Differential voltage protection reflects capacitor failure

What is a voltage differential in a fuseless capacitor bank?

When voltage differential is used for a fuseless capacitor bank, the bottom can in each phase is a single element protection module (PM). The voltage differential relay (87V) is connected to look at the difference between the bus voltage and the protection module voltage (see Figure 4).

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.

What are the protection objectives of a power capacitor?

All applications of power capacitors require the same basic protection objectives, including system short circuits between phases or to ground within the bank, and element overvoltages, caused by power system overvoltages or by the failure of other elements within the bank.

How to test the overload protection of a capacitor bank?

Step 1: Find out the nominal current of the capacitor bank. The nominal current of 80.37 Amps is used in the case study and its calculation is given in Appendix. Step 2 Select the appropriate current transformer ratio. The CT ratio of 120:1 is selected to test the overload protection for SCB’s.

What is a capacitor failure?

In general, we can look at failures from the perspective of a capacitor unit or a capacitor element. A failure of a single capacitor element, or even a few elements, does not necessarily result in the loss of the entire capacitor unit. From this perspective, ability to perform unbalance calculations for a partial unit failure is beneficial.

What is the differential protection principle?

TRANSFORMERTURN-TO-TURNFAULTPROTECTIONWITH 87Q ELEMENTS The differential protection principle follows Kirchhoff’s current law (KCL) in applications where a metallic per-phase connection exists between the terminals of the protected apparatus. These applications include buses, lines, generator and motor stators, and reactors.