Star/delta transformer - single phase fault on secondary

[acw260]

Homework Statement

A three-phase distribution transformer is configured as follows:
-primary side = star with solidly grounded neutral
-secondary side = delta, grounded via zigzag earthing transformer

A single phase-earth fault occurs on the secondary (delta) side of the circuit.

Homework Equations

Will current flow in the neutral connection on the primary side of the transformer (solidly grounded star)?

The Attempt at a Solution

I believe that the answer is 'no'.

If I understand correctly, the earth-fault current on the secondary (delta) side will flow back into the secondary side of the circuit via the zigzag earthing transformer and be evenly distributed between the phases. The primary (star) side of the transformer will therefore 'see' the fault as a balanced three-phase fault, with equal current flowing in each of the three legs of the delta windings. Therefore no current will flow on primary side neutral.

Is my understanding above correct? Any help would be much appreciated.

 

[KataKoniK]

Yes, your understanding is correct. In this configuration, the earth-fault current will flow back into the secondary side of the circuit via the zigzag earthing transformer and will be evenly distributed between the phases. This means that no current will flow in the neutral connection on the primary side of the transformer. This is due to the fact that the neutral is solidly grounded, which means that it is connected directly to the ground and does not allow any current to flow through it.

The purpose of the zigzag earthing transformer in this configuration is to provide a return path for the earth-fault current, ensuring that it does not flow through the primary side of the transformer. This helps to protect the transformer from damage and also prevents any potential hazards to the system.

In summary, in this configuration, the primary side of the transformer will not see any current flowing in the neutral connection in the event of a single phase-earth fault on the secondary side.