Ultra-high Frequency Detection Research Articles

The performance analysis of the laser heterodyne ultra-high frequency detection based on the optical phase-locked loop

The performance of the laser heterodyne ultra-high frequency detection based on the optical phase-locked loop is analyzed through theoretical calculations and numerical simulations, considering the residual phase error and carrier stability. Appling the Wiener–Khinchin theorem, a general expression of the residual phase variance with essential affecting factors is derived. Furthermore, we define the error gain factor based on the ultra-high frequency carrier stability, which consists of the amplitude deviation and frequency deviation. Then the model of the demodulation output with the amplitude deviation and frequency deviation is presented. According to numerical simulation results, we acquired the variation curve of the residual phase variance with the loop bandwidth and the performance of the carrier signal stability. For the residual phase variance expression, the minimum variance corresponding to the optimal parameters can be obtained through the numerical simulation. The simulation experiment proves that the numerical results are consistent with the theoretical analysis. Our model for evaluating the influence of the carrier stability on the heterodyne ultra-high frequency detection can provide powerful support for improving the demodulation accuracy. The quantitative analysis of the paper will be available for theoretical basis and guidance for laser heterodyne detection based on optical phase-locked loops.

The Positive Role of the Partial Discharge Monitoring System in the Partial Discharge Detection of GIS Equipment

When gas insulated metal enclosed switchgear and controlgear (GIS) has internal discharge, some faults are difficult to find during inspections due to the enclosed metal casing. This paper introduces the event of the floating potential discharge inside the GIS equipment of a 500kV substation found by GIS on-line monitoring system. Through on-site ultra-high frequency detection and precise positioning of the oscilloscope to determine the position of the discharge source at a certain switch, combined with the disassembly of the equipment, it is determined that the equipment defect is the discharge of the floating electrode of the switch fork.The results show that the on-line monitoring of GIS partial discharge has an important reference role in discovering the internal discharge of equipment during the test interval, and the monitoring and maintenance of GIS partial discharge on-line monitoring system should be strengthened in daily work.

Detection, Classification and Location of Sources of Partial Discharges Using the Radiometric Method: Trends, Challenges and Open Issues

In this article, it is provided a comprehensive survey on the most relevant research in the area of detection, classification and location of partial discharge (PD) sources using the radiometric or ultra high frequency (UHF) method, focusing mainly on the works related to the use of antennas. To the best of the authors knowledge, this is the first review paper that focuses on the application of antennas based on UHF method in the complete diagnosis of PD. Specifically, it is first presented the main contributions to the development and optimization of UHF sensors for application in the detection of PD sources. Second, articles that used the UHF method to identify different types of PD in high voltage equipment are described. Finally, the main contributions regarding the location of sources of defects using the radiometric method are presented. Summary of works in the area of UHF detection sensors, PD classification and PD location, with their respective contributions, are shown. Finally, research trends, challenging and open issues are discussed. The purpose of this article is to provide important information about the complete diagnosis of PD, which could be used to guide the development of more efficient techniques in this research area.

Present Situation and Development of Internal Sensors for Ultra-high Frequency Detection in Gas Insulated Switchgear

This paper discusses the application situation of the ultra-high frequency (UHF) method and optical method in the detection of partial discharge of gas insulated switchgear (GIS), and the differences between external and internal UHF sensors. The sensor is a key technology in the PD detection method, and its performance directly affects the validity of the monitoring results. Different partial discharge detection sensors have different characteristics and working environments. UHF sensor has the advantages of wide detection range and convenient layout. Optical sensors have the advantages of high sensitivity and fast response speed. Six main types of internal sensors are evaluated and the performance indicators of internal sensors are discussed which includes disc antenna, loop antenna, dipole antenna, planar spiral antenna, conical antenna, photoelectric composite sensor. Furthermore, some problems need to be solved are proposed for further research, which is of great significance to the safe and stable operation of power equipment.

