What Technical Means Are Used for 35kV Combined Transformer Fault Diagnosis？

For fault diagnosis and handling of 35kV combined transformers, the following technical means can be adopted:

Insulation Fault Diagnosis

Use equipment such as high-voltage test transformers, power frequency withstand voltage testers, and partial discharge detection systems to conduct a comprehensive assessment of the insulation performance of combined transformers. When the insulation resistance is found to be lower than 1000MΩ or the dielectric loss factor tanδ exceeds 0.5%, an application for shutdown and maintenance should be made immediately. For SF₆ equipment, the presence of gas leakage can be determined using an infrared leak detector or a pressure monitoring system.

Ferromagnetic Resonance Diagnosis

Identify the presence of resonance by analyzing changes in zero-sequence voltage (3U₀) and three-phase voltage unbalance through fault recording. When 3U₀ voltage is found to gradually increase or three-phase voltages are severely unbalanced, the possibility of ferromagnetic resonance should be considered. In addition, the risk of resonance can be assisted in judgment by monitoring changes in system parameters (such as the ratio of capacitive reactance to inductive reactance) and operation records (such as ground recovery and switching operations).

Electromagnetic Interference Diagnosis

Use electromagnetic compatibility testing equipment to evaluate the electromagnetic compatibility performance of combined transformers. Methods such as monitoring partial discharges via capacitive coupling, detecting discharge locations with ultrasonic waves, and observing abnormal temperature rises through infrared thermal imaging can identify the degree of influence of electromagnetic interference. For combined transformers in a GIS environment, it is also necessary to monitor the intrusion of high-frequency transient electromagnetic waves into low-voltage acquisition units.

Mechanical Vibration Diagnosis

Use acceleration sensors to monitor vibration waveforms and identify abnormal frequencies through spectrum analysis. By comparing with standard vibration signals, it can be judged whether there is vibration caused by partial discharge or mechanical structural looseness. In addition, infrared temperature measurement can also help detect local overheating caused by poor contact due to vibration.

Secondary Circuit Fault Diagnosis

Check the status of secondary fuses, measure the resistance of secondary circuits, and observe abnormal instrument indications. When a secondary fuse of a certain phase is found to be blown, check whether the indications of the voltmeter, power meter, etc. of that phase are reduced; if an open circuit in the secondary circuit is found, it will be accompanied by a loud "buzzing" sound and abnormal instrument indications, and power should be cut off for processing in a timely manner. In addition, partial discharge measurement can also detect discharge phenomena caused by abnormalities in the secondary circuit.

Calibration and Load-Related Fault Diagnosis

Use a three-phase calibration system to apply three-phase voltage and current simultaneously, simulate actual working conditions, and evaluate the measurement performance of the combined transformer. By comparing the error differences between the single-phase method and the three-phase method, the degree of influence of electromagnetic interference on measurement accuracy can be judged. In addition, infrared temperature measurement can also monitor abnormal temperature rises caused by overload.

SF₆ Gas Leakage Diagnosis

Use equipment such as infrared imaging leak detectors, wavelet analysis signal processing systems, and pressure monitoring devices to conduct a comprehensive assessment of the sealing performance of SF₆ equipment. Infrared imaging leak detection can visually locate leak points, while wavelet analysis can improve detection accuracy, making it suitable for monitoring micro-leaks. For SF₆ equipment with severe leaks, it should be immediately taken out of operation for maintenance.