1 phase with unequal impedance

[ePOWEReng]

There are some single phase banks transformer banks in our system which have back up transformers with different impedances. It could happen that if a certain transformer failed a backup may be used which has an impedance 10% different from the remaining 2. Has anyone ran into this before...having a bank of 3 single phase transformers that have unequal impedances?? What are the precautions??

Thanks in advance for any replys.

ePOWEReng

 

[waross]

Look at the regulation rather than the impedances. That will be more important than impedances for normal loads. Expect slightly different terminal voltages as reflected by the different regulation percentages. The difference will be less than the indication based on impedance calculations. Different impedances will affect the available fault currents.

Bill
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"Why not the best?"
Jimmy Carter

 

[ePOWEReng]

Thanks Waross.

Any ideas about what type of zero and negative sequence currents and voltages can be seen during normal loading? I would expect it to be trivial, but not really sure...