PD Signal Propagation in GIS: Ultra-High Frequency Detection-Based Modeling

Gas-insulated switchgears (GIS) have become essential parts of electrical power substations due to the associated merits of these capital assets. Although such resilient devices can rarely suffer from failure, partial discharge (PD) is responsible for around 85% of their recorded collapses. Ultra-high frequency (UHF) techniques have been widely used in the detection and localization of PD for a long time because of their immunity to noise and high sensitivity. Understanding electromagnetic (EM) wave behavior in GIS systems is significant for improving the utilization of UHF sensors in PD detection and for the optimal allocation of UHF antennas inside GIS systems. Thus, this paper is devoted to building a detailed 3D finite element (FE) model based on UHF detection techniques to understand the propagation behavior of EM waves inside GIS. A disk-type UHF sensor is used for acquiring EM waves inside the GIS. The sensitivity of the sensor has been obtained using a gigahertz transverse-electromagnetic (GTEM) test cell. The proposed model investigates the impact of multiple disconnecting parts including L-structure, relative angle between PD source and sensors, and disconnecting switches on the propagation of electromagnetic waves based on step 1 of the CIGRE recommendations. To validate the modeled GIS, a simple L-structured model is initially built, and a comparative analysis has been conducted between the built model and the experimental and analytical results from the literature.

Study on Characteristics of Different Internal UHF Sensors in GIS

The crucial point of the UHF detection is the UHF sensor, which affects the sensitivity and anti-interference ability of the UHF detection. In this paper. the introduction of 5 different kinds of internal sensors of the Ultra High frequency (UHF) technology used to monitor the PD in the GIS was made in detail. With comparion of the external sensors, the anti-interference ability of internal sensors is much better. In order to evaluate the property of different sensors more precisely, several indicators are introduced in this paper. Furthermore, some unsolved issues about the sensot inside the GIS are presented for researchers to solve.

Design of an Archimedes spiral antenna for PD tests under repetitive impulsive voltages with fast rise times

Partial discharge inception voltage measurements under repetitive impulsive voltages play an essential role in evaluating the reliability of inverter-fed low voltage rotating machines. Using impulsive voltages, partial discharge (PD) signals and the disturbance induced by power electronics switches have often similar energy distribution in the frequency domain. Thus, PD test technologies used with sinusoidal voltages are no longer effective. Under repetitive impulsive voltages, ultra-high frequency detection is recommended to couple high-frequency spectral components from the PD and remove the low-frequency disturbance coming from power electronics. However, to obtain high signal to noise (S/N) ratio, the parameters of the antenna used for PD detection should be designed considering the PD and the disturbance energy distributions in the frequency domain. In this paper, we discuss the design and show the properties of an antenna with Archimedes plane spiral structure intended for PD detection under repetitive impulse voltages. The simulation shows that the antenna has low voltage standing wave ratio (<2) and improved directivity in the frequency range from 0.5 to 2 GHz. Moreover, PD tests performed using repetitive square waves with different rise times demonstrate that the designed antenna can receive PD signals efficiently with high S/N.

On the Electromagnetic Wave Behavior Due to Partial Discharge in Gas Insulated Switchgears: State-of-Art Review

The rapid growth of gas insulated switchgears as a compact, efficient, and reliable device has recently been given great attention. Albeit gas insulated switchgears can seldom suffer from failure due to the high resiliency and robustness, some severe damages have been experienced by such devices particularly in the event of partial discharge. Thus, monitoring such accidents has become a vital part of power systems reliability. The ultra-high frequency techniques have recently shown superior performance in the detection and classification of electromagnetic waves produced by partial discharge. This is mainly due to the great immunity to the noise of the ultra-high frequency detection techniques compared with the very-high-frequency counterparts. This review paper highlights the mathematical aspects of the electromagnetic waves generated by partial discharge. It also delivers an overview of the electromagnetic wave behavior in the complex structure of gas insulated switchgears, and outlines the important characteristics of the internal and external partial discharge detection using ultra-high frequency methods.

