Capacitance and DF Measurement of Generators and Motors
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8 Capacitance and DF Measurement of
Generators and Motors
The DF - voltage characteristic (power- factor tip-up) of stator windings is used
primarily as a quality-control criterion in manufacturing high-voltage generators
and motors. It is sometimes used as an acceptance test on individual coils. DF
tip-up has been used as a maintenance test because a change in the tip-up
value over a period of time is an indication of change of condition of the coil
insulation. With increasing test voltage Partial Discharges (PD) may occur. This
can be seen in Figure 8-1. The sensitivity of the power-factor tip-up test
decreases with the length of coil included in the measurement.
Refer to IEEE Standard No. 286, July 1975, "IEEE Recommended Practice for
Measurement of Power-Factor Tip-Up of Rotating Machinery Stator Coil
Insulation", for a description of the DF tip-up test. A DF tip-up curve of a 6kV
motor is shown in Figure 8-1.
Tan Delta Motor 6kV
Figure 8-1 DF tip-up curve
1.6%
1.5%
1.4%
1.3%
1.2%
1.1%
1.0%
0.9%
0.8%
0.7%
0.6%
0V 1kV 2kV 3kV 4kV 5kV 6kV 7kV 8kV
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