From the Editor's desk

Detection of partial discharges (PDs) in power transformers can be seen as a means of anticipating imminent transformer failure and thus saving the transformer through planned maintenance. This work focuses on a ultra high frequency (UHF) technique for PD detection. A UHF antenna, capable of being fitted onto a standard DN5O transformer drain valve while maintaining an oil-tight seal, was designed for the purposes of this work. A surface discharge defect was created in the laboratory to study the effects that different antenna dimensions would have on the detected wideband UHF signal and determine an optimum frequency at which the defect can be detected.

This paper presents a novel self-sensing partial discharge (PD) detection method for power transformers that leverages the transformer's iron core as an ultra-high frequency (UHF) sensor. The method aims to address the limitations of traditional PD detection techniques, which either require intrusive internal sensors or are susceptible to external interference. The experiments conducted on a 220kV transformer model with a suspension discharge defect model demonstrate the high detection sensitivity and anti-interference performance of the proposed method. The results show that the iron core can effectively sense PD UHF signals, providing a reliable and practical approach for on-site PD detection in transformers. This PD detection method solves the problem that the internal UHF sensor has security risks while the external sensor is susceptible to interference. It provides a new method for PD detection of transformers in field.

In order to ensure the safe operation of the gas insulated switchgear (GIS), on-site impulse withstand voltage test is becoming more and more important. Oscillating impulse voltage (OIV) is very suitable for the test due to its high efficiency. By detecting the partial discharge (PD) when conducting on-site impulse withstand voltage test, the insulation state of GIS can be known overall. The pulse current, ultrasonic, and ultra high frequency (UHF) are the mainly PD detection methods up to now. Among them, the UHF method is the most suitable method to detect the PD under OIV. However, there are electromagnetic interference signals generated by the impulse voltage generator which will influence the UHF detection results during the on-site impulse withstand voltage test. In this paper, the interference signals for the PD detection using UHF methods are analyzed. Based on this, an interference elimination method by using multiple UHF sensors for PD detection under OIV is introduced. This method is tested both in a lab environment and in field. The analyses show the interference signals for the PD detection using UHF methods under OIV is mainly related to the sphere-gap switch of impulse voltage generator. The results of lab experiments and field tests both show that the interference elimination method by using multiple UHF sensors is suitable for the PD detection under oscillating impulse voltage.

With the rapid development of electrical equipment test technology, various types of partial discharge detector are widely used to detect the partial discharge status of electrical equipment in power sector. However, with the long-term use of partial discharge detector, the data accuracy acquired from the test device lacks effective verification, which greatly affects the operation personnel to formulate maintenance strategy. In view of this, based on the ultrahigh frequency (UHF) partial discharge detection technology, this paper proposes a new calibration method about the combination of high simulation signal source and real type of defect and a new evaluation system. We also developed a performance verification platform of UHF partial discharge detector, which can verify the sensitivity, linearity error, range amplitude frequency response and other performance parameters of partial discharge measuring instrument. Finally, a total of 132 partial discharge detectors ' performance tests were completed by the test platform. The results show that 45 partial discharge detectors have defects and the defect rate is as high as 34%. Therefore, performance verification platform of the partial discharge detector in this paper can find defects of partial discharge measuring instrument in advance, which is of great significance to enhance the power grid security.

A novel partial discharge (PD) detection method for transformers on site adopting its component as ultra-high frequency (UHF) sensor is proposed. The bushing tap, iron core, and high-voltage (HV) winding can be used as internal UHF sensor for UHF PD detection. The experiments are carried out on an 80-kV transformer model to prove the validity of this method. The results show that the proposed method has good detection sensitivity and anti-disturbance performance, and can measure the PD signals without additional sensor. It solves the problem of the lack of available unused valves for internal UHF sensor installation while the external sensor is susceptible to interference. It provides a novel method with application prospects for PD detection of transformers in field.

Partial Discharge (PD) activity is a pre-cursor for insulation degradation which may eventually lead to catastrophic failure of power apparatus with severe social and economic consequences. Electromagnetic emissions gathered over ultra-high frequency (UHF) range (0.5 to 3 GHz) during PD events is widely investigated for health monitoring of high voltage (HV) apparatus. However, large bandwidth of PD induced UHF signals requires high speed digitizer and large storage space which have restricted field deployment of UHF technique for online PD detection. In this work, we present UHF based PD pulse detection framework for remote monitoring and logging of faults in dielectric insulation using ThingSpeak<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> cloud. PD events captured by a calibrated UHF sensor from HV PD test cell using the proposed online PD detection framework indicated throughput as high as 83.8% compared with reference UHF sensor measurements gathered by a digital storage oscilloscope. PD detection throughput was observed to be limited by the envelope detection threshold.<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</sub> (10 mV) and cumulative propagation delay <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pd</sub> (∼1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μs</i>) in the architecture implementation. The proposed UHF sensing technique is low cost compared to conventional approaches, detects a wide range of insulation defects, and scalable for smart monitoring of HV assets using Internet of Things (IoT).

