Pressure Relief Devices

Description and general specifications.
Aim of the safety valves on electric transformers
The transformer tank filled with cooling liquid is a container subject to internal pressure and then has to be
provided with one or more safety valves suitably calibrated for the maximum allowed pressure, so that
overpressure caused by internal faults can be instantaneously relieved through the valves, thus avoiding
greater damages such as the deformation or even the burst of the tank and the spraying of hot oil with
subsequent fire risks. It is necessary to protect the transformer tank with a suitable equipment capable of
almost instantaneously discharging overpressure already at the development, before the structure integrity is
damaged and the safety valves has just this function.
General features
The safety valves consist schematically of:
 a valve base comprising the valve opening venting area with its specially profiled gasket and a seat
for an O-ring gasket on the flanged end towards the transformerís tank;
 a valve cap pressed against the profiled gasket by
calibrated helical spring, thus making the valve completely tight up to the rated pressure;
 a splash diverter to avoid damages caused by hot oil sprinkles (on request);
 a single or a double electrical contact (on request).

Mechanical protection degree : IP 65
Insulation : 2000V 50Hz between terminals and
earth for a 60 seconds time
Cable gland : PG 1 3,5

Microswitch breaking capacity :
1 0 A 250V AC
1 A 1 25V DC

Safety valves series VS : the advantage of safety valves serie VS consists in the total absence of projecting
parts in the transformers tank making the mounting point choose easier. These valves can be mounted, with
regards to their base plane, both horizontally on the cover and vertically on the transformer walls at the
points where their safety action is presumed to be more necessary.

Safety valves series T : the advantage of safety valves series T is that, showing a good effectiveness and
reliability of valves serie VS, their simplicity consent to obtain very competitive prices.