Question

Write a note on earthing transformers. Why and where are they used?

Answer 1

Earthing Transformer :-

An Earthing Transformer is a three phase transformer is connected to the power system to provide a ground(Neutral) connection.

It is connected to the ground either direction or via impedence

Here Neutral earthing resistors are used to limit the fault current in transformers when a phase to earth occurs,the fault current is only limited by the Soil Resistance.

The grounding of the system can be done in the following ways.

1)Delta Star grounding transformer

2)Zig Zag grounding transformer

Here the images of both Delta star and Zig zag grounding transformers

ull [im Imm nim mm mm Delta Star transformer grounding uwe mm т. -т. Пиш power transformer 3 2:0 - 20 transformer grounding CS Scanned with CamScanner

STAR-DELTA. Transformey If/3 mm mm s R mm tom .Y | IF/ B - m do B قفل lol 1 velt Earthing tronskorrer Connection of Earthing Transformer is STAR-DELTA transformer for Earth fault protection. CScanned with CamScanner
Now we can see the why we are used Earthing Transformer.

Earthing Transformers are used to provide a neutral connection for earthing where neutral connection is unavilable. It provides a low impedance path to the neutral and also limit the transient over voltage when the ground fault occur. In the system.

The earthing transformer is used to create a neutral point to the system

Why we have chosen Zig Zag transformer ?

It provides insulation between the ground and the components so that the system components may not be effected by the fault currents

Reduces the voltage stress under a fault connection

Here the transformer draws very small magnetizing currents.

Under the fault conditions,the impedance of grounding transformer is very low

Where Earthing Transformers are used.

1)Grounding transformers are sometimes used on distribution systems. A grounding transformer provides a source for zero sequence circuit. Some times they are used to 3-wire,ungrounded circuit into 4-wire,ungrounded circuit

2)Grounding transformer must handle the unbalanced load on the circuit as well as the duty during the line faults

3)Grounding transformers are also used where utilities need a ground connection in abnormal conditions

4)In many power stations Earthing Transformer s are used for neutral connection.