Q353 : Differences Between MALZ and HIFREQ in Input Impedance at High Frequency

Question
When I compare the input impedance of a small grid computed with HIFREQ and MALZ (at 1 MHz), I get different results. What explains this?

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Answer
Two reasons can explain the difference between the values computed by the two programs.

1. Mutual Impedance. MALZ doesn't account for mutual induction between conductors.

2. Self Impedance. When computing the self-impedance of conductors, MALZ assumes that the conductors are infinitely long. HIFREQ doesn't make this simplifying assumption, and uses the actual length of the conductors in all its calculations. Also, MALZ uses a simplified soil-model when computing the impedance, whereas HIFREQ uses the actual soil model.

Because of the above approximations, the self impedance computed by MALZ tends to be larger than that computed by HIFREQ. As a result, the current tends to leak out of the conductor closer to the point of energization in MALZ than in HIFREQ (since it is comparatively more difficult for the current to flow in the conductor). This in turn leads to a larger potential for the energization segment, and a larger input impedance.

This is why it is normally recommended to use HIFREQ for computations at higher frequencies.

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