Answer / sts

The difference is that in the unearth system the netural
will be floating or is not in the midpoint of the star
system therefore the earth to phase voltage will be some
what equal to or little less than the phase to phase
voltage.So the insulation level between the conductors are
increased in the unearthed cable

Answer / jasjit singh

If the electrical system is very efficiently earthed and all
protection are in place then we go for earthed cables and if
you have any doubt about the system earthing and its
protection then we go for unearthed cables. Basically its
the system earthing with which we choose earthed or
unearthed cables. I cannot say which is commonly used
because as I have mentioned earlier it will depend upon your
system earthing. But in few cases even if all protection are
in place and system is properly earthed we still go for
unearthed cables just to have extra safety margins.

Regards,

Sir,In our company there are 3 caterpillar make(capacity:(1) 3.3KV,2.5MW(2)3.3KV,2.5MW & (3)3.3KV,1.9MW) & 1 deutz make (capacity:11KV,3.8MW)gas engines utilised,all are running in paralell. There are three transformer utilised,(1) 6.25MVA,3.3KV/22KV,Impedence voltage:6.7% used for two generator,both are 2.5MW(2)5.5MVA,3.3KV/22KV,Impedence voltage:7.2% used for one generator of 2.5MW & (3) 5.5MVA,11KV/22KV,Impedence voltage:7.8% used for one generator of 2.5MW.all generator breakers capacity of 1250Amps. Sir,I want the details of fault level calculation of generator,transformer individually & for whole system. If you require any information from me.feel free for contact me sir.pl.send the answer of my question as the earliest as possible.

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