at high frequencies. This makes them particularly sensitive to surge voltages and can lead to the destruction of electronic components in IT systems. In addition to protection that is tailored to these systems, SPDs must also exhibit high-quality signal transmission behavior, as otherwise malfunctions are to be expected in the data transmission. This aspect is becoming increasingly important in the face of constantly increasing data transmission rates. To this end, when developing new SPDs for IT systems, the focus is on implementing high-quality signal transmission behavior. It is evaluated based on the ISO/IEC 11801 or EN 50173 standards.
Furthermore, a wide range of connection technology is seen in this area of application. For this reason, the protective devices must correspond to the electrical specifications and also be adapted to the interfaces to be protected. The SPD versions often differ only in their design and connection technology
The protective circuits usually combine fast-responding, low-capacitive suppressor diodes with powerful gas discharge tubes. Where required by the circuit technology, ohmic resistors decouple the two protection stages.
6.5.1 Ethernet and token ring interface
The architecture or structure of a network installation and the type of data transfer between the terminals in the data network are referred to as the topology.
In local networks, they have been tried and tested as bus, ring, and star topologies that can also be combined. To transmit information in data networks, twisted pair or fiber optics are used.
Data transmission requirements
Ethernet and token ring interfaces have been used for years. Ethernet systems have prevailed, however, due to their transmission speed and compact connectors. The transmission behavior of the Ethernet system is defined in standard IEEE 802.3. The transmission speed is up to 10 Gbps.
The transmission speed is defined (Table 11) depending on the performance categories (cat. 5 – cat. 7).
Newer systems with high transmission frequency requirements function in accordance with cat. 6 and cat. 7, and eventually cat. 8.1 or cat. 8.2.
Protective devices with RJ45 connection, where all eight signal paths are protected, are universally suited to the Ethernet, PROFINET and token ring interfaces.
Power over Ethernet (PoE)
Power over Ethernet (PoE) is a process in which the auxiliary energy for the connected devices is also transmitted via the Ethernet data cable.
The auxiliary power is applied either to the unused wire pairs (mode B, Fig. 100) or fed as phantom power (mode A, Fig. 99) between the signal wire pairs. In line with IEEE 802.3af, a maximum power of 13.5 W can be transmitted using this method. The subsequent IEEE 802.3at standard now allows 25.5 W with PoE+. PoE++ is being debated, which will make it possible to achieve even higher transmission capacities.
6.5.2 Serial interfaces
Serial interfaces allow for data exchange between computers and peripheral devices. During serial data transmission, the bits are transmitted over a cable (in series), one after the other. Particularly common are:
The DT-CAT-6AEA protective device optimally protects sensitive equipment, as quickly reacting protective components are used for the data cabling as well as for the PoE system.
ATEX is a widely used synonym for the ATEX directive issued by the European Union. The ATEX designation is derived from the French abbreviation for “atmospheres explosibles”
By binary signals, we mean digital signals that only take on the state of “high” or “low”. Generally, these signals relate to a common reference potential or a shared return conductor.
Insulation strength of the electrical circuits of a piece of equipment when compared to withstand and surge voltages with amplitudes above the maximum continuous voltage.
EMC stands for electromagnetic compatibility, the capacity of an apparatus, plant or system to work satisfactorily in an electromagnetic environment, without causing electromagnetic interference itself that would be unacceptable for the apparatus, plants or system in this setting.
Follow current interrupt rating (Ifi)
The follow current interrupt rating indicates the prospective r.m.s. value of the short-circuit current at the installation location of a voltageswitching SPD, up to which the SPD once again transitions into a high ohmic state if the maximum UC continuous voltage is being independently applied due to a surge current, without triggering an upstream overcurrent protective device.
Gas discharge tube, GDT
Gas-filled surge protective device
The attenuation value is defined as the ratio of voltages that occur immediately before and after the insertion point of the protective device to be tested. The result is expressed in decibels.
Lightning protection class
A standardized classification of lightning protection systems into classes I to IV. They are based on a set of lightning current parameter values with regard to probability, whereby the largest and smallest measured values in the event of naturally occurring strikes cannot be exceeded and the strikes can be safely discharged. Lightning protection class I thereby corresponds to the highest measured values and the greatest probability of capturing a strike. The values decrease accordingly, down to lightning protection class IV.
