Electrical equipment such as motors, transformers, solenoid valves, reactors, relays and other types of electromagnetic winding electrical devices have the most vulnerable and easily failing insulation structure in their enameled wire winding insulation. During operation, when the equipment is subjected to grid surges, operational overvoltages, lightning overvoltages, temperature thermal aging, mechanical vibration wear, etc., it is very likely to have insulation breakdown in the winding interlayers, micro short circuits, weakened interlayer insulation, local discharge and other latent defects. Such defects cannot be effectively detected through conventional insulation resistance tests or power frequency withstand tests. In the early stage, there are no obvious abnormalities, but after operation, it is very likely to cause winding burnout, interphase short circuits, equipment fire and other major failures.
The insulation interlayer electrical strength tester (official name in the industry: interlayer impulse withstand test instrument) is based on the principle of pulse impulse test and is specifically used to assess the electrical strength of winding interlayers and layer insulation. It can accurately identify minor insulation defects and is a core dedicated equipment for non-destructive testing, factory quality inspection, maintenance re-inspection, type test. This article systematically elaborates on the working principle, test procedures, on-site application scenarios, equipment selection methods, technical points and usage precautions of the instrument, providing complete technical references for electrical testing, manufacturing quality inspection and equipment operation and maintenance.
I. Basic Working Principle of the Instrument
The insulation interlayer electrical strength tester uses the core detection principle of high-voltage steep-front pulse impulse method. The internal high-voltage energy storage capacitor charges to the set test voltage and rapidly discharges to the tested winding within a microsecond time frame, forming a steep high-voltage impulse pulse.
The winding itself consists of conductor inductance L, winding resistance R, interlayer distributed capacitance C, forming a second-order oscillation circuit. Under the action of the impulse pulse, a free decay oscillation waveform is generated. The number of turns, wire diameter, winding process, interlayer insulation state directly determine the amplitude, frequency, attenuation speed, waveform area, phase and all characteristic parameters of the oscillation waveform.
II. Interlayer Impulse Withstand Test Process and Characteristics
The test process is divided into two stages: benchmark establishment and comparison determination. The specific process is as follows:
1. Benchmark waveform acquisition: Select a qualified and parameter-standard standard winding for the impulse test and store the standard oscillation waveform.
2. Tested winding detection: Apply a pulse impulse to the tested winding under the same test voltage and test conditions, and collect the measured waveform.
3. Intelligent difference determination: The instrument compares the amplitude difference, area difference, coincidence degree, attenuation coefficient, harmonic component of the two waveforms through built-in algorithms, and calculates the comprehensive difference rate. The deviation value is within the set allowable threshold and is judged as qualified; if the waveform distortion is severe and the difference exceeds the limit, it is judged as having interlayer insulation defects, interlayer micro short circuits, winding number deviation, winding fabrication defects, etc.
This test is a non-destructive test. The pulse duration is extremely short and the discharge energy is low. It does not cause insulation damage to qualified and intact windings, but only breaks through the insulation weak points. It balances the detection sensitivity and safety.
III. Relevant Test Standards and Specifications
Based on domestic mandatory standards for electrical equipment, test method standards, and special regulations for motors and transformers, the current applicable standards, test requirements, voltage selection rules, and qualification determination norms are as follows:
(1) Applicable National and Industry Standards
1. GB 14711-2022 “General Safety Requirements for Small and Medium-sized Rotating Motors”: Specifies the basic insulation safety requirements for rotating motors, clearly stipulates interlayer impulse test as a mandatory test item for motors, standardizes the test voltage level, test validity requirements, and constraints on winding insulation assessment indicators.
2. GB/T 22719.1-2022 “Interlayer Insulation Test for AC Low-Voltage Motors – Part 1: Test Method”: The core basic standard for interlayer tests in China, details the pulse impulse test method, test conditions, waveform comparison principle, test voltage selection rules, qualification determination basis, test procedures, and test safety requirements. 3. GB/T 22719.2-2022 “Inter-turn Insulation Test for Shunt-Wound Windings of AC Low-Voltage Motors – Part 2: Test Limits”: It clearly stipulates the impulse test voltage values, waveform difference allowable limits, and non-conformity determination criteria for different rated voltages and power motors. These are the direct basis for factory mass production inspection and type test.
4. JB/T 9615.2-2013 “Inter-turn Insulation Test Method and Limits for Shunt-Wound Windings of AC Low-Voltage Motors”: This is a traditional mechanical industry motor-specific standard. It details the test procedures for three-phase asynchronous motors, single-phase series-excited motors, and single-phase induction motors, and is widely used in the motor manufacturing industry.
5. GB/T 1094.10 “Power Transformers – Part 10: Sound Level Measurement and Guidelines for Inter-turn Insulation Test of Windings”: This standard is applicable to the electrical strength test of winding insulation for transformers and transformers-in-a-box.
6. GB/T 5171 Series Standard for Small-Power Motors: The basis for factory inter-turn detection of winding insulation for household appliances, miniature motors, and electric tools.
(II) Basic Provisions of the Test Standards
1. Environmental Requirements
Ambient temperature: 5℃～40℃; Relative humidity ≤85%; No strong electromagnetic interference, no corrosive gases, no dust; The instrument must be reliably grounded, and the test site must have good insulation.
2. Voltage Selection Procedure
The standard clearly stipulates that the impulse test voltage should be selected according to the rated working voltage of the tested winding, following the multiple principle:
Low-voltage low-power winding (rated voltage ≤ 110V): Test pulse voltage 1500V～2500V;
Low-voltage general-purpose motor (rated voltage 220V/380V): Test pulse voltage 3000V～5000V;
High-voltage winding, high-power industrial motor, special transformers: Test pulse voltage 6000V～10000V.
Core principle: The impulse test voltage should be ≥ 3～5 times the rated voltage of the winding, taking into account the defect detection capability and non-destructive test requirements. It is strictly prohibited to conduct arbitrary over-voltage tests to cause normal insulation breakdown.
3. Test Procedure Specifications
(1) Power-on self-check of the instrument, completing internal high-voltage discharge circuit self-check and grounding detection;
(2) Set the test voltage, waveform difference threshold, and number of impulse tests;
(3) Collect the standard qualified winding reference waveform and lock for storage;
(4) Connect the tested winding, ensuring good contact of the test terminals and no external parallel components;
(5) Single impulse or multiple consecutive impulse tests, the instrument automatically collects waveforms, performs calculation and comparison;
(6) Output the determination result and waveform difference data. Unqualified cases will trigger an automatic sound and light alarm;
(7) Test completion, the internal high-voltage capacitor of the instrument automatically discharges. The discharge must be completed before the test line can be removed.
4. Determination Procedure
According to GB/T 22719.2, the waveform comprehensive difference rate is used as the core determination index:
Difference rate ≤ 5%: Inter-turn insulation is intact, without defects, and is determined as qualified;
5% < Difference rate ≤ 15%: The insulation is weak, with potential hazards, belonging to a critical product;
Difference rate > 15%: There is a micro-short circuit in the inter-turn, insulation damage, or incorrect winding number, and is determined as unqualified.
Three-phase motors also require comparison of waveforms between each two phases. If any two-phase deviation exceeds the limit, the winding is determined to be unbalanced and have inter-turn faults.
5. Test Safety Provisions
During the entire test process, the high-voltage end must not be touched; The grounding resistance of the instrument must meet safety requirements; Forced delay discharge is required after the test; Live equipment and damp windings must not be tested directly; Multiple windings in parallel must not be tested simultaneously to avoid waveform interference and misjudgment.
Post time: May-09-2026