Advanced Repetitive Pulse Generator Applications for Partial Discharge and Dielectric Aging Studies
As electrical grids integrate more renewable energy sources and HVDC transmission lines, insulation systems face new forms of electrical stress. Unlike traditional AC or single-impulse tests, repetitive pulse generators (RPGs) produce controlled, high-frequency pulse trains that closely mimic stresses from power electronics, fast switching transients, and DC circuit breakers. This article examines advanced RPG applications in partial discharge (PD) diagnostics and accelerated dielectric aging research.
Why Repetitive Pulses Matter for Modern Insulation
Wide-bandgap semiconductors (SiC, GaN) generate steep voltage edges with repetition rates from hundreds of Hz to tens of kHz. Traditional 50/60 Hz or lightning impulse tests do not capture insulation response to repetitive nanosecond edges. An RPG bridges this gap by allowing engineers to replicate actual field conditions, revealing failure mechanisms such as charge accumulation, internal partial discharge activity, and dielectric heating that remain hidden under conventional test protocols.
Repetitive Pulse Generator Based Partial Discharge Analysis
When connected to a test object (e.g., stator bars, cable joints, or gas-insulated switchgear), an RPG energizes the insulation with adjustable pulse amplitude, rise time, and repetition frequency. Simultaneous phase-resolved partial discharge (PRPD) measurement using high-frequency current transformers (HFCT) or ultra-high-frequency (UHF) sensors provides:
PD inception voltage (PDIV) under repetitive stress: Often 15–30% lower than AC PDIV due to space charge memory effects.
PD pattern evolution over time: Identifies whether cavities degrade gradually or fail catastrophically.
Pulse repetition rate dependence: Higher rates accelerate PD-induced erosion, useful for comparative material screening.
Accelerated Dielectric Aging Protocols
RPGs enable time-compressed aging studies. A standard approach is to apply bipolar square pulses at 5–20 kHz, peak voltage 0.8–1.2× the rated voltage, at elevated temperature (e.g., 150°C for Class H insulation). Key metrics tracked include:
Capacitance change (ΔC/C₀) – indicates delamination or void growth.
Dissipation factor (tan δ) rise – points to bulk heating or conductive path formation.
Breakdown voltage retention – measured after every 100 hours of repetitive pulsing.
Studies show that 500 hours of RPG aging at 10 kHz correlates well with 10 years of field exposure in inverter-fed motor drives.
Case Example: Testing HVDC Cable Terminations
A European cable manufacturer used a 40 kV repetitive pulse generator with 1 kHz repetition rate, 100 ns rise time, and 5 μs pulse width to test 320 kV DC cable terminations. The RPG revealed that standard AC‑tested terminations developed surface discharges after only 200 hours of repetitive pulsing. Modifying the stress control tube geometry eliminated the issue, saving over €500,000 in potential field failures.
Selecting an RPG for Advanced Diagnostics
For PD and aging applications, choose a repetitive pulse generator with these features:
Adjustable rise time (20 ns to 1 μs) to simulate different switching speeds.
Programmable pulse patterns (bipolar, burst, or random sequences).
External trigger input for synchronizing oscilloscopes or PD detectors.
Output voltage stability ≤ ±2% over 8 hours of continuous operation.
Overcurrent protection with fast (μs-level) shutdown to protect valuable test objects.
Limitations and Best Practices
RPG testing generates electromagnetic interference (EMI) that can mask low-magnitude PD signals. Mitigation includes shielded test chambers, ferrite clamps on all cables, and differential PD sensors. Also, keep total cable length under 5 meters to avoid pulse reflection artifacts. Always run a reference test with a known PD-free object (e.g., a Teflon block) to confirm system noise floor below 5 pC.
Future Outlook
Next‑generation repetitive pulse generators will integrate real‑time PD analysis and machine learning for automated pass/fail decisions. Optical triggering and all-solid-state designs will push repetition rates beyond 100 kHz while reducing size and cost. For high‑voltage equipment manufacturers and utilities, adopting RPG‑based diagnostics today means staying ahead of reliability requirements for the renewable‑rich grid of tomorrow.
In summary, a repetitive pulse generator is no longer just a test tool—it is a strategic instrument for understanding and improving dielectric system durability under realistic, repetitive electrical stresses.
