Dry-type transformers play a crucial role in power systems, and their safe and stable operation directly affects the reliability of the entire power grid. During the operation of dry-type transformers, partial discharge is one of the key factors affecting their insulation performance and service life. Partial discharge typically occurs within air gaps, impurities, or areas of concentrated electric field within the insulation material. Although the discharge energy is relatively small, its long-term presence gradually degrades the insulation material, eventually leading to insulation breakdown. Therefore, accurate detection and effective prevention of partial discharge are of great significance for ensuring the safe operation of dry-type transformers.
Accurate detection of partial discharge in dry-type transformers requires a combination of techniques. Electrical testing is the most direct and commonly used method. A partial discharge detector is connected between the transformer's high-voltage terminals and ground, using the detection impedance to pick up the discharge pulse signal, and then analyzing parameters such as the amplitude, frequency, and phase distribution of the partial discharge. Oscilloscopes and radio interference meters are commonly used equipment in electrical testing, capable of visually displaying the characteristic waveforms of the discharge, helping to determine the type and severity of the discharge. In addition, ultrasonic testing is widely used for partial discharge localization. By detecting the ultrasonic signals generated by the discharge, the exact location of the discharge point is determined using the acoustic-electric time difference, providing accurate information for subsequent maintenance.
Besides electrical and ultrasonic testing methods, ultra-high frequency (UHF) testing technology has also demonstrated unique advantages in partial discharge detection of dry-type transformers in recent years. UHF testing utilizes the ultra-high frequency electromagnetic waves generated by partial discharge, receiving signals through a UHF sensor to achieve online monitoring and localization of the discharge. This method features strong anti-interference capabilities and high sensitivity, making it particularly suitable for partial discharge detection in complex electromagnetic environments. Furthermore, the high-frequency current transformer (HFCT) method, which involves installing an HFCT on the equipment's grounding wire to detect the high-frequency current generated by the power distribution diode (PD), is also an effective partial discharge detection method, offering advantages such as convenient installation and strong anti-interference capabilities.
Preventing partial discharge in dry-type transformers requires attention to multiple aspects, including design, manufacturing, installation, and operation and maintenance. During the design phase, the insulation structure should be optimized, and the electric field should be rationally arranged to avoid partial discharge caused by concentrated electric fields. Simultaneously, high-quality insulation materials should be selected to reduce internal air gaps and impurities, improving insulation performance. During manufacturing, process parameters should be strictly controlled to ensure the quality of key processes such as vacuum casting, drying, and curing, avoiding partial discharge caused by process defects. During installation, it is essential to ensure the cleanliness and tightness of all transformer components to prevent discharge phenomena caused by poor contact or floating potential.
During the operation and maintenance phase of dry-type transformers, regular inspections and condition monitoring are crucial measures for preventing partial discharge. Using methods such as infrared thermography, ultrasonic testing, and online partial discharge monitoring, the transformer's operating status can be monitored in real time, allowing for the timely detection and handling of potential partial discharge defects. Simultaneously, maintaining a clean and dry operating environment for the transformer is vital to prevent insulation performance degradation due to dust and moisture. For dry-type transformers with long operating times, preventative tests should be conducted regularly to assess trends in insulation condition and identify and eliminate potential partial discharge hazards early.
Furthermore, strengthening partial discharge management of dry-type transformers requires establishing a sound detection and evaluation system. A detailed partial discharge detection plan should be developed, clearly defining the detection cycle, methods, and standards to ensure the standardization and effectiveness of the detection work. For partial discharge phenomena detected during inspection, PRPD spectrum analysis and discharge signal localization technology should be combined to accurately determine the type and location of the discharge, providing a scientific basis for subsequent maintenance work. Simultaneously, a partial discharge data archive should be established to track and analyze the detection results over the long term, providing data support for transformer condition assessment and lifespan prediction.
