Surge Protection Device Overview (AC and DC POWER, DATALINE, COAXIAL, GAS TUBES)
Surge Protection Device (or surge suppressor or surge diverter) is an appliance or device designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. This article primarily discusses specifications and components relevant to the type of protector that diverts (shorts) a voltage spike to the ground; however, there is some coverage of other methods.
A power bar with built-in surge protector and multiple outlets
The terms surge protection device (SPD) and transient voltage surge suppressor (TVSS) is used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical surges and spikes, including those caused by lightning. Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels, to protect equipment in a household from similar hazards.
AC Surge Protection Device Overview
Overview of Transient Overvoltages
The users of electronic equipment and telephone and data-processing systems must face the problem of keeping this equipment in operation in spite of the transient overvoltages induces by lightning. There is several reasons for this fact (1) the high level of integration of electronic components makes the equipment more vulnerable, (2) interruption of service is unacceptable (3) data transmission networks cover large areas and are exposed to more disturbances.
Transient overvoltages have three main causes:
- Industrial and switching surges
- Electrostatic Discharge (ESD)
Lightning, investigated since Benjamin Franklin’s first research in 1749, has paradoxically become a growing threat to our highly electronic society.
A lightning flash is generated between two zones of opposite charge, typically between two storm clouds or between one cloud and the ground.
The flash may travel several miles, advancing toward the ground in successive leaps: the leader creates a highly ionized channel. When it reaches the ground, the real flash or return stroke takes place. A current in the tens of thousands of Amperes will then travel from ground to cloud or vice versa via the ionized channel.
At the moment of discharge, there is an impulse current flow that ranges from 1,000 to 200,000 Amperes peak, with a rise time of about a few microseconds. This direct effect is a small factor in damage to electric and electronic systems because it is highly localized.
The best protection is still the classic lightning rod or Lightning Protection System (LPS), designed to capture the discharge current and conduct it to a particular point.
There are three types of indirect lightning effects:
Impact on overhead line
Such lines are very exposed and may be struck directly by lightning, which will first partially or completely destroy the cables, and then cause high surge voltages that travel naturally along the conductors to line-connected equipment. The extent of the damage depends on the distance between the strike and the equipment.
The rise in ground potential
The flow of lightning in the ground causes earth potential increases that vary according to the current intensity and the local earth impedance. In an installation that may be connected to several grounds (e.g. link between buildings), a strike will cause a very large potential difference and equipment connected to the affected networks will be destroyed or severely disrupted.
The flash may be regarded as an antenna several miles high carrying an impulse current of several tenths of kilo-amperes, radiating intense electromagnetic fields (several kV/m at more than 1km). These fields induce strong voltages and currents in lines near or on equipment. The values depend on the distance from the flash and the properties of the link.
An industrial surge covers a phenomenon caused by switching electrical power sources on or off.
Industrial surges are caused by:
- Starting motors or transformers
- Neon and sodium light starters
- Switching power networks
- Switch “bounce” in an inductive circuit
- Operation of fuses and circuit breakers
- Falling power lines
- Poor or intermittent contacts
These phenomena generate transients of several kV with rising times of the order of the microsecond, disturbing equipment in networks to which the source of disturbance is connected.
Electrically, a human being has a capacitance ranging from 100 to 300 picofarads and can pick up a charge of as much as 15kV by walking on carpet, then touch some conducting object and be discharged in a few microseconds, with a current of about ten Amperes. All integrated circuits (CMOS, etc.) are quite vulnerable to this kind of disturbance, which is generally eliminated by shielding and grounding.
Effects of Overvoltages
Overvoltages have many types of effects on electronic equipment in order of decreasing importance:
- Voltage breakdown of semiconductor junctions
- Destruction of bonding of components
- Destruction of tracks of PCBs or contacts
- Destruction of trials/thyristors by dV/dt.
Interference with operations:
- Random operation of latches, thyristors, and triacs
- Erasure of memory
- Program errors or crashes
- Data and transmission errors
Components exposed to overvoltages have a shorter life.
Surge Protection Devices
The Surge Protection Device (SPD) is a recognized and effective solution to solve the overvoltage problem. For greatest effect, however, it must be chosen according to the risk of the application and installed in accordance with the rules of the art.
DC Power Surge Protection Device Overview
Background and Protection Considerations
Utility-Interactive or Grid-Tie Solar Photovoltaic (PV) Systems are very demanding and cost-intensive projects. They often require the Solar PV System to be operational for several decades before it can yield the desired return on investment.
