Answer / nadeem

B.delta-delta to star-delta not possible parallel
operation.
C.star-star to delta-delta that is possible parallel
operation.
D.delta-star to star-delta also that is possible parallel
operation.
A.delta-delta to delta-star not possible parallel operation
but im not conferm.

Answer / ravi

For parallel operation of transformers as you know the
requirements, 1. magnitude of the voltage, 2. phase angle
difference between the i/p and o/p voltages, 3. equal
percentage impedance of the transformers.

I don't think that whatever you are asked configurations
same vector symbol will get. So we can't do paralleling.
if you get the same phase angle difference ypu can go ahead
with paralleling.

Answer / vikas tomar

If the transformers are star-star or delta-delta, they can
not be paralleled with star-delta or delta-star,As there
will be the phase difference of 30 degree b/w the secondary
voltages for the same supply voltages across the primaries
of the two transformers.It will result the circulating
current in transformer windings.
Hence option (d)is correct answer.

Answer / sourabh

A)delta-delta or delta star is possible

There are two nos of 33Kv/11Kv 5MVA transformers conecting through HT cable from substation having metering at substation itself.One transformer used at a time another remains stand by.Further 11 nos of 11Kv/440V transformers are attached on it and each transformer is having its own Power factor correction panel.Now one 33/11Kv transformer at no load condition/Stand by condition is having power factor in leading side upto 0.21 and while when another tranformer at same situation have power factor in lagging 0.42. Now one thing is clear that transformer one is having 1.5 Km long 33kv cable due to that PF goes in leading side and another is having only 250 mtr length remains him lagging. Now i want to know that how i can maintain the Power factor at no load/ stand by position though both are behaving in seperate manner.

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