Guardian 4389 Repair Manual page 44

SECTION 2.4
DIAGNOSTIC TESTS
Figure 7. The Rotor Assembly
TEST 11 - CHECK AC OUTPUT FREQUENCY
DISCUSSION:
The generator AC frequency is proportional to the
operating speed of the rotor. The 2-pole rotor will sup-
ply a 60 Hertz AC frequency at 3600 rpm. The unit's
AC output voltage is proportional to the AC frequen-
cy. For example, a unit rated 240 volts (line-to-line)
will supply that rated voltage (plus or minus 2 per-
cent) at a frequency of 60 Hertz. If, for any reason,
the frequency should drop to 30 Hertz, the line-to-line
voltage will drop to a matching voltage of 120 volts
AC. Thus, if the AC voltage output is high or low and
the AC frequency is correspondingly high or low, the
engine speed governor may require adjustment.
PROCEDURE:
1. Connect an accurate AC frequency meter across the
Wires 11 and 44 terminals of the generator main line
circuit breaker (see Figure 1, Section 2.4).
2. Start the engine, let it stabilize and warm up at no-load.
GOVERNOR
SHAFT
GOVERNOR
CLAMP
BOLT
(7KW UNITS WITH SINGLE GOVERNOR SPRING)
Page 42
ADJUST
SCREW
Figure 8. Engine Governor Adjustment Single Cylinder Engines
PART 2
3. When engine has stabilized, read the frequency meter.
The no-load frequency should be about 61-63 Hertz.
RESULTS:
1. If the AC frequency is high or low, go on to Test 12.
2. If frequency is good, but voltage is high or low, go to
Test 13.
3. If frequency and voltage are both good, tests may be
discontinued.
TEST 12 - CHECK AND ADJUST ENGINE
GOVERNOR
DISCUSSION:
The generator AC frequency output is directly pro-
portional to the speed of the rotor. A two-pole rotor
(having a single north and a single south magnetic
pole) will produce an AC frequency of 60 hertz at
3600 RPM.
The generator is equipped with a "voltage over fre-
quency" type AC voltage regulator. The units AC out-
put voltage is generally proportional to AC frequency.
A low or high governor speed will result in a corre-
spondingly low or high AC frequency and voltage out-
put. The governed speed must be adjusted before
any attempt to adjust the voltage regulator is made.
PROCEDURE
(7KW UNITS WITH SINGLE GOVERNOR SPRING):
1. Loosen the governor clamp bolt (Figure 8).
2. Hold the governor lever at its wide open throttle position,
and rotate the governor shaft clockwise as far as it will
go. Then, tighten the governor lever clamp bolt to 70
inch-pounds (8 N-m).
GOVERNOR
SHAFT
GOVERNOR
CLAMP
BOLT
(7KW UNITS WITH DUAL GOVERNOR SPRINGS)
AC GENERATORS
SECONDARY
ADJUST SCREW
PRIMARY
ADJUST
SCREW