STAR AND DELTA CONNECTION OF CAPACITORS

Power capacitors in 3 phase capacitor bank connections are either delta connected or star (wye) connected.?Between the two types of connections, there are differences in their applications, kVAR rating, detection of failed capacitors etc. In this article the difference between star and delta connected capacitors and the advantage of star vs. delta connected capacitor bank is discussed.

Delta Connected Capacitor Bank

Delta connected capacitors are most commonly used at low voltage though it could be applied at higher voltages as well. Each capacitor will have the full phase-phase voltage applied across its terminal.?

Why low voltage capacitor banks are connected in delta??Remember that the kVAR generated varies as the square of applied voltage. The formula for VAR generated in a capacitor bank is given by:

Connecting the capacitor bank in delta produces more VAR compared to connecting in star. This is because in star connection only line-neutral voltage is applied across capacitor vs full phase-phase voltage is applied in the case of delta connection.

Connecting the capacitor bank in delta produces more VAR compared to connecting in star.

Delta connection of capacitors requires two bushings.?Since there is no connection to ground, the capacitor bank cannot be a ‘sink’ for any ground currents or zero sequence currents. Individual branch of the delta connected capacitor need to be protected against phase-phase short circuit by a current limiting fuse.

Star Connected Capacitor Bank

In star connection, the voltage across each capacitor is 1/sqrt(3) times the phase-phase voltage.?Hence the VAR produced also will be correspondingly smaller when compared to delta connection. Star connection is primarily used at medium voltage (>1 kV) systems.?One of the main advantage of using star?connection is that the capacitor need to be only rated for system phase-neutral voltage compared to phase-phase rated in a delta system.?Individual medium voltage capacitors hence will only be stressed at a lower voltage level thereby increasing its life.

VAR produced also will be correspondingly smaller when compared to delta connection.

Reference : voltage-disturbance.com/