Electrical Safety in Railway System

Introduction: 

Indian Railways is the biggest railway network in the world. Indian Railways cater millions of commuters and long-distance passengers daily. A  reliable & safe electrical system in signaling & inside coaches ensures safe and  efficient operation of trains and passengers’ safety. The shoulders of Indian Railways are entrusted with the safety & security of   thousands of  passengers who travel with it daily. A minor malfunction in the signaling system or in electrical  facilities inside the coaches like lights, fans, mobile charging points, chilling systems, because of earth leakage/fault can cause a catastrophe which is  unimaginable, leading to loss of life of thousands. 

Indian railway has recently launched its premium/ high-speed rail operations on selective  routes and Bullet Train is also in the pipeline -to be introduced in near future. All these initiatives necessitate a thorough upgradation of existing Indian railway infrastructure. For such reasons new technologies and the latest version of measuring, monitoring and control systems will be required. Automated On-line continuous monitoring of various distribution circuits in the signaling system and coaches is required which will strategically increase the throughput and safety of trains. Such arrangements would ensure that the faulty circuits are detected,  located and corrected within an hour without the need of shutting down the electrical power distribution system. 

Ungrounded power supplies have the advantage of avoidance of shock & fire and  ensure continuity of power to loads in the event of first ground fault. To get the  above benefits IEC 60364-4-41 recommends providing an on-line insulation  monitoring device to monitor & indicate the first ground fault. Further the first ground fault should be eliminated within the shortest practicable time. Therefore, to identify the faulty feeder as fast as possible and to support the maintenance staff, an online fault location system should be implemented in a large complex distribution  system. Further the measurement and monitoring technology shall be reliable and accurate built with state of the art technology in the presence of AC, DC and AC/DC loads and various electrical noises. Therefore the measuring and monitoring system shall be  in conformance to prevalent International standards for operation in the industrial environment. Online insulation monitoring shall conform to IEC 61557-8 and  online fault location up to feeder level shall conform to IEC 61557-9. Further the  system shall be qualified as per IEC 61326 for EMI/EMC.  

Grounded distribution systems are also utilized in various non-critical and auxiliary  electrical power distribution systems in railways. Grounded AC, DC & AC/DC  distribution systems are used. Rather than waiting for short circuit and catastrophic  failures a leakage current monitoring system to monitor the leakage currents due  to failure of insulation for advance leakage information shall be provided. Again  for using the monitoring system in industrial environment the solution shall be in  conformance to IEC 62020 

Reference Standards: 

1. EN 50122-1 : Railway applications – Fixed installations –Electrical safety,  earthing and the return circuit 

2. EN 50123-1 : Railway applications – Fixed installations –D.C. switchgear

3. IEC 61373 : Railway applications – Rolling stock equipment 

4. EN 45545 : Railway applications – Fire protection on railway vehicles

5. EN 50155 : Railway applications – Electronic equipment used on rolling  stock 

6. EN 50121 : Railway applications – Electromagnetic compatibility

7. IEC 60364-1 : Low voltage electrical installations – Part 1: Fundamental  principles, assessment of general characteristics, definitions  

8. IEC 60364-4-41: Electrical installations of buildings Part 4-41: Protection for  safety-Protection against electric shock 

9. IEC 61557-8 : Electrical safety in low voltage distribution systems up to 1 000  V a.c. and 1 500 V d.c. – Equipment for testing, measuring or monitoring of  protective measures – Part 8: Insulation monitoring devices for IT systems 

10. IEC 61557-9 : Electrical safety in low voltage distribution systems up to 1 000  V a.c. and 1 500 V d.c. – Equipment for testing, measuring or monitoring of  protective measures – Part 9: Equipment for insulation fault location in IT  systems 

11. IEC 62020-1 : Electrical accessories – Residual current monitors (RCMs) – Part 1: RCMs for household and similar uses 

Solution for signaling system:

Similar to British and European Railways, Indian Railway signaling systems  utilize various types of ungrounded low voltage power supplies like 110 V  AC/DC, 60 V AC/DC and 24 V AC/DC for the various signal & switching  circuits. The circuits include Track Point Switches, Track Motors, Signal Control  Relays and Signaling Lamps. The design generally conforms to national and  international standards. Most of the cables associated with the above-mentioned circuits are outdoor and run along railway tracks either buried or over ground.  They are exposed to the harsh weather and unfavorable environment. These affect 

their insulation resistance and are subject to deterioration in the harsh  environment over a period. This leads to mal-operation and unreliable operation  of signal systems, putting the life of thousands of commuters at stake. US, British  and European in-house railway standards recommend continuous monitoring of  the insulation resistance of these circuits to ensure reliable and safe movement of  trains. Further to detect the individual faulty feeder an online fault location system  shall be provided.  

