Partial discharge (PD) detection is a core and effective technical means for diagnosing the insulation status of high-voltage power equipment, and is widely used in preventive tests and online monitoring of various high-voltage equipment such as transformers, GIS, power cables, and switch cabinets. With the continuous iteration of detection technologies, current PD detection has formed several mainstream detection principles such as pulse current method, ultra-high frequency method, ultrasonic method, and high-frequency current method. Different detection devices based on different principles have significant differences in core performance indicators such as value definition, frequency response, and detection sensitivity. Therefore, establishing a scientific and standardized equipment verification system and unifying verification standards to ensure the accuracy and comparability of PD detection data is a core focus of the measurement management work in the power industry.
I. Verification Standard System for Partial Discharge Detection Devices
(1) Basic Standards
The basis for the verification of partial discharge detection devices is derived from the International Electrotechnical Commission standard IEC 60270 “High Voltage Test Technology – Partial Discharge Measurement”, and the equivalent national standard GB/T 7354-2018. The sixth part of this standard specifically makes systematic and detailed regulations for the calibration of measurement systems in complete test circuits, clarifying the core principles for the calibration of partial discharge measurement systems: by injecting known charge quantities of simulated discharge pulses into the test circuit to precisely calibrate the overall gain and response characteristics of the measurement system. This core concept is the fundamental methodological basis for the compilation of all specialized partial discharge calibration specifications, providing a unified technical underlying logic for the verification work across the industry.
(2) Calibration Specifications for Pulse Current Method
The pulse current method is the most mature and widely used PD detection technology at present, with a conventional measurement frequency range of 10 kHz to 500 kHz. For such detection devices, a two-level specialized calibration specification system has been established in China, including the national metrological specification JJF 1616-2017 “Calibration Specifications for Partial Discharge Testers by Pulse Current Method” and the power industry specification DL/T 356-2010 “Calibration Specifications for Partial Discharge Measurement Instruments”. The applicable scenarios and metrological requirements of these two specifications are different, but the core calibration logic remains consistent, focusing on systematic calibration of key core parameters such as the linearity of device charge quantity, frequency bandwidth, and pulse resolution time to ensure the metrological accuracy of PD detection equipment.
II. Verification Methods for Different Technical Routes Detection Devices
(1) Verification of Ultrasonic Partial Discharge Testers
The ultrasonic method relies on the acoustic wave signals generated during partial discharge detection to locate and assess the severity of the fault. The equipment operates in a conventional working frequency range of 20 kHz to 500 kHz. For ultrasonic detection devices, the national special metrological specification JJF 1856-2020 “Calibration Specifications for Partial Discharge Testers – Part 1: Ultrasonic Partial Discharge Testers” has been issued. This specification clearly uses the acoustic wave emission transducer as the standard excitation source and formulates a dedicated verification process, focusing on the calibration of core performance such as amplitude linearity, frequency response, and detection directionality, applicable to the metrological traceability and performance verification of various contact-type ultrasonic partial discharge testers.
(2) Verification of High-Frequency Current Method Partial Discharge Testers
The high-frequency current method (HFCT) couples the local discharge signal through a high-frequency current transformer installed on the grounding wire of the device. The standard measurement frequency band is 3 MHz to 30 MHz. This frequency band is highly susceptible to interference from line distribution parameters, and the traditional pulse current method calibration mode cannot meet the calibration requirements of this method. To solve the problem of value traceability for such equipment, a national group standard T/GZJL 2-2023 “Calibration Method for High-Frequency Current Method Partial Discharge Tester” was introduced, which specifically establishes an exclusive calibration system for high-frequency current method detection equipment. It clearly adopts standard pulse generators and network analyzers to calibrate the system gain and transmission impedance, effectively filling the technical gap in the metrological traceability of high-frequency current method partial discharge detection equipment.
III. Revision and Update of the Verification Standards for Cable Partial Discharge Test Systems
The cable partial discharge test system is the core key equipment for the factory test and commissioning test of power cables. The original basis for its verification was JB/T 10435-2004 “Verification Method for Cable Partial Discharge Test System”. Currently, the standard has started the revision process and is expected to be officially released and implemented in 2026. Based on the draft for revision of the standard, this update focuses on engineering practicability and verification scientificity. The core technical adjustments are as follows:
1. Optimize the test voltage waveform peak coefficient inspection points. The original standard’s 6 rated voltage inspection points (10%, 20%, 30%, 50%, 70%, 90%) have been streamlined to 3 core inspection points (10%, 50%, 90%). Under the condition of fully guaranteeing the verification quality and not lowering the equipment assessment standards, the on-site and laboratory verification efficiency has been significantly improved.