Investigation on the propagation characteristics of PD-induced electromagnetic waves in an actual 110 kV power transformer and its simulation results

Partial discharge (PD) detection using the ultra-high frequency (UHF) method is a well-known advanced insulation diagnosis method in power transformers. Investigation on propagation characteristics of electromagnetic (EM) waves in the power transformer is required for significant improvement of detecting PD signal by UHF method. In this paper, a 110/35/10kV three-phase oil-filled transformer with complete internal structure was utilized to investigate the propagation characteristics of EM waves. The amplitude, cumulative energy and frequency band energy of EM waves in different positions were analyzed. As a comparison, a simulation model whose size is same as the experimental transformer, built by CST Microwave Studio was also performed. The results show that the amplitude and cumulative energy of EM waves have similar change law, that is, they decrease non-linearly and the attenuation rate slows down with increasing distance from the PD source. During the propagation of EM waves, the higher frequency bands suffer greater attenuation leading to the less energy ratio. Compared with experimental results, numerical simulation brings about adequately accurate values and shows the similar trend with experiment. The results serve as the essential guides to improve the sensitivity of UHF detection and efficiency of online monitoring by UHF detection, and as a notable concern to optimize the band width for high-frequency detection.

UHF PD measurements on power transformers-advantages and limitations

Recently, Ultra-High Frequency (UHF) Partial Discharge (PD) measurements on power transformers has attracted a lot of attention. Despite numerous publications, there are still missing information about considerations and limitations of this method in regards to antenna characteristics, relation between IEC 60270 and UHF detection methods and robustness against external noises. In this paper, each of the mentioned sections is investigated in detail by simulation analysis or laboratory measurements. Applying the results obtained in each section leads to a more precise measurement, more accurate analysis of UHF PD data and solving some of the problems associated with it.

A combined preprocessing method for UHF PD detection based on kurtosis features

Ultra-high-frequency (UHF) partial discharge (PD) detection has been proved as a powerful tool to evaluate the status of electrical equipment. Unfortunately, on-site UHF detection suffers from intensive noise interference and great computational burden, which have long been the key bottleneck for its wide utilization in the field environments. In order to provide more valuable information for subsequent processing like PD location, pattern recognition, or severity assessment, a combined preprocessing method for UHF PD detection is proposed in this paper. This scheme integrates a novel Ensemble Empirical Mode Decomposition-based signal reconstruction method and a kurtosis-based pulse window extraction method. To demonstrate the effectiveness of the presented technique, both simulated and laboratory measured PD data are obtained and further tested. Results reveal that this preprocessing method can accurately detect and extract the PD pulse from raw data, which may lessen the computational burden for any further processing. In addition, more accurate and reliable feature information can be retained.

Partial discharge detection and analysis of needle-plane defect in SF6 under negative oscillating lightning impulse voltage based on UHF method

Gas insulated switchgear (GIS) is used in power system more and more widely. With the increased voltage level of power system, field impulse voltage withstand test becomes increasingly important. It would be beneficial for a comprehensive insulation evaluation to carry out the detection of partial discharge (PD) under impulse voltage withstand test in field. Metal protrusions or particles on HV conductor are typical defects in GIS and are critical at lightning impulse voltages. This paper therefore aims at PD characteristics study on needle-plane defect under oscillating lightning impulse (OLI). PD detection system was established based on ultra-high frequency (UHF) and pulse current detection. Then, the PD of a needle-plane defect under negative OLI was measured. The relation between statistical time lag, PD amplitude, PD times and the applied voltage was analyzed respectively based on UHF detection. The results show that UHF detection has high sensitivity and it is suitable in field impulse voltage withstand test. PDs occur around each wave peak of the applied voltage. With the increase of peak voltage, PD magnitude and PD times in each oscillation cycle both increase linearly. Further analysis indicates that the occurrence and development of PD under negative OLI can be interpreted by electron emission from metal surface, field detachment from negative ions and corona stabilization effect. This approach is valuable for PD measurement and analysis in field impulse voltage withstand test for GIS.

