Overvoltage During Earth Fault 1

[newelecteng]

Dears

We are experiencing an issue where, during an earth fault on our 33 kV outgoing feeder, the voltage measured by the ABB REF relay (Vo) on the incomer spikes to around 14 kV. This overvoltage is affecting our 0.4 kV system, which is fed by our ZNyn1 earthing transformer. Is this behavior normal for a system like ours?

 

[beyond86]

Kiribanda,
643А is not charging current, it's current which flow through neutral of ZNyn1 transformer. If you look at parameters you will see that this TR provide Io current 1000A during EF. 33 kV side works with low resistance neutral.

1) Is the 33kV system a real "DELTA" system?
Yes.

2) Does the 33kV system really needs an earthing transformer?
Some oil plants must have low resistance neutral for fast and selective trip of EF faults.


3) If yes, how it was sized?
Typically low resistance neutral has A current range 200-1000A.

 

[Kiribanda]

I have no further comments until I see the transformer connections (vector group) at the other end of all feeders H01 to H06 feeders which I have already requested
from newelecteng by my post on 28 Sep