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The above formula is valid for a single phase transformer






For three phase transformer single phase voltage ratio is not equal to 3 phase voltage ratio, why? because you need to consider the primary and secondary winding configuration. For delta to wye the multiplying factor for single phase voltage ratio is 1.732 [67/13.75*1.732 = 8.439] to get the calculated three phase voltage ratio as shown by the above circuit model. Modern turn ratio test instrument are using software lookup table to find the correct multiplying factor that correspond to the specified winding configuration entered during transformer TTR testing session. So make sure that the TTR test instrument winding configuration setting is the same with the transformer winding configuration.

It is a good practice to review the TTR test instrument winding configuration setting and make sure it is the same with the transformer winding configuration shown on the transformer nameplate. Factory test report calculated value for three phase transformer voltage ratio can be evaluated using single phase voltage ratio multiplied by a factor based on winding configuration. Shown below are the single phase multiplying factor based on transformer winding connection to convert line to phase voltage or current.

Application of lesson learned:

Given a Δ - Y, Dyn1 (IEC vector code) group 2, angular displacement is 30° (IEEE C57.12.70 ), 3 phase transformer with primary voltage 67 kV and Secondary voltage 13.75 kV, secondary neutral, X0 was brought out; Calculate the 3 phase voltage ratio


Valid for 3 Φ , Δ - Y only
You need to multiply the delta voltage by 1.732. It comes from wye-connection on secondary winding.

voltage ratio, " a "
=
kV Primary Voltage * 1.732

kV Secondary Voltage

Use your voice to enter data

Calculator 1

If your primary winding is shorted, you will expect to have a lower turn ratio (a) in your TTR measurement compare to factory test report. It is also indicated by lower primary voltage reading. Use the calculator below to do simulation.

Valid for 3 Φ , Δ - Y only

Given three phase turn ratio 8.4396 and Secondary voltage 13.75 kV; Calculate the primary voltage

three phase turn ratio, a
=
kV Primary Voltage *1.732

kV Secondary Voltage

Use your voice to enter data

Calculator 2

If your secondary winding is shorted, you will expect to have a higher turn ratio (a) in your TTR measurement compare to factory test report. It is also indicated by lower secondary voltage reading. Use the calculator below to do simulation.

Valid for 3 Φ , Δ - Y only

Given a three phase turn ratio 8.4396 and Primary voltage 67 kV; Calculate the secondary voltage

three phase turn ratio, a
=
kV * 1.732 Primary Voltage

kV Secondary Voltage

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Calculator 3


Valid for 1 Φ only

Given single phase voltage ratio 4.8727 and Secondary voltage 13.75 kV; Calculate the primary voltage

single phase voltage ratio, a
=
kV Primary Voltage

kV Secondary Voltage

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Calculator 4


Valid for 1 Φ only

Given a single phase turn ratio 5.5333 and Primary voltage 69 kV; Calculate the secondary voltage

Turn Ratio, a
=
kV Primary Voltage

kV Secondary Voltage

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Calculator 5


Valid for 1 Φ only

Given primary coils number of turns = 498 and secondary number of turns = 90; Calculate the turn ratio

Single phase turn ratio, a
=
Primary Coils

Secondary Coils

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Calculator 6


Valid for 1 Φ only

Given single phase turn ratio = 5.5333 and secondary number of turns = 90; Calculate the primary number of turns of coil

single phase turn Ratio, a
=
Primary Coils

Secondary Coils

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Calculator 7


Valid for 1 Φ only

Given single phase turn ratio = 5.5333 and primary number of turns = 498; Calculate the secondary number of turns of coil

single phase turn ratio, a
=
Primary Coils

Secondary Coils

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Calculator 8


Valid for 1 Φ only

Given secondary FLA = 1296.41 and primary FLA = 234.29; Calculate the single phase turn ratio

single phase turn ratio, a
=
A, Secondary current

A, Primary current

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Calculator 9


Valid for 1 Φ only

Given single phase turn ratio = 5.5334 and primary FLA = 234.29; Calculate the secondary FLA

single phase turn ratio, a
=
Secondary current

Primary current

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Calculator 10


Valid for 1 Φ only

Given single phase turn ratio = 5.5334 and secondary FLA = 1296.41; Calculate the primary FLA

single phase turn ratio, a
=
Secondary current

Primary current

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Calculator 11


Given 3 Phase MVA rating = 28 and secondary voltage = 69 kV; Calculate the primary FLA

3 Phase MVA RATED POWER TRANSFORMER

primary, Amp
=
3 Phase MVA Rating

Primary kV * 1.732

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Calculator 12


Given secondary FLA = 1296.41 and secondary voltage = 12.47 kV; Calculate the MVA rating of transformer

secondary, Amp
=
3 Phase MVA Rating

Secondary kV * 1.732

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Calculator 13


Given 3 phase kVA = 1000 and primary voltage = 480; Calculate the primary FLA

3 Phase KVA RATED POWER TRANSFORMER

primary, Amp
=
3 Phase kVA Rating

Primary V * 1.732

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Calculator 14


Given secondary FLA = 2405.70 and secondary voltage = 240; Calculate the kVA rating of transformer

secondary, Amp
=
3 Phase kVA Rating

Secondary V * 1.732

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Calculator 15


Given primary FLA = 1202.85 and 3 phase kVA = 1000; Calculate the primary voltage

primary, Amp
=
3 Phase kVA Rating

Primary V * 1.732

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Calculator 16