Hi,

The relays used in power system protection are of different types. Among them, differential relay is a very commonly used relay for protecting transformers and generators from localized faults.

The differential relay is one that operates when there is a difference between two or more similar electrical quantities exceeds a predetermined value. In the differential relay scheme circuit, there are two currents come from two parts of an electrical power circuit. These two currents meet at a junction point where a relay coil is connected. According to Kirchhoff Current Law, the resultant current flowing through the relay coil is nothing but the summation of two currents, coming from two different parts of the electrical power circuit. If the polarity and amplitude of both the currents are so adjusted that the phasor sum of these two currents, is zero at normal operating condition. Thereby there will be no current flowing through the relay coil at normal operating conditions. But due to any abnormality in the power circuit, if this balance is broken, that means the phasor sum of these two currents no longer remains zero and there will be non-zero current flowing through the relay coil thereby relay being operated.

I have covered the following topics in this course

- Transformer protection

- Basic Definition of differential relay

- Test Siemens differential relay 7UT 613

- Calculation For Transformer Differential Protection

- Prepare test procedure and test sheet.

- how u can do differential test automatic by using advance module of omicron

- how u can do differential test manually by using omicron

- Test Other Differential Relay ( RET 670 & MICOM P643)