Tettex MIDAS 2881, Operating Instructions Manual

Page: 153 / 164

Applications Guide 143
Measurement of a grounded two-bushing energy storage capacitor with additional resonating
inductor, connected for C
1
determination.
Test Connections
DUT High Voltage
to INPUT A
to HV GND
to Test Mode
C
1
2 1 Tank GND UST A
C
G1
2 1 Tank GND GST gA+B
C
G2
2 1 Tank GND GST gA+B
C
G1
+ C
G2
1 + 2 Tank GND UST A
Measuring Data Interpretation
When available the measurement results should be compared with the nameplate values or with
results obtained in previous measurements.
The power factor of the earth insulation is expected to be in the order of 0.5% or less. The main
capacitor should have a much lower power factor.
An increase in capacitance of several percent is an indication of short-circuited layers of the insulation
or the dielectric.
14.7 Circuit Breakers
For insulation measuring purposes high voltage circuit breakers can be classified into two groups.
Live tank breakers whose interrupting chamber is on HV potential and dead tank breakers whose
interrupter chamber is accommodated in an earthed metal housing.
The applied test voltage for breakers should not exceed 10% to 25% above their rated operating line-
to-ground voltage. That means in formula: