GE Industrial Solutions Seconday Substation Transformer - Manual (Page 9)

9
FILLING WITH INSULATING
LIQUID
A. CHECKING INSULATING LIQUID
Check the dielectric strength of the
insulating liquid while it is still in
containers. If free water is present, drain off
the water before putting the liquid through the
filter press. Continue passing liquid through
the filter press until the prescribed dielectric
strength is met.
B. NON-VACUUM FILLING
Although it is not recommended, in cases
where vacuum filling is not required, the tank
should be filled through the main drain valve.
A second opening at the top should be
provided to relieve the air being displaced.
Full voltage may not be applied to the
transformer for a period of 24 hours.
C. VACUUM FILLING
Entrapped air is a potential source of trouble
in all transformers. In general, therefore, it is
desirable to fill transformers with liquid under
as high a vacuum as conditions permit.
Particularly it is essential to vacuum-fill high-
voltage transformers shipped in nitrogen or
dry gas in order to develop their full insulation
strength before they are energized.