zigzag earthing transformer faults

[cigdemhazir]

We use zigzag transformer for grounding purpose. we connect the zigzap earthing transformer in secondary side of power transformer which is delta connected and have 100 MWA power. it is istalled in our transmission substation.
When the fault(when come from close point) is occured in distribution side our earting transformer is tripped with bucholz relay.
Can you tell me what might be the reasons? and what is the solution this type of problems? How can we overcome this problem?

 

[jghrist]

You might have too much current flowing in the transformer too long. What is the fault current? Rating and impedance of the grounding transformer? Fault clearing time? Is there a grounding resistor or is the system solidly grounded?

See thread238-204140

 

[slavag]

Hi.
Check buchholtz relay connection/installation. Are was rainy?
Best Regards.
Slava

 

[odlanor]

What is the power of zig-zag transformer?
I never saw zig-zag transformer protected by buchholz relay.
We used it usually for power equipment above 1 MVA.

 

[prc]

When fault current pass through the zig-zag trf, windings axially jump up pushing oil in to conservator.You may use a relay with higher flow rate or antiseismic contacts for the trip contact.