I. The Dual Logic of the Test System
The insulation testing of high-voltage electrical equipment involves a pair of complementary evaluation dimensions: one is to assess the insulation’s tolerance to overvoltage, and the other is to diagnose latent defects within the insulation. The former corresponds to the power frequency withstand voltage test, which examines whether the insulation undergoes a penetrating breakdown or flashover by applying a voltage far above the rated voltage and maintaining it for a specified period, resulting in a binary determination of “pass / fail”. The latter corresponds to the partial discharge measurement, which captures weak discharge signals generated by bubbles, impurities, or stratification positions within the insulation with a picocoulomb level of sensitivity, identifying potential hazards that can pass the withstand voltage test but deteriorate over time during long-term operation.
There are significant differences in the engineering significance of the two. The withstand voltage test belongs to a limit pressure test, used to determine whether the insulation can withstand high voltage; the partial discharge measurement belongs to a precise defect diagnosis, used to determine the insulation’s health status. Integrating the two functions into the same system can simultaneously complete the strength assessment and defect screening during a single voltage increase process, avoiding cumulative damage to the insulation caused by multiple voltage increases and improving the test efficiency and integrity of the detection information.
II. The Normative Framework of the Standard System
The operation of the power frequency withstand voltage and partial discharge test system requires compliance with a multi-layer standard system, divided into three levels: general technical requirements, test method specifications, and specific equipment standards.
2.1 General Technical Baseline
GB/T 16927.1—2011 “High Voltage Test Technology – Part 1: General Definitions and Test Requirements” belongs to the top-level specification for high-voltage tests, stipulating the generation methods of test voltage and current, test procedures, result processing, and qualification criteria. This standard adopts IEC 60060-1 for modification, establishing a unified framework for test circuit setup, voltage waveform control, and measurement uncertainty assessment. For the power frequency withstand voltage scenario, the standard sets clear requirements for test voltage waveforms (typically requiring a total harmonic distortion of less than 5%), ramp-up rate, and duration.
2.2 Specialized Specifications for Partial Discharge Measurement
GB/T 7354—2018 “High Voltage Test Technology – Partial Discharge Measurement” is the core method standard for partial discharge detection, modified to IEC 60270. This standard defines key parameters such as apparent charge, clarifying the setup methods of test circuits and measurement circuits, analog and digital measurement methods, calibration procedures, and interference discrimination criteria. The standard is applicable to AC voltage tests of 400 Hz and below, covering electrical measurement methods for impulse-type partial discharge, and providing reference guidance for non-electrical positioning methods.
IEC 60270:2025 has been released in its fourth edition, extending the scope to 500 Hz, reflecting the increasing demand for partial discharge measurement in power electronic equipment power supply scenarios.
2.3 Differentiation of Specific Equipment Standards
The requirements for withstand voltage and partial discharge for different types of equipment vary significantly. Low-voltage complete equipment follows GB/T 7251.1—2023, with the withstand voltage of the main circuit set according to the rated insulation voltage level, for example, when 300 V < Ui ≤ 690 V, the test voltage is 2500 V, and the duration is generally 1 second. The partial discharge test for wires and cables adopts GB/T 3048.12—2025, specifically stipulating the partial discharge measurement method for extruded insulation power cables. The requirements for gas-insulated metal-enclosed switchgear refer to DL/T 1630—2016, detailing ultrahigh frequency partial discharge detection technical content, including sensor installation, sensitivity calibration, and interference suppression.
The differentiation of standards indicates that the configuration and operation of the power frequency withstand voltage and partial discharge test system require matching corresponding product standards based on the type of tested equipment, and cannot rely solely on general specifications for testing.
III. Technical Key Points of System Integration
The integration of the power frequency withstand voltage and partial discharge test system is not a simple superposition of two types of equipment. Instead, it achieves compatibility between high-voltage output and weak signal detection under the condition of no partial discharge.
The non-discharge test transformer is the core component of the system. Under the rated voltage, its own partial discharge level must remain at an extremely low level. For gas-filled type, it is generally ≤ 5 pC, and for high-end configuration, it can be ≤ 2 pC to prevent the noise of the equipment itself from masking the true discharge signals of the tested item. DL/T 848.3—2004 has specific regulations on the technical conditions of non-discharge test transformers. According to the insulation medium classification, gas-filled (SF₆) has a small volume and low maintenance workload; epoxy bucket oil-immersed type has a low impedance and smaller waveform distortion. The selection needs to be comprehensively weighed based on the test scenario and maintenance conditions.
The design of the test circuit needs to simultaneously meet the power demand of the withstand voltage test and the anti-interference requirements of partial discharge measurement. The parameter matching between the coupling capacitor, detection impedance, and measurement instrument will directly affect the detection sensitivity. According to the requirements of GB/T 7354, the measurement system must be calibrated before it is put into use, and the performance of the calibrator should meet the normative clauses in the appendix B of the standard. For medium and high-level systems, such as 250 kVA/500 kV level, a complete integrated solution is often adopted, integrating the operation console, transformer, voltage divider, coupling capacitor, and partial discharge instrument to achieve full automation of the entire process of voltage boosting, withstand voltage timing, partial discharge collection, voltage reduction, and report generation.
Interference suppression is a key challenge in engineering implementation. Factory test experience of ultra-high voltage transformers shows that partial discharge signals are highly susceptible to external electromagnetic interference. Factors such as sharp points, suspended potentials, and the operation of surrounding equipment can cause abnormal fluctuations in the partial discharge reading. Reliable shielding filtering measures, standardized grounding design, and interference detection before the test are the basis for obtaining reliable partial discharge data.
IV. Key Points of Standard Implementation in Engineering
Converting the standard provisions into implementable test operation procedures requires attention to the following key points:
The timing control of the test procedure. The timing arrangement of power frequency withstand voltage and partial discharge measurement needs to comply with the standard logic. The conventional operation mode is: measure the partial discharge starting voltage (PDIV) before the withstand voltage test, continuously monitor the partial discharge level during the withstand voltage process, and re-measure the partial discharge extinction voltage (PDEV) after the withstand voltage test. GB/T 7354 stipulates the voltage application process, including pre-applied voltage, selection of measurement voltage, and time interval requirements. For special test items such as cables, GB/T 3048.12—2025 specifies the preparation of samples, test equipment, and operation procedures.
The differentiated understanding of qualification criteria. The withstand voltage test criteria are relatively clear: no breakdown or flashover within the specified time is considered qualified. The partial discharge measurement criteria are more complex, as it is necessary to determine whether the partial discharge quantity exceeds the limit and also assess whether the partial discharge characteristics are abnormal. The standard usually provides a quantitative limit for apparent charge, while the analysis of discharge spectrum morphology, such as discharge phase distribution and pulse repetition rate, can provide more diagnostic information. The content related to digital processing and positioning in the appendix of GB/T 7354 provides technical means for in-depth diagnosis.
Strict implementation of safety regulations. Safety requirements must be implemented throughout the high-voltage test process. Before the test, it is necessary to confirm that the pre-test items such as insulation resistance are qualified. The test area should be physically isolated and marked with warning signs. After the test, use a discharge rod to reliably ground. These basic procedures requirements are the bottom line for the safe operation of the system. System selection and on-site operation essentially involve converting standard provisions into reliable judgments of the insulation status of the tested equipment. In this process, accurately understanding the standards and rigorously controlling interference are equally important.
Post time: Sep-28-2026