Electrical insulation testing service

Electrical Insulation Testing Service – Comprehensive Evaluation of Dielectric Strength, Insulation Resistance and Long‑Term Reliability for Electrical Equipment and Components

As an ISO/IEC 17025 accredited independent testing laboratory, we offer comprehensive electrical insulation testing services to manufacturers, engineering contractors, and quality assurance teams across the power cable, electrical equipment, electronics, renewable energy, railway, and aerospace sectors. Electrical insulation performance is a critical factor in ensuring the safe and reliable operation of electrical systems – from high‑voltage power cables and transformers to printed circuit boards and connector assemblies. Our testing protocols evaluate the dielectric strength, insulation resistance, partial discharge behaviour, and long‑term ageing resistance of a wide range of insulating materials and finished products. All methods are aligned with IEC, ASTM, EN, and GB/T standards, including IEC 60243‑1 (Electrical strength of insulating materials – Test methods), ASTM D149 (Dielectric breakdown voltage of solid insulating materials), IEC 60156 (Insulating liquids – Determination of the breakdown voltage at power frequency), GB/T 1408 (Test method for the determination of the electrical strength of insulating materials), and GB/T 1695 (Test method for the breakdown voltage of vulcanized rubber). Our reports are recognised by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance.

Test Articles and Insulating Materials We Regularly Assess

Our electrical insulation testing laboratory accommodates a wide range of materials, components, and finished products. Typical test articles include:

Power and communication cables – medium‑ and high‑voltage XLPE cables, low‑voltage power cables, control cables, coaxial cables, and fibre optic cables with metallic strength members
Electrical equipment and components – transformers, switchgear, circuit breakers, motors, generators, and capacitor banks
Printed circuit boards (PCBs) and electronic assemblies – populated PCBs, power modules, and control units
Connectors, terminals and splices – electrical connectors, terminal blocks, and splice kits
Solid insulating materials – polymer films, sheets, varnishes, tapes, and compound insulations
Insulating liquids – transformer oils, silicone fluids, and ester‑based dielectric fluids
Insulating gases – SF₆ and other dielectric gases used in high‑voltage switchgear
Medical electrical equipment – diagnostic devices, therapeutic equipment, and implantable electronics
Battery systems and energy storage modules – battery packs, cells, and battery management systems (BMS)

Dielectric Strength and Breakdown Voltage Testing – Verifying the Insulation Margin

AC dielectric strength test – IEC 60243‑1 / ASTM D149 / GB/T 1408 – We apply a continuously increasing AC voltage (50 Hz) to a solid insulating material specimen (typically a sheet or film of known thickness) at a specified rate (e.g., 500 V/s or 2 kV/s) until dielectric breakdown occurs. The breakdown voltage (in kV) is recorded, and the dielectric strength (in kV/mm) is calculated. For typical insulating materials used in low‑voltage equipment, a dielectric strength of ≥ 20 kV/mm is required; for high‑voltage applications, values exceeding 40 kV/mm are often specified.
DC dielectric strength test – ASTM D149 / IEC 60243‑1 – For materials that are used in DC systems (e.g., battery packs, photovoltaic systems), we perform a DC dielectric strength test by applying a DC voltage ramp at a specified rate (typically 500 V/s). The breakdown voltage and the dielectric strength are recorded. The DC dielectric strength is typically 10‑20 % higher than the AC dielectric strength for most insulating materials.
Dielectric breakdown of insulating liquids – IEC 60156 / ASTM D1816 / GB/T 507 – For transformer oils and other insulating liquids, we measure the breakdown voltage (BDV) using a standardised test cell with spherical electrodes (per IEC 60156). The liquid sample is stirred (or left unstirred, depending on the method), and the voltage is applied at a specified rate (typically 2 kV/s). The breakdown voltage is recorded and compared to the specified minimum value (e.g., ≥ 30 kV for new transformer oil, ≥ 50 kV for high‑grade oil).
Dielectric breakdown of insulating gases – IEC 60243‑1 / GB/T 11023 – For gases such as SF₆ or air, we measure the breakdown voltage at a specified gas pressure using a pressurised test cell. The breakdown voltage is a function of the gas pressure and the electrode geometry.
Breakdown voltage of thin films and laminates – for precision insulation layers – For thin polymer films (e.g., PET, PI, PTFE) used in capacitors and flexible circuits, we perform the dielectric strength test using small‑diameter electrodes (e.g., 6 mm or 12 mm) and a controlled ramp rate. The results are reported as the average dielectric strength from multiple tests (typically 5‑10 specimens).