Discharge characteristic investigation on surface discharge initiated by metallic particles attached to gas‐insulated substation insulator

The ultrahigh frequency (UHF) method is used for detecting the three kinds of surface discharges started by metallic particles on the spacer insulators in gas‐insulated switchgear (GIS). Three different designs of the same surface defect are applied to ensure the consistency of the results. The present experiments are made on a 220‐kV GIS, which is close to the actual situations to study the surface discharge characteristic. A measuring system for this purpose consists of an oscilloscope connected to UHF sensors. Partial discharge (PD) data was captured by UHF detection using an oscilloscope and stored as phase‐resolved pulse sequence (PRPS) data. Since PRPS data contain the complete information of the PD, PRPS analysis (PRPSA) pattern and three‐dimensional ϕ − q − n (3D PRPD) pattern can be calculated from the recorded PRPS datasets. The PRPSA data also allows us to obtain the actual test voltage (rms) of every cycle, the number of measuring cycles, and phase information of all PD pulses, together with their peak values, so that a statistical analysis of these data can be discussed. Besides, this paper also focuses on the frequency analysis and time–frequency analysis of the single‐pulse time‐domain signal. It is shown that the characteristic parameters obtained from the PRPS data, frequency spectrum, and time–frequency spectrum have the potential to be used as PD characteristic interpretation and further research on PD pattern identification. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Investigation of frequency characteristics of typical PD and the propagation properties in GIS

The secure operation of Gas Insulated Switchgear (GIS) is crucial for the bulk power systems, since the failure of GIS apparatus would cause severe interruption of power transforming and power supply at substations. Therefore, the monitoring and maintenance schemes of GIS devices have gradually taken the reliability-based indices into account, of which Partial Discharge (PD) levels in online monitoring are of substantial significance because PD serves as a major cause of insulation break-down. Ultra High Frequency (UHF) method is becoming widely adopted as the major inspection approach for PD in GIS. This paper presents the experiment-based results of the frequency characteristics of UHF signals caused by PD in typical defects using entire GIS operating system platforms. Specifically, the results covered the propagation attenuation of the UHF signals with peak to peak value and cumulative energy through typical structures, including basin-type insulators, L-shaped branch, isolating switches, current transformers, etc. The results serve as substantial criteria for optimal band width selection for high frequency detection, and as notable concerns to improve the sensitivity of UHF detection and the efficiency of online monitoring by effectively locating the external sensors for PD UHF detection.

Present Situation and Prospect of Internal Sensors for UHF Detection in GIS

This paper summarizes the application situation of the ultra-high frequency (UHF) method in gas insulated switchgear (GIS) partial discharge detection, as well as the differences between internal and external UHF sensors. The performance indicators of internal sensors are introduced, and five main types of internal sensors are discussed and evaluated. In addition, several problems to be solved are posed for researchers.

Application of On-Line Ultrasonic and UHF Partial Discharge Detection in 1000kV GIS

This paper introduces the detecting principle、range of application and interferencerejection of Ultrasonic And UHF Partial Discharge Detection In GIS(Gas Insulated Switchgear).In view of the advantages and disadvantages of ultrasonic and UHF detection,this paper proposesa quick joint detection method, which uses UHF (Ultra High Frequency) method to online detectthe suspected discharge range in real time, adopts ultrasonic method to determine the specificdischarge points, finally through a concrete instance in a 1000KV UHV(Ultra High Voltage)Substation verified the feasibility of the joint detection method.

Study on the Application of an Ultra-High-Frequency Fractal Antenna to Partial Discharge Detection in Switchgears

The ultra-high-frequency (UHF) method is used to analyze the insulation condition of electric equipment by detecting the UHF electromagnetic (EM) waves excited by partial discharge (PD). As part of the UHF detection system, the UHF sensor determines the detection system performance in signal extraction and recognition. In this paper, a UHF antenna sensor with the fractal structure for PD detection in switchgears was designed by means of modeling, simulation and optimization. This sensor, with a flat-plate structure, had two resonance frequencies of 583 MHz and 732 MHz. In the laboratory, four kinds of insulation defect models were positioned in the testing switchgear for typical PD tests. The results show that the sensor could reproduce the electromagnetic waves well. Furthermore, to optimize the installation position of the inner sensor for achieving best detection performance, the precise simulation model of switchgear was developed to study the propagation characteristics of UHF signals in switchgear by finite-difference time-domain (FDTD) method. According to the results of simulation and verification test, the sensor should be positioned at the right side of bottom plate in the front cabinet. This research established the foundation for the further study on the application of UHF technique in switchgear PD online detection.

