Page 153 - Practical Power System and Protective Relays Commissioning

152 Practical Power System and Protective Relays Commissioning

The tests of GIS are done as follows:
Inspection after transport
Visual check the GIS for completeness, obvious transport damage, etc.
well before commencement of the installation.
The following tests should be undertaken:

1. Measurement of voltage drop
The voltage drop test is done by injecting 100 Amp DC and measur-
ing any voltage drop in different locations of the system.
2. Check of gas tightness
All flanges and any connecting parts of the GIS compartments
should be checked for their tightness.
3. Contact resistance test for main circuit
This test is performed at different points in the GIS and the results
are compared to the one assembled and measured at factory.
4. SF 6 leakage test
In this test we put a plastic cover around each compartment of the
GIS and leave it for 24 hours then check for any leakage using a SF 6
gas detector. If there is any leakage then investigate the source of this
leakage and rectify it before putting the system in service.
5. Insulation test of control circuits
All control cables and connections in GIS should be checked using a
Megger at 2000 V DC for 1 minute and the insulation should be more
than 100 mega-Ohms.
6. Dew point measurement
The dew point measurement is performed once the gas compart-
ments have been filled and pressurized with SF 6 to its correct pressure.
In order to allow an equalization, this measurement should not be car-
ried out immediately after the filling. This test should be undertaken for
each SF 6 compartment.
7. SF 6 pressure gauge meter test
In this test we will activate the operation of the alarm contact and
trip contact of the SF 6 gauges in each compartment and check that the
signals are transferred to LCC and/or central control room if it exists.
8. Time testing
In this test we measure the opening and closing time of all CB and
compare the results with those supplied by the manufacturer at both
nominal DC voltage and at reduced DC voltage. This is done for each
phase and to measure any difference in opening and closing time for the
CB phases that is not detected by phase discrepancy protection off the
CB. The closing and opening time of disconnectors and earthing
switches are measured and compared with the specifications supplied
by manufacturer.