Lightning protection system
System consisting of external interception rods, protective devices, and grounding system, as well as equipotential bonding system and coordinated SPD system within the physical structure to protect against damage caused by surge voltages and surge currents from lightning strikes.
Lightning protection zone (LPZ)
A zone in which the electromagnetic environment is determined with regard to risk of lightning. All (supply) lines that cross zone limits must be included in the lightning protection equipotential bonding by means of corresponding SPDs. The zone limits of a lightning zone are not necessarily physical limits (e.g., walls, floor or ceiling).
Maximum continuous voltage (UC)
Maximum r.m.s. value of the voltage that can continuously be applied to the mode of protection of the SPDs. The maximum continuous voltage must be at least 10% higher than the value of the nominal voltage. In systems with greater voltage fluctuations, SPDs with a greater difference between UC and UN must be used.
Nominal discharge current (In)
Peak value of the current flowing through the SPD with pulse shape (8/20 μs). The pulse shape (8/20 μs) of a surge current is characteristic of the effects of an indirect lightning strike or switching operation. The value of the nominal discharge current is used for a variety of tests on an SPD, including those used to determine the voltage protection level. Depending on the lightning protection class assigned to a lightning protection system, the
SPDs must have minimum values that correspond to this value.
Nominal load current (IL)
Maximum r.m.s. value of the nominal current, which can flow to an ohmic load that is connected to the protected output of the SPD. This maximum value is specified by the parts carrying operational current within the SPDs; these must be able to withstand the continuous thermal current load.
Nominal voltage (UN)
The nominal value of the voltage of the current or signal circuit based on the use envisaged for the SPDs. The nominal voltage stated for an SPD corresponds to the system voltage of the typical SPD installation site for a standard three phase system, e.g., 230/400 V AC. Lower system voltages can also be protected by the SPD. In the event of higher system voltages, it must be decided on a case-to-case basis as to whether the SPD can be used and if there are restrictions to observe.
Off-load voltage (UOC)
Off-load voltage of the hybrid generator at the terminal points of the SPD. A hybrid generator creates a combined surge, i.e. in off-load, it supplies a voltage pulse with a defined pulse shape, generally (1.2/50 μs), and in a short circuit, a current pulse with a defined pulse shape, generally (8/20 μs). The combined surge is characteristic of the effects of an induced surge voltage. Depending on the protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this value.
Overcurrent protective device, OCPD
Overcurrent protective device
Division of equipment into categories I to IV depending on their surge voltage resistance. Overvoltage category I corresponds to the lowest value and consists of particularly sensitive (end) devices. These values increase accordingly, up to overvoltage category IV. The values for the individual categories also depend on the voltage level of the power supply system.
Power over Ethernet (PoE)
Power over Ethernet is a process in which the auxiliary energy for the connected devices is also transmitted via the Ethernet data cable.
Pulse discharge current (Iimp)
Peak value of the current flowing through the SPD with pulse shape (10/350 μs). The pulse shape (10/350 μs) of a surge current is characteristic of the effects of a direct lightning strike. The value of the pulse discharge current is used for special SPD tests to demonstrate carrying capacity with regard to high-energy lightning currents. According to the lightning protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this value.
Short-circuit withstand capability (ISCCR)
Maximum prospective short-circuit current of the electrical network, for which the SPD is rated in conjunction with the upstream overcurrent protective device. The short-circuit withstand capability indicates the maximum prospective short-circuit current at which the SPD can be used at the installation location. The corresponding tests to determine this value are carried out in connection with the upstream overcurrent protective device. In the event that the special surge protective devices for PV systems correspond to the value ISCPV, this is the maximum DC short-circuit current of a system up to which the SPD may be used.
A pulse-shaped current that is characterized by a significant rise in current within a short period of time. Typical pulse shapes are (8/20 μs), with which the voltage-limiting behavior of SPDs can be checked, and (10/350 μs), with which the lightning current capacity of the SPDs can be tested.
