## Calculation of the X0/R0 ratio for a Zig Zag transformer

## Calculation of the X0/R0 ratio for a Zig Zag transformer

(OP)

I'm trying to calculate the X0/R0 ratio of a Zig Zag transformer. I got the following information:

-Winding connection: Zig Zag

-Short time neutral current: 3500 A 5 sec.

-Continuous neutral current : 250 A

-Voltage : 26.4 kV

-Zero sequence impedance: 7.5 ohms/ph

-No load losses: 1951 W

-Load losses : 18214 W

How do we calculate the X0/R0 ratio using these informations?

Thank!

-Winding connection: Zig Zag

-Short time neutral current: 3500 A 5 sec.

-Continuous neutral current : 250 A

-Voltage : 26.4 kV

-Zero sequence impedance: 7.5 ohms/ph

-No load losses: 1951 W

-Load losses : 18214 W

How do we calculate the X0/R0 ratio using these informations?

Thank!

## RE: Calculation of the X0/R0 ratio for a Zig Zag transformer

## RE: Calculation of the X0/R0 ratio for a Zig Zag transformer

## RE: Calculation of the X0/R0 ratio for a Zig Zag transformer

## RE: Calculation of the X0/R0 ratio for a Zig Zag transformer

I have verified your data and found these:

1) The information on the short-time neutral current of 3500A for 5 seconds and the continuous neutral current rating does not correspond to the IEEE 32 numbers that I found. The continuous current if we use IEEE 32 will yield 105A. The continuous current for a 10-second time rating is 3% of the ground fault (3500 X 0.03 = 105A). Instead, your data fits with a grounding duty for 1 minute (7% of ground fault current, 3500 X 0.07 =245 ~ 250A).

2) You can use the no-load and full-load losses to calculate the resistance. no-load losses = core losses and full-load losses = core losses + copper losses. Therefore your copper losses = 18,241 - 1951 = 16,263 W. Equate those losses to 3I

^{2}R and you get R which is equal to 0.813 ohms.3) Using the Z

_{0}_{}= 7.5 ohms, you'll get x_{0}= square root (7.5^{2}-0.813^{2}) = 7.46 ohmsI got x

_{0}/r_{0}= 9.2