Hobart 60PL20 Operation And Maintenance Manual page 62

OM-2053
(30) Check operation of the line switch (5) . 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 indi-
cated when the switch is placed in LINE-TO-LINE position.
(31) Check accuracy of frequency meter.
(a) Connect a master frequency meter of known accuracy to the frequency meter (1) terminals.
(b) Compare meter readings. Error must not exceed 1% of full scale.
(32) Operate the unit not less than 10 minutes under full load. The overload device (Ref. 1-1; 7, Fig.
11) MUST NOT trip.
(33) Operate at 125% rated load for 5 minutes immediately following the fullload run. The overload de-
vice MUST trip within 5 minutes and the overload indicating light (1-1; must come ON to indicate an
overload condition) .
(34) Reduce load to normal. Turn off indicating light by pressing reset switch (6, Fi g. 1).
(35) Check engine oil pressure at governed speed (2000 RPM) . Gage should indicate at least 38 PSI
when the engine is hot. Check engine coolant temperature. Gage should indicate in the range of 180
degrees to 190 degrees depending upon ambient temperature.
(36) Check operation of fuse interlock (Ref. 1-1; 8, Fig. 7) . With unit operating normally under load, re-
move protective relay circuit fuse (10, Fig. 1). The load contactor should open immediately. This indi-
cates that the fuse interlock relay is functioning properly. Replace fuse and apply load.
NOTE: Make all protective relay tests with the unit operating under load.
(37) Check operation of overvoltage relay and indicating light.
(a) With the unit running at normal load, adjust the voltage regulator rheostat (27, Fig. 1 ) to in-
crease voltage (turn clockwise) until the overvoltage sensing relay actuates the protective monitor
to open the load contactor and turn on the overvoltage indicating light. The overvoltage sensing
relay should trip when voltage reaches 130 V to 134 V.
(b) Return unit to normal operating conditions by adjusting voltage regulator rheostat and press-
ing reset switch (6) .
(38) Check operation of undervoltage sensing relay, indicating light, and time delay. Before starting
this check, let us understand the sequence of events which should happen when voltage is reduced
to 103 V or lower. At some value between 103 V and 93 V, the undervoltage sensing relay (Ref. 1-1;
4, Fig. 7) should function to activate the undervoltage time delay circuit. Five seconds after the time
delay circuit is activated, (if the undervoltage condition continues) it should function to open the protec-
tive monitor relay which, in turn, will open the load contactor to stop power delivery. As a result of the
action, the undervoltage indicating light should be turned ON. A stopwatch or sweep-second-hand
watch is required for this check. Proceed as follows:
(a) With unit running at normal load, use the voltage regulator rheostat (27, Fig. 1) to reduce volt-
age to 104V. The load contactor should NOT open after a 5-second delay.
(b) Reduce voltage in steps of 1 V, with a delay of at least 5 seconds between steps. Restart stop-
watch or note position of sweep-secondhand each time voltage is reduced. At some voltage value
between 103 V and 93 V, and 4 to 12 seconds after a new voltage setting is made, the load con-
tactor should be opened and the undervoltage indicating light should be turned on by the step-by-
step action of the undervoltage sensing relay, time delay circuit, and protective monitor relay.
NOTE : The 4 to 12 second time delay is generally set at 5 seconds. It may be necessary to switch
to MANUAL control to obtain these low voltages.
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December 31/91 Revised