Question

During a 3-phase bolted fault with zero fault impedance (0 Ohm), the inverter current response appears correct, but the measured positive-sequence active/reactive current components (I1P/I1Q or i1P/i1Q) at the fault location show implausible or unexpected values.

Is this a calculation error in PowerFactory?

Answer

No. This behaviour is expected for an ideal solid short circuit.

The quantities I1P/I1Q (or i1P/i1Q) are not direct phase currents. They represent the decomposition of the positive-sequence current into active and reactive components relative to the positive-sequence voltage vector.

This decomposition requires:

• a non-zero voltage magnitude, and
• a well-defined voltage angle as reference.

During a solid 3-phase short circuit with exactly 0 Ohm fault impedance, the voltage at the fault location collapses to approximately zero. In this situation, the voltage vector is no longer properly defined and the separation into active and reactive current components loses its physical meaning.

As a consequence:

• the inverter may still inject the correct current magnitude,
• the phase currents may still look correct,
• but the calculated I1P/I1Q components can become numerically unstable or appear implausible.

Small numerical deviations are sufficient to produce large changes in the calculated dq-components when the reference voltage approaches zero.

This effect is especially visible at locations close to the fault.

If a small fault impedance is used instead (for example 0.01 Ohm, depending on the short circuit power), the voltage does not fully collapse. A valid voltage reference still exists and the I1P/I1Q quantities become stable and physically meaningful again.

Therefore, this behaviour should not be interpreted as a modelling or calculation error of the inverter model or PowerFactory itself, but as a fundamental limitation of evaluating active/reactive current components under ideal zero-voltage fault conditions.

For solid short circuits, the phase currents and current magnitude are the physically meaningful quantities to evaluate.