1.1 Zero Partial Discharge Variable Frequency Power Supply
As the control core of the entire test system, it provides a power source with continuously adjustable frequency and voltage. By precisely adjusting the output frequency, the entire test circuit can achieve resonance, providing a stable and controllable power foundation for subsequent voltage elevation tests. It is a key unit in regulating the entire testing process.
1.2 Zero Partial Discharge Excitation Transformer
Its primary function is to step up voltage and supply energy by increasing the low-voltage output from the variable frequency power supply, continuously delivering power to the resonant test circuit. Designed with special structural features and precision manufacturing, this equipment exhibits extremely low partial discharge levels, avoiding interference with transformer test results and meeting fundamental requirements for high-precision partial discharge testing.
1.3 Zero Partial Discharge Resonant Reactor
This is the core component enabling resonant voltage boosting. It forms a series resonant circuit together with the input capacitance of the tested transformer. Featuring a gas-insulated design, the reactor does not generate partial discharges during operation, eliminating test interference at the equipment level and ensuring the authenticity of test data.
1.4 Capacitive Voltage Divider
Primarily used to accurately capture and measure the test voltage applied to the transformer under test, it also feeds real-time high-voltage side voltage signals back to the system’s control unit. Based on real-time feedback, the system dynamically adjusts the output voltage to maintain stability, minimizing the impact of voltage fluctuations on the test.
1.5 Partial Discharge Detector
A dedicated device for directly detecting and observing partial discharge signals in transformers, integrating functions such as signal acquisition, amplification, filtering, data analysis, and display. It accurately captures weak discharge pulses generated inside the transformer and presents discharge data and waveforms via connected display terminals and analytical software, providing direct evidence for assessing insulation condition.
Principle of Zero Partial Discharge Withstand Voltage Testing
The entire test system operates based on the principle of series resonance. During testing, by adjusting the output frequency of the variable frequency power supply, the inductance of the resonant reactor is matched with the ground capacitance of the tested transformer, achieving a series resonance condition.
Once the circuit reaches resonance, a high voltage several times higher than the input voltage can be generated at either the reactor or excitation transformer terminal, stably applied to the transformer under test. The main advantage of this test mode lies in its extremely low input power requirement during resonance, along with a pure sine wave output, offering strong anti-interference capability and excellent adaptability. This makes it ideal for complex field conditions and represents the mainstream method for on-site partial discharge testing of power transformers.
Main Standards and Regulations for Partial Discharge Testing
Transformer partial discharge testing must strictly follow national and industry-specific standards to ensure uniformity in test methods, operational procedures, calibration rules, and acceptance criteria, guaranteeing standardization, accuracy, and authority. Key applicable standards are as follows:
3.1 GB/T 7354-2018 “Partial Discharge Measurement”
This is the general foundational standard for partial discharge measurement, aligned with international standards. It defines professional terminology, definitions, general measurement methods, and equipment calibration procedures, serving as the fundamental reference for all partial discharge tests.
3.2 GB 1094.3-2017 “Power Transformers – Part 3: Insulation Levels, Insulation Tests and External Insulation Clearances”
This is the core specialized standard for partial discharge testing of power transformers. It specifically specifies the voltage application method, standardized pressurization procedure, duration of voltage application, test operation guidelines, and criteria for equipment qualification—forming the essential basis for test execution and result evaluation.
3.3 GB 50150-2016 “Code for Handover Tests of Electrical Equipment Installation Projects” Applicable to handover tests prior to commissioning newly installed transformers, this document specifies the requirements for partial discharge (PD) testing of new transformers, including test conditions and acceptance limits, serving as a critical reference for verifying transformer insulation performance during project handover.
3.4 DL/T 417-2019 “Guidelines for On-site Partial Discharge Measurement of Electrical Equipment”
Focusing on complex field test environments characterized by multiple interferences and complicated operating conditions, this standard establishes specialized test guidelines, covering practical aspects such as suppression of background interference, PD fault localization, and data correction, providing technical guidance for accurate on-site testing.
Main Test Procedures and Parameters for Partial Discharge Testing
4.1 Basic Test Methods and Parameter Requirements
Transformer PD testing uniformly adopts the method of applying voltage on the low-voltage side while inducing voltage on the high-voltage side, following the long-time induced withstand voltage test procedure. To avoid core saturation affecting test results, the test power frequency is set between 100 Hz and 400 Hz—higher than the equipment’s rated frequency.
4.2 Standard Voltage Application Test Procedure
Pre-boost phase: First raise the test voltage to a lower preset value of 1.1 times the rated phase voltage, then continue increasing it to 1.5 times the higher working phase voltage. Maintain this voltage level stably for a period to observe the PD level. Proceed to the main test phase only after confirming that the discharge data shows no abnormal fluctuations and has stabilized.
Main test phase: Gradually increase the voltage to the standard-specified PD test voltage (not less than 1.58 times the rated phase voltage), then begin timing. The test duration follows the formula: T = 120 × (rated frequency / test frequency) seconds, with a minimum duration of no less than 15 seconds.
4.3 Acceptance Criteria for Partial Discharge Quantity
Handover test criterion: Under the specified test voltage conditions, internal partial discharge quantity of the transformer must be ≤100 pC.
Factory test criterion: For power transformers rated at 110 kV and above, the measured partial discharge quantity must be ≤100 pC.
Supplementary criteria: Throughout the entire voltage ramp-up process, the PD level must not show a continuous upward trend; during stable voltage testing, there should be no sudden, sharp fluctuations or abnormal variations in discharge data.
Key Points for On-site Partial Discharge Testing
5.1 Strict Control of Background Noise and Environmental Interference
On-site testing environments are complex, with external electromagnetic fields, grounding systems, and radio signals all potentially causing interference that affects PD signal accuracy. During testing, optical isolation technology should be employed to achieve complete electrical separation between the high-voltage test zone and the data acquisition and control zone, eliminating electrical interference at its source. Additionally, optimizing test wiring and installing filtering devices further suppresses external noise, ensuring collected signals represent actual discharges from the transformer.
5.2 Pre-test Self-check and Calibration of Test Equipment
Before connecting the transformer under test and commencing formal testing, the entire test system must undergo an open-circuit calibration. With no test object connected, raise the test voltage to the preset level and verify the inherent PD level of the test system itself. The system’s self-generated discharge must be <5 pC. This step effectively eliminates interference originating from the test equipment, ensuring all detected discharge signals originate solely from within the transformer under test—a crucial prerequisite for reliable test data.
5.3 Accurate Identification of Partial Discharge Types
Test operators must rely on output waveforms such as elliptical patterns, sine waves, and pulse phase distribution diagrams to accurately identify discharge types. By analyzing waveform characteristics, they can distinguish between internal bubble discharges, floating metallic particle discharges, and external corona interference, precisely differentiating genuine fault signals from noise. This provides precise technical support for subsequent analysis of internal insulation defects and assessment of equipment operational condition.
Post time: May-28-2026