Lightning impulse voltage testing serves as a fundamental dielectric test to verify the insulation strength of high-voltage equipment, such as power transformers, against transient overvoltages caused by lightning strikes. These tests are performed using a Marx Impulse Generator (MIG) circuit, which subjects the test object to standardized high-voltage impulses with specific wave shapes. The capability to withstand these transient stresses is critical for ensuring the operational reliability and safety of power systems.

According to international standards, including IEC 60060-1, a standard full lightning impulse (LI) voltage is defined with a front time (T1) of 1.2 μs (±30%) and a time to half-value (T2) of 50 μs (±20%)[citation:4]. The test circuit, comprising an impulse generator, front and tail resistors, and the test object, must be precisely configured to generate this waveform. Inadequate selection of circuit parameters, such as front (R1) and tail (R2) resistances, can lead to non-standard wave shapes, overshoot, or oscillations, potentially causing insulation failure during testing[citation:1].

Beyond full wave tests, the standards also specify chopped lightning impulse tests. During these tests, the voltage wave is abruptly chopped after a specified time delay, typically between 3 to 6 microseconds after the peak. The peak value of the chopped wave must exceed that of the full wave. The chopping circuit must introduce minimal impedance to ensure the voltage drops to zero rapidly after chopping, though a minimum impedance may be required if the subsequent voltage overswing exceeds 30% of the peak voltage[citation:1].

A significant challenge in LI testing is managing the total inductance of the test circuit, which includes the internal inductance of the impulse generator and the inductance of the connecting leads. This inductance, interacting with the load capacitance (comprising the test object and measurement system capacitance), can cause high-frequency oscillations and overshoot at the impulse crest[citation:4][citation:7]. Standards stipulate that the relative overshoot magnitude should not exceed 10%[citation:4]. This becomes particularly critical for testing Ultra-High Voltage (UHV) equipment above 800 kV, where achieving standard wave shapes is more challenging due to larger physical setups and higher inherent inductances[citation:7].

Accurate modeling and simulation of the entire test circuit, including the high-frequency behavior of the test object, are essential for predicting wave shapes and optimizing generator parameters before physical testing. Methods range from complex Multi-Transmission Line models to simpler lumped-parameter models, each with its own trade-offs between accuracy, complexity, and computational speed[citation:1]. Furthermore, the recent standard IEC 60060-1:2024 introduces updated tolerances, such as extending the positive tolerance for the front time of lightning impulses for UHV equipment to 100% (2.4 μs), to accommodate the practical difficulties in testing these systems[citation:5].

In conclusion, the Lightning Impulse Voltage Generator Test System is a sophisticated setup vital for qualifying high-voltage equipment. Its operation is governed by stringent international standards that define impulse parameters, test procedures, and permissible tolerances. Continuous development in circuit modeling, parameter estimation, and standard revisions ensures the test's relevance and accuracy, especially for advancing UHV technology.