Electronics Guide

Traction Power Systems

Electric railways draw power from overhead catenary or third rail systems at voltages ranging from 600V DC for light rail to 25kV AC for high-speed rail. The traction power converters on modern rolling stock generate significant electromagnetic emissions as they control the high-power motors that propel trains. Power electronic converters using thyristors, IGBTs, or other switching devices produce conducted emissions on the traction supply and radiated emissions that can affect lineside equipment and systems on adjacent tracks.

Traction current return paths through the running rails create magnetic fields along the right-of-way. These fields can induce interference in parallel cable routes and affect magnetic-field-sensitive equipment. The return current also creates rail-to-earth potentials that can couple into earthed equipment and structures. Managing these effects requires attention to bonding, cable routing, and shielding throughout the railway infrastructure.

Regenerative braking returns energy to the traction supply when trains decelerate, creating power quality issues and potential EMC effects. The traction supply voltage may rise during regeneration, and the energy returned to the system can create interference for other trains and wayside equipment. Modern systems include energy storage or resistive braking to manage regenerated energy.

Switching and Protection Transients

Railway electrical systems include numerous switches, circuit breakers, and protection devices that generate transients when operating. Traction supply switchgear operates at high voltages and currents, creating substantial transients that propagate throughout the electrical system. These transients can couple into signaling and communication systems if not properly controlled.

Lightning protection is essential for railway systems, which present extensive exposed structures vulnerable to direct strikes and nearby lightning effects. Surge protection devices throughout the infrastructure limit lightning-induced transients, but the protection coordination must ensure that protective devices operate without disrupting normal operations or creating secondary problems.

Radio Frequency Emissions

Traction power converters generate radio frequency emissions that can extend from audio frequencies through the lower radio frequency bands. The harmonic content of converter switching creates conducted emissions on power systems and radiated emissions from traction power cables and pantograph-catenary contact. Arc discharges at the current collection interface add broadband RF noise that can affect radio communication and signaling systems.

Auxiliary power systems on trains supply lighting, HVAC, and passenger services using power converters that add to the overall emission environment. While individually smaller than traction converters, these systems can affect nearby electronics and contribute to the cumulative electromagnetic environment experienced by train-borne equipment.

Environmental Factors

Railway equipment operates across wide temperature ranges, from summer heat to winter cold, sometimes with rapid transitions as trains enter and exit tunnels or climate-controlled stations. Humidity, precipitation, and condensation affect equipment reliability and can degrade EMC performance over time. Vibration from train motion and track irregularities stresses mechanical connections that are critical for EMC.

Tunnels and underground sections create enclosed electromagnetic environments where emissions from one train can affect nearby trains and infrastructure equipment. The metallic tunnel structure provides some shielding from external interference but can also enhance propagation of interference generated within the tunnel.

EN 50121 Series

The EN 50121 series of European standards addresses railway EMC comprehensively. EN 50121-1 provides general guidance and defines the railway electromagnetic environment. EN 50121-2 addresses emission and immunity of the whole railway system, providing guidance for system-level EMC management. EN 50121-3 covers rolling stock apparatus and traction equipment, defining requirements for equipment on trains.

EN 50121-4 addresses signaling and telecommunications equipment, specifying limits and test methods appropriate for these safety-critical systems. EN 50121-5 covers fixed power supply installations, addressing substations and power distribution equipment. The standard series ensures consistent EMC requirements throughout the railway system while recognizing the different characteristics and requirements of various subsystems.

IEC Standards

IEC 62236 mirrors the EN 50121 series structure and provides international railway EMC requirements. Other IEC standards address specific aspects of railway systems: IEC 62280 covers communication, signaling, and processing systems; IEC 62278 addresses system reliability, availability, maintainability, and safety (RAMS); IEC 62425 covers safety-related electronic systems for signaling. These standards work together to ensure comprehensive coverage of railway EMC requirements.

Regional and National Requirements

Beyond international standards, regional and national requirements may apply to railway systems. European Union regulations mandate compliance with applicable EN standards for equipment placed on the market. The U.S. Federal Railroad Administration and Federal Transit Administration establish requirements for rail systems under their jurisdiction. National railway authorities may impose additional requirements based on their specific operating environments and practices.

