Partial discharge (PD) testing of cables is a core technical method for assessing cable insulation condition and identifying potential equipment defects. Currently, the relevant test standards are undergoing a critical update phase. Accurately understanding the key requirements and evolution trends between old and new standards can provide direct and effective practical guidance for test operators, equipment managers, and procurement personnel. This paper systematically reviews the technical aspects of cable partial discharge testing from two dimensions: core test equipment and the test standard system and its updates.
1. Main Test Equipment
The cable partial discharge testing system consists of an integrated collaborative circuit in which various components work together to fully realize the application, coupling, acquisition, and analysis of partial discharge signals. According to GB/T 3048.12-2025, the standard test circuit must be equipped with essential core devices and supporting auxiliary equipment, as detailed below:
(1) High-voltage Power Supply
The high-voltage power supply serves as the energy source for the entire test system, and its performance directly determines the validity of test results. The standard clearly specifies that test high-voltage power supplies should preferably use test transformers or series resonant devices, with a typical output frequency range of 45 Hz to 55 Hz. The output waveform should closely resemble a standard sine wave, and the ratio of peak value to root-mean-square (RMS) value must be controlled within √2 ± 0.05. For testing extra-long cables, power supplies with frequencies not less than 10 Hz may be used upon mutual agreement.
Currently, two types of high-voltage power supplies are commonly used: power-frequency series resonant test systems and 0.1 Hz ultra-low-frequency withstand voltage testers. Among them, the 0.1 Hz ultra-low-frequency tester is better suited for on-site inspection of long cables.
(2) Core Components of Partial Discharge Testing
1. Coupling Capacitor
The coupling capacitor is connected in series within the high-voltage circuit. Its primary function is to couple high-frequency pulse signals generated by partial discharges into the measuring impedance while isolating the power-frequency high voltage, thereby preventing high-voltage breakdown and protecting downstream measurement equipment. The typical capacitance range is 100 pF to 1000 pF. It must possess excellent high-frequency response characteristics and sufficient voltage withstand capability. The performance of this device directly affects signal coupling efficiency and overall measurement sensitivity.
2. Measuring Impedance and Detection Instrument
The measuring impedance, also known as the input unit, is installed between the coupling capacitor and the detection instrument. Its main function is to convert the collected high-frequency current signal into a recognizable voltage signal, enabling matched signal transmission. The core component of the detection instrument is the partial discharge detector, integrating amplifier, filter, oscilloscope, and other functional modules.
Current mainstream digital partial discharge detectors feature intelligent functions such as phase-resolved spectrum analysis, multi-channel synchronized sampling, and automatic noise suppression. With a low detection threshold down to 0.1 pC, they can accurately capture weak partial discharge signals.
3. Discharge Quantity Calibrator
The calibrator is a key device ensuring the accuracy of test measurements. Prior to any test, a known charge amount must be injected into the test circuit via the calibrator to complete system scale factor calibration. The standard specifies clear performance requirements: the injected charge error range should be -30% to +10%, pulse rise time must not exceed 0.1 μs, and pulse tail length must be no less than 50 μs. For cable tests exceeding 100 meters in length, the calibration capacitance must not exceed 150 pF.
4. Terminal Impedance and Reflection Suppressor
During testing of long cables, reflected waves often occur at the far end of the cable, interfering with measurement accuracy. To eliminate such interference, terminal impedance or reflection suppressors must be installed at the far end of the cable. The terminal impedance value must match the cable’s characteristic impedance, typically 50 ohms or 75 ohms. Before use, the device must undergo applicability verification to ensure it effectively absorbs traveling wave energy and eliminates reflection interference.
5. Dual Pulse Generator The dual-pulse generator is a dedicated core device used during the debugging phase of test circuits, primarily for evaluating circuit characteristics. The equipment can output two sets of equal pulses with an adjustable pulse interval ranging from 0.2 microseconds to 100 microseconds, and a pulse rise time not exceeding 20 nanoseconds. By plotting dual-pulse response curves, it accurately distinguishes whether the tested cable is short or long, thereby determining whether reflection suppression measures are required, ensuring compliance and accuracy in testing.
(3) Auxiliary Equipment
In addition to the above core equipment, a complete partial discharge testing system also includes supporting auxiliary devices and accessories. These mainly consist of a high-voltage voltmeter for calibrating voltage indications, an insulation resistance tester for assessing overall cable insulation condition, as well as specialized connecting wires, terminal oil cups, and other basic components, comprehensively ensuring smooth test operations.
