Generally, Fixed Shunt Reactors are designed and located in a way to be connected to the network most of the time. However, lately it is often required by the electrical utilities to perform automatic switching in/out operations on Switchable Fixed Shunt Reactors by monitoring the bus-bar voltage level. Figure 8-1 illustrates a typical Switchable Fixed Shunt Reactor control scheme.
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| Figure 8-1: Typical On/Off switching control of a Fixed Shunt Reactor |
As seen in Figure 8-1, the normal operating range is 85% to 125% of bus-bar nominal voltage. For voltages higher than 125% of the nominal voltage, the switch-in (On) command is issued. Likewise, for voltages lower than 85% of the nominal voltage, the switch-out (Off) command is issued. This control system is interlocked with a zero voltage detection which is considered as voltages very lower than 20-80% of the nominal voltage; in this case, the bus-bar will be assumed dead and the control function will be blocked. As shown, this switching function is delayed in order to ensure that the voltage change in network is stable. The aforementioned functionality is quite easy to integrate into multi-functional numerical relays.
Moreover, 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 on the cooling circuit depending on the status of the shunt reactor circuit breaker. The control action can be initiated by either the circuit breaker auxiliary contact or the operation of an Over-Current relay which is set to 50% of the reactor rated current. By using Over-Current relay, more secure control action is achieved when Shunt Reactor is energized regardless of the circuit breaker auxiliary contact status.