Purchasing an HV Lightning Impulse Voltage Generator is only the beginning of a quality assurance journey. Factory acceptance testing (FAT) and site commissioning are the decisive stages where theoretical specifications become verified performance. A rigorous, well-documented commissioning process protects the buyer's investment, establishes a traceable performance baseline, and prevents costly disputes after installation. This article outlines the structured approach that laboratories and manufacturers should follow to confirm that a newly delivered impulse generator meets all contractual and standards-based requirements.

Factory acceptance testing begins at the manufacturer's facility, before shipment, and serves as the first formal verification of design promises. The cornerstone of FAT is waveform verification into a dummy load that emulates the intended test object's capacitance and impedance. A typical dummy load consists of oil-filled capacitor banks and resistor networks arranged to present a representative burden. The generator is fired at multiple voltage levels, usually at 50, 70, and 100 percent of rated output, with each shot recorded by a calibrated reference measurement system. The resulting waveforms are evaluated for front time, tail time, peak voltage, and overshoot in accordance with IEC 60060-1 tolerances, and any deviation beyond the permitted window triggers investigation before shipment is approved.

Efficiency and linearity testing form the second pillar of FAT. Efficiency, defined as the ratio of output peak voltage to the theoretical charging voltage multiplied by the number of stages, typically ranges from 85 to 95 percent for well-designed Marx generators. Linearity requires that output voltage scale proportionally with charging voltage across the full operating range. A generator that produces correct waveforms at low voltage but distorts at rated output indicates inadequate energy storage, excessive circuit inductance, or spark gap instability. Manufacturers should provide efficiency curves and linearity plots as part of the FAT documentation package, along with oscillograms for every test point.

Chopped-wave and special waveform tests complete the factory verification matrix. If the procurement contract includes chopped-wave capability, the manufacturer must demonstrate reliable chopping at the specified delay times, with the chopping gap triggering consistently across repeated shots. Statistical analysis of at least ten consecutive shots establishes the repeatability of both peak voltage and time parameters. For laboratories testing transformers, a reduced-scale or actual transformer may serve as the load during FAT, providing early insight into how the generator interacts with real high-capacitance, high-inductance burdens. Any waveform anomalies observed at this stage are far cheaper to correct at the factory than on site.

Site commissioning begins upon delivery and installation, and it must replicate and extend the factory test program under actual laboratory conditions. The first task is mechanical and electrical installation qualification: verifying foundation integrity, grounding grid resistance, clearance distances, and the integrity of all high-voltage connections. Grounding resistance should be measured and documented, with values below one ohm preferred for impulse laboratories. The charging supply, control system, and safety interlocks are then energized and tested independently before any high-voltage impulse is generated, ensuring that protection systems function correctly under fault conditions.

The heart of site commissioning is the repetition of waveform verification using the laboratory's own measurement chain. This step validates not only the generator but also the voltage divider, impulse analyzer, and software that will be used for routine testing. Differences between factory and site results often trace to grounding configuration, lead routing, or electromagnetic interference unique to the installation. Commissioning engineers should perform a step response test on the measurement system, confirming that the divider's settling time and overshoot remain within specification after installation. Calibration certificates for all measurement instruments should be current and traceable to national standards.

Safety system validation deserves dedicated attention during commissioning. Each interlock, emergency stop, grounding switch, and warning device must be tested under realistic conditions, with results recorded in a formal checklist. The automatic discharge system should be timed to confirm that residual voltage falls to safe levels within the specified interval after a trip or emergency stop. Personnel training on the new system, including lockout tagout procedures and emergency response, should be completed before the generator is released for routine production testing. A formal handover document, signed by both manufacturer and buyer, marks the transition from commissioning to operational status.

Finally, documentation closes the commissioning loop. The complete package should include factory test reports, site commissioning records, calibration certificates, as-built drawings, software backups, maintenance schedules, and spare parts lists. A performance baseline file, containing reference waveforms and measured parameters at defined test points, becomes the benchmark for future annual verification. When the generator is re-tested months or years later, any drift from this baseline signals the need for maintenance or recalibration. Laboratories that invest in disciplined commissioning and thorough documentation enjoy shorter troubleshooting cycles, higher confidence in test results, and stronger accreditation standing under ISO 17025. Properly executed, commissioning transforms a high-voltage asset from a delivered machine into a trusted instrument.