Voltage Rating for 6.6 kV Neutral Earthing Resistor

Cu cable of 1312 Amp, 6.6 KV rating.

As this is resistance earthing , so cable shall be rated for 6.6/6.6 KV. and this is the standard practice in case of resistance / reactance or Isolated neutral earthing.

But , Cable Phase to earth insulation can be optimised , ie calculating the actual voltage across Neutral of trafo and earth during line to ground fault.

But beside doing this, it is always better to go to cable suitable non effectively eathed system.

Thanks

Anurag

So long as you can design a safe step and touch potential the earth countinuety conductor does not need any special precaution and 500 v insulation is satisfactory.

Conventionally and without going into detailed assessment the insulation should meet phase to ground voltage level that is 6.6kv/sqrt3 ( will be 3.81kv) or in case of 11 kv side being earthed 11kv/sqrt3.

Dear Mountk2,

As this is non effectively earthed system so during L-G fault, Healthy phase earthed voltage will be more than 0.8X 6.6 KV, so cable shall be rated for 6.6 / 6.6 kV.

You are correctec when , neutral solidly earthed.

Thanks

Anurag

Dear Mr. Singh,

I am sorry to say that you are passing on judgement on a subject you may not be competent to deal.

By your yard stick far an EHV substation say 400 KV the ground cable should be rated >300 KV and what about a Super EHV substation rated 1000 KV; are you going to propose 800 KV cable? If YES please tell us who manufactures this cable and with what insulation specifications.

I would in turn propose that if you can visit an EHV substation, please check that cable yourself for a conceptual clarity.

Dear Mr. Khi,

First see the subject of discussion

As in above subject 6.6 kV (Secondary) if neutral is earthed using resistance .

So during L-G fault , what will be healthy phase to ground Voltage????

Phase to earth insulation with stand voltage rating will be depend on type of earthing.

and what voltage is exactly across healthy phase to groung during earth fault.

In 400 kv or super EHV substation , please let me know the vector group of used transformer and between whom cable is being connected. and earthing detail of Trafo (if neutral ).

Then , i will let you know exactly what should be the rated voltage of cable.

Really it is interested discussion.

Thanks

Anurag

The transformer vector group is DYn11, earthing is not solid but through a neutral earthing transformer, output of neutral earthing transformer is connected to a protection relay installed in the control room where operators are regularly working.

Star side of transformer is 1000 kv, please go ahead and give the cable insulation rating.

(please feel free to assume any missing requirement)

Can i know exact about which cable are talking???

Dear Mr. Khi,

I think there is some confusion , if are talking about cable between trafo (secondary which 6.6 kv) to load and neutral is of 6.6 kv is earthed through resitance then this cable will reated for 6.6/6.6 kv. if soildly earhed then 6.6/3.81 kV.

If you are talking about cable beween neutral point of 6.6 kv winding to NGR , obiously it will rated for 6.6/1.732 = 3.81 kv as in any fault condition voltage between eath and neutral point will never go more than 6.6/1.732=3.81 kv.

Thanks

Anurag Singh

Dear Mr. Mountk2,

I think there is some confusion , if are talking about cable between trafo (secondary which 6.6 kv) to load, and neutral is of 6.6 kv is earthed through resitance then this cable will reated for 6.6/6.6 kv. if soildly earhed then 6.6/3.81 kV.

If you are talking about cable beween neutral point of 6.6 kv winding to NGR , obiously it will rated for 6.6/1.732 = 3.81 kv as in any fault condition voltage between eath and neutral point will never go more than 6.6/1.732=3.81 kv.

Thanks

Anurag Singh

Dear Mr. diwan jafar khan husain,

I think there is some confusion , if are talking about cable between trafo (secondary which 6.6 kv) to load and neutral is of 6.6 kv is earthed through resitance then this cable will reated for 6.6/6.6 kv. if soildly earhed then 6.6/3.81 kV.

If you are talking about cable beween neutral point of 6.6 kv winding to NGR , obiously it will rated for 6.6/1.732 = 3.81 kv as in any fault condition voltage between eath and neutral point will never go more than 6.6/1.732=3.81 kv.

Thanks

Anurag Singh

you can go ahead with 3.81 kv single core cable.