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What is Capacitor Bank?

Capacitor Bank is a group of several capacitors of the same rating that are connected in series or parallel with each other to store electrical energy.

Application Of Capacitor Bank

The resulting bank is then used to counteract or correct a power factor lag or phase shift in an alternating current (AC) power supply.

Types Of Capacitor Bank

The capacitor units are manufactured as single phase unit. These single phase units are connected in star or delta to form a complete 3 phase capacitor bank.

1) Externally fused capacitor bank.

2) Internally fused capacitor bank.

3) Fuseless capacitor bank.

Let us Discuss This Types

Externally Fused Capacitor Bank

In this type of capacitor bank, the fuse unit is provided to each capacitor unit externally. On a fault, in any unit, the externally provided fuse of that unit will be blown out. As the fusing system disconnects the faulty capacitor unit, the bank will continue its service without any interruption. 

In this type of capacitor, units are connected in parallel.As there are several capacitor units connected parallelly per phase of the capacitor bank, on the failure of one unit, there will be not much affected on the performance of the entire bank. As one capacitor unit is missing in one phase the capacitance of that phase will be lower than that of other two phases. 

This will result higher voltage in other two phases of the bank. If the capacity of one capacitor unit in a bank is low enough then in absence of any unit in the bank there will not be much voltage unbalance. This is why the VAR rating per capacitor unit in a bank is restricted up to a specified limit.

In the externally fused capacitor bank, the faulty unit can easily be identified by identifying blown out fuse unit through visual inspection.

The rating of capacitor unit is typically from 50 KVAR to 40 KVAR.

The drawback of this type of capacitor bank is that, on a failure of any fuse unit, there will be unbalance sensed, even all capacitor units of the bank are healthy.

Internally Fused Capacitor Bank

The entire capacitor bank is constructed in a single arrangement. As per rating of entire bank, several capacitor elements are connected parallel and series. Each of the capacitor elements is individually protected with fuse unit. As the fuses and capacitor elements are placed inside the same casing, the bank is called internally fused capacitor bank. In this type of capacitor bank, each capacitor element is very small in ratings, so that if any of the elements are out of service, there will be no remarkable effect in the performance of the bank. Internally fused capacitor bank can run satisfactorily even more than one capacitor elements are out of service.

The main drawback of this bank is that, on a failure of any number of capacitor elements, the entire bank is to be replaced. There is no scope for single unit replacement.

The main advantage is that it is quite easy to install and also easy to maintain.

Fuse-Less Capacitor Bank

In this type of capacitor bank required a number of fuse units is connected in series to form a capacitor string. Then a required number of required number of these strings is connected in parallel to farm capacitor bank per phase. Then three similar per phase bank is connected in star or delta to farm entire 3 phase capacitor bank. The units of the capacitor strings are not at all protected by any internal or external fusing arrangement. 

In this system, if one of the units of a string fails due to short circuit, there will be no remarkable change in current through this string as there are many other capacitors connected in series along this path. As the effect of a short-circuited unit in the string is small enough, the bank can be run up to prolong the time before replacement of the faulty unit. This is the reason, why the fuse is not required to isolate the faulty unit from the system in this type of capacitor bank immediately after unit becomes faulty.


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