Sir we have 12.5 MVA(110/11KV) transformer (Y-Y) connected,which tripped showi

Sir we have 12.5 MVA(110/11KV) transformer (Y-Y)
connected,which tripped showing earth fault,when we charged
transformer it stood OK ,but on connecting 11 KV feeders it
tripped showing earth fault.our service engineers found that
the B phase and R phase phase connecting to neutral broken
from HV OLTC(on load tap changer),and R phase and Neutral is
ok.Dissolved gas analysis shows that accetline content is
high,tan delta value is 12.My dout is it is an internal
fault of transformer,why REF or diffrential relay is not
acted?

Question Posted / manu

1 Answers
5021 Views
I also Faced
E-Mail Answers

Sir we have 12.5 MVA(110/11KV) transformer (Y-Y) connected,which tripped showing earth fault,when ..

Answer / k.prakashchandra

REF relay does not act as the unbalanced current is equal to
NCT current in all respects. And for diff relay, it also
does not act as the corresponding ct currents in HT and
sides for each phase are equal.If there is current in only
one phase ,EFR will trip as current's return path is through
the EFR.But why there is current in the single good phase as
all dist Trs are delta/ star connected ? May be due to star
connected line capacitors or dist trs/loads are also star
connected with neutrals earthed.

Is This Answer Correct ?

0 Yes

0 No

Post New Answer

More Electrical Engineering Interview Questions

which oil is used in transformer?

7 Answers

Starting times for soft starter & power factor is thier any standard or datas available in manufactures list. Kindly suggest.

0 Answers

power 148kw i need exat cable size in 148 kw in 3phase what size of cable can i used.

3 Answers

anti pumping relay function

3 Answers Hofincons,

What happens to the synchronous generator when reverse power is given to it?

1 Answers

what is CRGO Transformers?

6 Answers MSETCL Maharashtra State Electricity Transmission Co Ltd, TATA,

what is the difference between delta delta and star delta connection transformer? why we use delta delta transformer since it need earthing transformer for grounding?

0 Answers

How to detect voltage vector shifting in interconnection protection.

0 Answers

Which are resistive loads & which one are inductive loads : Refrigerator, Split air conditioner, ceiling fans, well pump, fluoresecent bulbs, T.V, CRT Monitors, Adsl Routers, C.P.U, Printers, Deep Freezers, Speakers, DVD Players, Microwave oven etc. ? Output Power for these Appliances Would be same like this : P = V * A * P.F Or would be changed ? thanks

0 Answers

A shopkeeper allows 10% discount on the price of an article and sells it for Rs 7,600. What is the marked price of the article?

1 Answers

How to select the cable and voltage drop in circuit?

0 Answers DEWA,

why is electricity produced and distributed in multiples of 11. 440V, 11KV, 22KV, 132KV etc

2 Answers Bhel,

For more Electrical Engineering Interview Questions Click Here