Insulation Resistance and Volume Resistivity – Measuring the Intrinsic Insulating Property

Insulation resistance (IR) test – ASTM D257 / IEC 60093 / GB/T 1410 – We measure the insulation resistance of a solid insulating material (or an assembled component) by applying a DC voltage (typically 100 V, 500 V, or 1 000 V, depending on the insulation class) and measuring the current leakage after a specified time (e.g., 1 minute, 10 minutes). The insulation resistance (in MΩ) is reported. For high‑quality insulation, a value of ≥ 100 MΩ at 500 V is typical; for critical applications, values > 1 GΩ are required.
Volume resistivity (specific resistance) – ASTM D257 / IEC 60093 / GB/T 1410 – For solid insulating materials, we calculate the volume resistivity (in Ω·cm) from the measured insulation resistance and the specimen dimensions. The volume resistivity is a material property that is independent of the specimen size. For most polymer insulations, the volume resistivity is ≥ 10¹⁴ Ω·cm. A value below 10¹⁰ Ω·cm indicates that the material is semi‑conductive and may not be suitable as an insulator.
Surface resistivity – ASTM D257 / IEC 60093 / GB/T 1410 – We measure the surface resistivity (in Ω) of the material surface by applying the voltage between two ring electrodes placed on the surface. The surface resistivity is important for assessing the risk of surface tracking and flashover in humid environments.
Polarisation index (PI) – IEC 60034‑27 / GB/T 20160 – For high‑voltage equipment (e.g., motors, generators, transformers), we measure the insulation resistance at 1 minute and at 10 minutes (applying a DC voltage of 500 V or 1 000 V). The polarisation index is the ratio of the IR at 10 minutes to the IR at 1 minute. A PI ≥ 1.5 is generally considered acceptable; a PI < 1.0 indicates a degraded insulation system.
Dielectric absorption ratio (DAR) – IEC 60034‑27 / GB/T 20160 – Similar to the PI, we measure the insulation resistance at 60 seconds and at 30 seconds. The DAR is the ratio of the IR at 60 seconds to the IR at 30 seconds. A DAR ≥ 1.3 is considered acceptable.

Partial Discharge (PD) Testing – Detecting Incipient Defects

Partial discharge measurement – IEC 60270 / GB/T 7354 – For high‑voltage equipment (cables, transformers, switchgear), we perform partial discharge (PD) testing to detect localised electrical discharges that occur within voids, cracks, or contaminated areas of the insulation. The PD measurement is performed at a sensitivity of 1‑5 pC, using a calibrated PD detector and a coupling capacitor. The apparent charge (in pC) and the phase‑resolved PD pattern are recorded. A PD level of ≥ 10 pC is considered a significant defect for most HV equipment.
PD inception voltage (PDIV) and PD extinction voltage (PDEV) – We determine the PD inception voltage (the voltage at which PD starts) and the PD extinction voltage (the voltage at which PD stops) by gradually increasing the voltage and monitoring the PD activity. A high PDIV and a small hysteresis between PDIV and PDEV are indicators of good insulation quality.
PD pattern analysis – for identifying the defect type (void, surface discharge, corona) – We analyse the phase‑resolved PD pattern (PRPD) to identify the type of discharge: (a) internal voids – characterised by symmetrical PD patterns at low frequencies; (b) surface discharges – characterised by asymmetric patterns; (c) corona discharges – characterised by high‑frequency pulses at the voltage peaks. The pattern analysis helps to identify the root cause of the insulation defect.
PD testing at elevated temperatures – for assessing thermal dependence – For equipment that operates at elevated temperatures, we perform PD testing at the specified service temperature (e.g., 80 °C, 100 °C) using a temperature‑controlled chamber. The PD level and the PDIV are recorded as a function of temperature.

Dielectric Loss and Dissipation Factor – Assessing the Quality of the Insulation

Dielectric loss (tan δ) and capacitance measurement – IEC 60156 / ASTM D150 / GB/T 1409 – We measure the dielectric loss (loss factor, tan δ) and the capacitance of the insulating material (or the assembled component) using a bridge‑type (Schering bridge) or a digital tan δ meter at a specified frequency (typically 50 Hz or 1 kHz). The tan δ is a measure of the energy dissipated in the insulation; a low tan δ (< 0.01) indicates a high‑quality insulation with low losses.
Relative permittivity (dielectric constant) – ASTM D150 / IEC 60250 / GB/T 1409 – From the capacitance measurement and the specimen geometry, we calculate the relative permittivity (εr). The εr is a material property; for most polymer insulations, it ranges from 2.0 to 4.0. A high εr indicates a high polarisation, which can be beneficial for certain applications (e.g., capacitors) but detrimental for high‑frequency cables.
Tan δ at elevated temperatures and frequencies – for characterising the insulation performance under service conditions – We measure the tan δ as a function of temperature (up to 200 °C) and frequency (50 Hz to 1 MHz). The temperature dependence of tan δ provides information about the glass transition temperature (Tg) and the thermal stability of the insulation.

