Capacitor Bank and Power Factor Improvement
Capacitor Bank is an assembly of capacitors which has the same rating arranged in series or parallel.
In AC power supplies Capacitor Banks are mainly used to improve the power factor of the AC Loads.
Power factor, Pf =cos Φ. The Power factor decreases with an increase in lag or lead of current from the voltage. That is higher the phase angle or phase shift lesser the pf.
cos Φ is maximum at Φ = 0. The value of cos Φ decreases towards +90 and -90.
The current leads for a capacitive load and lags when the load is inductive.
Majority of the industrial loads are inductive in nature because of the use of heavy motors. Due to this cause a lagging current which results in a low power factor. How much the power factor is low that much reactive power in the load.
So apart from active load in kW, reactive power in kvar is consumed by the load which draws more current from the supply. It causes high power consumption compared to the same active load with a high power factor. This waste of supply is a burden for the electricity supply companies as they have to manage the excess power requirement. Thus they demand an improved power factor on the loads. It is the responsibility of the consumer to ensure that the average power factor is not falling below the recommended PF value else electricity supply companies impose fines or penalties over them.
How the power factor can be improved by using a capacitor bank?
As a capacitor can constitute leading phase shift the capacitor bank compensates for the lagging phase shift of the inductive reactance; leading current counteract the lagging current. Thereby it maintains a unity power flow by reducing the overall phase shift and the reactive component when connected in parallel with the load.
Thus an improved power factor offers less current requirement.
In addition to power factor improvement, the capacitor banks improve the voltage stability also.
In DC power supplies it acts as a filter which reduces the AC ripple. It can provide a constant DC supply and eliminate sudden spikes and fluctuations in the line.