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IS it necessary that all the transformers should have same % impedance to work in parallel?
and what about the MVA capacity?
and what about the MVA capacity?
Ameya... the simple answer to each of your questions is... no! However, there are certain constraints that must be satisfied.
I suggest you search the Control.Com archives for "parallel transformers." If you are unable to find a suitable answer, contact me directly at:
cepsicon[at]AOL[dot]com
Regards, Phil Corso
I suggest you search the Control.Com archives for "parallel transformers." If you are unable to find a suitable answer, contact me directly at:
cepsicon[at]AOL[dot]com
Regards, Phil Corso
P
Process Value
> IS it necessary that all the transformers should have same %
> impedance to work in parallel? and what about the MVA capacity?
parallel operation of transformers
a. The phase sequence of the transformers must be the same on the connected bus. in other words, the RYB of one transformer must match the RYB of the other. this is the strictest condition and must be satisfied. other wise huge circulating currents will flow tripping the transformer.
b. Similar voltage ratios. There can be slight variations in this. a 110/6.6KV transformer can be connected to 110/7.07KV without much problem. but if you connect a 110/6.6 to a 110/11 to the same bus then again circulating current will flow.
c. Similar % impedance on the Base MVA. this is also not necessary. the main desired criterion for parallel operation is that under all loaded conditions the transformers must have the same terminal voltage so that there is no unnecessary circulating current. %impedance is numerically equal to the "regulation" at full load. now if you connect transformers with unequal impedance there will be no problem at no load conditions , but once you start loading the transformers their terminal voltages will begin to differ and this will again give rise to circulating currents.
from the above it can be said that only condition "a" is absolutely necessary. the other two are desirable conditions.
you can find much better explanations in any electrical engineering text book
. If you are in India you can have a look at PS Bimbra and JB Gupta. both excellent textbooks.
> impedance to work in parallel? and what about the MVA capacity?
parallel operation of transformers
a. The phase sequence of the transformers must be the same on the connected bus. in other words, the RYB of one transformer must match the RYB of the other. this is the strictest condition and must be satisfied. other wise huge circulating currents will flow tripping the transformer.
b. Similar voltage ratios. There can be slight variations in this. a 110/6.6KV transformer can be connected to 110/7.07KV without much problem. but if you connect a 110/6.6 to a 110/11 to the same bus then again circulating current will flow.
c. Similar % impedance on the Base MVA. this is also not necessary. the main desired criterion for parallel operation is that under all loaded conditions the transformers must have the same terminal voltage so that there is no unnecessary circulating current. %impedance is numerically equal to the "regulation" at full load. now if you connect transformers with unequal impedance there will be no problem at no load conditions , but once you start loading the transformers their terminal voltages will begin to differ and this will again give rise to circulating currents.
from the above it can be said that only condition "a" is absolutely necessary. the other two are desirable conditions.
you can find much better explanations in any electrical engineering text book
. If you are in India you can have a look at PS Bimbra and JB Gupta. both excellent textbooks.
