Hobart 6921 Series Operation And Maintenance Manual page 81

OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
(27) Check voltage regulator, at intervals, from no-load to full load, and on up to 125% load. Observe
and note voltage at various loads. Voltages should vary no more than plus or minus 1% from
115 V.
(28) Check accuracy of voltmeter.
a. Open generator control tray (15, Fig. 1).
b. Connect a master voltmeter of known accuracy to terminals of the voltmeter (3).
c. Compare unit voltmeter reading with master meter. Error must not exceed 4% of full scale.
(29) Check accuracy of AC ammeter.
a. Connect a master ammeter of known accuracy to the AC ammeter (4) terminals.
b. Compare unit ammeter reading with master meter under various loads. Error must not
exceed 4% of full scale.
(30) Check operation of meter selector switch (6) . A voltage value should be shown in each switch
position.
(31) Check operation of the line switch (7) . A normal voltage of 115 V AC should be indicated when
the switch is in LINE-TO-NEUTRAL position. A voltage of approximately 200 V AC should be
indicated when the switch is placed in LINE-TO-LINE position.
(32) Check accuracy of frequency meter.
a. Connect an accurate master frequency meter to the frequency meter (1) terminals.
b. Compare meter readings. Error must not exceed 1% of full scale.
(33) Operate the unit for a full 10 minutes under full load. The overload device (Ref. 1-1; 7, Fig. 13)
MUST NOT trip.
(34) Operate at 125% rated load for 5 minutes immediately following the full-load run. The overload
device MUST trip within 5 minutes and the overload indicating light (10, Fig. 9) must come ON
to indicate an overload condition.
(35) Reduce load to normal. Turn off indicating light by pressing reset switch (7, Fig. 9).
(36) Check engine oil pressure and oil temperature at rated operating speed (2000 RPM) . Oil
pressure gage should indicate at least 38 PSI when the engine is hot. Oil temperature gage
should indicate 190 F (88 C) 5 F (3 C) when engine is hot.
(37) Check operation of fuse interlock (Ref. 1-1; 2, Fig. 9) . With unit operating normally under load,
remove protective relay circuit fuse (Ref. 17, Fig. 9) . The load contactor should open
immediately. This indicates that the fuse interlock relay is functioning properly. Replace fuse
and apply load.
NOTE :Perform all protective relay tests with the unit operating under load.
(38) Check operation of overvoltage relay and indicating light.
a. With the unit operating at normal load, adjust the voltage regulator rheostat (37, Fig. 1) to
increase voltage (clockwise), until the overvoltage sensing relay activates the protective
monitor. This will open the load contactor and turn on the overvoltage indicating light. The
overvoltage sensing relay should trip when voltage reaches 130V to 134V.
February 28/94 Revised Chapter 2-3
Page 7