Interoperability requirements for cross-border rail operations add complexity to EMC compliance. The European Technical Specifications for Interoperability (TSI) include EMC provisions to ensure that rolling stock from different manufacturers and nations can operate together without interference.

Track Circuit Protection

Track circuits detect train presence by using the running rails as electrical conductors. When a train's wheels and axles shunt the rails, the track circuit detects the reduced resistance and indicates occupancy. This simple principle becomes complex in the railway electromagnetic environment, where traction current, rail-to-earth potentials, and external interference can create false readings.

Audio frequency track circuits operate at frequencies selected to avoid interference from traction system harmonics. Filtering at the track circuit equipment rejects interference at other frequencies. The track circuit design must maintain reliable detection despite variations in rail condition, weather, and electromagnetic interference levels.

Jointless track circuits use coded signals to distinguish between adjacent track sections, allowing continuous rail (needed for modern high-speed operation) while maintaining track circuit functionality. The coding frequencies and detection algorithms must be robust against electromagnetic interference that could corrupt the codes or create false detections.

Axle Counter Systems

Axle counters detect train wheels passing detection points rather than relying on rail conductivity. Wheel sensors use magnetic or inductive principles that must function despite the magnetic fields from traction current and nearby equipment. The counting algorithms must correctly handle high-speed trains, multiple wheels in close proximity, and electromagnetic disturbances that could create false counts.

Axle counter systems require extremely high reliability since undercounting could permit conflicting train movements while overcounting could block traffic unnecessarily. EMC design and testing for axle counters address both immunity to interference and potential failure modes that could affect count accuracy.

Balise Systems

Balises are transponders installed between the rails that communicate with passing trains. Fixed balises transmit pre-programmed data providing location information and speed restrictions. Switched balises can transmit variable information based on signaling system status. The brief communication window as a train passes requires robust signal processing that can extract valid data despite noise and interference.

The European Train Control System (ETCS) uses eurobalises as a key component of train location determination. The balise-train communication must function reliably across all environmental conditions and interference levels. Testing verifies both the balise equipment and the train-borne reader to ensure proper system operation.

Communication-Based Train Control

Modern communication-based train control (CBTC) systems use continuous radio communication between trains and wayside equipment. These systems must maintain reliable communication despite the challenging railway RF environment. Frequency selection, antenna design, and protocol design all consider the electromagnetic environment and potential interference sources.

The radio communication link must provide low latency and high availability for safety-critical train control functions. Redundancy in communication paths and protocols that handle brief interruptions ensure continued safe operation. EMC testing addresses both the immunity of the communication system to interference and the potential for system emissions to affect other railway electronics.

Traction Drive Systems

Traction drives convert electrical power from the supply system to mechanical power at the wheels. Modern drives use power electronic converters with IGBTs or other high-power switching devices that generate emissions across a wide frequency range. Emissions from traction systems are among the most significant EMC challenges on railways, affecting both onboard equipment and lineside systems.

Input filters on traction converters reduce conducted emissions on the traction supply. These filters must handle the high voltages and currents of the traction system while providing effective attenuation across the required frequency range. Filter design also considers the supply system characteristics to avoid resonance effects that could amplify rather than attenuate emissions.

Radiated emissions from traction power cables and equipment must be controlled to protect lineside equipment and comply with emission limits. Shielding, cable routing, and equipment placement all contribute to emission control. The physical constraints of rolling stock, including weight limitations and accessibility requirements, challenge EMC designers to achieve compliance within practical constraints.

Train Management Systems

Train management systems coordinate the operation of all train subsystems, including traction, braking, doors, HVAC, and passenger information. These systems must communicate reliably despite the electromagnetic environment on the train. Train networks using standards such as MVB (Multifunction Vehicle Bus) or Ethernet are designed for the railway environment but require proper implementation to achieve their potential reliability.

Safety-critical functions within train management systems require appropriate safety integrity levels (SIL) and the EMC performance to support those levels. The interaction between EMC and functional safety drives rigorous requirements for immunity and availability of safety-critical equipment.

Passenger Information and Entertainment

Passenger information systems provide destination displays, announcements, and real-time service information. Entertainment systems offer internet connectivity, personal device charging, and onboard media. These systems must not emit interference that affects safety-critical train systems, and they must continue operation despite the electromagnetic environment.

Wireless services for passengers, including WiFi and cellular repeaters, require coordination with train control communications to prevent interference. The onboard RF environment management must balance passenger expectations for connectivity with the safety requirements for train control systems.

