Pressure Relief Device - Westinghouse PS-1002 Instruction Book

8
rupture of the tank walls and cover. The design pressure
on the transformer nameplate is the greatest pressure (or
vacuum) that will not permanently distort the tank walls.
On oil-filled units, the pressure-vacuum gauge is fur­
nished in combinatio n with a pressure regulator (Seale­
daire ® valve) that will automatically bleed off gas if the
pressure exceeds 6.5 psig positive or add make-up air to
the tank if the pressure exceeds 6.5 psig negative. The
pressure regulator is fitted with a valve and a hose fitting
to take gas samples or for purging the gas space. Under
normal operating conditions the Sealedaire ® valve elimi­
nates breathing. For further description of Sealedaire
connections, send for Instruction Leaflet 48-063-2.

5.7 Pressure Relief Device

All transformers above 2500 kV A are normally fur­
nished with a mechanical pressure relief device on the
Fig. 4
Relief Del'ice in Sealed Position
transformer cover. The device consists of a self-resetting,
spri n g-loaded diaphragm and a mechanical operation in­
dicator (semaphore). Should the tank pressure increase
above 10 psig, the gas pressure will lift the diaphragm and
vent the excess pressure. Immediately after the pressure
returns to normal, the diaphragm will reset and reseal the
transformer. The mechanical operation indicator (sema­
phore) must be reset manually after each operation.
Replace the relief device with a blind flange before
testing the transformer tank for leaks with pressure
greater than 8 psi. The relief device will withstand full
vacuum and need not be removed from the transformer
tank during any vacuum treatment.
The relief device may be furnished with SPDT alarm
contacts. The alarm device is mounted on the side of the
relief device cover. Refer to Table 1, page 4, for alarm
SEMAPHORE
(TRIPPED POSITION)