In the field of high-voltage engineering, ensuring the dielectric strength of power transformers and other critical apparatus against transient over-voltages is paramount. The Lightning Impulse (LI) test, a routine high-voltage test defined by international standards such as IEC 60060-1, is designed for this exact purpose. This test simulates the stress caused by lightning strikes on electrical insulation systems.

A typical HV Lightning Impulse Voltage Generator Test System is based on a Marx generator circuit. This circuit involves multiple stages of capacitors charged in parallel and then discharged in series to generate a high-voltage impulse with a specific waveform. The standard full lightning impulse is defined as a 1.2/50 microsecond wave, meaning it has a front time of 1.2 microseconds and a time to half-value of 50 microseconds. The test system must produce this waveform within strict tolerances to ensure valid and reproducible results. Key components like front and tail resistors are adjusted to shape the waveform correctly, while the system's inherent inductance must be controlled to prevent unwanted oscillations and overshoot at the voltage peak, which according to standards, should not exceed 10% [citation:4].

Beyond the full wave test, the system must also generate chopped lightning impulses. In this test, the voltage wave is abruptly chopped after a few microseconds, creating an even more severe stress on the insulation to simulate the effect of a flashover. Standards like IEC 60060-1 specify that the chopping must occur within a defined time window after the peak, and the circuit must be designed to ensure a rapid collapse of voltage without excessive reverse overvoltage [citation:1].

Precise modeling of the entire test circuit, including the generator, connecting leads, and the test object itself, is crucial. The high-frequency behavior of the transformer or other equipment under test significantly impacts the resulting wave shape. Engineers employ various models, such as Multi-Transmission Line or lumped parameter models, to predict the system's performance and avoid non-standard waveforms that could lead to incorrect conclusions about the insulation's integrity [citation:1]. The recent update to IEC 60060-1 also extends the tolerance for the front time for systems above 800 kV, reflecting the evolving challenges in ultra-high-voltage testing [citation:5].

Finally, accurate measurement is as important as the generation of the impulse. Standards such as GB/T 16896.1-2024, the Chinese national standard equivalent, detail the stringent requirements for digital recorders and instruments used in these high-voltage and high-current tests. These instruments must meet specific performance and calibration criteria to guarantee the measurement uncertainty is within acceptable limits, ensuring that every test is both accurate and reliable [citation:2][citation:10].