Causes of capacitor protection action

What is the purpose of capacitor bank protection?

The objective of the capacitor bank protection is to alarm on the failure of some minimum number of elements or units and trip on some higher number of failures. It is, of course, desirable to detect any element failure. II. ELEMENT AND UNIT FAILURES EXAMINED

What causes a capacitor to overload?

It is the total peak voltage, the fundamental and the harmonic voltages together, that can cause overload of the capacitors. The capacitor can withstand 110% of rated voltage continuously. The capability curve then follows an inverse time characteristic where withstand is approximately 1 second -180%, 10 cycles -210%.

What happens if a capacitor is faulty?

The capacitor units are designed to withstand 110% of the rated voltage continuously. If this level is exceeded, or if the faulty units capacitance have decreased below 5/6 of the nominal value, the capacitor bank must be taken out of service.

What happens if a capacitor element fails?

Failed capacitor elements can cause failure of the entire bank due to overvoltage on the individual failed elements. As elements fail, the subsequence overvoltage caused by the failure increases the risk of further failures.

What causes a capacitor to fail?

Along with short circuit failure as a result of electrical over stress, open circuit failure resulting from corrosive damage is a relatively common event. The capacitor must be manufactured in a very clean environment to prevent contamination with any ionic species which might promote corrosion of the metal film.

What happens if a capacitor fails in open circuit mode?

The open circuit failure mode results in an almost complete loss of capacitance. The high ESR failure can result in self heating of the capacitor which leads to an increase of internal pressure in the case and loss of electrolyte as the case seal fails and areas local to the capacitor are contaminated with acidic liquid.