Rectifier Tests

Even though the transformers, chokes, tubes, and capacitors have been tested before assembly of the rectifier, performance tests of the rectifier are desirable. These generally include tests of output, regulation, efficiency, ripple, and input kilovolt-amperes or power factor. Accurate meters should be used, and polyphase rectifiers should have balanced supply voltages. Wiring is tested at some voltage higher than normal, preferably with transformers, tubes, and capacitors disconnected to avoid damage during the test. Ordinary care in testing is sufficient except for regulation tests. If the regulation is low, the difference in meter readings at no load and full load may be inaccurate. Differential measurements are sometimes used, such as a voltmeter connected between the rectifier and a fixed source of the same polarity and voltage. Artificial loading of a high-voltage rectifier is often a problem. Water rheostats have been used for this purpose. Load tests, preferably in combination with the transmitter or other apparatus which the rectifier is to supply, are safeguards against field troubles. Operating tests are essential when the load is keyed or modulated, so that overheating or inadequate transformer operation may be detected.

Ripple is measured either with a special hum-measuring instrument or with a capacitance-resistance network arranged to block the direct current from the measuring circuit. Capacitance and resistance values in the measuring circuit should be so chosen as to avoid influencing the ripple or loading the rectifier transformer. Sometimes capacitance dividers are used for this purpose. The problem of proper values becomes particularly critical with high-voltage low-current rectifiers. The effect of stray capacitance is especially important.