The oscillation or overshoot of the waveform measured by thelightning impulse voltage generatoris mainly due to the parasitic inductance and capacitance in the test circuit forming an unwanted resonant circuit.

Core Reasons:

1.Loop Stray Inductance (Primary Cause): Long high-voltage leads and the equipment itself have inherent inductance. The current changes extremely rapidly (very high di/dt). This inductance generates a back electromotive force (EMF), causing overshoot and subsequent oscillation.

2.Stray Capacitance to Ground: The test object, voltage divider, and leads all have capacitance to ground. This forms unintentional LC resonant circuits with the loop inductance.

3.Wave Reflection and Impedance Mismatch: If the high-voltage leads are too long, they act like transmission lines. If the generator's output impedance doesn't match the lead's characteristic impedance, voltage waves reflect back and forth, distorting the waveform and causing overshoot and ringing.

Main Solutions:

Minimize loop inductance: Shorten all high-voltage connecting leads and use flat copper straps instead of round wires to minimize the loop area. This is the most effective measure.

Add damping: Connect a small, non-inductive damping resistor in series at the front of the test object or divider to absorb reflective energy and suppress oscillations.

Optimize measurement and grounding: Ensure the measurement system (divider, cable) has sufficient bandwidth and proper impedance matching; use a low-inductance and reliable grounding method.