High-voltage (HV) lightning impulse voltage generator test systems are critical for evaluating the dielectric strength of power equipment, such as transformers and switchgear, against transient overvoltages caused by lightning strikes or switching operations. These systems simulate standard lightning impulses (LI) to ensure compliance with international standards like IEC 60060-1, which defines test requirements for equipment with rated voltages above 1 kV AC or 1.5 kV DC. This article delves into the components, operational principles, and key challenges of lightning impulse testing, emphasizing industry benchmarks and technological advancements.

Components of Lightning Impulse Test Systems

A typical lightning impulse test system consists of a Marx impulse generator (MIG), front and tail resistors, a chopping circuit, and measuring instruments. The MIG, often used in high-voltage laboratories, employs stacked capacitors discharged through spark gaps to generate impulses with specific wave shapes. The front resistor (R1) controls the rise time (T1) of the impulse, while the tail resistor (R2) regulates the time to half-value (T2). Standard LI waves require a front time of 1.2 μs ±30% and a tail time of 50 μs ±20% [citation:4]. For chopped wave tests, a chopper interrupts the impulse at peak voltage, with a time delay of 3–6 milliseconds, to simulate insulation breakdown scenarios [citation:1].

Importance of Standards and Waveform Compliance

Adherence to IEC 60060-1 ensures reproducibility and accuracy in dielectric tests. The standard permits a tolerance of 2.4 μs for the front time in ultra-high-voltage (UHV) systems above 800 kV [citation:5]. Overshoot—a damped oscillation at the impulse peak—must not exceed 10% of the nominal voltage to prevent undue insulation stress [citation:4]. Excessive overshoot often results from high circuit inductance or improper resistor settings, leading to non-standard waveforms. For UHV equipment, achieving compliant waveforms becomes challenging due to larger test object capacitance (C2) and stray inductance (Ls), necessitating precise parameter adjustments [citation:10].

Challenges in Testing and Mitigation Strategies

Key challenges in lightning impulse testing include overshoot, oscillations, and difficulties in achieving standard waveforms for high-capacitance loads. Overshoot is influenced by circuit inductance, which arises from long connecting leads or generator design [citation:7]. To mitigate this, laboratories use computerized simulation tools to model test circuits, optimizing parameters like front resistance and load capacitance. For transformer testing, high-frequency (HF) models, such as multi-transmission line (MTL) or lumped parameter models, account for transient behavior in windings [citation:1]. Additionally, the recent IEC 60060-1 revision introduces updated procedures for manual waveform calculation and software-based evaluation, enhancing measurement reliability [citation:5].

Advances in Impulse Testing Technology

Modern impulse generators incorporate low-inductance designs and digital measurement systems to improve waveform accuracy. Research focuses on estimating stray inductance and load capacitance to expand testable load ranges [citation:7]. For UHV applications, increasing the front time tolerance has proven effective in testing larger capacitive loads while maintaining overshoot limits [citation:10]. Furthermore, standards now address composite test voltages and switching impulses, reflecting evolving grid demands. These advancements ensure that HV equipment withstands real-world overvoltage stresses, safeguarding power system reliability.