I. Startup and Preheating
Set the time base display mode switch to the “Ellipse” position.
The preheating duration of the instrument should be no less than 5 minutes to ensure the stability of the equipment operation.
Take measures to protect the instrument from direct sunlight and keep it away from strong magnetic sources to prevent interference with the test.
II. System Calibration
Calibration is the core step to ensure the accuracy of partial discharge measurement data. The specific operation process is as follows:
1. Wiring operation
Complete the wiring according to the test circuit diagram. Before applying the test voltage, connect the output end of the calibration pulse generator to both ends of the test sample, and connect the red terminal lead to the high-voltage end of the test sample.
2. Inject calibration pulse
Inject a fixed charge quantity square wave pulse into the test sample. The commonly used charge quantities include 50pC, 100pC, and 200pC.
3. Adjust gain
Adjust the coarse and fine adjustment knobs of the amplifier to control the height of the injected pulse on the oscilloscope screen within 2 cm, ensuring that the readings of the digital meter and the pointer meter are consistent with the injected known charge quantity.
4. Lock parameter settings
After calibration, the fine adjustment knob should not be changed and should remain at the position during calibration to avoid parameter deviation.
5. Remove calibration equipment
After the calibration work is completed, the connection between the calibration square wave generator and the test circuit must be disconnected to prevent the equipment from being broken down and damaged during the high-voltage test.
III. Partial Discharge Test Procedure
1. Background Noise Measurement
In the state where the test sample is not connected or there is no discharge on the test sample, apply the test voltage to the rated value and record the background noise data. The background noise should be lower than the threshold of the concerned discharge quantity. It is recommended that the background noise be ≤ 20pC; for a qualified test system, the background partial discharge quantity should be ≤ 5pC.
2. Voltage Rise Measurement and PDIV Determination
Connect the high-voltage test circuit power supply and set the zero mark switch to the “On” position.
Start the voltage rise from a value far below the expected PDIV (partial discharge initiation voltage) at a uniform rising rate. The recommended rate is 0.5 – 1 kV/s.
Slowly increase the test voltage until two zero mark pulses appear on the ellipse interface.
Adjust the “Ellipse Rotation” switch to adjust the ellipse angle to facilitate the observation of the discharge phenomenon.
Continue the voltage rise and observe the state where the equipment first shows continuous discharge.
The PDIV determination criterion: When the discharge quantity first exceeds the specified threshold (such as 50pC) during the test, the corresponding test voltage value is the partial discharge initiation voltage.
3. Continuous Voltage Rise Measurement
(1) Voltage Rise Standard
Factory test: The test voltage is increased to 1.5 – 2 times the rated voltage; Preventive test: The test voltage is increased to 1.2 – 1.5 times the rated voltage.
(2) Stabilization Time
According to the test requirements, stabilize the voltage for a conventional duration of 1 – 5 minutes.
(3) Observation and Record Content
Real-time observe and record the maximum discharge quantity (Qmax), discharge pulse repetition rate, and PRPD graph features.
(4) Discharge Quantity Reading Method
When the discharge pulse height on the display screen is within the range of 0.2 – 2 cm and the effective digit of the digital meter reading does not exceed 120.0, convert the reading of the digital meter head with the coarse adjustment switch to the gear ratio multiplier to obtain the actual discharge quantity value; the full-scale value of the digital meter head is 100, and if the value exceeds the limit, adjust the gain coarse adjustment switch to the low gain gear position.
4. Voltage Drop Measurement and PDEV Determination
Reduce the test voltage at the same rate as the voltage rise and record the voltage value at which the discharge pulse first drops below the specified threshold. This value is the PD extinction voltage (PDEV). Note: The voltage rise rate will affect the PDIV value, while the voltage amplitude, stabilization time, and voltage drop rate will affect the PDEV value.
IV. Report Generation
After the test is completed, an automatic test report can be generated, which includes test data and voltage rise curve graph, and supports A4 paper report printing. The complete report should include the following contents: sample identification, environmental conditions, test circuit, calibration records, PDIV/PDEV values, the maximum discharge amount at each voltage level, PRPD spectra, and test conclusions.
V. Key Parameters and Qualification Criteria
1. Discharge Limit Requirements
System background discharge: ≤ 5 pC
High-voltage motor factory test: Discharge amount ≤ 50 pC
Preventive test for running motor: After subtracting background noise, the discharge amount should be ≤ 100 pC
2. Defect Diagnosis of PRPD Spectra
By observing the position and distribution characteristics of discharge pulses on the elliptical time-base interface, the type of insulation defect can be determined. The specific features are as follows:
Internal discharge: The discharge pulses are symmetrically distributed near the peak values of the positive and negative half-waves, presenting a “running rabbit’s ears” shape.
Surface discharge: The phase of the discharge pulses has a slight deviation, and the pulse dispersion is relatively large.
Electrical discharge: The discharge pulses are concentrated near the voltage peak, with a narrow and isolated pulse shape.
3. Analysis of PDIV/PDEV Ratio
For some insulating materials, when the voltage first rises to PDIV, only intermittent local discharge will occur; in some cases, the discharge amount will increase rapidly, and the discharge phenomenon disappears after stabilizing for a period of time. If the PDEV value is lower than 0.6 times the PDIV, it indicates that the insulation of the sample may have serious defects.
Post time: May-21-2026