Voltage Transformer Earthing - Working, Advantages and Disadvantages

Working: 

In this method, the neutral of the system is earthed through the primary winding of the voltage transformer as shown in the figure.

The characteristic of this type of earthing is similar to that of the isolated neutral type.

The primary winding of the voltage transformer provides a high impedance to the neutral to earth. 

In addition to this, the indication of fault can be given by measuring the secondary voltage.

Difficulty in this method is that the earthed neutral becomes the point of reflection for the traveling wave through the winding of the machine. So there is the effect of high voltage on the winding.

Advantages :

1. With this method the characteristics similar to isolated neutral can be achieved.

2. Secondary winding of the potential transformer can be used to drive the relay or for the fault indication

Disadvantages :

1. Neutral becomes the reflecting point for the traveling waves so there is the effect of high voltage on the winding

2. Voltage induced in the secondary is proportional to the fault current. So if the fault current is less, there is difficulty in the operation of the relay, and the relay is damaged if the value of the fault current is more.

3. This system is less efficient.