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Capacitance and DF Measurement on High-Voltage Bushings
appendix or as recommended by the bushing manufacturer. The dissipation
factor value of the dissipation factor tap insulation for most of the bushings
discussed earlier is generally in the order of 1.0 percent or less.
Figure 7-5 GST bushing test (C2)
7.6 Grounded Specimen Test (GST)
This test measures the quality of the insulation between the current carrying or
center conductor and the mounting flange of a bushing. This test is conducted
on bushings that have been removed from equipment, bushings connected to
de-energized equipment, spare bushings, or bushings that have been isolated
from connected windings and interrupters. The test is performed by energizing
the bushing conductor and grounding the flange.
7.7 Hot Collar Test
This test measures the condition of a specific small section of bushing insulation
between an area of the upper porcelain rain shed and the current carrying or
center conductor. The test is performed by energizing one or more electrodes
placed around the bushing porcelain with the bushing center conductor
grounded. This test is used to supplement the three previous tests. It is also
GST g A+B
Equalizers
C1 Layer
Voltage tap
Mounting flange
C2 layer (always
grounded to flange)
Paper insulation
Main conductor
IN A
IN B
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