UNGROUNDED SYSTEM GENERATOR 13.8 KV
UNGROUNDED SYSTEM GENERATOR 13.8 KV
(OP)
Hi,
To all,
We have 2.1 MW Diesel Power plant supply the small grid , generator rated voltage of 13,8KV and ungrounded or floating nuetral . Our problem is the generator potential transformer wye connected primary and wye connected secondary and broken delta connected secondary , primary PR fuse blown 3 times.
What is the problem why PT primary fuse blow?
Please help!
AJ
To all,
We have 2.1 MW Diesel Power plant supply the small grid , generator rated voltage of 13,8KV and ungrounded or floating nuetral . Our problem is the generator potential transformer wye connected primary and wye connected secondary and broken delta connected secondary , primary PR fuse blown 3 times.
What is the problem why PT primary fuse blow?
Please help!
AJ






RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
grounded too. Then the ground potential will rise from 0 to this phase potential.
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
Firstly check damping resistor are installed ( if installed ) in the Brocken delta circuit.
size must be about 30-40Ohm and 400-500W
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
or possible order antyferroresonace VT.
Yes, ferroresonance is first reason for damages of PT.
In this case: ferroresonance is resonance between capacity of system and inductivity of PT.
reason of wye PT. "Standard" problem in the ungrounded or compensated networks.
If you need more information, I will found some theoretical documents and will attach here.
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
provided with grounding fault detector. One of the ungrounded system phases could be accidentally
grounded and then the grounding potential would rise up to this phase potential. The primary winding
of the potential transformer voltage –between Y point and the terminal of the other phase [not grounded]
would rise 1.73 times.
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
What will be the best solution so that i can run the unit in ungrounded system?
It is okay to change the generator PT from wye connected primary to open delta? What is the effect?
Thanks all you Sir.
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
In case there is a line to ground fault in the grid, since my generator is ungrounded or floating nuetral , the effect is the unfaulted phases increase twice or trice ? Right?
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
First move, we replace the withdrawble PT and fus, then thesame fuse blown.
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
Do you have cable link from switchgear to generator?.
All the small details, cleaning, trace are influenced on the ferroresonance phenomena.
ok, this is a grid, what is a grounding system of grid?
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
Why the bus PT limiting fuse not blown but generator PT blown?
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
this is difference between both PTs, problem is started before synchronizing.
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
its all, simple and standard practic
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
I will raise this concern because , recently after we tried to back the unit online after replacing the fuse, explosion occurred again but now fuse are okay. During last explosion I observed that there was arcing evidence originated from the VCB. The relay indicates current differential and over-current and voltage restraint.
Then, I will check all VCB replaced after 3 times explosion happened.
After inspection and checked of all VCB, it was found out that there was a flash-over or insulation failure of the load side terminal phase B of the VCB.
My question now is what causes the VCB insulation failed?
Why only phase B insulation failed only then phase A & C are okay.
Specs of the VCB VD4 ABB 17.5 KV/630 Amps. , 25 KA
Here is the pictures.
Help me Sir.
Thanks,
RE: UNGROUNDED SYSTEM GENERATOR 13.8 KV
If you have an earth fault on one phase then the other phases will rise to full line voltage with respect to earth. If this breaker is designed for use on an impedance-earthed system then it may not have adequate insulation for continuous service with one phase earthed. If so then I think you have identified the weakest point in the insulation system.