Solutions for Railways & Transportation Surge Protection Devices and Voltage Limiting Devices
Why to protect?
Protection of railway systems: Trains, metro, trams
Rail transportation in general, whether underground, ground or by trams, put great emphasis on the safety and reliability of traffic, especially on the unconditional protection of persons. For this reason all the sensitive, sophisticated electronic devices (e.g. control, signalling or information systems) require a high level of reliability to meet the needs for safe operation and protection of persons. For economic reasons, these systems do not have sufficient dielectric strength for all possible cases of effects from overvoltage and therefore optimal surge protection must be adapted to the specific requirements of rail transportation. The cost of complex surge protection of the electric and electronic systems on the railways is only a fraction of the total cost of the protected technology and a small investment in relation to possible consequential damages caused by failure or destruction of equipment. The damages can be caused by the effects of surge voltage in both direct or indirect lightning strikes, switching operations, failures or due high voltage induced to the metal parts of railway equipment.
The main principle of optimal surge protection design is the complexness and coordination of SPDs and equipotential bonding by direct or indirect connection. Complexness is ensured by installing surge protective devices on all inputs and outputs of the device and system, that all power lines, signal and communication interfaces are protected. The co-ordination of the protections is ensured by installing SPDs with different protective effects consecutively in the correct order so as to progressively limit the surge voltage pulses to the safe level for the protected device. Voltage limiting devices are also an essential part of the comprehensive protection of electrified rail tracks. They serve to prevent impermissible high touch voltage on the metal parts of the railway equipment by establishing a temporary or permanent connection of the conductive parts with the return circuit of the traction system. By this function they protect primarily people who can get in touch with these exposed conductive parts.
What and how to protect?
Surge Protective Devices (SPD) for railway stations and railways
Power supply lines AC 230/400 V
The railway stations serves primarily to stop the train for the arrival and departure of passengers. In the premises there are important information, management, control and safety system for rail transportation, but also various facilities such as waiting rooms, restaurants, shops, etc., which are connected to the common power supply network and, due to their electrically proximate location, they may be at risk from a failure on the traction power supply circuit. To maintain trouble-free operation of these devices, three-level surge protection must be installed on the AC power supply lines. The recommended configuration of LSP surge protective devices is as follows:
- Main distribution board (substation, power line input) – SPD Type 1, e.g. FLP50, or combined lightning current arrester and surge arrester Type 1+2, e.g. FLP12,5.
- Sub-distribution boards – second level protection, SPD Type 2,e.g. SLP40-275.
- Technology / equipment – third level protection, SPD Type 3,
– If the protected devices is located directly in or close to the distribution board, then it is advisable to use SPD Type 3 for the mounting on the DIN rail 35 mm, such as SLP20-275.
– In cases of direct socket circuits protection into which IT devices such as copiers, computers, etc. can be connected, then it is suitable SPD for additional mounting into socket boxes, e.g. FLD.
– Most of the current measurement and control technology is controlled by microprocessors and computers. Therefore, in addition to overvoltage protection, it is also necessary to eliminate the effect of radio frequency interference that could disrupt the proper operation, e.g. by “freezing” the processor, overwriting data or memory. For these applications LSP recommends FLD. There are available also other variants according to the required load current.
In addition to its own railway buildings, the another important part of the whole infrastructure is the railway track with a wide range of control, monitoring and signalling systems (e.g. signal lights, electronic interlocking, crossing barriers, wagon wheel counters etc.). Their protection against the effects of surge voltages is very important in terms of ensuring trouble-free operation.
- To protect these devices it is suitable to install SPD Type 1 into power supply pillar, or even better product from the range FLP12,5, SPD Type 1+2 which, thanks to a lower protection level, better protects the equipment.
For railway equipment that are connected directly to or close to rails (for example, a wagon counting device), it is necessary to use the FLD, the voltage limiting device, to compensate possible potential differences between the rails and the protective ground the equipment. It is designed for easy DIN rail 35 mm mounting.
