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11/0.4 kV transformer neutral earthing

11/0.4 kV transformer neutral earthing

(OP)
1500 kVA transformer, 11/0.4 kV Dyn11 installed in a substation
what is the standard or practice for earthing the LV side neutral point ?
is it required that the neutral point should have a separate earthing point/system or it can be connected with the substation earthing system?
what is the advantages, and disadvantages in both cases (separate earthing or earthing with the substation earthing)?

RE: 11/0.4 kV transformer neutral earthing

Its better to separate neutral point from substation earthing system. But in my country we use to connect neutral and substation earthing together. Only lightning protection grounding remain separate from all. For LV side you must have separate earthing system for your equipment.

https://www.anelectricalengineer.com

RE: 11/0.4 kV transformer neutral earthing

Normal practice is to bond the LV neutral point to the substation earth grid. If the earth potential rise due to an 11kV fault at the substation is excessive then the LV earth can be separated, but this can be problematic as segregation of the HV and LV earths has to be maintained for some distance away from substation.
Regards
Marmite

RE: 11/0.4 kV transformer neutral earthing

In the US, the neutral would be bonded to the substation ground grid. Separation introduces other problems as Marmite indicates. "Isolated" grounds are not really totally isolated in most cases. And lightning strikes will laugh at your "separation".

RE: 11/0.4 kV transformer neutral earthing

REF is more important with impedance grounded transformers because winding faults close to the neutral are harder to detect. The normal transformer differential protection will adequately protect solidly grounded transformers, but normally I would use REF if a neutral CT is available and the relay has the REF element built in.

RE: 11/0.4 kV transformer neutral earthing

I agree with dpc. However, according to IEC [or BS EN 50522/2012] there are some conditions in order to use the same grounding grid for high voltage and low voltage installations- chapter 6 Measures to avoid transferred potential.
See Table 2 Minimum requirements for interconnection of low voltage and high voltage earthing system based on EPR limits.
Following Annex A and B one may calculate the touch voltage.
The lightning protective grounding it is recommended to be connected with the substation grounding grid .See Annex F for further details.
You may read also IEEE 80/2013. chpt.17.9 Transferred potentials.

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