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1ZSE 5492-115 en, Rev. 5
5 Pressure relay
5. Pressure relay
5.1 General
The tank of the on-load tap-changer is supplied with a pressure relay. In the event of over-
pressure in the tank the relay, if correctly connected, will trip the transformer’s main circuit
breakers. It is also recommended to connect the pressure relay in the trip circuit of the
power supply during testing of the transformer.
CAUTION
After a pressure relay trip follow the instructions under chapter ”Pressure Relay” in the Repair
Guide.
Taking the transformer into service after a pressure relay trip without opening the front cover
and carrying out a careful investigation of the active part and repairing any faults may cause
severe damage to the on-load tap-changer and the transformer.
The pressure relay can easily be tested by applying air pressure, using a pump, to the test
tap on the valve. The handle can be padlocked in the service position.
CAUTION
The pressure relay is a calibrated monitoring instrument. It must be handled with care and
protected against careless handling or any kind of mechanical damage.
5.2 Installation
Remove the cover from the pressure relay and connect the cables to the terminal block.
The cable gland includes an O-ring seal between the gland and the pressure relay housing.
If the gland has to be changed to another type, the seal against the housing must be se-
cured by a gasket or sealing liquid (e. g. Loctite 275).
CAUTION
Tighten the cable gland with care, torque max. 5 Nm.