Repetitive Pulse Generator vs. Lightning Impulse Generator: Selecting the Right Test Source
High-voltage insulation testing traditionally relied on lightning impulse generators (LIGs) producing the classic 1.2/50 μs voltage waveform or 8/20 μs current waveform. However, modern power electronics and renewable energy systems expose insulation to repetitive nanosecond-edge pulses that bear little resemblance to lightning strikes. This has elevated the repetitive pulse generator (RPG) to a complementary or sometimes superior test tool. This article provides a side-by-side technical comparison to guide test engineers in selecting the appropriate source for each application.
Fundamental Waveform Differences
The waveform characteristics define the stress mechanism on insulation materials:
Lightning impulse (1.2/50 μs): Front time 1.2 μs (±30%), time to half-value 50 μs (±20%). Represents indirect lightning strikes on transmission lines. Single-shot or very low repetition rate (one pulse per minute maximum).
Repetitive pulse (nanosecond to microsecond edges): Rise times from 5 ns to 500 ns, pulse widths 50 ns to 10 μs, repetition rates from single-shot to 200 kHz. Represents switching transients from IGBTs, SiC MOSFETs, or GW-scale converters. Often applied as pulse trains of thousands or millions of events.
A lightning impulse generator delivers high energy per pulse (kilojoules to megajoules) but cannot sustain high repetition. A repetitive pulse generator delivers lower energy per pulse (millijoules to joules) but can operate continuously, enabling accelerated aging studies that lightning generators cannot perform.
Application-Specific Suitability
| Test Application | Recommended Source | Rationale |
|---|---|---|
| Distribution transformer lightning withstand (IEC 60076) | LIG | Standard requires 1.2/50 μs waveform, single shot, up to 200 kV |
| Inverter-fed motor insulation aging (IEC 60034-18-41) | RPG | Standard specifies repetitive bipolar pulses at 5–20 kHz for 100–1000 hours |
| Gas-insulated switchgear (GIS) lightning test | LIG | Very high voltage (up to 1.5 MV) required, single impulse sufficient |
| Partial discharge inception under fast transients | RPG | Rise time control allows systematic PDIV measurement at different dV/dt |
| Surge arrester energy withstand | LIG | High energy per pulse (up to 10 kJ) validates thermal stability |
| PCB and low-voltage electronics EMC immunity | RPG | Repetitive pulses at 5 kHz identify intermittent sensitivity |
Technical Comparison Matrix
| Parameter | Lightning Impulse Generator | Repetitive Pulse Generator |
|---|---|---|
| Typical voltage range | 100 kV to 2.5 MV | 1 kV to 200 kV |
| Rise time | 0.5–5 μs (standardized) | 5–500 ns (adjustable) |
| Pulse duration | 20–100 μs (half-value time) | 50 ns – 10 μs (programmable width) |
| Max repetition rate | 0.017 Hz (one per minute) | 200,000 Hz (200 kHz) |
| Energy per pulse | 1 kJ to 50 MJ | 1 mJ to 100 J |
| Total pulse count capacity | 10–100 pulses before component wear | 10⁹ pulses (solid-state designs) |
| Typical footprint | 10–50 m² (large Marx tower) | 1–4 m² (rack or cabinet) |
| Warm-up time | 5–15 minutes (charging circuit) | <1 minute |
| Typical cost (new) | $50,000 – $500,000+ | $30,000 – $150,000 |
When to Use Both Generators in the Same Lab
Many high-voltage test facilities now maintain both a lightning impulse generator and a repetitive pulse generator. Complementary usage includes:
Qualification sequence: First apply lightning impulse (single shot) to verify basic insulation level (BIL). Then apply repetitive pulse aging (1000 hours) to validate long-term reliability. Some products fail only repetitive stress, others fail only lightning impulse.
Failure analysis: Use RPG to identify weak points through partial discharge mapping at variable dV/dt. Then characterize dielectric strength using LIG to determine residual withstand margin.
Standard compliance: Regulatory standards increasingly require both. IEC 61800-5-1 (adjustable speed drives) mandates both lightning impulse for clearance verification and repetitive pulse for insulation system qualification.
Upgrading from Legacy LIG to Modern RPG
For labs with a traditional lightning impulse generator but no repetitive pulse capability, the most cost-effective upgrade path is adding a modular solid-state RPG rather than replacing the LIG. The RPG complements rather than replaces the LIG. However, if your primary testing involves inverter-fed loads, renewable energy converters, or automotive traction drives, an RPG should be the first priority. For utility transmission and distribution equipment, LIG remains mandatory but should be supplemented with an RPG for emerging stress conditions.
Hybrid Solutions
Recent innovations include hybrid impulse generators that combine Marx bank energy storage (high energy) with solid-state closing switches (moderate repetition). These systems achieve up to 500 kV at 100 Hz repetition—filling a gap between traditional LIG and high-frequency RPG. However, cost typically exceeds $250,000, limiting adoption to national laboratories and major equipment manufacturers.
Decision Flowchart Summary
Select a lightning impulse generator if:
You must comply with legacy standards specifying 1.2/50 μs or 8/20 μs waveforms.
Test object voltage exceeds 200 kV.
Energy per pulse requirement exceeds 500 J.
Total required pulses per test is under 100.
Select a repetitive pulse generator if:
Testing insulation for inverter-fed, switched-mode, or HVDC applications.
Need to study aging, partial discharge evolution, or thermal effects over time.
Require adjustable rise time from 5 ns to 500 ns.
Want to run tests unattended for hours or days (repetition enables automation).
For most modern high-voltage equipment—from EV traction motors to grid-tied solar inverters—the repetitive pulse generator has become the more relevant test source for real-world operating stresses. Lightning impulse generators remain essential for utility transmission standards but no longer suffice as the sole impulse test capability in advanced high-voltage laboratories.