An important part of rail transportation systems are also all communication technologies and their proper protection. There can be various digital and analogue communication lines working on classic metal cables or wirelessly. For the protection of the equipment connected to these circuits can be used for example these LSP surge arresters:
- Telephone line with ADSL or VDSL2 – e.g. RJ11S-TELE at the entrance to the building and close to the protected equipment.
- Ethernet networks – universal protection for data networks and lines combined with PoE, for example DT-CAT-6AEA.
- Coaxial antenna line for wireless communication – e.g. DS-N-FM
Control and data signal lines
The lines of measuring and control equipment in the rail infrastructure must be, of course, also protected from the effects of surges and overvoltage in order to maintain the maximum possible reliability and operability. An example of the application of LSP protection for data and signal networks can be:
- Protection of the signal and measuring lines to railway equipment – surge arrester ST 1+2+3, e.g. FLD.
What and how to protect?
Voltage Limiting Devices (VLD) for railway stations and railways
During normal operation on the railways, due to voltage drop in the return circuit, or in relation with fault condition, there may occur impermissible high touch voltage on the accessible parts between return circuit and the earth potential, or on grounded exposed conductive parts (poles, handrails and other equipment). At the places accessible to people such as railway stations or tracks, it is necessary to limit this voltage to a safe value by installation of the Voltage Limiting Devices (VLD). Their function is to establish transient or permanent connection of exposed conductive parts with the return circuit in case when permissible value of touch voltage is exceeded. When choosing VLD it is necessary to consider whether function of VLD-F, VLD-O or both is required, as defi ned in EN 50122-1. Exposed conductive parts of the overhead or traction lines are usually connected to the return circuit directly or through VLD-F type device. So, voltage limiting devices type VLD-F are intended for the protection in case of faults, for example short-circuit of the electric traction system with exposed conductive part. Devices type VLD-O are used in normal operation, i.e. they limit increased touch voltage caused by the rail potential during the train operation. The function of voltage limiting devices is not the protection against lightning and switching surges. This protection is provided by Surge Protective Devices (SPD). The requirements on the VLDs have undergone considerable changes with the new version of standard EN 50526-2 and there are considerably higher technical demands on them now. According to this standard, VLD-F voltage limiters are classified as class 1 and VLD-O types as class 2.1 and class 2.2.
LSP protects the railway infrastructure
Avoid system downtime and disruptions in the railway infrastructure
The smooth running of railway technology depends on the proper functioning of a variety of highly sensitive, electric and electronic systems. The permanent availability of these systems is, however, threatened by lightning strikes and electromagnetic interference. As a rule, damaged and destroyed conductors, interlocking components, modules or computer systems are the root cause of disruptions and time-consuming troubleshooting. This, in turn, means late trains and high costs.
Reduce costly disruptions and minimise system downtime… with a comprehensive lightning and surge protection concept tailored to your special requirements.
Reasons for disruptions and damage
These are the most common reasons for disruptions, system downtime and damage in electric railway systems:
- Direct lightning strikes
Lightning strikes in overhead contact lines, tracks or masts usually lead to disruptions or system failure.
- Indirect lightning strikes
Lightning strikes in a nearby building or the ground. Overvoltage is then distributed via cables or inductively induced, damaging or destroying unprotected electronic components.
- Electromagnetic interference fields
Overvoltage can occur when different systems interact due to their proximity to one another, e.g., illuminated sign systems over motorways, high-voltage transmission lines and overhead contact lines for railways.
- Occurrences within the railway system itself
Switching operations and triggering fuses are an additional risk factor because they can also generate surges and cause damage.
In rail transport attention is generally to be paid to the safety and operational non-interference, and unconditional protection of persons, in particular. Due to the above reasons the devices used in rail transport have to feature high level of reliability corresponding to the necessities of safe operation. The probability of occurrence of a failure due to unexpectedly high voltages is minimized by the use of lightning stroke current arresters and surge protection devices made by LSP.