Partial discharge (PD) is one of the major factors causing insulation damage of gas insulated system (GIS). The conventional PD detection methods are too susceptible to disturbances and unsuitable for on-line monitoring. The ultra-high-frequency (UHF) PD detection technique can detect and locate the PD sources inside GIS by detecting electromagnetic wave emitted from PD source. The narrow band UHF method was emphasized in this paper, because it can avoid the electromagnetic interference by selecting the appropriate frequency. A PD detection system using narrow band UHF method was designed. The typical defects that can cause partial discharge in GIS were simulated in laboratory. Using this detection system the PD waveform of frequency domain and time domain could be gotten. The results show that the time domain waveforms of the same defect have very similar distribution characteristics and those of different defect have different ones. So it would be very convenient for the recognition of PD types.

Partial Discharge (PD) measurement is a precise diagnosis to give the knowledge about the condition of the insulation. There are several methods to detect and measure the PD such as Electrical, Acoustic, Optical, Chemical and Ultra High Frequency (UHF) detection methods. Among all these methods, UHF sensor plays crucial role to detect the PD, efficiently with high sensitivity. PD pulses tend to appear only in the time of nano-seconds, which pulses can be detected without any power outage by using high bandwidth antenna i.e. UHF sensor. UHF sensor is conical in shape with base diameter 2.5cm and axial length 10cm. This sensor can detect the electromagnetic interference signals without any background noise in the range of 300 MHz to 1.5 GHz. In this paper, the experimental work was presented to study the characteristics of PD by using the designed UHF conical monopole antenna with the help of high bandwidth digital oscilloscope connected through co-axial cables in two distinct lengths. FFT analysis was applied to deduce the frequency response of the PD signal and sensitivity of the antenna.

Self-organizing feature map based unsupervised technique for detection of partial discharge sources inside electrical substations

Detection of winding deformation and partial discharge (PD) is essential for monitoring and failure risk assessment of power transformers. Recently, an online method based on electromagnetic waves has been proposed for detecting radial deformation (RD) in high-voltage (HV) transformer winding using ultra wide band pulses, called the hyperboloid method. In this method, a short pulse is transmitted toward HV winding and its reflection captured using a set of antennas. By comparing and analyzing signals in sound and deformed conditions, the RD can be detected. On the other hand, signals radiated from PD defect in transformers are generally appeared in the range of UHF band (0.3–3-GHz frequencies). In this paper, the hyperboloid method is proposed for implementation in UHF band, and the PD effect on the result of the hyperboloid method is investigated. Thus, a set of UHF sensors can be used for the detection of PD and detection and localization of RD defect. Results show that PD signals can affect the signal of the hyperboloid method and lead to wrong localization of RD. In order to solve this problem, the UHF stepped-frequency method is proposed, utilized, and tested on the HV winding of a 1.6-mega volt ampere (MVA) distribution transformer. Experimental results show the capability of the proposed method for detecting both defects using only one set of UHF antennas.

The most common pre-breakdown phenomenon in high voltage (HV) equipment is partial discharge (PD). The presence of PD activity is a warning indicator that the insulation deterioration would worsen over time, leading to catastrophic failure if the associated defects are not addressed early. Ultra-high frequency (UHF) has been proposed as a non-conventional method for detecting PD because of its resilience to external noise, high sensitivity, and online measurement potential. The UHF detection approach uses sensors to detect electromagnetic waves emitted by the PD source. The sensor is thus one of the most important parts of UHF PD detection. Microstrip patch antenna is widely used as a UHF sensor due to its merits of simple structure, compact profile, low cost, and ease of fabrication. This project deals with the development of the microstrip antenna for PD detection. To evaluate the antennas' performance, five antennas are built and simulated using Computer Simulation Technology (CST) Microwave Studio software. Return loss, voltage standing wave ratio (VSWR), and surface current are among the simulated results. These five antennas operate in the range of at least 80% of UHF and have the acceptable size that can be installed on the dielectric window or mounted on the flange.

