## Understanding test result of 3 winding transformer

## Understanding test result of 3 winding transformer

(OP)

Dear Engineers,

I would like to know how to interpret/understand the test result of a three winding transformer specifically the %Z value, from the diagram below i managed to extract the some of the details, however the details of the %Z between LV1 and LV2 winding is not identifiable.

Also i need some guidance to calculate the short circuit current at the LV side which is 11kV when both the LV windings are paralleled. Which %Z value shall be referred?

I have attached the transformer test result and the diagram.

The Transformer brief detail:

1.) Three Winding Transformer

2.) 150MVA/75MVA/75MVA

3.) 275kV/11kV/11kV

Your input and guidance would be much appreciated.

I would like to know how to interpret/understand the test result of a three winding transformer specifically the %Z value, from the diagram below i managed to extract the some of the details, however the details of the %Z between LV1 and LV2 winding is not identifiable.

Also i need some guidance to calculate the short circuit current at the LV side which is 11kV when both the LV windings are paralleled. Which %Z value shall be referred?

I have attached the transformer test result and the diagram.

The Transformer brief detail:

1.) Three Winding Transformer

2.) 150MVA/75MVA/75MVA

3.) 275kV/11kV/11kV

Your input and guidance would be much appreciated.

## RE: Understanding test result of 3 winding transformer

## RE: Understanding test result of 3 winding transformer

Use 22 kV and 150 MVA to calculate the Available Short Circuit Current of the 11 kV windings.

I get 20,053 Amps ASCC for either of the 11 kV windings.

I do find the note "Base 150 MVA" troubling when applied to a 75 MVA rated winding.

The full load current of a 75 MVA winding at 11 kV will be 6818 Amps.

Basing the % imp on a 150 MVA base would imply that the % imp test was done at 13616 Amps. (2 x full load current)

I think that a call to the manufacturer may be in order.

--------------------

Ohm's lawNot just a good idea;

It's the LAW!## RE: Understanding test result of 3 winding transformer

Impedance between LV1 and LV2 will be = 2x 0.925 x 18.9 = 35 % on 75 MVA base,

The above constants are from typical similar transformers.

## RE: Understanding test result of 3 winding transformer

Referring to your reply , I'm lost in this part:

HV-LV1+lV2 impedance will be 17/0.9 =18.9 % on 150 MVA base.Please assist.

Thanks

powerven

## RE: Understanding test result of 3 winding transformer

## RE: Understanding test result of 3 winding transformer

See annexed what I have got in the J&P Transformer Book.

Cheers,

Herivelto S. Bronzeado

Brasília, Brazil

https://www.linkedin.com/in/heriveltobronzeado/

https://www.researchgate.net/profile/Herivelto_Bro...

## RE: Understanding test result of 3 winding transformer

## RE: Understanding test result of 3 winding transformer

Is there any reference documents which i can refer to understand the calculations which you have shown?

I'm kind lost with that....

Thanks

powerven

## RE: Understanding test result of 3 winding transformer

Giorgio Bertagnolli -Short Circuit duty of Power Transformers –The ABB approach -ABB Transformatori, Legnano, Milano, Italy Ed1.0 Pages 190 -1996, Ed2.0 Pages 190-1998, Ed3.0 Pages 225- 2007

## RE: Understanding test result of 3 winding transformer

Is the formula applicable for any type of LV1&LV2 winding arrangement? Is it applicable for LV1 & LV2 axially in stack?

Thanks,

Fouad

## RE: Understanding test result of 3 winding transformer

## RE: Understanding test result of 3 winding transformer

Referring to your calculation, below are my further queries related to the numerical derivation:

Your guidance is appreciated.

Thanks

powerven

## RE: Understanding test result of 3 winding transformer