Each galvanically isolated separate supply source will consist of an online  insulation monitor connected near to the source main bus. Individual feeders will  be installed with special highly sensitive sensors over the complete feeder wires  along with multichannel earth fault detectors to which the sensors shall be  connected for identifying automatically the faulty feeder without shutting down  the distribution system. After identifying the faulty feeder, with the help of a portable handheld fault locator exact location of earth fault can be identified.  Portable devices also trace the signal injected by the insulation monitoring device.  

A typical sketch of the solution is shown below.

Solution for Railway Coaches: 

An ungrounded power supply is also used inside coaches’ electrical systems to have some benefits like:   

a) Prevents fire due to insulation leakage.  

b) Prevents fatal electrical shock to the passengers. 

c) Availability of loads 

The main incomer power supply to individual coaches is either 800 V 3 phases 3 wire  ungrounded or 800 V 3 phase 4 wire grounded system depending on the design  requirement of RDSO. Which is later being stepped down to 415V 3 phase, 230 & 110V  single phase as per the load requirement inside the coaches. Each and every relay  should have MODBUS RTU communication system to directly communicate with  HMI system 

Each galvanically isolated separate supply source will consist of an online insulation monitor  connected near to the source main bus. It will measure the insulation resistance of the  complete connected distribution system up to individual loads and provides alarm whenever  the earth fault insulation resistance is below set limits. The maintenance staff can plan for  fault identification and repair.  

Portable handheld fault evaluator suitable up to 800V AC system can be used to localize faults during running condition of the train or at loco shed. 

A typical sketch of the solution is shown below. 

Electrical safety in Railway Tunnels:  

Train routes in mountainous landscapes lead across a sequence of tunnels and bridges. To ensure passenger safety and efficient incident response, our route operations plan must prioritize preparedness for tunnel emergencies. Along the route, fire brigades and Technical Relief Services must be equipped for assistance in case of a catastrophe. Additionally, To support the rescue concept, hydrants and  emergency power supply points must be installed in the tunnels. Rescue teams thus  can have quicker access to water and electrical energy in sufficient quantities.  According to the guideline 95401, in Germany the power supply has to be  designed as an ungrounded system. 

Securing a functioning power supply for rescue teams even in case of catastrophe: This allows rescue teams to rely on a functioning power supply in the  event of a catastrophe, continuous insulation monitoring is required. Critical  installation conditions are reported to the supervising system in a timely manner.

Fast localisation of insulation faults: Even in the case of extensive routes,  insulation faults can be allocated to the individual tunnel sections when using  insulation fault location systems such as signaling systems. A further advantage is that they find insulation faults during ongoing operations, without cable  disconnection. 

Case study  

1. Bender offered Solution in Signaling System: 

BENDER, the world leader in this technology provides universal and customized  solutions in on-line monitoring insulation resistance and fault location in  ungrounded AC & DC electrical systems. Suitable for signaling systems. 

BENDER with its large amount of experience and R&D efforts over more than 70  years provides ingenious solution for on-line insulation monitoring and fault  location up to individual feeder level in AC/DC systems in the presence of various  industrial electrical noises without spurious operation and indications (EMI/EMC  qualified). Bender Insulation Monitoring Device conforms to IEC 61557-8, Fault  location system conforms to IEC 61557-9 and EMC qualifies as per IEC 61326. The implementation schematic in Indian Railway Signaling is below: 

As shown in the figure above, the insulation monitoring scheme for ungrounded  systems consists of Insulation Monitor ISO 685 connected to the main ungrounded  distribution source bus. The insulation monitor may derive its power from the  same system and it can accept a wide range of power input from both AC & DC from 0  to 600 Volts. The insulation monitor injects a special Bender patented bi-directional signal into the system with respect to earth and will on-line monitor  the insulation of the complete ungrounded distribution system of all feeders  including loads supplied from same source with respect to earth and indicate the  value in the range of 1 Kohm – 10 Mohm. It will generate an alarm in case the  insulation of the complete distribution system falls below the set value. Typical  set value for the alarm can range between 50 to 100 ohms/ Volt of the system voltage and it can have another unique feature that allows it to generate two different alarms indicating gradual degradation of insulation resistance. 

