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How to Connect Power Transformer Neutral to Earth Through NGR?

10/05/2012 12:08 AM

Case : Earthing of Power Transformer Neutral to Earth through NGR.

Transformer rating 35MVA, 33/6.6kV

Doubt : It is necessary to earth from Xmer NCT terminal to NGR through 6.6kV rated Cable Only? or we can use the bared Earthing Strip from Xmer NCT Terminal to NGR??

Regards,

T.D.

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Guru
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#1

Re: How to connect Power transformer Neutral to earth through NGR??

10/05/2012 1:00 AM

I recommend that you not get involved.

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#2

Re: How to connect Power transformer Neutral to earth through NGR??

10/05/2012 1:04 AM

Yes. Use 6.6 kV rated cable. Do not use bare earthing strip.

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#4
In reply to #2

Re: How to connect Power transformer Neutral to earth through NGR??

10/05/2012 6:58 AM

But transformer manufacturer provided bare earthing strip from Transformer neutral bushing to upto Bottom of transformer on epoxy support at regular interval.

Will this right??

At a time of earth fault on one phase a L-N voltage (6.6kV/1.732) will be between the NCT terminal and NGR/Ground and approx. line to line (6.6kV) voltage on other phases, is it?????

Regards,

T.D.

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#5
In reply to #4

Re: How to connect Power transformer Neutral to earth through NGR??

10/05/2012 12:47 PM

Assuming the transformer manufacturer know what they are doing and obviously you don't. I think you would be best served by leaving the whole matter in their hands.

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#6
In reply to #4

Re: How to connect Power transformer Neutral to earth through NGR??

10/05/2012 11:17 PM

Who is the manufacturer and in which country it was made. Nowadays European manufacturers have plants in Asia,Africa & South america.

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#3

Re: How to Connect Power Transformer Neutral to Earth Through NGR?

10/05/2012 6:40 AM

The transformer manufacturer will have recommendations on the basis of best practice, if not national electrical standards. If the user manual that was supplied with the transformer has somehow gone missing, use the telephone to obtain correct advice.

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#7
In reply to #3

Re: How to Connect Power Transformer Neutral to Earth Through NGR?

10/06/2012 11:57 AM

From my own experience, you can use bare conductor to do this connection(i.e. from the NCT to the NGR and to ground.)

The Neutral point is at ZERO POTENTIAL under steady state conditions and consequently current flowing is also ZERO. Hence you can use BARE CONDUCTOR to do the connection and save money.

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#8
In reply to #7

Re: How to Connect Power Transformer Neutral to Earth Through NGR?

10/06/2012 10:32 PM

I have seen MV cable connecting transformer(34.5/13.8kV) neutral to earthing resistor in Saudi Arabia,for which project consultants were from UK.

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#9
In reply to #7

Re: How to Connect Power Transformer Neutral to Earth Through NGR?

10/09/2012 12:23 AM

but what about ground fault condition....??? 6.6/1.732 voltage will appear between neautral and ground??? isn't it? plz advice

Regards,

T.D.

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#10

Re: How to Connect Power Transformer Neutral to Earth Through NGR?

10/09/2012 12:37 AM

"Upstream" of the NGR could have substantial voltage w.r.t. ground; thus insulation would make sense.

"Downstream" of the NGR is small voltage to ground, but the cable resistance still means that the end next to the NGR will have some voltage. Ohm's Law can tell you how much. I don't think most Codes require this cable to be insulated, but check locally.

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#11
In reply to #10

Re: How to Connect Power Transformer Neutral to Earth Through NGR?

06/17/2015 10:02 PM

Regarding the downstream cable from NGR. Do you have any international code reference that it can be bare or low voltage, irrespective of transformer L-N voltage.

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