Many manufacturers will guarantee a system life of greater than 20 years while the inverter is generally guaranteed for only 5-10 years. All costs and return on investments are calculated based on these time periods. However, many PV systems are not reaching maturity due to the exposed nature of these applications and its interconnection back to the AC utility grid. The solar PV arrays, with its metallic frame and mounted in the open or on rooftops, act as a very good lightning rod. For this reason, it is prudent to invest in a Surge Protective Device or SPD to eliminate these potential threats and thus maximize the systems life expectancy. The cost for a comprehensive surge protection system is less than 1% of the total system expenditure. Be sure to use components that are UL1449 4th Edition and are Type 1 Component Assemblies (1CA) to ensure that your system has the best surge protection available on the market.
To analyze the full threat level of the installation, we must make a risk assessment.
- Operational Downtime Risk – Areas with severe lightning and unstable utility power are more vulnerable.
- Power Interconnection Risk – The greater the surface area of the solar PV array, the more exposure to direct and/or induced lightning surges.
- Application Surface Area Risk – The AC utility grid is a likely source of switching transients and/or induced lightning surges.
- Geographic Risk – Consequences of system downtime are not only limited to equipment replacement. Additional losses can result from lost orders, idle workers, overtime, customer/management dissatisfaction, expedited freight charges and expedited shipping costs.
1) Earthing System
Surge Protectors shunt transients to the earth grounding system. A low impedance ground path, at the same potential, is critical for the surge protectors to function properly. All power systems, communication lines, grounded and ungrounded metallic objects need to be equipotential bonded for the protection scheme to work efficiently.
2) Underground Connection from External PV Array to Electrical Control Equipment
If possible, the connection between the external Solar PV Array and the internal power control equipment should be underground or electrically shielded to limit the risk of direct lightning strikes and/or coupling.
3) Coordinated Protection Scheme
All available power and communication networks should be addressed with surge protection to eliminate PV system vulnerabilities. This would include the primary AC utility power supply, Inverter AC output, Inverter DC input, PV string combiner and other related data/signal lines such as Gigabit Ethernet, RS-485, 4-20mA current loop, PT-100, RTD, and telephone modems.
Data Line Surge Protection Device Overview
Data Line Overview
Telecommunication and data transmission devices (PBX, modems, data terminals, sensors, etc…) are increasingly more vulnerable to lightning induced voltage surges. They have become more sensitive, complex and have an increased vulnerability to induced surges due to their possible connection across several different networks. These devices are critical to a companies communications and information processing. As such, it is prudent to insure them against these potentially costly and disruptive events. A data line surge protector installed in-line, directly in front of a sensitive piece of equipment will increase their useful life and maintain the continuity of the flow of your information.
Technology of Surge Protectors
All LSP telephone and data line surge protectors are based on a reliable multistage hybrid circuit that combines heavy duty Gas Discharge Tubes (GDTs) and fast responding Silicon Avalanche Diodes (SADs). This type of circuit provides,
- 5kA Nominal Discharge Current (15 times without destruction per IEC 61643)
- Less than 1 nanosecond response times
- Fail-safe disconnection system
- Low capacitance design minimizes signal loss
Parameters for Selecting A Surge Protector
To select the correct surge protector for your installation, keep the following in mind :
- Nominal and Maximum Line Voltages
- Maximum Line Current
- Number of Lines
- Data Transmission Speed
- Type of Connector (Screw Terminal, RJ, ATT110, QC66)
- Mounting (Din Rail, Surface Mount)
To be effective, the surge protector must be installed in accordance with the following principles.
The ground point of the surge protector and of the protected equipment must be bonded.
The protection is installed at the service entrance of the installation to divert impulse current as soon as possible.
The surge protector must be installed in close proximity, less than 90 feet or 30 meters) to protected equipment. If this rule cannot be followed, secondary surge protectors must be installed near to the equipment.
The grounding conductor (between the earth output of the protector and the installation bonding circuit) must be as short as possible (less than 1.5 feet or 0.50 meters) and have a cross sectional area of at least 2.5 mm squared.
The earth resistance must adhere to the local electrical code. No special earthing is necessary.
Protected and unprotected cables must be kept well apart to limit coupling.
Test Standards and installation recommendations for communication line surge protectors must comply with the following standards :
UL497B : Protectors for Data Communications and Fire-Alarm Circuits
IEC 61643-21 : Tests of Surge Protectors for Communication Lines
IEC 61643-22 ; Choice/Installation of Surge Protectors for Communication Lines
NF EN 61643-21 : Tests of Surge Protectors for Communication Lines
Guide UTE C15-443 : Choice/Installation of Surge Protectors
Special Conditions : Lightning Protection Systems
If the structure to be protected is equipped with a LPS (Lightning Protection System), the surge protectors for telecom or data lines that are installed at the buildings service entrance need to be tested to a direct lightning impulse 10/350us wave form with a minimum surge current of 2.5kA (D1 category test IEC-61643-21).