Protection of the 230/400 V AC power supply mains
In order to ensure defect-free operation of rail transport systems it is recommended to install all three stages of SPDs into the power supply line. The first protection stage consists of the FLP series surge protection device, the second stage is formed by the SLP SPD, and the third stage installed as close as possible to the protected equipment is represented by the TLP series with HF interference suppressor filter.
Communication equipment and control circuits
The communication channels are protected with SPDs of FLD type series, depending on the communication technology used. Protection of control circuitry and data networks can be based on the FRD lightning stroke current arresters.
Lightning Protection: Driving that Train
When we think of lightning protection as it pertains to industry and disasters we think about the obvious; Oil and Gas, Communications, Power Generation, Utilities etc. But few of us think about trains, railways or transportation in general. Why not? Trains and the operating systems that run them are just as susceptible to lightning strikes as anything else and the result of a lightning strike to the railway infrastructure can be impeding and sometimes disastrous. Electricity is a major part of railway system operations and the multitude of parts and components it takes to build the railroads across the world are numerous.
Trains and railway systems getting hit and impacted happens more often than we think. In 2011, a train in Eastern China (in Wenzhou city, Zhejiang Province) was struck by lightning which literally stopped it in its tracks by the power being knocked out. A high-speed bullet train hit the incapacitated train. 43 people perished and another 210 were injured. The total known cost of the disaster was $15.73 Million.
In an article published in the UK’s Network Rails it states that in the UK “Lightning strikes damaged rail infrastructure an average of 192 times each year between 2010 and 2013, with each strike leading to 361 minutes of delays. In addition, 58 trains a year were cancelled due to damage by lightning.” These occurrences have a huge impact on the economy and commerce.
In 2013, a resident caught on camera lightning hitting a train in Japan. It was fortunate that the strike didn’t cause any injuries, but could have been devastating had it hit in just the right place. Thanks to they chose lightning protection for railway systems. In Japan they have chosen to take a proactive approach to protecting the railway systems by using proven lightning protection solutions and Hitachi is leading the way in implementation.
Lightning has always been the number 1 threat for the operation of railways, especially under the recent operation systems with sensitive signal networks against surge or Electromagnetic Pulse (EMP) resulted from a lightning as its secondary effect.
Following is one of the case studies of lighting protection for the private railways in Japan.
Tsukuba Express Line has been well known for its reliable operation with minimal down time. Their computerized operation and control systems has been equipped with conventional lightning protection system. However, in 2006 a heavy thunderstorm damaged the systems and disrupted its operations. Hitachi was asked to consult the damage and propose a solution.
The proposal included the introduction of the Dissipation Array Systems (DAS) with the following specifications:
Since the installation of DAS, there has been no lightning damage at these specific facilities for more than 7 years. This successful reference has led to the continuous installation of DAS at each station on this line every year since 2007 till present. With this success, Hitachi has implemented similar lighting protection solutions for other private railway facilities (7 private railway companies as of now).
To conclude, Lightning is always a threat to facilities with critical operations and businesses, not limited to only the railway system as elaborated above. Any traffic systems which depend on smooth operations and minimal downtime needs to get their facilities well-protected from the unforeseen weather conditions. With its Lightning Protection Solutions (including the DAS technology), Hitachi is very keen to contribute and ensure business continuity for its customers.
Lightning Protection of Rail and Related Industries
The rail environment is challenging and merciless. The overhead traction structure literally forms a huge lightning antenna. This requires a systems thinking approach to protect elements that are rail bound, rail mounted or in close proximity to the track, against lightning surges. What makes things even more challenging is the rapid growth in the use of low powered electronic devices in the rail environment. For example, signaling installations have evolved from mechanical interlockings to being based on sophisticated electronic sub elements. Additionally, condition monitoring of the rail infrastructure has brought in numerous electronic systems. Hence the critical need for lightning protection in all aspects of the rail network. The author’s real experience in lighting protection of rail systems will be shared with you.
