Surge Currents in Protective Devices

Abstract

ties, more definite information than that ascertain-recorded by several successive hourly tests. About able by the usual indicating and recording instruments 30 per cent of the failures have been detected on will be available in the future. these tests. At monthly intervals a complete check is made of MAINTENANCE all tubes by means of a portable test set. At the same time all 132 kv circuit breakers are tripped by The carrier equipment is checked hourly by the the relays to insure that all electrical and mechanical substation operators and readings of carrier signal devices are in proper working condition. strength noted on ammeters connected in each reAt penrodic intervals a complete calibration test ceiver relay circuit. The test is quite simple and is made of all line protective relays. As the time can be completed in a very short interval, since it settings are very short and the selectivity between requires only the pressing of a button to transmit the vanrous relays is in the order of a few cycles, special signal, and the reading of an ammeter.high speed timing devices are used for this purpose. A code signal is used to identify the line being At Pleasant Valley the automatic oscillograph is tested, and by means of a prearranged schedule, the used for checking the timing of the relays after they initiating station transmits a warning signal and re-have been individually calibrated. The record ceives a "ready" signal by the receiving substation. shows the performance of the combined relay inSignals of approximately 2 seconds' duration are then stallation, including the time margins between starttransmitted by the initiating station and answered ing of the carrier signal and individual relay tripping by the receiving station, thus permitting a check of and resetting operations. signal strength of each circuit at each substation.At other substations an electronic timer is used Poor condition of any of the tubes is usually in-for checking the calibration of the individual relay dicated by a gradual decrease in signal strength as units.