Power Transformer Protection

Transformer Differential Protection

Generally Differential protection is provided in the electrical power transformer rated more than 5MVA. The Differential Protection of Transformer has many advantages over other schemes of protection.

• Why both buccholz & differential used together -: both type of protection used to detect internal faults in power transformers.
The faults occur in the transformer inside the insulating oil can be detected by Buchholz relay. But if any fault occurs in the transformer but not in oil then it can not be detected by Buchholz relay. Any flash over at the bushings are not adequately covered by Buchholz relay. Differential relays can detect such type of faults. Moreover Buchholz relay is provided in transformer for detecting any internal fault in the transformer but Differential Protection scheme detects the same in more faster way.


•Working Principle-:The protection scheme is based on the principle of Kirchhoff's current law, which states that the sum of all currents entering a node must be equal to the sum of all currents leaving the node.

In a transformer differential protection scheme, current transformers are connected to the primary and secondary windings of the transformer. The current transformers measure the currents entering and leaving the transformer and send the signals to a differential relay. The differential relay compares the currents and, if there is a difference, it sends a tripping signal to the circuit breaker to isolate the transformer.

The differential protection scheme is designed to operate only when there is a fault inside the transformer. During normal operating conditions, the currents entering and leaving the transformer are balanced, and the differential relay remains inactive.

The transformer differential protection scheme is highly sensitive and provides fast and reliable protection against internal faults. It is widely used in power systems to protect transformers of all sizes and voltages.