Dielectric strength testing is the core method for evaluating the electrical performance of insulating materials. Its testing methods and criteria mainly follow the national standard system. Currently, the series of standards GB/T 1408 “Test Methods for Electrical Strength of Insulating Materials” constitute the general testing basis in this field. These series of standards are in line with the IEC 60243 series documents of the International Electrotechnical Commission and are the guiding technical specifications for conducting electrical strength measurements of solid insulating materials under power frequency, direct current, and impulse voltages.
General testing standard system
According to the different types of test voltages, the GB/T 1408 series standards are divided into three independent parts, respectively stipulating the corresponding test conditions and operation requirements:
GB/T 1408.1 – 2016 “Electrical Strength Test Methods for Insulating Materials – Part 1: Test at Power Frequency (48 Hz – 62 Hz)” This part is a basic general standard and is applicable for determining the short-term electrical strength of solid insulating materials under power frequency (48 Hz – 62 Hz) conditions. It is the recommended basis for most conventional insulating material tests.
GB/T 1408.2 – 2016 “Insulating Materials – Methods of Electrical Strength Test – Part 2: Additional Requirements for DC Voltage Tests” This part serves as a supplement to Part 1, proposing additional technical requirements for the specific characteristics of tests conducted under DC voltage conditions. It is applicable for the specialized assessment of insulation performance under DC conditions.
GB/T 1408.3 – 2016 “Insulating Materials – Test Methods for Electrical Strength – Part 3: Supplementary Requirements for 1.2/50 μs Impulse Test” This part is also a supplementary standard, which specifies additional procedures for conducting electrical strength tests under the standard impulse voltage waveform of 1.2/50 μs. It is applicable for evaluating the insulation performance under simulated lightning or operational overvoltage scenarios.
Typical material-specific test standards
For the characteristics of specific types of insulating materials, relevant industries have formulated more targeted specific test standards. These standards usually refer to the GB/T 1408 series as the basic testing methods, while elaborating on exclusive requirements such as sample preparation, electrode systems, and criteria. Typical standards include:
GB/T 1695-2005: Applicable to vulcanized rubber, for the determination of alternating current breakdown voltage strength and withstand voltage.
GB/T 3333-1999: Applicable to cable paper, for the alternating current breakdown voltage test.
HG/T 3330 series: Applicable to breakdown strength determination of insulating paint films.
GB/T 5591.3-2018: For electrical insulating flexible composite materials, the electrical strength test items refer to the provisions of GB/T 1408.1.
GB/T 7752-2025: Applicable to alternating current dielectric strength and withstand voltage tests of insulating adhesive tapes (this standard was released in August 2025 and will be officially implemented in March 2026).
Key elements of general test procedures
Based on the above standards, the test procedures of dielectric strength testers usually include the following common technical elements.
Test method selection
Common test methods mainly include:
Breakdown test: Continuously and uniformly increase the voltage at a specified rate until the sample breaks down, and record the breakdown voltage value.
Withstand voltage test: Raise the voltage to a predetermined value and maintain it for a specified period, observing whether the sample breaks down or flashes.
Stepwise voltage increase test: Increase the voltage in pre-set step levels and maintain for a specific duration to determine the withstand voltage level.
Setting of voltage increase rate
The voltage increase rate directly affects the test results. Depending on different standards and material characteristics, the rate can be adjusted and selected within the range of 0.1 kV/s to 5 kV/s, and the specific value must follow the clear provisions of the corresponding standards.
Test medium and anti-flashover measures
To avoid interference from surface discharge of the sample on the test results, the sample and electrode system are usually immersed in transformer oil for testing. For specific occasions, tests can also be conducted in a dry and clean air medium, but effective measures must be taken to prevent surface flashover.
Standard electrode system configuration
The general electrode configuration scheme is a coaxial metal cylindrical electrode system with an upper electrode diameter of 25 mm and a lower electrode diameter of 75 mm, suitable for standard tests of plate-shaped solid insulating materials.
Sample state adjustment requirements
The environmental temperature and humidity of the sample have a significant impact on its electrical strength. The standard stipulates that the sample should be subjected to state adjustment for no less than 24 hours under standard atmospheric conditions of temperature (23 ± 2) °C and relative humidity (50 ± 5)%, before conducting the test.
In actual testing operations, the test personnel should first determine the most applicable technical specifications based on the category of the tested material from the general standards (GB/T 1408 series) and specialized standards. For the vast majority of conventional solid insulating materials, GB/T 1408.1-2016 is the most fundamental and commonly used test basis. At the same time, strictly following the operation procedures for sample pre-treatment, electrode installation, voltage rise program, and medium environment, etc., is the prerequisite for ensuring the accuracy, comparability, and repeatability of the test results.
Post time: Aug-05-2026