TYPICAL CONTROL SCHEMES OF SHUNT REACTOR

The shunt reactors are generally designed for natural cooling with the radiators mounted directly on the tank. However sometimes it is required to have some control action in the cooling circuit depending on the status of the shunt reactor circuit breaker. The control action can be initiated by the circuit breaker auxiliary contact or by operation of an overcurrent relay set to 50% of the reactor rated current. By using overcurrent relay secure control action is obtained when reactor is energized regardless the circuit breaker auxiliary contact status.

In order to improve power system performance, lately it is often required by the electrical utilities to perform automatic shunt reactor in and out switching, by monitoring the busbar voltage level. This functionality is quite easy to integrate into multifunctional, numerical relay.

However user must carefully check relay performance regarding the following points:

• over/under voltage relay with reset ratio or 1% or better is required for such application.

• typically more than one over/under voltage level with independently settable time delays are required within the relay.

• over/under voltage relay shall be capable to operate only when all three voltages are above/below set operate level or relay must be capable to measure and operate on the value of the positive sequence voltage.