Partial discharges (PD) measurement is a well-known technique for judgment of the condition of power transformer offline. Phase-resolved PD measurement is a normalized technique for PD tests, but noise, especially by PD-measurements onsite is sometimes difficult to reject, and a post-processing of a pattern is necessary to separate different sources. Higher-frequency-detection devices and processing strategies are useful for PD classification and identification. Recently, ultra-high-frequency (UHF) detection by means of antennas has been shown to be a promising detection system for both offline and online PD-measurements. However, it is necessary to assess whether PD source separation and classification is possible by means of pulse analysis because some additional UHF noise sources are coupled to the detected signals, and it is not clear whether different sources produce different pulses. In this study, the attenuation effect of the metallic tank of a power transformer on the inner PD activity when measured outside the tank was studied. Additionally, experiments were conducted to detect and characterize two different PD sources (internal and external discharges) using two antennas measuring the same phenomenon inside and outside of a transformer. It will also be shown that broadband UHF signals are useful for PD recognition and that a deep study of frequencies below 500 MHz can separate PD occurring inside from those occurring outside when measured with an antenna outside the tank.

Rapid and accurate detection of partial discharge (PD) of metal enclosed AC switchgear (HV switch cabinet for short) is of great significance for safe operation of the power grid and high reliability of power supply. The existing methods such as transient earth voltage (TEV), ultra-high frequency (UHF) and acoustic emission (AE) methods still have shortcomings, and the optical pulse method has not been applied yet. Additionally, due to mutual independence, heavy workload, low efficiency and measurement limitations of testing equipment, as well as the single criterion of signal source, technicians have great doubts about whether there are insulation defects in the interior of switchgear cabinets. Therefore, in this paper, an integrated electromagnetic composite sensor for HV switchgear cabinet wall is designed and its installation method is given. The preliminary experimental study in the laboratory shows that the designed sensor can detect TEV and UHF signals simultaneously, which provides a new research direction for the effective detection of partial discharge signals of HV switchgear cabinets.

Radio frequency (RF) detection of partial discharges (PD) is a long-established principle, being described in the international standard for partial discharge measurement. The growing market for mobile communication devices in recent years has led to big reductions in the cost of electronic hardware operating in the VHF and UHF bands, making advanced measurements of PD in these bands increasingly affordable. Some 20 years ago, ultra-high frequency methods for PD detection were pioneered in gas-insulated substations (GIS) and have since become widely accepted. Locating PD in GIS is essentially a one-dimensional problem. More recent research into PD location in power transformers, also using the UHF method, has had to address the more challenging problem of PD location in three-dimensions. Both the GIS and transformer applications monitor enclosed volumes, where the PD is within a metalclad system that traps the signal and provides good screening of external RF interference. At the same time, other researchers have developed RF detection and location systems for open environments, such as complete air-insulated substations. When deployed in a fixed installation or a surveying vehicle equipped with GPS, this system is capable of monitoring insulation defects as they develop, and provides a location capability using sophisticated signal processing. This paper begins with an overview of some aspects of radiometric monitoring techniques and goes on to outline some research challenges which it is hoped will attract the attention of the many researchers who are continuing to advance the areas of radiometric PD detection, measurement and location technology.

The development of printable ultrahigh-frequency (UHF) antennas as partial discharge (PD) sensors for high-voltage equipment has been extensively studied. However, achieving ultrawideband (UWB) UHF PD sensors frequently requires larger sizes, unsuitable for certain applications requiring compact sensors for dielectric windows in HV equipment. This research objective is to obtain PD sensors with a wider bandwidth (0.3–3 GHz) and a compact size fitting a less-than-100mm-length gas-insulated switchgear (GIS) dielectric window. A circular patch microstrip antenna (CPMA) was chosen for its small size and potential for UWB performance. This paper discusses the design modification of the CPMA to obtain a wider bandwidth for PD detection in GIS. Simulations and lab-scale experimental verifications were conducted to evaluate the optimized sensor. The modified sensor, with a size of 60 × 73 mm², achieved a bandwidth of 3.08–3.14 GHz, a reflection coefficient of -44 dB, and several resonant frequencies of 0.3–2.3 GHz. This is a seven-time wider bandwidth compared to earlier bowtie antennas while keeping a dimension of less than 100 mm². These properties allow for efficient PD detection in GIS and other insulating media. Experimental results indicate the sensor's capacity to reliably detect and analyze PD signals while responding appropriately to variations in voltage. Doi: 10.28991/ESJ-2024-08-05-03 Full Text: PDF