# Transformer Impedance

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My power transformer capacity is 30/35MVA, 6.6KV.. the transformer impedance is 18%..

Is it advisible to have such value??

What will be the benefit and impact of having higher impedance for a power transformer?

Pragathees.

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As far as i know, that, percentage impedance tell us,How much percentage of short circuit currrent

Could Limit by the transformer.

for example as you mentioned in your question the percentage impedance 18%,it means you transformer limit a short circuit current 82% and only 18% follow in the transformer.

so it should be minimum to protect the transformer.

Usually for Power transformer 31.5MV/40MVA has Percentage Impedance 10%.

This value come from short circuit test.

Regards,

Shahid Hafeez

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Hello Pragathees

An increasing transformer impedance has the effect of reducing the fault current, and also reducing the voltage regulation.

From a voltage regulation perspective, you want to have a very low impedance. If you want a low fault current you want to have a high impedance.

Generally, in most applications, a low impedance is preferable.

Best regards,

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• 1 month later...
My power transformer capacity is 30/35MVA, 6.6KV.. the transformer impedance is 18%..

Is it advisible to have such value??

What will be the benefit and impact of having higher impedance for a power transformer?

Pragathees.

HI,

I think high impedence is useful only in case of welding transformer, for power transformer 18 % impedence is quite more so ,it will not be benificial to you .It will increase the losses

With Regards,

Hemant

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• 3 weeks later...

erm,the percentage that is included with the transformer description (e.g. 18%, 10%,etc) is the short circuit current or the impedance of the transformer?

If it is the impedance of the transformer, can we use it to calculate the secondary and primary impedance of the transformer?

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