We can define the 1st alarm as a pre-alarm and the 2nd one as a critical alarm. For safe running of the system one can set the pre-alarm value at 200 ohm/Volt and critical alarm value at 100 ohm /volt which is in line with IEC (e.g. for system voltage 110 V, the pre-alarm setting is 40 Kohm  and critical alarm is 20Kohm). The Operation & Maintenance staff will get to  know of the insulation fault in advance owing to the indication of the pre-alarm and further plan the maintenance activity as per their convenience and resource availability. 

The main power supply is distributed into various feeders as per the requirement  of the station signaling system. To locate the actual faulty feeders, each of the  load feeders will be installed with specialized highly sensitive Bender patented  core balance Current Transformers (CT), with sensitivity of 5 mA. All CT’s will  be connected to required nos. of 12 channel evaluators EDS440. The EDS440 may draw its power from the main distribution system. In case of insulation fault  (lower than both the alarm settings) in any feeder , the ISO 685 will first produce  a visual alarm followed by injecting a test current (adjustable by user) in the  distribution system with peak value limited to 25 mA. 

The peak value of 25 mA is  much below the dropout current of 40 mA of relays used in railway signal circuits thus, won’t interfere with the functioning of the system. This test current will  pass through the faulty feeder via earth and the corresponding faulty feeder CT  will detect and indicate on-line the fault in the corresponding channel of EDS440.  ISO 685 & EDS-440 are also interconnected with 2-wire RS 485 interface hence ISO 685 will also indicate the channel number of the faulty feeder. Further with the help of  Bender make portable fault evaluator EDS 3090 identification of the exact faulty  component also possible. A Bender make gateway may also be used to indicate  the faulty feeder in the control room on a PC.  

In this way the complete system will be monitored online 24X7, Which is very much  required for the railway signaling system.  

 Bender Model BOQ for signaling system application: 

Sr.  No.	Item description	Model	Remarks
1	Online insulation Monitoring  Device	Iso685-S-P+FP200/  iso685-D-P	1 no. per source
2	12 channel Earth Fault Evaluator	EDS440-L-4	Depends on number  of feeders
3	Core Balance Current Transformer	WS20X30	Depends on number  of feeders
4	Portable Fault locator	EDS3096-PG	1 no. per RRI

Bender India  

A Typical Panel of Bender Solution in Railway Signal Station CTs Installed in Outgoing Signal Cables 

2. Bender Solution in Coaches: 

BENDER with its large amount of experience and R&D efforts over more than 70  years provides ingenious solution for on-line insulation monitoring and fault location  up to individual feeder level in AC/DC systems in presence of various industrial  electrical noises without spurious operation and indications (EMI/EMC qualified).  Bender Insulation Monitoring Device conforms to IEC 61557-8, and EMC qualifies  as per IEC 61326. The implementation schematic in Indian Railway Coaches is  below.  

Bender manufactured Insulation Monitor relay suitable to monitor the insulation of  800 V 3 phase , 415V 3-phase, 230 Volt, 110 Volt single phase AC power circuits &  24V DC emergency light circuits in coaches and thereby generating alarm whenever  the insulation value with respect to earth decreased below the set value without  tripping the circuit. thereby ensuring passenger safety and protection of assets. 

Bender also manufactures residual current relay with CBCT to monitor the earth  leakage current of 800VAC 3-phase 4-wire earthed/grounded supply to coaches and  thereby generating alarm whenever the leakage current exceeds the set value  ensuring safety of passengers and railway coach assets. This is in accordance with IEC  62020-1. 

Bender Model BOQ for Coach application 

Sr.  No.	Item description	Model	Remarks
1	Online Insulation Monitoring  Device for 800 V AC	isoHV425+AGH420	1 no. per source
2	Online Insulation Monitoring  Device for 415V AC, 230AC, 110V,  24VDC	Iso415R-2	1 No. Per source
3	Residual Current Monitoring Device  for 750V AC 3 Phase	RCM410R-2 &  CTAC70	For 750V3 Phase 4  wire system

Bender India 

Bender Insulation Monitoring in Coaches 

Bender Residual Current Monitoring in Power Cars

In Locomotives with frequency-converters the iso685 is common to have an optimal protection for people and best reliability.

Author:

Mahesh C. Yadav  
Director/Indotech Global System 
Ex. IRSSE,Chartered Engineers(I), MIE(I) , 
MIRSTE, MIRT, MIUT, MIET (UK), MIMA 
(Rtd.) Dy Chief Signal & Telecommunication Engineer (RE/IR)