Power failure operation of parallel capacitor bank

What happens if a capacitor bank fails?

V. INTERNAL OVERVOLTAGE AND ITS APPLICATION IN SETTING THE UNBALANCE PROTECTION ELEMENTS A failure in a capacitor bank causes an internal overvoltage inside the bank (see Fig. 9 and Fig. 10). This overvoltage may cause more failures, which in turn creates even higher overvoltage, and eventually, leads to a cascading failure.

Why do capacitor bank voltages and currents unbalance in per-unit values?

We achieved this simplicity by working in per-unit values. It is apparent that an unbalance in capacitor bank voltages and currents is a result of a difference between the faulted and healthy parts of the bank. As such, the per-unit voltage or current unbalance is independent of the absolute characteristics of the faulted and healthy parts.

Can a capacitor bank cause an unbalance signal?

For certain capacitor bank configurations some faults within the bank will not cause an unbalance signal and will go undetected. For example: a) rack-to-rack faults for banks with two series groups connected phase-over-phase and using neutral voltage or current for unbalance protection; and, b) rack-to-rack faults for certain H-bridge connections.

What happens if a capacitor element fails in a fuseless bank?

A few capacitor elements fail short in a fuseless bank. These failures could short the entire capacitor unit, less than one capacitor unit, or more than one capacitor unit. Typically, capacitor element failures put the highest voltage stress on the rest of the failed capacitor unit.

Why is parallel energy a non-issue for internally fused capacitor banks?

Parallel energy has typically been viewed as a non-issue for internally fused capacitor banks because the current limiting fuses are commonly used. However, fuse sizing/rating must still be considered when designing the unit to ensure fusing selection is appropriate to handle discharge energy into the shorted element through its fuse.

What is bank stability for a fuseless capacitor bank?

Bank stability for a fuseless capacitor bank is similar to that of an externally fused capacitor bank and defined by shorted series sections, internal to individual capacitors. The voltage on the remaining series sections in the string should not exceed 110% of its rated voltage.