7.4.7 RESIDUAL VOLTAGE CHECK This procedure is applicable to generators with either SX460
or SX440 or SX421 AVR.
With the generator set stationary remove AVR access cover
and leads X and XX from the AVR.
Start the set and measure voltage across AVR terminals 7-8
on SX460 AVR or P2-P3 on SX440 or SX421 AVR.
Stop the set, and replace leads X and XX on the AVR
terminals. If the measured voltage was above 5V the
generator should operate normally.
If the measured voltage was under 5V follow the procedure
below.
Using a 12 volt d. c. battery as a supply clip leads from battery
negative to AVR terminal XX, and from battery positive
through a diode to AVR terminal X. See Fig. 10.
Important ! A diode must be used as shown below to
ensure the AVR is not damaged.
Important ! If the generating set battery is used for field
flashing the generator main stator neutral
must be disconnected from earth.
Restart the set and note output voltage from main stator,
which should be approximately nominal voltage, or voltage at
AVR terminals 7 and 8 on SX460, P2-P3 on SX440 or SX421
which should be between 170 and 250 volts.
Stop the set and unclip battery supply from terminals X and
XX. Restart the set. The generator should now operate
normally. If no voltage build-up is obtained it can be assumed
a fault exists in either the generator or the AVR circuits.
Follow the SEPARATE EXCITATION TEST PROCEDURE to
check generator windings, rotating diodes and AVR. Refer to
subsection 7.5.
7.5 SEPARATE EXCITATION TEST PROCEDURE The generator windings, diode assembly and AVR can be
checked using the appropriate following section.
7.5.1 GENERATOR WINDINGS, ROTATING DIODES and
PERMANENT MAGNET GENERATOR (PMG)
7.5.2 EXCITATION CONTROL TEST.
7.5.1 GENERATOR WINDINGS, ROTATING DIODES and PERMANENT MAGNET GENERATOR (PMG) Important ! The resistances quoted apply to a standard
winding. For generators having windings or
voltages other than those specified refer to
factory for details. Ensure all disconnected
leads are isolated and free from earth.
Important ! Incorrect speed setting will give
proportional error in voltage output.
Start the set and run at rated speed. Measure the voltages at
the AVR terminals P2, P3 and P4. These should be balanced
and within the following ranges :-
50Hz generators - 170-180 volts
60Hz generators - 200-216 volts
Should the voltages be unbalanced stop the set, remove the
PMG sheet metal cover from the non drive endbracket and
disconnect the multipin plug in the PMG output leads. Check
leads P2, P3, P4 for continuity. Check the PMG stator
resistances between output leads. These should be balanced
and within +/-10% of 2.3 ohms. If resistances are unbalanced
and/or incorrect the PMG stator must be replaced. If the
voltages are balanced but low and the PMG stator winding
resistances are correct - the PMG rotor must be replaced.
This procedure is carried out with leads X and XX
disconnected at the AVR or transformer control rectifier bridge
and using a 12 volt d.c. supply to leads X and XX.
Start the set and run at rated speed.
Measure the voltages at the main output terminals U, V and
W. If voltages are balanced and within +/-10% of the
generator nominal voltage, refer to 7.5.1.1.
Check voltages at AVR terminals 6, 7 and 8. These should be
balanced and between 170-250 volts.
If voltages at main terminals are balanced but voltage at 6, 7
and 8 are unbalanced, check continuity of leads 6, 7 and 8.
Where an isolating transformer is fitted (MX321 AVR) check
transformer windings. If faulty the transformer unit must be
replaced.
If voltages are unbalanced, refer to 7.5.1.2.
7.5.1.1 BALANCED MAIN TERMINAL VOLTAGES If all voltages are balanced within 1% at the main terminals, it
can be assumed that all exciter windings, main windings and
main rotating diodes are in good order, and the fault is in the
AVR or transformer control. Refer to subsection 7.5.2 for test
procedure.
If voltages are balanced but low, there is a fault in the main
excitation windings or rotating diode assembly. Proceed as
follows to identify :-