Although this paper focus on experience in the rail environment, the protection principles will equally apply for related industries where the installed base of equipment is housed outside in cabinets and linked to the main control / measurement system via cables. It is the distributed nature of various system elements that require a somewhat more holistic approach to lightning protection.
The rail environment
The rail environment is dominated by the overhead structure, which forms a huge lightning antenna. In rural areas the overhead structure is a prime target for lightning discharges. An earthing cable on top of the masts, ensure that the whole structure is at the same potential. Every third to fifth mast is bonded to the traction return rail (the other rail is used for signalling purposes). In DC traction areas the masts are isolated from earth to prevent electrolyses, while in AC traction areas the masts are in contact with earth. Sophisticated signaling and measurement systems are rail mounted or in close proximity of the rail. Such equipment is exposed to lightning activity in the rail, picked up via the overhead structure. Sensors on the rail are cable linked to wayside measurement systems, which are referenced to earth. This explains why rail mounted equipment are not only subjected to induced surges, but are also exposed to conducted (semi-direct) surges. Power distribution to the various signalling installations is also via overhead power lines, which is equally susceptible to direct lightning strikes. An extensive underground cable network links together all the various elements and subsystems housed in steel apparatus cases along the trackside, custom built containers or Rocla concrete housings. This is the challenging environment where properly designed lightning protection systems are essential for equipment survival. Damaged equipment results in unavailability of signalling systems, causing operational losses.
Various measurement systems and signalling elements
A variety of measurement systems are employed to monitor the health of the wagon fleet as well as undesirable stress levels in the rail structure. Some of these systems are: Hot bearing detectors, Hot brake detectors, Wheel profile measurement system, Weigh in motion / Wheel impact measurement, Skew bogie detector, Wayside long stress measurement, Vehicle identification system, Weighbridges. The following signalling elements are vital and need to be available for an effective signalling system: Track circuits, Axle counters, Points detection and Power equipment.
Transverse protection indicates protection between conductors. Longitudinal protection means protection between a conductor and earth. Triple path protection will include both longitudinal and transverse protection on a two conductor circuit. Two-path protection will have transverse protection plus longitudinal protection only on the neutral (common) conductor of a two-wire circuit.
Lightning protection on power supply line
Step down transformers are mounted on H-mast structures and are protected by high voltage arrestor stacks to a dedicated HT earth spike. A low voltage bell type spark gap is installed between the HT earthing cable and the H-mast structure. The H-mast is bonded to the traction return rail. At the power intake distribution board in the equipment room, triple path protection is installed using class 1 protection modules. Second stage protection comprise of series inductors with class 2 protection modules to the central system earth. Third stage protection normally comprise of custom installed MOV’s or Transient Suppressors inside the power equipment cabinet.
A four-hour standby power supply is provided via batteries and inverters. Since the output of the inverter feeds via a cable to the trackside equipment, it is also exposed to rear end lightning surges induced on the underground cable. Triple path class 2 protection is installed to take care of these surges.
Protection design principles
The following principles are adhered to in designing protection for various measurement systems:
Identify all cables entering and exiting.
Use triple path configuration.
Create a bypass route for surge energy where possible.
Keep system 0V and cable screens separate from earth.
Use equipotential earthing. Refrain from daisy-chaining of earth connections.
Do not cater for direct strikes.
Axle counter protection
To prevent lightning surges to be “attracted” to a local earth spike, the trackside equipment is kept floating. Surge energy induced in the tail cables and rail mounted counting heads must then be captured and directed round the electronic circuitry (insert) to the communication cable that link the trackside unit to the remote counting unit (evaluator) in the equipment room. All transmit, receive and communication circuits are “protected” this way to an equipotential floating plane. Surge energy will then pass from the tail cables to the main cable via the equipotential plane and protection elements. This prevents surge energy from passing through the electronic circuits and damaging it. This method is referred to as bypass protection, has proved itself as very successful and is used frequently where necessary. At the equipment room the communication cable is provided with triple path protection to direct all surge energy to the system earth.
