TM 5-6115-593-34NAVFAC P-8-631-34TO-35C2-3-463-2Figure 17-21. 500 KW Exhaust SystemThe utility monitor circuit which includes 120 VACover/under voltage relay (27/59N), under frequencyrelay (81N-U), over frequency relay 81N-0), 1.5 - 15second (adjustable) time delay relay (TD), 50/60Hzfrequency select switch and a run rely (RR), continuallymonitors the 120 VAC utility voltage from the line sideof the utility breaker.When the utility power is normal, relays 27/59N, 81N-Uand TD are energized (81N-0 will only energize duringan over-frequency condition) and the normal poweravailable lamp will be on.If the utility power completely fails or voltage varies bymore than ±10% and/or frequency varies more than±3%, TD relay after a 1.5 - 15 second time delay willallow all generators to begin a start-up cycle providingthe generators are in the automatic mode. Relays27/59N, 81N-U, TD and RR de-energize allowing 24volts D. C. to energize the K5 engine start circuit vianormally closed contacts TD and RR through TB4-5, 6,7, 8 through J3-B through the automatic position of theauto-trip manual switch (s53) on each set. The utilitybreaker (located within user switchgear will open viaadditional sets RR contacts at TB3-17, 18, and 19.As the generators run up to speed, each generator'squality circuit (81G-0, 81G-U, 27/59G and CR) monitorsthe condition of their respective set. This circuit hasidentical voltage and frequency specifications as theutility monitor circuit in the ACM and is only completelyfunctional if the generator set is in the automatic mode.17-28
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