How to make Z bus matrix

I've been working on code to calculate a balanced three-phase fault without using PSS/E. The issue I'm facing is with the fault impedance at a specific bus.

I used the diagonal element of the Z-bus, which I obtained by inverting the Y-bus matrix. However, when I compared my results with the fault impedance from PSS/E's 'ASCC' calculation on IEEE-9 bus system, the values were significantly different.

So I have a few questions:

How does PSS/E calculate the fault impedance?
If PSS/E uses the Z-bus to determine the fault impedance, how does it construct the Z-bus matrix?
Is there another way to accurately construct the Z-bus matrix?

I'd greatly appreciate any insight into these questions.

If your comparison is showing significantly different results, it may be worth double checking whether you're using FLAT settings in ASCC for your comparison, and that you're using the same type of machine source impedance.

The program application guide might help to shed some light your first question - for PSSE v34.8.2 section 11.4 covers how fault currents are calculated for ASCC.

Regarding your second question about the specific algorithms used, section 11.4 doesn't go into detail. It's possible that at that level of detail, intellectual property may be a concern?

For the third question, two conceptual algorithms that can be used to construct Z bus for faults are Lower/Upper triangular matrix decomposition, and 'bus building' where the Sherman-Morrison formula is used to iteratively increase the dimension of a reduced Zbus until the whole network is accounted for.

QuinnP

answered 2024-10-02 02:45:34 -0500, updated 2024-10-02 02:46:28 -0500

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