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ASAD MALIK
Active Contributor

Join Date: Nov 2009
Posts: 17

Nos. of NGR Connection to Power Plant

12/27/2011 1:31 AM

I have question about the Nos. of Neutral ground resistor connected to Ground mesh in power plant. For example if there are 4 x 6MW Gas turbines connected to 11KV bus & each have seprate NGR of 100 A , cont rating , with common Grid mesh for all , is all NGR can connect to ground mesh or only 1 of them . If so why we connect only 1 of the 4 Nos. of NGR to the system . Please provide the reason .

Regard

ASM
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electricalexpert65
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Join Date: Oct 2009
Posts: 2061
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#1

Re: Nos. of NGR Connection to Power Plant

12/29/2011 5:03 AM

Connecting only one generator neutral to earth when many generators were operated in parallel - was to reduce the circulation of third harmonic currents between the generators (thereby avoid the overheating caused by such circulating currents) when all the neutrals were connected to earth.

But, this is no more necessary as all modern generators are wound to 2/3rd Pitch, which offers a higher impedance to circulation of third harmonic currents. So, if all your generators operating in parallel are wound to the same 2/3rd pole pitch, you need not isolate any generator neutral from earth and all generator neutrals can be connected to earth.

Reference is drawn to the IEEE Green Book, which emphasises the above.
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