Power surges, also known as overvoltage or a line surge can cause damage to railway power equipment and systems. They can also cause interference with the normal operation of signals, communication systems and train control systems.
A power surge is an increase in voltage that lasts transiently, lasting for less than one second or for several seconds. The effects of a power surge depend on its magnitude and the duration of the surge, however modern-day power supplies are often designed with overvoltage protection keeping the connected equipment safe.
Power surges can be caused by a number of factors, including:
- Lightning strikes
- Utility company equipment problems
- Faulty electrical equipment
- Short circuits caused by improper wiring, animals and falling tree limbs
Power surges can cause damage to electrical equipment and systems, including:
- Damage to circuit breakers and other switchgear
- Damage to motors and generators
- Damage to transformers
- Degrade electronics, small power surges may slowly damage electronics and stop them from working time, reducing their lifetime.
- Damage to insulation
- Burning or melting of wires
A circuit breaker may protect the electrical equipment in the system and a secondary power source will usually power the equipment, however during this switchover the equipment will momentarily lose power. Hold up time provides the equipment with sufficient energy for a specified length of time during a fault or power surge allowing the equipment to carry on operating without shutting down or resetting. Often the power is supplied from a capacitor bank until the system is operational again or an alternative power source is connected.
What are the railway power supply system requirements?
The railway power supply system must provide a safe, reliable and efficient supply of power to the control, signalling and communication systems, as well as to the traction system itself.
In order to achieve this, the system must be designed to meet a number of requirements, including:
- The ability to maintain a constant voltage under conditions of varying load, while minimising EMI and complying with EN 50121 EMC standards
- The ability to withstand short-circuits, voltage surges, other abnormal conditions and provide adequate power at all times
- To meet fire protection (EN 45545), railway applications (EN 50155) shock and vibration (EN 61373) standards
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