Transformer Local Discharge Monitoring

Date: September 16, 2025 08:24:36

  1. Transformer partial discharge (referred to as "local discharge") refers to the transformer internal insulation medium under the action of electric field, the local area of non-penetrating discharge phenomenon, this discharge will not immediately cause insulation breakdown, but the long-term existence of the insulating material will continue to deteriorate, and ultimately may lead to serious insulation failures, so the local discharge monitoring is to ensure that transformer Therefore, local discharge monitoring is the core link to ensure the safety of transformer insulation.​
  1. The core principle of transformer discharge monitoring is to capture all kinds of physical signals generated in the process of discharge through special sensors, which cover electrical signals (such as pulsed current, ultra-high frequency electromagnetic wave), acoustic signals (such as ultrasonic) and optical signals, etc., and then through the signal processing and analysis technology, restore the real state of the discharge to provide a basis for fault judgment.​
  1. Pulsed current method is a commonly used electrical signal detection technology in transformer local discharge monitoring, which collects the pulsed current signal generated by the local discharge by connecting a special detection impedance in series at both ends of the transformer grounding circuit or winding. This method can directly reflect the charge size of the local discharge, and the measurement sensitivity is high, is one of the mainstream technology of the early local discharge monitoring, widely used in the transformer factory test and field offline detection, and now also gradually integrated into the online monitoring system.​
  1. Ultra-high frequency monitoring technology for the localization process of ultra-high frequency electromagnetic wave (frequency is usually in 300MHz-3GHz) for detection, localization occurs inside the transformer, will be accompanied by high-frequency electromagnetic radiation, ultra-high frequency sensors can be through the tank wall of the special window or built-in way to capture these signals. This technology has the advantage of strong anti-interference ability, can effectively avoid the influence of industrial frequency interference and other low-frequency interference signals in the power grid, and accurately locate the position of local discharge.​
  1. Ultrasonic monitoring technology focuses on the ultrasonic signal formed by the mechanical vibration of the local discharge (frequency generally in 20kHz-200kHz), ultrasonic sensors are usually installed in the outer wall of the transformer tank, and the monitoring is realized through the reception of ultrasonic vibration signals triggered by the local discharge. Because ultrasonic waves propagate in solid media when the attenuation is faster, the technology can better realize the spatial localization of the local discharge, and when used in combination with the electrical signal monitoring technology, it can greatly improve the accuracy of the judgment of the local discharge.​
  1. Transformer local-amplitude monitoring system signal processing is crucial, the original signal collected is often mixed with a large number of interference signals, such as external electromagnetic interference, equipment vibration noise, etc.. Therefore, it is necessary to remove the interference through filtering techniques (such as digital filtering, adaptive filtering), and then use signal amplification, waveform recognition algorithms, to extract the characteristic parameters of the local discharge signal (such as pulse amplitude, rise time, repetition frequency), in order to lay the foundation for subsequent analysis.​
  1. Pattern recognition of local discharge signals is a key technology for determining the type of local discharge, and different types of local discharges (e.g., insulation discharge along the surface, air gap discharge, corona discharge) correspond to different signal features. The monitoring system establishes a library of local discharge signal features, and adopts intelligent algorithms such as machine learning and neural network to match and identify the extracted signal features, so as to determine the specific types of local discharges and help operation and maintenance personnel analyze the root causes of faults.​
  1. The sensitivity of transformer local discharge monitoring directly affects the timeliness of fault warning, and a high-quality monitoring system should be able to detect local discharge signals with a charge below the level of tens of picocuries (pC). In order to enhance the sensitivity, in addition to the selection of high-precision sensors, it is also necessary to optimize the signal transmission path to reduce signal attenuation, while using low-noise signal acquisition module to reduce the impact of the system's own noise on the monitoring results.​
  1. Local discharge localization function is an important part of transformer local discharge monitoring, for large power transformers, accurately determining the local discharge location can significantly shorten the troubleshooting time. At present, the commonly used positioning methods include time difference positioning method (through the time difference between the signals received by multiple sensors to calculate the location of the local discharge), amplitude comparison positioning method (according to the amplitude difference between the signals received by different sensors to determine the local discharge area), and some of the advanced systems are also combined with the three-dimensional modeling technology, to achieve the visual display of the location of the local discharge.​
  1. Online local discharge monitoring system can realize 24-hour uninterrupted monitoring of transformer local discharge status, the system consists of two parts: on-site monitoring unit and background analysis center. The on-site monitoring unit is responsible for signal acquisition and preliminary processing, and transmits the data to the backstage through wired or wireless communication, while the backstage analysis center carries out in-depth analysis of the data, generates the monitoring report and sends out the alarm message when the local discharge is abnormal, which is applicable to the main transformer equipment of important substations.​
