Even well-equipped high voltage laboratories encounter problems during lightning impulse testing. Many of these issues stem from recurring mistakes that are well documented but frequently overlooked. Recognizing these pitfalls early saves time, protects expensive equipment, and preserves the credibility of test results. This article examines the most common problems encountered with HV lightning impulse voltage generator test systems and offers practical guidance for avoiding them.

Inadequate Grounding Arrangements

Grounding deficiencies rank among the most frequent causes of poor impulse waveforms. Long ground leads, multiple ground paths, and high-impedance connections introduce unwanted inductance into the discharge circuit, producing overshoot and oscillation at the wave crest. The solution involves establishing a single-point, low-impedance ground reference with short, wide, flat conductors. All components, including the generator, divider, and test object, should connect to this reference through the shortest practical path. Verifying ground integrity before testing prevents many waveform problems from occurring in the first place.

Neglecting Test Object Preparation

The condition of the test object significantly influences results. Contaminated surfaces, residual moisture, and improper connections can cause premature flashover or erratic breakdown behavior. Cleaning and drying procedures should follow documented protocols before every test session. Connections to the test object must be secure and properly rated for the impulse currents involved. For transformer testing, understanding winding configuration and tap settings ensures that the applied impulse stresses the intended insulation paths. Skipping these preparations often leads to inconclusive or misleading test outcomes.

Measurement Chain Errors

Errors within the measurement chain can invalidate otherwise successful tests. Common problems include mismatched divider impedance, incorrect scale factor settings, inadequate digitizer bandwidth, and electromagnetic interference from nearby equipment. Regular calibration against traceable standards identifies drift before it affects results. Shielding signal cables and using fiber-optic transmission reduce noise coupling. Operators should also verify that the measurement system's response parameters, particularly front time and settling behavior, meet the requirements of the applicable standard for the voltage levels being tested.

Improper Waveform Parameter Adjustment

Achieving the standard 1.2/50 microsecond waveform requires careful adjustment of front and tail resistances for each test object. A common mistake involves using settings from a previous test without recalculating for the new load capacitance. This oversight produces waveforms outside tolerance and may lead to unnecessary repeated testing. Simulation software allows operators to predict waveform behavior before energizing the system, reducing trial-and-error adjustments. Keeping detailed records of successful settings for common test objects builds a valuable reference library for future work.

Ignoring Environmental Conditions

Temperature, humidity, and atmospheric pressure affect both the generator's performance and the test object's behavior. High humidity promotes surface flashover and alters spark gap breakdown voltage. Low pressure reduces air density, effectively lowering insulation strength. Laboratories should monitor environmental conditions and apply appropriate corrections where standards require them. Testing outside specified environmental ranges may produce results that cannot be properly interpreted or compared with reference data.

Overlooking Safety Protocol Violations

Fatigue and routine familiarity sometimes lead operators to relax safety practices. Skipping grounding checks, bypassing interlocks, or entering restricted areas without proper authorization creates serious risks. Establishing clear written procedures, conducting regular refresher training, and enforcing accountability help maintain a strong safety culture. Automated safety systems should be treated as essential safeguards, not obstacles to be circumvented. Consistent adherence to safety protocols protects personnel and equipment while supporting reliable testing outcomes.

Avoiding these common pitfalls requires discipline, documentation, and continuous attention to detail. Laboratories that institutionalize best practices achieve more consistent results, reduce downtime, and maintain the confidence of clients and accreditation bodies alike.