EARTHING TRANSFORMERS 1

[rukmal]

I have come across a strange problem with earthing transformers(with zig-zag windings).It's a common practice that an auxiliary secondary winding is wound with an earthing transformer internally for auxiliary power supply for the sub station equipment. Recently we have came across that when there is a line fault the auxiliary winding voltage increases significantly.this was reported for several substation. Theoritically this should not happen as the flux through the core if zero. Can some one explain the real situation?

 

[RRaghunath]

Rukmal,

When an earth fault occurs in one of the phases (in thre phase AC power system), the voltage collapses in that phase (with reference to earth) but raises in the remaining two healthy phases. The extent of voltage raise depends on the type of system earthing adopted and (phase - earth voltage)can go up to the L-L voltage (1.732 * phase - E voltage) in case of unearthed system.

I didn't understand your question properly (Could you please make it more clear with info such as what are the name plate details of the transformers, type of neutral earthing etc) and I do not know how far the inforamtion will be useful.

 

[jbartos]

Suggestion: Please, clarify the line fault in terms of:
1. Line-line-line
2. Line-line-line-ground
3. Line-line
4. Line-line-ground
5. Line-ground