CP TD1 Reference Manual V 1.44
112
Test Connections
There are six overall tests performed when the breaker is open. Each bushing
is individually tested in the overall GST test mode. Three overall tests are
performed with the breaker closed in the GST test mode. If the bushing is
equipped with a test tap, the C
1
main insulation test can be performed in the UST
mode along with the overall GST test without making a lead change.
All tests are performed at 10kv or a lower voltage suitable for the insulation.
9.3
Oil Poor Circuit Breakers (Live Tank)
Oil poor circuit breakers with one contact (chamber) per phase normally have
vertical tubes out of porcelain with the breaker contacts inside. The DF of the
contact chamber can be measured, if the contacts are open. This way the oil
quality and decomposition of the oil can be determined.
Oil poor CB's with more than one contact per phase are normally mounted in Y
or T form. Grading capacitors in parallel to the contacts equalize the voltage
drop across the contacts if they are open. These capacitors have to be removed
when the oil quality in the chambers is tested. The capacitance values of the
described capacitors are important for a proper operation of the circuit breaker.
An increase of the capacitance value is an indicator for partial breakdowns of
some sections.
High DF readings on grading capacitors may be the result of deteriorated
grading capacitors or, in some cases, surface leakage.
9.4
SF6 Circuit Breakers (Dead Tank with Bushings)
For these CB's the test of the bushing is of importance.
Additional Hot-Collar tests may be conducted on breakers equipped with gas-
filled bushings to detect internal contamination or exterior cracks and other
problems that may have occurred along the surface of the bushing.
9.5
Vacuum Circuit Breakers
These circuit breakers operate on a different principle from other breakers
because there is no gas to ionize when the contacts open. They are hermetically
sealed so consequently they are silent and never become polluted. Their
interrupting capacity is limited to about 30kv. For higher voltages, several circuit
breakers are connected in series.
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