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1ZSE 5492-118 en, Rev. 4
6. Pressure relay
6.1 General
The selector switch housing of the on-load tap-changer is supplied with a pressure relay.
In the event of overpressure in the selector switch housing and, if correctly connected, the
relay trips the transformer 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 in the chapter ”Pressure Relay” in the Re-
pair Guide.
To take the transformer into service after a pressure relay trip without carrying out a careful
investigation of the selector switch by lifting it out of the selector switch housing, and repair-
ing faults, if any, may cause severe damages to the on-load tap-changer and the transform-
er.
The pressure relay can easily be tested by applying air pressure by means of a pump to the
test tap on the valve and the handle can be pad-locked 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. Do not open the
package of the pressure relay until you are about to install it on the on-load tap-changer.
6.2 Installation
Remove the cover from the ange on one of the tube bends on the upper part of the on-
load tap-changer and install the pressure relay. Make sure that the gasket is correctly tted.
Remove the cover from the pressure relay and connect the cables to the terminal block.
The cable gland includes an O-ring sealing between the gland and the pressure relay hous-
ing.
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 (example Loctite 275).
CAUTION
Tighten the cable gland with care, torque max 5 Nm.
6 Pressure relay
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