II. Test Standard System
Current cable partial discharge testing relies on two core standards to establish a complete and standardized framework, covering test methods and equipment calibration respectively. These standards work in tandem, each fulfilling its role, to support full-process compliance in testing.
(1) Test Method Standards
GB/T 3048.12 “Test Methods for Electrical Properties of Wires and Cables—Part 12: Partial Discharge Test” serves as the primary guidance standard for testing. It clearly specifies technical parameters of test equipment, sample preparation, complete test procedures, and calibration methods, forming the core basis for implementation, operation, and acceptance of cable partial discharge tests.
The latest version, GB/T 3048.12-2025, was released on October 5, 2025, and officially implemented on May 1, 2026, fully replacing the previous version, GB/T 3048.12-2007.
(2) Equipment Calibration Standards
JB/T 10435 “Calibration Method for Cable Partial Discharge Testing Systems” is a dedicated calibration specification designed to verify whether partial discharge testing systems meet metrological requirements. It provides exclusive technical criteria to ensure measurement accuracy and operational reliability of test equipment.
III. Key Updates in Test Method Standards
The new edition, GB/T 3048.12-2025, fully aligns with the international standard IEC 60885-3:2015. Compared to the 2007 version, it introduces multiple technical improvements and upgrades, with key changes focused on detection capability, calibration requirements, and scope of application.
(1) Significantly Enhanced Detection Sensitivity
The updated standard refines detection requirements, strengthening the ability to identify and detect minute defects within cable insulation. It effectively identifies early-stage hidden flaws such as insulation impurities, micro air gaps, and microscopic cracks, greatly reducing the risk of undetected early hazards and substantially improving the effectiveness and reliability of cable partial discharge testing.
(2) More Detailed and Standardized Calibration Requirements
The new standard provides standardized definitions for two critical parameters—background noise and detection sensitivity—and introduces corresponding calibration methods. This update prevents signal distortion caused by excessive system background noise or improper calibration, effectively avoiding masking of genuine partial discharge signals by noise, thus ensuring precision and credibility of test measurements.
(3) Expanded Scope of Application
The revised standard adds classification and compatibility requirements for non-partial-discharge cable terminals, enabling adaptation to more field testing scenarios. It effectively addresses the limitations of the previous version regarding insufficient adaptability to special terminal types and limited coverage, enhancing the standard’s universality and practicality.
IV. Optimization Directions for Equipment Calibration Standards
The updated JB/T 10435 standard has undergone multiple improvements in calibration procedures, technical indicators, and conceptual definitions, further standardizing the calibration process for partial discharge testing systems and enhancing both efficiency and technical rigor. Key optimization points include: (1) Simplifying Calibration Procedures to Improve Operational Efficiency
The new standard significantly streamlines the voltage calibration steps. For example, in the case of high-voltage power waveform peak factor calibration, the previous version required measurements at six voltage points—10%, 20%, 30%, 70%, 80%, and 90%. The updated standard reduces these to three key points: 10%, 50%, and 90%. This adjustment substantially shortens the calibration time for individual test systems while maintaining calibration accuracy, thereby effectively enhancing efficiency in equipment calibration and acceptance.
(2) Quantifying Background Noise and Clarifying Acceptance Criteria
For the first time, the new standard formally defines background noise and establishes clear quantitative technical indicators. It explicitly requires that background noise levels in both no-load and loaded conditions must not exceed 4 picocoulombs. This quantified criterion provides a unified and clear basis for judging compliance during equipment factory acceptance, routine verification, and fault diagnosis, standardizing calibration practices. Currently, mainstream digital partial discharge detectors in the industry can maintain background noise below 1.0 picocoulomb under both operating conditions, exceeding the standard’s requirements.
(3) Harmonizing Technical Definitions for International Compatibility
The new standard refines the core definition of sensitivity by abandoning the previous approach of defining sensitivity as “twice the background interference.” Instead, it aligns with the international standard IEC 60885-3:2015, redefining sensitivity as the minimum discharge level detectable by the equipment. This revision eliminates conceptual differences between domestic and international standards, unifies technical evaluation criteria, and lays the foundation for international recognition of test results and global technical alignment.
Post time: Jun-01-2026