Component Testing — Dielectric & ESD Testing

The challenge

The challenge in component testing is reproducing the stress the component will actually experience in service — not a simplified approximation that is easier to generate in a lab.

For cables and connectors, standard dielectric withstand tests apply a steady voltage at mains frequency and check whether breakdown occurs. This tells you something, but not everything. A connector that holds at 50 Hz may fail early in service if the actual stress is repetitive fast-rising transients, because the failure mechanisms are different. Partial discharge — localised ionisation in voids, at interfaces, and around conductor edges — is a cumulative process. It erodes insulation material pulse by pulse. A 50 Hz test that runs for a minute does not replicate ten years of operation at switching frequency.

Electric vehicles are where this gap is most consequential. Modern traction inverters switch at 10–100 kHz, with dV/dt rates at the winding terminals that can reach tens of kilovolts per microsecond. The motor windings, busbars, phase cables, and connector housings are exposed to these transients continuously. The insulation system is not being stressed at the system voltage — it is being stressed by the shape of the switching waveform, repeated millions of times per hour, throughout the vehicle's operating life.

The voltage level is also rising. 400 V architectures are giving way to 800 V systems, with some platforms moving to 1000 V and beyond, driven by faster charging and reduced cable weight. Higher system voltage raises the partial discharge inception voltage requirement across the insulation system. Components that were adequate at 400 V may not be at 800 V — and the failure mode is not immediate breakdown but accelerated degradation that shortens service life in ways that are difficult to detect without the right test methodology.

The mechanism

Pulsed high-voltage testing developed as a way to expose insulation failure modes that AC tests miss and to accelerate ageing in a controlled, reproducible way.

The underlying logic is straightforward. Insulation degradation under repetitive transient stress is proportional to the charge deposited per pulse, the repetition rate, and time. A pulsed test that replicates the actual service waveform — amplitude, rise time, and repetition rate — produces ageing data that maps directly onto operating conditions. A test that uses a different waveform and extrapolates is making assumptions about the degradation mechanism that may not hold.

For EV powertrain components, this means testing with waveforms that match the inverter output. Fast rise times in the range the winding terminals actually see. Bipolar transients if the inverter topology produces them. Sustained operation at the switching frequency the drive system runs, not a reduced rate chosen to make the test equipment's job easier. The goal is not to find the breakdown voltage of a pristine component — it is to characterise how the insulation behaves under the stress profile it will accumulate over a decade of operation.

Partial discharge measurement under pulsed excitation adds a further dimension. The discharge behaviour at switching-relevant frequencies reveals which voids and interfaces in the insulation are active, how they respond to the specific dV/dt of the drive system, and whether the component is on a degradation trajectory that matters. This is not information that AC partial discharge testing provides — the discharge physics at 50 Hz and at 50 kHz are not the same.

Where we fit

The parameters that define an insulation test are the parameters that define the stress: voltage amplitude, rise time, pulse duration, repetition rate, and waveform shape. Equipment that fixes any of these removes a degree of freedom from the test design.

Rise time is particularly significant for EV component testing. Partial discharge inception voltage and insulation stress are both rise-time dependent — a winding insulation system that shows acceptable discharge behaviour under a slowly rising field may discharge at lower voltage under a fast transient, because the charge distribution across the insulation layers has not equilibrated. Testing EV motor windings with a rise time of microseconds when the inverter delivers tens of nanoseconds at the terminals produces optimistic results. Adjustable rise time means the test waveform can be matched to the drive system, not assumed away.

High continuous frequency is the other constraint that separates general-purpose HV equipment from what pulsed insulation testing requires. Accelerated ageing tests run at or near the service switching frequency to compress the ageing timeline predictably. For EV applications this means sustained operation in the 10–100 kHz range for the duration of the test — hours, not seconds. Equipment that derates thermally at sustained high repetition rates cannot do this test correctly.

Other capabilities relevant to insulation and component testing:

Bipolar pulsing — many inverter topologies stress winding insulation with bipolar transients; the test waveform needs to match the topology
Wide voltage range — 400 V, 800 V, and emerging 1000 V+ architectures on the same platform; no re-tooling as the system voltage of the component under test changes
Arbitrary sequencing — withstand tests, step-stress tests, and accelerated ageing protocols all require precise control over the number of pulses delivered and how they're spaced; sequencing steps give that control natively, not as a workaround
Overcurrent protection — a breakdown event during a withstand or ageing test creates a sudden short circuit; the generator has to survive that fault without damage to itself or the rest of the test setup

Relevant capabilities

Relevant products

Testing insulation on EV components or high-voltage cables?

Tell us what you're working on — we'll figure out the right solution together.

Get in touch