Substations and Power Distribution

Traction power substations convert utility power to the voltages and frequencies required by the railway. AC railways typically use 25kV at commercial frequency, while DC railways operate at various voltages from 600V to 3000V. Substation equipment includes transformers, rectifiers, circuit breakers, and protection systems that generate transients and may be susceptible to interference from the traction system.

Power quality on traction systems affects both railway equipment and nearby utility customers. Harmonic currents from traction loads can distort utility voltages, while power factor variations affect system efficiency. Standards specify limits for power quality disturbances that railways can impose on the supply system.

Platform Systems

Station platforms host passenger information displays, public address systems, CCTV, ticketing equipment, and platform screen doors. These systems must operate in the electromagnetic environment created by passing and stopping trains. Platform screen door systems are particularly critical, as they must synchronize precisely with train door positions despite electrical noise from the traction system.

Maintenance and Depot Facilities

Maintenance facilities include test equipment, maintenance management systems, and workshop machinery that must achieve EMC within the facility. Testing of train equipment may require shielded facilities or careful scheduling to prevent interference with operational systems. Shore power connections and equipment under test can create conducted interference paths that require management.

Laboratory Testing

Laboratory testing of railway equipment follows procedures defined in EN 50121 and related standards. Emission testing measures conducted emissions on power and signal lines and radiated emissions from the equipment. Immunity testing subjects equipment to conducted disturbances, radiated fields, and transient events representative of the railway environment.

Test levels for railway equipment generally exceed those for commercial equipment, reflecting the severe railway electromagnetic environment. Some tests are specific to railways, such as immunity to magnetic fields from traction current. Laboratory testing provides controlled, repeatable verification but cannot fully replicate the actual operating environment.

Vehicle-Level Testing

Testing at the complete vehicle level verifies that the integrated rolling stock meets emission requirements and that subsystems achieve compatibility. Vehicle emission measurements are typically performed on a test track section with controlled conditions. The traction system operates through representative duty cycles while emissions are measured at standard distances from the vehicle.

Integration testing verifies that subsystems function correctly when operating together. This testing may reveal interaction effects not apparent during subsystem testing. The test program should exercise all normal operating modes plus identified worst-case conditions.

On-Track Testing

Testing on operational or test tracks validates performance under realistic conditions. These tests may include compatibility with existing infrastructure, performance at maximum speed, and behavior during unusual operations such as emergency braking. On-track testing is particularly important for verifying compatibility with track circuits and other infrastructure that cannot be fully replicated in the laboratory.

Route compatibility testing verifies that new rolling stock operates correctly throughout its intended service territory. Different routes may have different infrastructure, signaling systems, and electromagnetic environments. Testing or analysis must demonstrate acceptable performance across all planned operating areas.

System Commissioning

System commissioning verifies that all elements of a railway system work together correctly. This testing goes beyond EMC to include functional verification, safety validation, and operational readiness. EMC-related commissioning activities verify that signaling systems correctly detect trains, communication systems maintain connectivity, and no interference problems affect normal operations.

Increased Electrification

Electrification of previously diesel routes introduces traction power systems and their associated EMC challenges into new areas. Legacy signaling and communication systems may require upgrading to maintain reliable operation with electric traction. The interface between electrified and non-electrified sections requires particular attention to ensure safe transitions.

Higher Power and Faster Speeds

High-speed rail and increased traffic density drive higher traction power levels and more intensive use of the electromagnetic spectrum. Regenerative braking returns significant energy to the system during deceleration of heavy, fast trains. EMC requirements must evolve to address these increased power levels while maintaining compatibility with existing infrastructure.

Wireless Communications Expansion

Increased use of wireless communications for train control, passenger services, and operations support creates new EMC coordination challenges. GSM-R, the current railway communication standard, is being succeeded by FRMCS (Future Railway Mobile Communication System) based on LTE and 5G technologies. Managing the transition while maintaining safety and reliability requires careful EMC planning.

Autonomous Train Operation

Autonomous train operation (ATO) systems increase reliance on sensors, communication, and processing that must function despite electromagnetic interference. The reduced human oversight in autonomous operation increases the importance of robust EMC design. Safety cases for autonomous operation must address EMC risks and demonstrate adequate mitigation.