What is a Transformer ? Types and Transformer protection


What is a Transformer device?

The transformer is a device that transfers electrical energy from one circuit to another through the magnetic field without change of frequency.

Types of Transformer

Based on service
1.Power Tr
2.Distribution Tr.

What is the use of transformer?

In this age of modern transmission system with optimal loss it is necessary to transmit the power at very high level.it is not economical to produce electrical power at such a high voltage.Here comes the vital role of transformer,which enhances the voltage level from generating voltage to such a high level where the loss is minimal.

It is also used as booster in distribution system to give better voltage regulation.

General Fault In Transformer

General Fault in transformer are
1.Open circuit Fault
2.Over heating
3.Winding short circuit fault
4.faults due to lightening

Protection For Transformer

1.Buchholz Relay
2.Earth Fault Relay
3.Over current relay
4.Differential relay
5.Digital relay

Earth Fault Protection

An earth fault usually involves a partial breakdown of winding insulation to earth
Under this circumstance it is profitable to employ an earth fault relay
One method of protection is core balance protection

Differential Protection

Merz price circulating current principle or differential protection is commonly employed for power transformer protection from internal fault.

Points to be noted
1.The different of current in primary and secondary must be equalized in diff relay by using appropriate turns on CT’s connected with both primary and secondary

2.The phase difference of current still generates a relay current.To neutralize it is case of healthy condition it is required to connect the CT’s in phase opposition with respect to adjoint.

Protection Against Lightening

It is necessary to provide protection of transformer against transient & surges.The most commonly used devices for protection against lightening surges are
a)Earthing screen
b)Overhead Ground wires
c)Lightning arrestor


Thank you for your explanation from above. I always like to see there are a guys out there trying to help explaining about the mandatorily need of protection devices. I´d like to add some information regarding protection devices.
Generally there needs to be distinguished between protection devices for hermetically sealed transformers and devices for transformers with expansion tank (get in direct touch with its ambient air).

Devices for Transformers with expansion tank

  1. Buchholz relay MBP. This great device has experienced many improvements the last several years. Now its a reliable and durable device which detects oil level and gas accumulation as well internal pressure.
  2. Magnetic oil level indicator MOLC which is placed on the front side of the expansion tank. It meaures oil level and can be equipped with min. and max. switches.
  3. Pressure safety valve MPRV which works with a pre-adjusted pressure value. If this value gets exceeded, the valve opens up and releases internal pressure. After decreasing pressure, the valve closes. It can be equipped with either one or two switches.

Protection devices for hermetically sealed distribution transformers
There are also protection devices for hermetically sealed transformers, you can find a short list below.

1.transformer protection device MCHD which detects oil level and temperature, gas accumulation and internal pressure. It´s the mostly used device for hermetically sealed distribution transformers as it is a all-in-one device.
2. Bimetallic thermometer MBT which detects oil temperature. It can be equipped with min. and max. limit switches.
3. Protection device MHPR which detects oil level. It is equipped with a switch to alarm.
4. Pressure safety valve MPRV as mentioned above.

I´m now working in this market for a long time and I hope to have shown you a short overview about the protection devices. As said, depending on the transformer properties, there are different devices needed.
If somebody has a question about this products, you can gladly get in touch with me.:grinning:

A few pictures of the devices

Protection device MCHD