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Conneting Y Generator to Y Transformer

Conneting Y Generator to Y Transformer

Conneting Y Generator to Y Transformer

(OP)
Dear all,

I have a 1.2MW,400V Gas Engine-Generator with Y Genrator and i want to connect it to Y side of a Dyn5 (0.4/20KV) transformer to parallel with grid. in Etap when i earth both of generator and transformer solidly , 56KA phase to earth fault detects. for limiting this current i want to use a NGR.
now when i connect the NGR to Genrator and transformer remains solidly earthed the fault current remains high value from transformer(35KA). this situation is the same for transformer. when transformer connect to earth with NGR and generator is solidly earthe the E/F remains High. when both of them connect earth with two NGR everything is ok and e/f current limits.
now, i have three question:
1- can i connect neutral point of Genrator and transformer in a same place on neutral bus-bar of the Main LV Panel and connect one NGR to this neutral busbar for earthing both genrator-transformer , or not?
2- for the NGR which type of earthing you propose? high resistance earthing or low resistance earthing? i want to use a protection Calss CT in NGR decting Un-restricted E/F.
3- for 20KV Side of transformer with delta connection there is no path for earht. e/f currents in 20KV side are small but in this case i want only detect it by 59N (Residual voltage protection) from open delta connection of bus VT . is it true or you propose to use earthing transformer or etc.

regards
lightfoot2

RE: Conneting Y Generator to Y Transformer

1- No. It is not enough. You have to install NGR at neutral generator either.

2- I suggest 400A-NGR at neutral generator annd 600A-NGR a neutral transformer.

3-No. Otherwise you can change the grounding configuration of your 20kV system.

RE: Conneting Y Generator to Y Transformer

(OP)
dear odlanor,

thanks for your reply.

- there is problem for case no.3. i can't change the transforemr vector group. the consultant don't authenticate this case. because our upper side in 63/20KV Substation the connection of 20KV is delta and there is an earthing transformer for detecting earth fault in upper side substation. changing the vector group of transformer to step up (Ynd) or using earthing transformer in my power plant may make upper side substation blind in case of detecting earth fault.

- in case of no.1 what is the reason for your reply? in some configuration we can choose one resistor for multiple generators in parallel. why we can't use one NGR for both parallel Generator and transformer?

RE: Conneting Y Generator to Y Transformer

When a wye delta distribution transformer transformer is fed from the wye side and the wye side neutral is connected there may be heavy circulating currents in the event of voltage unbalances and phase loss conditions. Many of us hesitate to use a four wire connection to a wye delta transformer or bank. The issues may not be as serious in the case of a direct connection to a generator but the hesitation remains.
Using one resistor for the generator or group of generators and a second resistor for the transformer wye point avoids these issues.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Conneting Y Generator to Y Transformer

lightfoot2 ,
I understand your system:
400V grounded generator => 52CB => setup-transf 400V-yYn/20kV-D // auxiliary trasformer
When 52CB is open , with generator and setuptrans energized, both system must be grounded

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