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5.2 Recommended test before energization
5.2.1 Overview
The tests should be done to check the insulation, sealing and current path of the bushing.
NOTE!
The tests should be done after installation, but before connecting the outer terminal of the bushing
to the power circuit.
5.2.2 Tightness test between transformer and bushing flange
Many different methods can be used, and we thus refer to the instructions given by the company responsible
for field erection.
For example, the tightness of the seal between the transformer and the bushing flange can be examined when
the transformer is oil-filled, with chalk or paper strips.
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 Hitachi ABB Power Grids 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.
2.
Increase the oil-level to just below the bushing flange, to raise the pressure in the center tube.
54
NOTE!
The oil-level of the transformer must be above the bottom end of the bushing, but below the
bushing flange.
Installation and commissioning guide
1ZSC000563-AAF EN, REV. 4, 2021-06-23
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