is a key step to ensure the long-term reliable operation of these devices. Partial discharge can accelerate the aging of insulating materials, which may lead to equipment failures. Below is some information and methods about partial discharge detection for voltage transformers and current transformers:
Detection Methods
Pulse Current Method: This is one of the earliest methods applied to partial discharge detection. By connecting a detection impedance or current transformer into the detection circuit, the pulse current caused by partial discharge is obtained, and combined with a digital signal processing system, relevant information about partial discharge is obtained.
Ultrasonic Detection: This method measures the size and location of partial discharge by detecting the ultrasonic signals generated by partial discharge. The frequency band of ultrasonic sensors is approximately 70~150 kHz (or 300 kHz) to avoid ferromagnetic noise from the core and mechanical vibration noise from dry-type transformers.
Gas Chromatography: After partial discharge occurs, the gases produced by the insulating materials of power transformers are mainly acetylene and hydrogen. Gas chromatography can determine the existence of problems in transformers by detecting these two gases. However, the detection accuracy of this method is relatively low because it is highly sensitive to all gases.
High-Frequency Instrument Monitoring Method: This method uses high-frequency instruments to monitor the high-frequency signals generated during partial discharge, suitable for online monitoring of partial discharge.
Ultra-Wideband Measurement Method: This method detects partial discharge by measuring the ultra-wideband signals generated, and is suitable for partial discharge detection in large industrial transformers.
Non-Electrical Measurement Methods: For example, using thermal imaging cameras to detect temperature changes caused by partial discharge.
Detection Process
Preparation Phase: Ensure that all test equipment has been calibrated and maintained according to relevant regulations.
Select Detection Method: Choose the most suitable detection method based on actual conditions.
Implement Detection: Carry out partial discharge detection according to the selected method.
Data Analysis: Carefully analyze the detection results to determine the location and severity of partial discharge.
Maintenance Recommendations: Develop a maintenance plan or repair measures based on the detection results.
Detection Standards
Partial discharge measurement should be carried out simultaneously with AC withstand voltage test: This means that during the AC withstand voltage test, partial discharge measurement can be performed simultaneously to reduce equipment outage time.
For voltage transformers and current transformers with voltage levels of 35~110kV, partial discharge measurement can be conducted on a 10% sampling basis: For transformers at this voltage level, a 10% sampling rate can be taken for partial discharge measurement. If the partial discharge amount is found not to meet the specified requirements, the sampling ratio should be increased.
For transformers with voltage levels of 220kV and above, partial discharge measurement should be carried out when there is suspicion about insulation performance: For transformers at higher voltage levels, if there are any signs of doubt about their insulation performance, partial discharge measurement should be performed.
During partial discharge measurement, the applied primary voltage should be monitored on the high-voltage side: This indicates that when conducting partial discharge measurement, the applied primary voltage should be monitored on the high-voltage side.
Detection Techniques and Measurement Methods
Partial discharge detection techniques: Including but not limited to pulse current method, ultrasonic detection, ultra-high frequency (UHF) detection, etc.
Measurement methods: Including direct measurement methods and indirect measurement methods, such as ultrasonic detection and ground wave detection, etc.
Interference Suppression
Test whether there is interference before the circuit is energized: The main sources are switching operations in circuits outside the test circuit, nearby high-voltage electric fields, motor commutation, and radio transmission, etc.
Interference generated after the test circuit is energized: This interference usually increases with voltage, including partial discharge from the test transformer itself, corona or poor contact discharge on high-voltage lines, partial discharge on the low-voltage power supply side, and interference caused by coupling into the measurement circuit through the test, etc.
Measurement Voltage and Apparent Discharge Quantity
Measurement voltage: Should meet specific voltage level requirements.
Apparent discharge quantity: Should comply with relevant standards.
Conclusion
Partial discharge detection of voltage transformers and current transformers is a complex process involving multiple detection techniques and methods. Correctly selecting and using appropriate detection tools and techniques is crucial for ensuring the safe operation of the power system. If you need more detailed technical parameters or operating guidelines, please inform me of the specific details so that I can provide you with more precise assistance.
