Inductance L_0 of zero-sequence flux path return (Three-Phase Transformer)

Hello everyone,

I am currently working on simulations, including the "Three-Phase Transformer (Two Windings)" model. I am looking to represent this transformer with three limbs, and I am in need of the zero inductance L_0, which has a significant impact, especially in the case of asymmetric operation. Does anyone have tabulated values for the zero inductance of different power transformers in the distribution network?

Thank you in advance!

Best regards,

Torben

Answer 1

[Shivam Gothi]

Hello @Torben,

As per my understanding, you are trying to simulate a three phase transformer and you want to model its zero sequence inductance that plays significant role during transient conditions.

For this purpose, you can use “Three-Phase Transformer Inductance Matrix Type (Three Windings)” block from “Simscape / Electrical / Specialized Power Systems / Power Grid Elements” library as shown in the below figure.

It is a three-phase transformer with a three-limb core and three windings per phase, as shown in the below figure:

Please refer to the below documentation for more information regarding “Three-Phase Transformer Inductance Matrix Type (Three Windings)” block.

https://www.mathworks.com/help/sps/powersys/ref/threephasetransformerinductancematrixtypethreewindings.html

Open the “block parameters” and set the core type to “Three limb or 5 limb core”.

You will then be prompted to enter the transformer's zero-sequence impedances, as illustrated in the diagram below.

“X12”, “X23”, and “X13” are the The zero-sequence short-circuit reactances in PU (Per-Unit). “Xij” is the reactance measured from winding “I” when winding “j” is short-circuited. The defaulted values are “[0.1, 0.2, 0.3]”

Now addressing your second question:

“Does anyone have tabulated values for the zero inductance of different power transformers in the distribution network?”

The zero-sequence impedance of a three-phase transformer depends on its connection type and can vary between different manufacturers. Here’s an example table that lists hypothetical values for zero-sequence inductance for different transformer configurations

Additionally, please refer to the following test report of power transformer by ABB (page 31):

https://www.scribd.com/doc/48206698/46428300-Testing-of-Power-Transformer

It states that:

“The zero-sequence impedance is usually given as a percentage of the rated

phase impedance. When the transformer has a three-limb core and no delta-

connecter windings, the zero-sequence impedance is about 30...60 %. When

the transformer has a delta-connected winding, the zero-sequence impedance

is 0.8...1.0 times the corresponding short-circuit impedance”

Please refer to the above test report to have a clear understanding of how the zero sequence impedances are measured.

I hope this helps !

[Torben]

Hello,

Thank you for your extremely detailed response! It will be helpful to me.