ABB GSC 200, Installation And Maintenance Manual

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Installation and maintenance guide
1ZSC000563-AAX EN, REV. A, 2019-03-21
5.2.3 Tightness test of bushing outer terminal
Overview
Because the outer terminal is often situated above the oil level of the transformer oil expansion system, a leak
at the outer terminal is serious. Water could enter directly into the transformer insulation. It is thus
recommended to do a tightness test after installation of the bushing, both with vacuum and pressure.
Different methods can be used, and ABB refers to the instructions given by the company responsible for the
field erection of the bushing.
Example procedure
1. Put tracer gas into the center tube before installation of the outer terminal.
NOTE!
The oil level of the transformer must be above the bottom end of the bushing, but below the
bushing flange.
2.
Increase the oil level to just below the bushing flange, to raise the pressure in the center tube.
3.
Find leaking gas with gas detector (sniffer) near
the gasket.
G003147
End of instruction
5.2.4 Measurement of capacitance and dissipation factor
Overview
After installation of the bushing, it is recommended to measure the capacitance values for future reference,
such as repairs, service etc. This can be done on an installed bushing because it has an insulated test tap.
Refer to 2750 515-142, “Bushing diagnostics and conditioning”.
• C
1
is the capacitance between the test tap and the outer terminal.
• C
2
is the capacitance between the test tap and ground.
NOTE!
The transport container must be removed before measuring the capacitance and dissipation factor
(tan δ).