2. Detail the verification rules for the test voltage output indication value. According to the voltage level of the tested equipment, set differentiated verification intervals. For equipment below 50 kV, set 1 inspection point for every 5 kV; for equipment from 50 kV to 300 kV, set 1 inspection point for every 10 kV; for equipment above 300 kV, set 1 inspection point for every 50 kV. This makes the verification plan more in line with the actual operating characteristics of different specifications of equipment, improving the scientificity and operability of the verification work.
3. Add verification requirements for background noise. Referencing the IEC 60270 international standard, clearly define the definition of background noise for the partial discharge test system, which is the various interference signals generated in the test circuit, including white noise, radio waves, rectifier equipment interference, etc. At the same time, it is clearly stipulated that the background noise level of the system shall not exceed 4 pC, strictly constraining the detection performance of the equipment in complex electromagnetic environments.
4. Optimize the verification system for partial discharge sensitivity. Referencing the IEC 60885-3 standard, revise the definition and verification method of the equipment sensitivity, focusing on the minimum stable detectable discharge quantity under the actual cable operating length and real test frequency conditions, making the equipment performance assessment indicators highly consistent with the actual engineering application scenarios.
IV. On-site Verification Method for Online Monitoring Devices
The online monitoring devices for partial discharge that have been put into operation, with the typical representative being the Ultra-High Frequency (UHF) partial discharge monitoring system, have their sensors mostly installed internally in GIS, transformers, etc., and cannot be disassembled for inspection. The traditional laboratory calibration method is not applicable. In response to this operation pain point, the industry has studied and applied the on-site verification technology based on the cross-comparison idea, which can achieve efficient verification of the monitoring devices of operating equipment.
The core theoretical basis of this technology is: for power equipment of the same voltage level and the same wiring method, the operating electromagnetic environment of different intervals and phases has a high degree of similarity, and the propagation law and attenuation characteristics of the partial discharge signals have stable comparable features. During the verification process, through the cross-amplitude comparison between phases and the mirror consistency comparison of the same sensor channel as input and output, instead of traditional amplitude evaluation, relative amplitude comparison is carried out to accurately detect various typical equipment defects such as sensor sensitivity attenuation, antenna gain abnormality, signal acquisition module failure, and unreasonable installation position. The cross-comparison method is not a substitute for standardized laboratory calibration; rather, it is an engineering-based supplementary solution for scenarios where equipment cannot be disassembled for calibration. This method does not require dedicated standard signal sources or coupling devices. It can complete the comparison and calibration by relying on the background noise of the equipment and the built-in calibration pulses of the system. The operation is simple, efficient, and suitable for annual equipment inspections and daily operation maintenance tasks involving rapid screening of device anomalies.
V. Precautions for Partial Discharge Device Calibration Work
To ensure the accuracy and effectiveness of the calibration results for partial discharge detection devices, it is necessary to standardize the calibration workflow. During actual operations, four key points need to be focused on: calibration cycle, standard instruments, environmental conditions, and result processing.
In terms of the calibration cycle, according to the requirements of standards such as JJF 1616-2017, the calibration cycle for conventional partial discharge detection devices should not exceed one year. For monitoring devices that operate continuously for a long time, the calibration cycle can be adjusted reasonably based on the equipment operation conditions, daily maintenance records, and historical calibration data. The longest calibration interval should not exceed three years.
In terms of the traceability of standard instruments, the standard pulse generators, standard capacitors, digital oscilloscopes, and other measuring instruments used for calibration must hold valid metrological verification or calibration certificates. The measurement uncertainty of the instruments must be better than one-third of the allowable error of the calibrated device to ensure the reliability of the calibration data from the source.
In terms of calibration environmental conditions, laboratory calibration requires strict control of environmental parameters. The laboratory temperature should be maintained between 15 ℃ and 35 ℃, the relative humidity should not exceed 80%, and the power supply voltage fluctuation should not exceed the rated value by ±10%. For on-site calibration operations, active measures should be taken to avoid strong electromagnetic interference sources. When there is a risk of interference, shielding protection measures should be taken in advance to eliminate the impact of environmental interference on the calibration results.
In terms of calibration result processing, the calibration certificate must clearly list core information such as the test data and measurement uncertainty of each calibration item. After the equipment is calibrated, the performance of the equipment should be determined based on the calibration results to ensure that it meets the usage standards. At the same time, the confidence level determination standard for subsequent detection data should be adjusted to ensure the effective application of the equipment detection data.
Post time: Jul-06-2026