Hilbert fractal antenna for UHF detection of partial discharges in transformers

Electromagnetic waves generated due to partial discharge (PD) can be captured by ultra-high-frequency (UHF) antennas. The size and frequency band of an UHF antenna for PD online monitoring are critical factors for practical installation inside a transformer. This paper presents a compact multi-band UHF Hilbert fractal antenna with wide frequency band and suitable size for easy installation. Design criteria of a PD antenna were proposed and the Hilbert fractal antenna was selected as an appropriate candidate for PD detection. Principle of Hilbert fractal antenna was discussed and a fourth order Hilbert fractal antenna was optimized for detecting PD signals. Actual PD experiments have been carried out for two typically artificial insulation defect models while the antenna was used for the PD measurement. More simulation studies and actual PD experiments have been done to further examine the effects of electromagnetic wave refraction and reflection by transformer components. The results show that the proposed UHF antenna is qualified for PD online monitoring.

Analysis of the intrinsic characteristics of the partial discharge induced by typical defects in GIS

Partial discharge (PD) monitoring plays an important role in the maintenance of the high voltage (HV) apparatus, such as transformer and gas-insulated substation (GIS). In recent years, the ultra high frequency (UHF) method for PD detection arouses great interest of many researchers because of its high sensitivity and anti-interference capability. The coupling of UHF signal and process of the signal constitute the UHF detection method. There are three key components for the coupling of UHF signal in GIS, including the frequency spectrum characteristics of the PD source, the propagation characteristics in GIS, the coupling style and the capability of the UHF coupler. Many researchers are interested in the recognition algorithm and the analysis procedure of the PD data. But the intrinsic attributes of the partial discharges should attract more attentions because they are the foundation of the UHF detection method. This paper focuses on the intrinsic characteristics of the typical defects in GIS, such as the amplitude of the time-domain signal and frequency spectrum characteristics. Four types of typical partial discharge sources are designed and fabricated, including floating metal, protrusions, particle on the spacer, and void in solid insulation. Several different structure sizes of each defect are applied to ensure the consistency of the results and discover the factors that affect the frequency spectrum characteristics. The results of the study present the essential characteristics of the partial discharge. It can be applied to the design of the coupler and amplifier circuit. In addition, the sensitivity and anti-interference capability of the UHF method are promoted effectively, and it is valuable for calibrating the intensity of PD in GIS.

A Transformer Partial Discharge Measurement System Based on Fluorescent Fiber

Based on the physical phenomena of optical effects produced by the partial discharge (PD) and on the characteristics of fluorescent fiber sensing of weak fluorescent signals, a PD measurement system using a fluorescent fiber sensor was designed. The main parameters of the sensing system were calculated, an experimental testing platform for PD simulation in the lab was established, and PD signals were then detected through ultra-high frequency (UHF) and optical methods under a needle-plate discharge model. PD optical pulses in transformer oil contained signal-peak and multi-peak pulse waveforms. Compared with UHF detection results, the number of PD pulses and the elapsed PD pulse phase time revealed a good corresponding relationship. However, PD signal amplitudes presented the opposite, thus indicating that PD UHF signals reflected pulse amplitude value, whereas PD optical signals reflected pulse energy magnitude. The n-u-φ three-dimensional distributions indicated that most of the PD signals concentrated in the nearby industrial frequency voltage peak value. Overall, the proposed fluorescent fiber sensing system design can be used successfully in transformer PD signal detection.