Coaxial Surge Protection Device Overview
Protection For Radio Communication Equipment
Radio communication equipment deployed in fixed, nomadic or mobile applications is especially vulnerable to lightning strikes because of their application in exposed areas. The most common disruption to service continuity result from transient surges originating from direct lightning strikes to the antenna pole, surrounding ground system or induced onto connections between these two areas.
Radio equipment utilized in CDMA, GSM/UMTS, WiMAX or TETRA base stations, must consider this risk in order to insure uninterrupted service. LSP offers three specific surge protection technologies for Radio Frequency (RF) communication lines that are individually suited for the different operational requirements of each system.
RF Surge Protection Technology
Gas Tube DC Pass Protection
Gas Discharge Tube (GDT) DC Pass Protection is the only surge protection component usable on very high frequency transmission (up to 6 GHz) due to its very low capacitance. In a GDT based coaxial surge protector, the GDT is connected in parallel between the central conductor and the external shield. The device operates when its sparkover voltage is reached, during an overvoltage condition and the line is briefly shorted (arc voltage) and diverted away from sensitive equipment. The sparkover voltage depends on the rise front of the overvoltage. The higher the dV/dt of the overvoltage, the higher the sparkover voltage of the surge protector. When the overvoltage disappears, the gas discharge tube returns to its normal passive, highly insulated state and is ready to operate again.
The GDT is held in a specially designed holder that maximizes conduction during large surge events and still very easily removed if maintenance is required due to an end of life scenario. The P8AX Series can be used on coaxial lines running DC voltages up to -/+ 48V DC.
DC Pass – CXF60 series
DC Blocked – CNP-DCB series
Hybrid DC Pass Protection is an association of filtering components and a heavy duty gas discharge tube (GDT). This design provides an excellent low residual let through voltage for low frequency disturbances due to electrical transients and still provides a high surge discharge current capability.
Quarter Wave DC Blocked Protection
Quarter Wave DC Blocked Protection is an active band pass filter. It has no active components. Rather the body and corresponding stub are tuned to one quarter of the desired wave length. This allows only a specific frequency band to pass through the unit. Since lightning operates only on a very small spectrum, from a few hundred kHz to a few MHz, it and all other frequency’s are short-circuited to ground. The PRC technology can be selected for a very narrow band or wide band depending on the application. The only limitation for surge current is the associated connector type. Typically, a 7/16 Din connector can handle 100kA 8/20us while an N-type connector can handle up to 50kA 8/20us.
UL497E – Protectors for Antenna Lead-in Conductors
Parameters for Selecting a Coaxial Surge Protector
The information required to properly select a surge protector for your application is the following:
- Frequency Range
- Line Voltage
- Connector Type
- Gender Type
The proper installation of a coaxial surge protector is largely dependent on its connection to a low impedance grounding system. The following rules must be strictly observed:
- Equipotential Grounding System: All the bonding conductors of the installation must be interconnected to each other and connected back to the grounding system.
- Low Impedance Connection: The coaxial surge protector needs to have a low resistance connection to the Ground System.
Gas Discharge Overview
Protection for PC Board Level Components
Today’s microprocessor-based electronic equipment are increasingly more vulnerable to lightning-induced voltage surges and electrical switching transients because they have become more sensitive, and complex to protect due to their high chip density, binary logic functions and connection across different networks. These devices are critical to a company’s communications and information processing and typically can have an impact on the bottom line; as such it is prudent to ensure them against these potentially costly and disruptive events. A Gas Discharge Tube or GDT can be used as a standalone component or combined with other components to make a multistage protection circuit – the gas tube acts as the high energy handling component. GDT’s are typically deployed in the protection of communication and data line DC voltage applications because of its very low capacitance. However, they provide very attractive benefits on the AC power line including no leakage current, high energy handling and better end of life characteristics.
GAS DISCHARGE TUBE TECHNOLOGY
The gas discharge tube may be regarded as a sort of very fast switch having conductance properties that change very rapidly, when a breakdown occurs, from open-circuit to quasi-short circuit (arc voltage about 20V). There are accordingly four operating domains in the behavior of a gas discharge tube:
The GDT may be regarded as a very fast acting switch having to conduct properties that change very rapidly when a breakdown occurs and transforms from an open-circuit to a quasi-short circuit. The result is an arc voltage of about 20V DC. There are four stages of operation before the tube fully switches.
- Non-operating domain: Characterized by practically infinite insulation resistance.
- Glow domain: At the breakdown, the conductance increases suddenly. If the current is drained off by the gas discharge tube is less than about 0.5A (a rough value that differs from component to component), the low voltage across the terminals will be in the 80-100V range.
- Arc regime: As the current increases, the gas discharge tube shifts from low voltage to the arc voltage (20V). It is this domain that the gas discharge tube is most effective because the current discharge can reach several thousand amperes without the arc voltage across the terminals increasing.
