Manual for Induction Motors and Generators
106 - Trouble Shooting
3BFP 000 050 R0101 REV E
8.3 Electrical performance, excitation, control and protection
The electrical performance of a rotating electrical machine is mostly defined by the condition of
the rotor and stator windings, and the operation of the excitation system, if applicable. The main
machine winding maintenance is described in Chapter 7.6 Maintenance of stator and rotor
windings. In this chapter, the focus is on the trouble shooting of the excitation, the control and
protection systems.
8.3.1 Protection trips
The machine needs to be protected with alarms and trips for abnormal running conditions, both
electrical and mechanical. Some of these protections can be reset and the machine restarted
directly as the fault is located.
Examples of protections that, if they give an alarm or trip, may need further investigation:
• Diode fault protection
• High temperature in bearing, see Chapter 7.5 Maintenance of bearings and lubrication
system
• High temperature in winding or in cooling air, see Chapter 7.6 Maintenance of stator and
rotor windings and Chapter 8.5 Thermal performance and cooling system
• Overcurrent, current and voltage unbalance, bus bar voltage
• Vibration protection, Chapter 7.4.2 Vibration and noise.
8.3.2 Pt-100 resistance temperature detectors
Pt-100 resistance temperature detectors are an essential part in the machine's condition
monitoring and protection system. They are used to measure temperatures in the windings,
bearings and in the cooling air. The Pt-100 detector uses a fine platinum filament for the
temperature measurement, which can be damaged e.g. by incorrect handling or excessive
vibration.
The following symptoms might suggest a problem in a Pt-100 detector:
• Infinite or zero resistance over the detector
• Disappearance of measurement signal during, or after start up
• A significantly different resistance value in a single detector.
If a Pt-100 failure is suspected the findings should always be confirmed from the connection
box, by measuring the resistance at the detector with its cables disconnected. The findings
should by registered. For the correct measuring current see the appropriate Pt-100 detector. For
resistance values at different temperatures, see Table 8-1 Temperature values for Pt-100
elements.
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