Key Components and Maintenance of an HV Lightning Impulse Generator System

An HV Lightning Impulse Generator Test System is a complex assembly of electrical and mechanical components that must work in precise harmony to generate the standard 1.2/50 µs waveform. Understanding these core components and implementing a proactive maintenance regimen is critical for operational safety, measurement integrity, and system longevity.

Core System Components and Their Function

The system is centered around the Marx Generator, a multi-stage circuit where capacitors are charged in parallel through charging resistors and then rapidly switched to discharge in series via spark gaps. The High-Voltage DC Charging Supply provides the initial energy, typically with a positive polarity output for transformer testing. The Wave-Shaping Network, comprising front (Rf) and tail (Rt) resistors along with a load capacitor (C2), defines the impulse's rise time and decay. Finally, the Measurement System, including a calibrated resistive or capacitive voltage divider and a high-speed digital recorder, captures the waveform for analysis.

Preventive Maintenance Checklist

Regular maintenance prevents drift in performance and catastrophic failure. A core checklist includes:
• Visual Inspection: Check all high-voltage connections, busbars, and shielding for corrosion or looseness. Inspect insulating columns and structures for contamination or tracking.
• Capacitor Health: Measure the insulation resistance and capacitance of individual Marx generator capacitors annually. Re-form capacitors if the system has been idle for extended periods.
• Spark Gap Maintenance: Clean and polish spherical electrodes to remove oxidation and pitting. Verify and adjust the gap distance according to the voltage setting tables.
• Resistor Verification: Periodically measure the value of front and tail resistors, as they can drift with heat stress.

Calibration and Performance Diagnostics

Annual system calibration is non-negotiable for standards compliance. This involves a No-Load Test to verify the generated waveform's front time, tail time, and overshoot against IEC 60060-1 tolerances using a reference measurement system. A Divider Calibration should be performed, checking its scale factor and step response with a step generator. Additionally, performing a Load Test with a known dummy load (e.g., a pure capacitive load) validates the system's ability to maintain waveform shape under typical test conditions.

Troubleshooting Common Performance Issues

Deviations from the standard waveform often point to specific component issues. An excessively long front time suggests the front resistance is too high or the generator's stage capacitance is low. A prematurely decaying tail indicates insufficient tail resistance or excessive load. High-frequency oscillations on the wavefront are typically caused by excessive loop inductance in the test circuit, requiring shorter, straighter connections. Inconsistent firing of the Marx stages can result from dirty or misaligned spark gaps or uneven capacitor charging.

Conclusion: Reliability Through Systematic Care

The reliability of an impulse test system directly impacts the validity of the test data it produces. By investing in structured maintenance, regular calibration, and informed troubleshooting, operators ensure the system performs as a precision instrument rather than just a high-voltage source. This disciplined approach minimizes downtime, reduces safety risks, and delivers the consistent, accurate results required for certifying high-voltage equipment.