- Extinction: At a bias voltage roughly equal to the low voltage, the gas discharge tube covers its initial insulating properties.
Protecting a two-wire line (for example a telephone pair) with two 2-electrode gas discharge tubes may cause the following problem:
If protected line is subjected to an overvoltage in the common mode, the dispersion of the spark overvoltages (+/- 20%), one of the gas discharge tubes sparks over a very short time before the other (typically a few microseconds), the wire that has the spark over is therefore grounded (neglecting the arc voltages), turning the common-mode overvoltage into a differential mode overvoltage. This is very dangerous for the protected equipment. The risk disappears when the second gas discharge tube arcs over (a few microseconds later).
The 3-electrode geometry eliminates this drawback. The spark over of one pole causes a general breakdown of the device almost immediately (a few nanoseconds) because there is only one gas-filled enclosure housing all the affected electrodes.
End of Life
The gas discharge tubes are designed to withstand many impulses without destruction or loss of the initial characteristics (typical impulse tests are 10 times x 5kA impulses for each polarity).
On the other hand, a sustained very high current, i.e. 10A rms for 15 seconds, with simulate the dropping out of the AC power line onto a telecommunication line and will take the GDT immediately out of service.
If a fail-safe end of life is desired, i.e. the short circuit that will report a fault to the end user when the line fault is detected, the gas discharge tube with the fail-safe feature (external short-circuit) should be selected.
Selecting a Gas Discharge Tube
- The information required to properly select a surge protector for your application is the following:
DC spark over voltage (Volts)
- Impulse spark over voltage (Volts)
- Discharge current capacity (kA)
- Insulation resistance (Gohms)
- Capacitance (pF)
- Mounting (Surface Mount, Standard Leads, Custom Leads, Holder)
- Packaging (Tape & Reel, Ammo pack)
The range of DC spark over voltage available:
- Minimum 75V
- Average 230V
- High Voltage 500V
- Very High Voltage 1000 to 3000V
*Tolerance on the breakdown voltage is generally +/-20%
This depends on the properties of the gas, the volume and the material of the electrode plus its treatment. This is the major characteristic of the GDT and the one that distinguishes it from the other protection device, i.e. Varistors, Zener Diodes, etc… The typical value is 5 to 20kA with an 8/20us impulse for standard components. This is the value the gas discharge tube can withstand repeatedly (minimum 10 impulses) without the destruction or alteration of its basic specifications.
Impulse Sparkover Voltage
The spark over voltage in the presence of a steep front (dV/dt = 1kV/us); the impulse spark over voltage increases with the increasing dV/dt.
Insulation Resistance and Capacitance
These characteristics make the gas discharge tube practically invisible during normal operating conditions. The insulation resistance is very high (>10 Gohm) while the capacitance is very low (<1 pF).
Test Standards and installation recommendations for communication line surge protectors must comply with the following standards:
- UL497B : Protectors for Data Communications and Fire-Alarm Circuits
To be effective, the surge protector must be installed in accordance with the following principles.
- The ground point of the surge protector and of the protected equipment must be bonded.
- The protection is installed at the service entrance of the installation to divert impulse current as soon as possible.
- The surge protector must be installed in close proximity, less than 90 feet or 30 meters) to protected equipment. If this rule cannot be followed, secondary surge protectors must be installed near to the equipment
- The grounding conductor (between the earth output of the protector and the installation bonding circuit) must be as short as possible (less than 1.5 feet or 0.50 meters) and have a cross-sectional area of at least 2.5 mm squared.
- The earth resistance must adhere to the local electrical code. No special earthing is necessary.
- Protected and unprotected cables must be kept well apart to limit coupling.
LSP gas discharge tubes require no maintenance or replacement under normal conditions. They are designed to withstand repeated, heavy-duty surge currents without damage.
Nevertheless, it is prudent to plan for the worst-case scenario and, for this reason; LSP has designed for the replacement of protection components where practical. The status of your data line surge protector can be tested with LSP’s model SPT1003. This unit is designed to test for the DC spark over voltage, clamping voltages and line continuity (optional) of the surge protector. The SPT1003 is a compact, push button unit with a digital display. The voltage range of the tester is 0 to 999 volts. It can test individual components such GDT’s, diodes, MOVs or stand-alone devices designed for AC or DC applications.
SPECIAL CONDITIONS: LIGHTNING PROTECTION SYSTEMS
If the structure to be protected is equipped with a LPS (Lightning Protection System), the surge protectors for telecom , data lines or AC power lines that are installed at the buildings service entrance need to be tested to a direct lightning impulse 10/350us waveform with a minimum surge current of 2.5kA (D1 category test IEC-61643-21).