  1. Portable LD monitoring equipment has the advantage of high flexibility and is suitable for transformer regular inspection, fault troubleshooting and other scenarios. Compact size, easy to carry, the equipment can be temporarily installed by the way of sensor acquisition of local discharge signals, with special analysis software to achieve on-site data processing and diagnosis, can quickly determine whether the transformer has local discharge problems, for operation and maintenance personnel to provide immediate decision-making support.​
  1. The anti-interference design of the local discharge monitoring system is the key to ensure the reliability of the monitoring data. There are a large number of electromagnetic interferences in the operating environment of the power system, such as corona interference of the high-voltage lines and electromagnetic radiation from nearby equipment. For this reason, the system needs to take multiple anti-interference measures, including sensor shielding design, shielding and grounding of the signal transmission cable, electromagnetic compatibility design of the data acquisition link, as well as the software level of interference signal identification and rejection algorithms.​
  1. Trend analysis of local discharge monitoring data can provide a long-term basis for the assessment of transformer insulation status, through a period of time (e.g., months, years) of the local discharge data tracking, analyzing the local discharge charge, frequency and other parameters of the trend. If the local discharge parameters are stable, it means that the transformer insulation performance is good; if the parameters appear to continue to rise or sudden change, it indicates that the insulation may be accelerated deterioration, and need to take timely intervention measures.​
  1. The synergistic application of local discharge monitoring and other monitoring techniques can improve the comprehensiveness of transformer condition assessment, for example, the combination of local discharge monitoring and gas monitoring in the oil, the authorities discharge occurs, the transformer oil may produce characteristic gases (such as hydrogen, acetylene), the two kinds of monitoring data corroborate each other, and can more accurately determine the type of faults and the severity of the faults; and the synergistic application of temperature monitoring, it can be understood that whether the local discharge is accompanied by the phenomenon of localized overheating. The two monitoring data corroborate each other, which can more accurately determine the type and severity of the fault.​
  1. The alarm threshold setting of the local discharge monitoring system needs to be personalized according to the transformer model, operating years, voltage level and other factors, too high a threshold may lead to omission of alarm (missing early local discharge faults), and too low a threshold may lead to false alarms (increasing unnecessary operation and maintenance costs). Usually need to combine the transformer factory test data, historical operation data and relevant standards, to develop a scientific and reasonable alarm strategy, part of the intelligent system can also automatically adjust the threshold according to the operating conditions.​
  1. Regular calibration of the local-radiation monitoring system is a necessary measure to safeguard the monitoring accuracy, as the performance of the sensors and the accuracy of the signal-acquisition module may change with the passage of operating time. Therefore, it is necessary to calibrate the system regularly with a standard local-radiation signal source in accordance with relevant standards to check the sensitivity of the sensors, the integrity of the signal transmission link and the accuracy of the data processing algorithms, so as to ensure the credibility of the monitoring data.​
  1. For older transformers, local discharge monitoring is of greater importance. The old transformer insulation material has entered the aging stage, the probability of local discharge is relatively high, and the fault development speed may be faster. By installing the local discharge monitoring system, the insulation deterioration process can be grasped in real time, and the maintenance or replacement plan can be planned in advance, so as to avoid transformer shutdown due to insulation failure, and to ensure the continuity of power supply.​
  1. The local discharge monitoring system plays an important role in the construction of smart grid, as a key component of power equipment condition monitoring, its monitoring data can be connected to the integrated automation system of substation or regional power dispatching center to realize remote monitoring and centralized management of transformer status. The dispatching center can coordinate the operation and maintenance resources according to the local discharge data of multiple transformers to improve the overall intelligent operation and maintenance level of the power grid.​
  1. The development trend of local discharge monitoring technology presents intelligent and integrated characteristics, on the one hand, the application of artificial intelligence algorithms in the analysis of local discharge signals continues to deepen, such as the local discharge signal recognition model based on deep learning, which can further improve the accuracy of the judgment of the type of local discharge; on the other hand, the monitoring module of the local discharge has been gradually integrated with the transformer's other monitoring functions (e.g., temperature and vibration monitoring) to form an integrated monitoring of multi-parameters. On the other hand, the local discharge monitoring module is gradually integrated with other monitoring functions of the transformer (such as temperature and vibration monitoring) to form a multi-parameter integrated monitoring terminal, which reduces the installation space and cost of the equipment and improves the overall efficiency of the system.​
  1. The operation and maintenance management of the local discharge monitoring system needs to establish a perfect system, including regular data backup, equipment inspection, fault handling procedures. Operation and maintenance personnel need to be familiar with the working principle and operation method of the system, and be able to deal with the faults of the monitoring system itself (such as sensor failure, communication interruption), to ensure that the system continues to operate stably, and provide a strong guarantee for the safe and reliable operation of the transformer.