Answer / raj

Nothing harm in placing the breaker beffore 1km distance,
but the system will suffer with the following disadvantages.

1) One KM long cable protection has to be taken care which
will cost heavily.
2) local supply providing authorities may object, since
this kind of arrangement is not allowed as per ie rules.
3)Running the pilot wires for the protection signal
sampling and the control wiring of the breaker will become
a tedious job.
4)Proper and cautious co-ordination is required in the
operation and maintenance point of view before every
operation.

Answer / khor

No harm at all,but finding cable is a problem.11kv cable
supply for 12.5MVA must carry 650A per phase which is too
big for most standard cables.Standard VCB are 630A,1250A &
2000A,2500A.The more commonly available large size 3-core
300sqmm 11kv copper(450Amp) or alluminium conductor
cables,which is still flexible and can be transported &
coiled in drums of 250 to 300 metre lengths.There are
500sqmm 11kv 1-core xlpe/awa/pe cables available.
If you use only one transformer which is more
economical,the 3.3 KV side will be more than 2187Amp(plus
additional amp on losses and fans).While you can find 2500A
VCB,you will need more than 600sqmm copper conductors which
is not flexible/practical.
For the better/optimum design,seperate the final 415V and
3.3KV loads required and divide them into 2 groups and look
at the MVA and size them in seperate circuits.If 12.5 MVA
is all in 3.3Kv then employ 2 Main transformers where you
are not putting all the eggs in one basket.You need to
remember to look at the short circuit capacity( in KA 1 sec
or 3sec ) of the cables in circuit where small MVA is
involved.For e.g.1 MVA needs 52A @11KV but you cannot use
35sqmm cables,as it will blow like a fuse during fault
situation.
1 km of cables will have quite enough impedence to
limit/lower the fault level of the system.Protection of
this cable can be done with Pilot protection relays on
sending and rereving end,operated by class X CTs mounted in
the 11KV VCB panels.1 KM of Pilot wires of 2.5 sqmm 7-cores
alomg this cable is requird.So far I am assuming that it is
uderground cable is used.For Ariel Bundle Cable,3-core 185
sqmm aluminium is available.

Answer / darklord

No immediate harm ,but during maintenance this 11kv line
between VCB and transformer need to be discharged with out fail,
Also during switching action their would be switching surge
created due to oscillating of wave between vcb and
transformer which will heat and may damage insulation of
transformer.

Their would also be control voltage drop for 1000mtr wire
which will have significant effect on protection of transformer.
but proper control strategies will sort this problem

Answer / rednaxela

it will damage the device if the system encounter electrical fault.

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