The electrical quantity monitoring of partial discharge in power transformers mainly includes the monitoring of internal charge distribution, electrical signal tracking, and insulation performance monitoring of insulating materials. Common monitoring methods include high-frequency instrument monitoring, current-voltage alternating conversion, and ultra-wideband frequency measurement.
1. Ultra-High Frequency Partial Discharge Monitoring
Ultra-high frequency partial discharge monitoring mainly utilizes the powerful data analysis capability of computers to effectively track the loss of charge by comparing the input and output charge differences at both ends of the transformer, thereby directly visualizing the damaged parts of the insulation layer, facilitating timely maintenance by technicians. The disadvantage of this method is that due to the complex internal structure of power transformers and collisions during charge flow, certain errors may be introduced into computer measurements and data acquisition.
2. Ultra-Wideband Partial Discharge Monitoring
The ultra-wideband partial discharge monitoring method is suitable for partial discharge detection in large industrial transformers. By utilizing high-frequency spectrum scanning and low probability of inaccuracy, it can simultaneously monitor the insulation layers of transformers over a wide range. Due to its advantages of wide monitoring range, comprehensive coverage, and large information collection, it is widely applied in partial discharge monitoring of transformers in large-scale operating equipment.
3. Non-Electrical Measurement Methods for Partial Discharge
Non-electrical measurement methods for partial discharge were initially applied in biology and chemistry, mainly for detecting and tracking trace charges in organisms. With the development of modern science and technology, disciplines can communicate well with each other, especially those with related research content, where professional measurement methods can be well shared. This method uses chemical quantitative analysis to determine the chemical properties of ions inside the transformer, analyze chemical cycles, and thus identify regions with active chemical properties. Similar to non-electrical measurement methods are the transformer oil chromatography online monitoring method and transformer oil hydrogen concentration online monitoring, collectively known as the three major chemical methods for transformer partial discharge monitoring.
4. Optical Fiber Technology Detection Method for Partial Discharge
Optical fiber technology is currently a relatively successful ultrasonic detection method. Combining optical fiber technology with partial discharge detection in power transformers has achieved technological innovation in transformer partial detection. Using optical fiber for partial discharge detection has obvious advantages: the optical fiber propagates unidirectionally within the transformer's internal path, thus avoiding the repetitiveness of partial discharge signals and preventing secondary effects on composite circuits. The measurement principle is that when the insulation layer of a power transformer is broken down, the ultrasonic signal emitted from the discharge location propagates along the path of the optical fiber, without collisions of charge volumes during the process, thereby avoiding additional charge loss. When the charge propagates to a certain extent, an external modem connected to a computer extracts the electrical signal generated by the partial discharge, converts it into data information, and imports it into the connected computer, which then performs high-speed quantitative calculations.
5. Infrared Detection Method for Partial Discharge
Infrared detection is also applied to partial discharge detection in power transformers. Infrared detection is based on the temperature rise at the partial discharge point, utilizing the thermal imaging principle of infrared detectors to achieve hot spot measurement. However, due to the complexity of transformer structure and heat transfer processes, it is very difficult to directly detect partial discharge located inside the transformer body using infrared imaging methods. Currently, infrared detection for transformers is effective for external faults (including poor conductor connections, eddy currents in the tank caused by magnetic flux leakage, cooling device failures, and transformer bushing faults, etc.).
Electromagnetic Interference and Suppression in Partial Discharge Detection
Partial discharge detection in transformers can most directly and effectively reflect the actual insulation condition of the transformer. However, in actual measurements, due to constraints from external environmental factors, the measurement results are often degraded, and in severe cases, the measurement work may even be unable to continue.
The factors that prevent partial discharge detection from proceeding normally are diverse and can be classified into different categories according to different classification conditions. Common interferences include periodic interference, pulse-type interference, white noise interference, and laboratory shielding interference. Targeted suppression measures should be taken for different types of interference. As of the current interference suppression situation, no completely effective method has been found. Existing measures all have some adverse factors to varying degrees and have a narrow applicability. According to relevant professional reports, a more advanced digital anti-interference processing system is currently being established. With the help of modern scientific and technological means, good progress has been made. It is hoped that with the continuous development of related research work, a new type of anti-interference system for transformer partial discharge with strong specificity and wide applicability can be developed in the future.
The ultimate goal of partial discharge detection is to better ensure the safety performance of power transformers. With the continuous improvement of computer technology and digital signal processing technology in the power industry, partial discharge detection can provide sufficient data support for the overall performance improvement and upgrading of power transformers, and will be more widely applied in the future.