Environmental and Ageing Testing – Assessing Long‑Term Reliability

Thermal ageing – ASTM D3045 / ISO 2578 / GB/T 7141 – We age the insulating material in a temperature‑controlled oven at a specified temperature (typically 100 °C, 135 °C, or 155 °C) for a specified period (e.g., 7 days, 28 days, 168 days). After ageing, we perform dielectric strength, insulation resistance, and tan δ tests to assess the degradation of the insulation. A significant reduction in dielectric strength (> 20 %) or a significant increase in tan δ (> 50 %) indicates thermal ageing.
Humidity and condensation testing – IEC 60068‑2‑30 / GB/T 2423.4 – We expose the insulating material to cyclic humidity (e.g., 25 °C to 55 °C, 90‑95 % RH) for up to 5 cycles. After conditioning, we perform insulation resistance and dielectric strength tests to assess the moisture resistance of the insulation. A reduction in insulation resistance of > 50 % is considered a failure.
Salt spray and corrosion testing – ASTM B117 / ISO 9227 / GB/T 10125 – For insulation materials used in coastal and marine environments, we perform salt spray testing (5 % NaCl fog, 35 °C) for 24‑240 hours. After the test, we inspect the insulation for any signs of corrosion, blistering, or electrical degradation.
Chemical resistance – ASTM D543 / ISO 175 / GB/T 11547 – We test the resistance of insulating materials to common chemicals (acids, alkalis, oils, solvents) by immersing the specimen in the chemical for a specified period (e.g., 168 hours) and then measuring the dielectric strength and the insulation resistance.
UV and weather resistance – ASTM G154 / ISO 4892‑3 / GB/T 16422 – For outdoor insulation materials (e.g., for overhead lines, photovoltaic systems), we expose the specimen to UVA‑340 lamps (0.89 W/m², 60 °C, 8h dry / 4h condensation cycles) for 500‑2 000 hours. After exposure, we measure the dielectric strength and the surface condition.

Regulatory Compliance and Product Certification – Supporting Industry Standards

Our electrical insulation testing services are performed in accordance with the most widely used international and national standards. The most commonly requested include:

IEC 60243‑1 – Electrical strength of insulating materials – Test methods – the primary standard for dielectric strength testing
ASTM D149 – Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials – the North American standard for dielectric strength
IEC 60156 – Insulating liquids – Determination of the breakdown voltage at power frequency – for insulating liquids
ASTM D257 – Standard Test Methods for DC Resistance or Conductance of Insulating Materials – for insulation resistance and resistivity
IEC 60270 – High‑voltage test techniques – Partial discharge measurements – for partial discharge testing
ASTM D150 – Standard Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation – for tan δ and permittivity
GB/T 1408 – Test method for the determination of the electrical strength of insulating materials – the Chinese national standard for dielectric strength
GB/T 1695 – Test method for the breakdown voltage of vulcanized rubber – for rubber insulation
GB/T 1410 – Test method for volume resistivity and surface resistivity of solid insulating materials – for resistivity
GB/T 7354 – Partial discharge measurement – the Chinese national standard for PD testing

Report Acceptance and Regulatory Recognition

All electrical insulation tests are conducted under our ISO/IEC 17025 accreditation, using calibrated dielectric testers, insulation resistance testers, partial discharge detectors, and environmental chambers, all traceable to national and international reference standards. Our final test reports include: a complete description of the test article (material, dimensions, manufacturer), the test method and conditions (voltage level, temperature, humidity, test duration), the measured parameters (dielectric strength, breakdown voltage, insulation resistance, tan δ, partial discharge level), a statistical summary (mean, standard deviation, coefficient of variation), and a clear pass/fail verdict against your specified acceptance criteria. These reports are accepted by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance. All reports are issued in English, and bilingual (English/Chinese) versions are available upon request to facilitate submissions to domestic and international authorities and to support your global market access.