Hermetic Protection Relay MHPR for Transformers

The Vertical Protection Relay MHPR was developed in conjunction with transformer manufacturers and electric utilities and is used for hermetically sealed distribution transformers. It's main purpose is to monitor the oil level in hermetically sealed transformers. Falling oil level in the fill pipe of a hermetically sealed transformer operates a switch contact. The protection relay MHPR is available in two different lengths and can upon request be equipped with an gasket.

Construction of hermetic protection relay MHPR

The Vertical Protection Relay MHPR replaces the pipe plug on the fill pipe of the transformer. The housing of the device is fabricated of an
aluminium alloy, which provides a positive metal seal withstanding pressures of up to 0,5 bars. Vertical movement of the float is transmitted to
the snap-action-alarm switch of the MHPR. The float is made of an oil-resistant closed-pored material, which eliminates the risk of leaks in the float and guarantees constant buoyancy.

Your benefits at a glance

  • Monitors the oil level
  • Falling oil level operates a switch contact
  • Corrosion resistant materials
  • 1/8“ ball valve for oil sampling and air venting

Operation Principle of protection relay MHPR

In a properly filled transformer the oil keeps the float at the top position. If oil level decrease occurs, the float moves downwards and switches a switch which triggers an alarm.

 Technical Data
Switching Capacity   240 V AC / 0,4 A
  24 V DC / 3 A
Max. Operating Pressure  50 kPa
Max. Ambient Temperature  100 °C
Assembly instruction

The Vertical Protection Relay MHPR will be installed in the filling pipe and replaces the R 1 1/2" pipe plug. Under no circumstances should an angle of 15 off vertical be exceeded. We recommend placing the fill pipe near one corner of the transformer cover to avoid trapping gas occurs while filling the transformer with oil. When the transformer tank and fill pipe are completely filled, approximately 100 cm3 of oil has to be removed before installing the Vertical Relay MHPR. This will avoid oil overflow during installation of the Vertical Protection Relay.

For more information please refer to download below.

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