Electrical substation Transformer Protection

Transformer Protection

Question
Q) Give the different types of protection schemes used for traction transformers with a typical layout.

Answer

The various protective schemes are adopted for traction transformer. As, the transformer is the component of the device it is installed with various primary and secondary or back up protection schemes.
Figure shows the protective arrangement for main traction transformer.

Over current protection (Primary Protection) : Over current induction relay is Low Voltage (L.V.) side to provided on the protect the transformer from short circuit current.
Over current protection (Secondary Protection) : An inverse time over current induction relay is provided on High Voltage (H. V.) side for this purpose.
Buchholz relay : As the transformer is oil immersed, Buchholz relay is applicable to protect the transformer by providing alarms on incipient faults and trip command on very much severe faults.
Overload protection : A thermal relay is provided for this purpose on the secondary side of transformer.
All the non current carrying metal parts are effectively grounded.
In addition to the relays and protection devices for the traction transformer protection, additional set of following relays are provided at the traction sub-stations especially for 2x25 kV Auto transformer feed system.