Gen Step Up Trafo EF Protection
Gen Step Up Trafo EF Protection
(OP)
Hi,
I found a drawing of a VT in the Gen step up trafo where the VT is connected parallel to the trafo neutral earth switch (please refer to the attachement)
I know VT can be connected parallel to the power transformer neurtal resistance grounding to detect earth fault.
From the drawing, why do they need the earth switch anyway?. Some help please..
Thanks
I found a drawing of a VT in the Gen step up trafo where the VT is connected parallel to the trafo neutral earth switch (please refer to the attachement)
I know VT can be connected parallel to the power transformer neurtal resistance grounding to detect earth fault.
From the drawing, why do they need the earth switch anyway?. Some help please..
Thanks






RE: Gen Step Up Trafo EF Protection
The connection vide the attachment makes the 220kV system unearthed. If true, it is strange since 220kV system is generally solidly earthed system in most parts of the world.
Is the 220kV transmission by cables in your case?
Is earth switch normally open or closed, what is the operating philosophy?
Transformer 220kV winding is normally made with graded insulation and cannot be safe if neutral point is unearthed. What is the rating of Surge Arrester in the neutral circuit. Appropriately rated surge arrester may be able to provide protection to the 220kV winding against over voltages.
RE: Gen Step Up Trafo EF Protection
Yes, the 220kv of the trafo connected by a XLPE cable to the nearby GIS.
From what I understand, the earth swith is normally closed, and motor operated from remote.
surge arrester name data: type: SB-132/20.4-1
Rated Voltage: 132kv
Count. Voltage: 106kv
Thanks
RE: Gen Step Up Trafo EF Protection
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If we learn from our mistakes I'm getting a great education!
RE: Gen Step Up Trafo EF Protection
345kV system could operated grounding or ungrounding.
At ungrounded condition you have neutral lightning arrester
with open delta protection from TP.
RE: Gen Step Up Trafo EF Protection
RE: Gen Step Up Trafo EF Protection
From the neutral switching and the series reactor in the OHL, it appears that the fault level in 220kV system is exceeding the rating of switchgear like CBs etc. in some of the substations. May be you can confirm.
So, when earth switch is closed, VT will be of no significance but when the earth switch is open the voltage on secondary of VT should be providing earth fault alarm to the operator in the control room.
SA rating of 132kV suggests that the transformer neutral insulation is rated to 132kV (if not more).
If earth switch is normally closed, can you find out from your control room operator under what situations, do they open the earth switch.
RE: Gen Step Up Trafo EF Protection
It's practic in few places, as Scotty saied, for limit ground fault, but AFAIK, not with GSU transformer , it's usually solid grounded ( except MV industrial application).
About VT, maybe some kind of meas U in case of ungrounded neutral, don't know. Are VT connected to some voltage relay?
Best Regards.
Slava
RE: Gen Step Up Trafo EF Protection
The Kuwaitis definitely have the capability to switch out the neutral CB on their GSU transformers as well as those on the transmission system. I was quite surprised to learn this when I worked on a Kuwaiti project but it appears to work satisfactorily in a small nation with a relatively large amount of generation and terrible earthing conditions (hot dry rocks).
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If we learn from our mistakes I'm getting a great education!
RE: Gen Step Up Trafo EF Protection
RE: Gen Step Up Trafo EF Protection
RE: Gen Step Up Trafo EF Protection
I have no doubt! Any ungrounded busbar install TP with open delta secondary to connect 59N.
It is the only protection to detect fault-to-ground on ungrounded system.