Page 154 - Practical Power System and Protective Relays Commissioning

Gas Insulated System Substations Chapter | 14 153

9. Instrument transformer tests
Polarity test: this test is done to check the correct polarity of the CT
and VT.
Ratio test for CT and VT.
Voltage withstand test at 2 kV for 30 seconds for CT and VT.
Winding resistance test for CT and VT.
Loop resistance or burden test for CT and VT.
Magnetizing curve test for CT.
Insulation resistance test by Megger for CT and VT—both primary
and secondary.
10. High voltage test for GIS
This test is done by using cascaded resonance instruments at a specified
voltage:
Vtest 5 0:8V of the rated voltage, with frequency about 45 300 Hz.
With all CB and disconnectors closed and all earthing switches opened,
all CT’s secondary Winding are to be short circuited and all VT miniature
CB to be opened. A Megger test should also be undertaken after this test.

14.12 SF 6 GAS HANDLING

14.12.1 SF 6 Gas Filling Cylinder
Fig. 14.13 shows how to fill the GIS compartments when the gas density is
less than the desired one for that compartment due to SF 6 leakage.

FIGURE 14.13 SF 6 gas filling cylinder setup.