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7.7 Maintenance related to electrical performance, excitation,
control and protection
The electrical performance of a synchronous machine is mostly defined by the
condition of the rotor and stator windings and the operation of the excitation
system.
Chapter 7.6. Maintenance of stator and rotor winding. In this chapter the focus is
on the maintenance of the excitation system and the control and protection
systems. For optional PMG-unit, see Annex 9. Permanent Magnet Regulator
(PMG) User's Manual.
7.7.1 Exciter insulation resistance measurement
The insulation resistance in the exciter can be tested with the winding insulation
resistance test. The procedure is described in detail in Chapter 7.6. Maintenance
of stator and rotor winding. The test voltage for the exciter stator should be 500
VDC and the test should be performed in the terminal box after the cables have
been disconnected.
The resistance of the exciter rotor is usually measured jointly with the rotor of the
main machine, see Chapter 7.6.4. Insulation resistance test. The resistance of the
exciter rotor can also be measured separately, but this requires special
arrangements.
7.7.2 Protection trips
The synchronous machine needs to be protected with alarms and trips in case of
abnormal running conditions, both electrical and mechanical. Some of these
protections can be reset and the machine restarted directly as the fault is located.
7.7.3 Automatic voltage regulator (AVR)
The automatic voltage regulator (AVR) is important in controlling and protecting
the machine, and problems in connections or settings of the AVR might lead to
different types of operational faults. These include for example performance
deviations and loss of excitation. For detailed information about AVR connection
and settings see Annex 3. Main Connection Drawing and Annex 6. Automatic
Voltage Regulator User's Manual.
7.7.4 Insulation resistance measurement for auxiliaries
To ensure correct operation of the machines protections and other auxiliaries, their
condition can also be determined by an insulation resistance test, however this is
not recommended. Contact After Sales for more information
7.7.5 Diode fault
If a diode in the rotating rectifier fails, the generator must be tripped. To
determine and locate a faulty diode:
Open the covers at the non-drive end of the machine and measure the insulation
resistance with an ohm-meter over one of the diodes.
If diode failure is detected, disconnect all diodes and test them separately to locate
the faulty diode.
NOTE: Do not open the service covers or end shields unless it is certain that the
To replace faulty diodes:
The
main
machine
machine is isolated from its driving source.
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winding
maintenance
is
described
in
.
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