Protection of rail mounted measurement systems
Weighbridges and various other applications make use of strain gauges that are glued to the rails. The flash over potential of these strain gauges is very low, which leaves them vulnerable to the lightning activity in the rails, especially due to the earthing of the measurement system as such inside the nearby hut. Class 2 protection modules (275V) are used to discharge the rails to system earth via separate cables. To further prevent flash over from the rails, the screens of the twisted pair screened cables are cut back at the rail end. The screens of all cables are not connected to earth, but discharged via gas arrestors. This will prevent (direct) earthing noise from being coupled into the cable circuits. To function as a screen per definition, the screen should be connected to the system 0V. To complete the protection picture, the system 0V should be left floating (not earthed), while the incoming power should be properly protected in triple path mode.
Earthing via computers
A universal problem exists at all measurement systems where computers are employed to perform data analyses and other functions. Conventionally the chassis of computers are earthed via the power cable and the 0V (reference line) of computers is also earthed. This situation normally violates the principle of keeping the measurement system floating as a safeguard against external lightning surges. The only way of overcoming this dilemma is to feed the computer via an isolation transformer and isolating the computer frame from the system cabinet into which it is mounted. RS232 links to other equipment will once again create an earthing problem, for which a fiber optic link is suggested as a solution. The key word is to observe the total system and find a holistic solution.
Floating of low voltage systems
It is safe practice to have external circuits protected to earth and power supply circuits referenced and protected to earth. Low voltage, low power equipment however, is subject to noise on signal ports and physical damage resulting from surge energy along measurement cables. The most effective solution for these problems is to float the low power equipment. This method was followed and implemented on solid state signaling systems. A particular system from European origin is designed such that when modules are plugged in, they are automatically earthed to the cabinet. This earth extends to an earth plane on the pc boards as such. Low voltage capacitors are used to smooth out noise between the earth and the system 0V. Surges originating from the trackside enters via signal ports and break through these capacitors, damaging the equipment and often leaves a path for the internal 24V supply to completely destroy the pc boards. This was despite triple path (130V) protection on all incoming and outgoing circuits. A clear separation was then made between the cabinet body and the system earthing bus bar. All lightning protection was referenced to the earth bus bar. The system earth mat as well as the armoring of all external cables were terminated on the earth bus bar. The cabinet was floated from earth. Although this work was done towards the end of the most recent lightning season, no lightning damage was reported from any of the five stations (approximately 80 installations) done, while several lightning storms did pass over. The next lightning season will prove whether this total system approach is successful.
Through dedicated efforts and extending the installation of improved lightning protection methods, lightning related faults have reached a turning point.
As always if you have any questions or need additional information please feel free to contact us at firstname.lastname@example.org
Wenzhou Arrester Electric Co., Ltd. (LSP) is a fully Chinese-owned manufacturer of AC&DC SPDs to a wide range of industries throughout the world.
LSP offers the following products and solutions:
- AC surge protection device (SPD) for low-voltage power systems from 75Vac to 1000Vac according to IEC 61643-11:2011 and EN 61643-11:2012 (type test classification: T1, T1+T2, T2, T3).
- DC surge protection device (SPD) for photovolatics from 500Vdc to 1500Vdc according to IEC 61643-31:2018 and EN 50539-11:2013 [EN 61643-31:2019] (type test classification: T1+T2, T2)
- Data signal line surge protector such as PoE (Power over Ethernet) surge protection according to IEC 61643-21:2011 and EN 61643-21:2012 (type test classification: T2).
- LED street lights surge protector
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