Apparatus for identifying defective electric power distribution capacitors

An apparatus for detecting incipient faults in an individual capacitor unit having a phase terminal within a capacitor bank mounted within a common phase bus and common neutral bus, including in combination:

• an alternating current power source comprising a storage battery having an output of between 12 and 24 volts and an inverter having an input of between 12 and 24 volts D.C. and output of 120 volts at a frequency of about 60-800 hertz;
• a variable transformer for varying the output voltage of the said power source, said variable transformer having an output from 0 to 480 volts;
• connecting means for supplying alternating output voltage of said variable transformer to the capacitor bank having the individual capacitor units therein to be tested;
• voltage detection means for setting and measuring a predetermined alternating voltage supplied by said connecting means at the common phase and neutral buses of the capacitor bank thereby permitting setting and reading a voltmeter means in conjunction with the controls of said variable transformer;
• an open and closed type, split-magnetic core probe positioned about the phase terminal of the individual capacitor unit for sensing the charging current to the individual capacitor unit operatively connected to the capacitor bank from said variable transformer to the individual capacitor unit operatively connected to the capacitor bank;
• and
• an ammeter for measuring the magnitude of the current output from said split-magnetic core probe to thereby detect the condition of the capacitor unit.

A method for testing an individual power capacitor unit, which is part of a capacitor bank having at least a phase terminal, for detecting incipient or fully developed faults therein, without disconnecting the capacitor unit from the capacitor bank, comprising the steps of:

• a. applying an alternating voltage variable from 0 to 480 volts at a frequency range of 60-800 hertz of a predetermined magnitude to the power capacitor bank, wherein the magnitude of the predetermined voltage is measured at the terminals of the capacitor bank;
• b. measuring the value of the portion of total charging current entering the capacitor bank which enters each of the individual capacitor units with an associated ammeter without disconnecting the individual capacitor from the capacitor bank by means of a split magnetic core probe having a distributed winding around the case and having an accuracy of about 3 percent of the determined value;
• and
• c. comparing the measured values of the charging currents through the individual capacitor unit with the known allowable values for the individual capacitor reactive power rating for the applied predetermined voltage, the thereby detect incipient faults in the capacitor unit when the measured charging current is outside the range of the known allowable value.