Switchable Capacitor Bank or Switched Capacitor Bank

It is not always economical to keep a capacitor bank in service throughout the day and night. This is because, a capacitor also provides reactive power to the system as inductor but in opposite direction. Actually capacitive reactive power provided by capacitor neutralizer the inductive reactive power generated in the system due to inductive load. In this way overall reactive power of the system is reduced hence power factor of the system is improved as result voltage profile of the system is improved but if the inductive load of the system is quite low, then the power factor of the system will be quite good, no need of any capacitor bank to improve it further. But if still a capacitor bank is connected to the system, there may be a quite high reactive power in the system due capacitive effect. In this situation the power factor of the system becomes poorer instead of being improved.

So it is preferable to use a switchable or switched capacitor bank in the system where inductive load fluctuates enough. The switched capacitor bank is generally installed at primary network of a power sub-station hence, it also helps to improve power profile of entire system including its transformers and feeders.
A capacitor bank can be automatically switched ON and OFF depending upon condition of different parameters of the system-

1. Capacitor Bank can be controlled automatically depending upon voltage profile of the system. Since the voltage of the system depends upon the load, hence capacitor may be switched on just below a certain preset voltage level of the system and also it should be switched OFF above a preset higher voltage level.

2. Capacitor bank can also be switched ON and OFF depending upon the Amp of the load.

3. The function of capacitor bank is to compensate or neutralize reactive power of the system. Reactive power in measured in KVAR or MVAR. So, switching scheme of capacitor bank can be operated depending upon the load KVAR and MVAR. When the KVAR demand is increased beyond a preset value, the bank is switched ON and it is switched OFF when this demand comes under another lower preset value.

4. Power factor can be used as another system parameter to control a capacitor bank. When the power factor of the system comes below a predetermined value the bank is automatically switched ON to improve the pf.

5. Capacitor bank can also be switched ON and OFF by using timer. A capacitor bank is switched OFF at end of every shift of a factory and this can be done by using timer.

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