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What will happen if DC supply fails in an electrical substation?

Purpose of use of DC supply in an electrical substation

We use circuit breakers and switch-gears for power supply distribution for safe and systematic utilization of electrical power. The breaker is mainly used for making the electrical supply on and off. The circuit breaker also carries out protection functions.

The protection system trips the circuit breaker to cut off the supply to the faulty section during an electrical fault. Thus, a breaker is used in an electrical network for;

  • Closing
  • Cut off
  • Tripping of the breaker in the case of fault

The circuit breaker performs on /off and trip function when we feed 110 VDC supply to closing and tripping coil. The protection relay issues a tripping command to the breaker in the case of fault. The tripping coil of the breaker is of 110 Volts rating. If the 110 volts supply gets failed, the breaker can not trip, and the heavy current flows through the electrical network. In this case, the upstream breaker will also not get tripped in absence of DC supply. The fault will be not cleared if the breaker does not trip, and the heavy current flowing in the electrical network may cause heavy damage to electrical switch gears and electrical equipment. In this case, the fire hazard can not be negated.

Thus the 110 volts DC system has prime importance as far as protection of an electrical network is concerned.

What additional protection system required for 110 VDC  supply continuous monitoring? 

Looking to the importance of the DC power supply, the trip circuit supervision relay is used to monitor the healthiness of the power supply during breaker closing and tripping. The breaker will not close if the 110 DC circuit is not healthy. In normal running conditions, if there is a problem in the 110 VDC supply system, the trip circuit supervision relay outputs an alarm signal to facilitate early troubleshooting of the supply system.

To make the 110 VDC supply more reliable we can have two trip circuits, and in the case of failure of one trip circuit, another trip circuit will function.

Thus, it is prime important to ensure the healthiness of the tripping circuit at all times for safeguarding of an electrical network.