Earth leakage protection relay | Power semiconductor drive lab report


  1. To recognize the construction and the concept of operation of earth leakage protection relay.
  2. To be familiar with the earth leakage protection relay and methods of connecting in power circuits


This type of relays is considered as a protection element used to protect human who working on the loads and electrical connections in factories. Also, it is used to protect devices from danger of contacting with the earth. The sensitivity of this relay in our experiment is 30 mA.

This relay consists of magnetic coil fixed on a metallic ring with three phase contacts, any current passes through the magnetic ring produces an equaled magnetic field, which means that the resultant will equal zero in disconnecting coil.

When the current are equaled, if we have an earth leakage in any line then an earth leakage current will produce a magnetic field disconnecting the contacts.


Construct the circuit as shown in the figure below

This table includes the phase currents and the earth leakage current


  1. Earth leakage protection relays are used to protect from contacts with the earth, which can be dangerous to human working on the machines.
  2. The concept of working that if we have unbalanced load, which is needed in some applications, the relay will disconnect the power source.
  3. Every earth leakage relay has sensitivity current to work at.
  4. Every earth leakage relay has a test button to be test with.

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