19.1 Management of Protection

A protective system is considered 100% perfect if the number of circuit breakers opened under a fault are as per the design configuration. However, there are occasions when a few protective relays incorrectly operate or fail to operate. There could be many reasons but the principal reasons could be:

• The internal faults in the relays

• Defects in the wiring to the relays

• Wrong and poorly coordinated settings

• Unforeseen faults at the design stage

• Mechanical failures.

Protection systems must be kept 100% operational at all times as one never knows when or where faults are likely to occur. The systems must therefore be maintained and managed properly to ensure safe and efficient operation of the power network.

Although the relays are tested prior to commissioning a system, it is most likely that the relays may not be operating due to the soundness of the system. However, it cannot be assumed that the relay did not operate because of the system healthiness. Hence, it is very vital that the relays should be periodically checked and tested at fixed intervals. It is also important that the records must be kept about the tests being conducted and the details of results for future reference and records.

The functions required for good maintenance are listed on the following schedule A and it is important that good records are kept of the system parameters, wiring schematics, relay settings and calculations, CT magnetization curves and so on. Some suggested formats of test sheets...