Surge protective device, SPD
Surge protective device
A pulse-shaped voltage that is characterized by a significant rise in voltage within a short period of time. A typical pulse shape is (1.2/50 μs). The response behavior of SPDs or the surge voltage resistance of equipment can also be tested with this.
TVS stands for Transient Voltage Suppression.
Voltage protection level (Up)
Maximum voltage that can occur on the connection terminal blocks of the SPD while loaded with a pulse of specific voltage steepness and a discharge surge current of specified amplitude and wave form. This value characterizes the surge voltage protective effect of the SPD. In the event of a surge voltage phenomenon within the performance parameters of the SPD, the voltage is safely limited to a maximum of this value at the protected connections of the SPD.
 International Electrotechnical Commission. IEC 62305-1 – Lightning protection – Part 1: General principles. s.l. : VDE Verlag GmbH, 2010.
 International Electrotechnical Commission. IEC 62305-2 – Lightning protection – Part 2: Risk management. s.l. : VDE Verlag GmbH, 2010.
 International Electrotechnical Commission. IEC 62305-3 – Lightning protection – Part 3: Physical damage to structures and life hazard. s.l. : VDE Verlag GmbH, 2010.
 International Electrotechnical Commission. IEC 62305-4 – Lightning protection – Part 4: Protection against lightning. Electrical and electronic systems within structures. s.l.: VDE Verlag GmbH, 2010.
 International Electrotechnical Commission. IEC 60364-4-44 – Low-voltage electrical installations – Part 4-44: Protection for safety – Protection against voltage disturbances and electromagnetic disturbances. s.l. : VDE Verlag GmbH, 2015.
 International Electrotechnical Commission. IEC 61643-11 – Surge protective devices connected to low-voltage power systems – Requirements and test methods. s.l. : VDE Verlag GmbH, 2011.
 International Electrotechnical Commission. IEC 61643-21 – Surge protective devices connected to telecommunications and signaling networks – Performance requirements and testing methods. s.l. : VDE Verlag GmbH, 2000.
 International Electrotechnical Commission. IEC 61643-31 – Low-voltage surge protective devices – Requirements and tests for surge protective devices to be used in photovoltaic installations. Requirements and test methods. s.l. : VDE Verlag GmbH, 2015.
 International Electrotechnical Commission. IEC 60664-1 – Insulation coordination for equipment within lowvoltage systems – Part 1: Principles, requirements, and tests. s.l. : VDE Verlag GmbH, 2007.
 International Electrotechnical Commission. IEC 60364-1 – Low-voltage electrical installations – Part 1: Fundamental principles, assessment of general characteristics, definitions. s.l. : VDE Verlag GmbH, 2005.
 International Electrotechnical Commission. IEC 60364-5-53 – Electrical installations of buildings – Part 5: Selection and erection of electrical equipment; Section 53: Switchgear and control. s.l. : VDE Verlag GmbH, 2015.
 International Electrotechnical Commission. IEC 60364-4-43 – Low-voltage electrical installations – Part 4-43: Protection for safety – Protection against overcurrent. s.l. : VDE Verlag GmbH, 2008.
 European Committee for Electrotechnical Standardization. CLC/TS 50539-12 – Low-voltage surge protective devices connected to photovoltaic installations – Selection and application principles. s.l. : VDE Verlag GmbH, 2013.
 Phoenix Contact GmbH & Co. KG. TRABTECH surge protection – user manual for specialist electrical planners. 2015.
 International Electrotechnical Commission. IEC 61643-12 – Surge protective devices connected to low-voltage power systems – Selection and application principles. s.l. : VDE Verlag GmbH, 2010.
 International Electrotechnical Commission. IEC 61643-22 – Low-voltage surge protective devices – Surge protective devices connected to telecommunications and signaling – Selection and application principles. s.l. : VDE Verlag GmbH, 2007.
 International Electrotechnical Commission. IEC 60079-11 (VDE 0170-7) – Explosive atmospheres – Part 11: Equipment protection by intrinsic safety “i” VDE-VERLAG GMBH, 2012
 International Electrotechnical Commission. IEC 61643-32 – Low-voltage surge protective devices – Requirements and tests for surge protective devices