Overall Composition of the Detection System
To conduct off-line partial discharge detection on transformers, a complete high-voltage test circuit needs to be set up. According to the detection functions and principles, the instruments and equipment are divided into two categories: the pulse current method system for benchmark quantification and the ultrasonic / ultra-high frequency detector for auxiliary location.
Overview of Core Equipment Configuration
(1) Pulse Current Method (Quantitative Benchmark)
No partial discharge test transformer: It provides a high-voltage power source and its own partial discharge quantity should be less than 10pC, serving as the core power source for the test.
No partial discharge variable frequency power supply: It provides variable frequency input to the test transformer and, together with the resonant reactor, forms a series resonant device, which can reduce the overall weight of the equipment.
No partial discharge excitation transformer: It is used to match the variable frequency power supply with the test circuit and should meet the requirement of partial discharge quantity ≤ 10pC to achieve electrical isolation and voltage boosting.
No partial discharge coupling capacitor and detection impedance: They are used to extract the discharge pulse signal. The capacitor couples the high-voltage end pulse to the detection impedance, forming a complete measurement circuit.
Partial discharge detection instrument main unit: It completes measurement, display and data recording, and can display the partial discharge quantity in pC and PRPD/PRPS diagrams.
Calibration pulse generator: It is used for test circuit calibration. Before the test, a standard signal needs to be injected into the circuit to complete the calibration of the partial discharge quantity.
(2) Auxiliary Detection Equipment (Location and Screening)
Ultrasonic partial discharge tester: It can precisely locate the discharge source. It adopts a handheld design and supports contact / non-contact detection, and can identify external discharges.
Ultra-high frequency partial discharge detector: It has anti-interference capability and is suitable for related power equipment. It detects signals in the 300–2000MHz frequency band and can effectively avoid corona interference.
High-frequency current transformer: It is used to detect the discharge signal on the grounding wire. It adopts a clamp structure and can be directly clamped on the transformer core, clamping piece or bushing grounding wire.
Multi-functional inspection instrument: It is used for comprehensive detection and rapid screening. It integrates TEV, ultrasonic, high-frequency and other sensors and is suitable for on-site rapid inspection.
Detailed Explanation and Selection Suggestions for Partial Discharge Test System Equipment
1. Complete Set of Pulse Current Method Devices
This device is the standard configuration for quantitative detection and can output the apparent discharge quantity in picocoulombs (pC), which is the core basis for determining whether the equipment is qualified.
The core components usually include a no partial discharge test transformer, a protection resistor, a no partial discharge coupling capacitor, a detection impedance and a partial discharge detection instrument main unit.
For large-capacity transformers, a series resonant method is generally adopted, using a no partial discharge variable frequency power supply and a no partial discharge reactor to replace the traditional test transformer. This system has a relatively large overall weight but requires a small power supply capacity, making it convenient for on-site transportation.
Key selection indicators: The background noise level of the equipment, that is, its own partial discharge quantity, must be much lower than the allowable partial discharge quantity of the test sample. The typical requirement is less than 10pC.
2. Multi-sensor Fusion Auxiliary Location Equipment
To make up for the inability of the pulse current method to locate, the following portable detection instruments are usually used on-site:
Ultrasonic detector: It can achieve precise location. By attaching to the oil tank wall, it receives the discharge sound wave and is suitable for discovering internal suspended particles or mechanical looseness problems in the transformer.
Ultra-high frequency detector: It is used for anti-interference detection. Through built-in or external antennas, it receives electromagnetic waves above 300MHz and can effectively avoid on-site air corona interference, with a high signal-to-noise ratio.
High-frequency current transformer: It is used for auxiliary verification. It can be clamped on the transformer core, clamping piece or bushing grounding wire to detect the discharge pulse on the grounding wire.
Test Process and Usage Suggestions
Calibration First, Then Testing
Before applying voltage for testing, a standard signal must be injected into both ends of the test sample using a calibration pulse generator. The gain of the detection instrument should be adjusted to ensure the accuracy of the partial discharge quantity measurement.
Combination of Main and Auxiliary, Cross-Verification
The pulse current method is used as the standard for determining whether the partial discharge quantity exceeds the limit. If over-limit discharge is detected, immediately use a portable ultrasonic or UHF instrument to locate the transformer body and determine the specific discharge location.
Interference Elimination
On-site offline tests are prone to interference from broadcast signals, other test circuits, etc. The characteristics of UHF detectors that can avoid low-frequency interference or ultrasonic detectors that are not affected by electromagnetic interference can be utilized to effectively distinguish real discharge signals from external noise.
Post time: Mar-24-2026