3. What is Impedance Voltage in Transformer?

Answer Posted / manoj kumar tiwari

The percentage impedance of a transformer is the volt drop
on full load due to the winding resistance and leakage
reactance expressed as a percentage of the rated voltage."

"It is also the percentage of the normal terminal voltage at
on side required to circulate full-load current under short
circuit conditions on other side."

The impedance of a transformer has a major effect on system
fault levels. It determines the maximum value of current
that will flow under fault conditions.

It is easy to calculate the maximum current that a
transformer can deliver under symmetrical fault conditions.
By way of example, consider a 2 MVA transformer with an
impedance of 5%. The maximum fault level available on the
secondary side is:

2 MVA x 100/5 = 40 MVA

and from this figure the equivalent primary and secondary
fault currents can be calculated.

A transformer with a lower impedance will lead to a higher
fault level (and vice versa).

The figure calculated above is a maximum. In practice, the
actual fault level will be reduced by the source impedance,
the impedance of cables and overhead lines between the
transformer and the fault, and the fault impedance itself.

Is This Answer Correct ?    26 Yes 3 No



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