Ultra-high Frequency Sensors Research Articles

Effect of Magnetic Field on Partial Discharge Initiated by Metallic Particle in Thermally Aged Natural Esters Under AC and Harmonic Voltages

This paper reports the experimental and theoretical investigations of particle levitation voltage on thermally aged ester fluid, under AC and harmonic AC voltages, in the presence of both electric and magnetic fields (130 mT and 160 mT). The results indicate a higher sensitivity to identify partial discharge (PD) initiated due to particle movement in aged ester fluids with an ultra-high frequency (UHF) sensor than the fluorescent fiber technique. The cause for the reduction in sensitivity of PD detection due to the fluorescent fiber technique with thermally aged fluid is analyzed using steady-state fluorescent measurement. The reduction in the levitation voltage noticed under high-frequency AC voltages is much more severe than its impact under the fundamental frequency of AC supply voltage. In addition, the presence of a magnetic field reduces the magnitude of levitation voltage substantially. The UHF signals generated due to particle movement-initiated discharges with aged ester fluids indicate a shift in its dominant frequency of 0.9 GHz under the absence of a magnetic field to around 0.6 GHz with the effect of a magnetic field.

Analysis of Partial Discharge Spectrum Based on Ultra-High Frequency Detection Method

Oil immersed power transformer is the most widely used large power transformer in power system and its insulation structure is mainly composed of oil, paper and other solid insulation materials. Partial discharge monitoring is an effective means to find dielectric faults of transformer in an early stage of development. Ultra-high frequency(UHF) partial discharge detection technology has high detection frequency and strong anti-interference ability, which is suitable for transformer online detection. In this paper, five typical transformer discharge models are built, and the discharge spectra of each model are measured by a UHF sensor. The test results show that the surface discharge and wedge discharge most occurs near the voltage peak, the discharge phase distribution of floating part discharge is very wide, the internal air gas discharge mostly occurs in the area where the absolute value of voltage increases, and the point-to-plane discharge has a typical polarity effect.

An Ultrawideband Conical Monopole With Radome for Detection of Partial Discharges

Localized electric field strength in high-voltage (HV) equipment results in electrical discharges which radiate electromagnetic waves in ultrahigh frequency (UHF) range of 0.3-3 GHz. Due to the large antenna dimensions in UHF regime and lack of radome, existing UHF sensors have limited use in HV equipment for online partial discharge (PD) detection. In this work, we present the design and experimental verification of a UHF antenna with relatively small aperture and radome for PD detection. The proposed UHF sensor is a compact conical monopole with ground plane and protective radome. The monopole shape was optimized for broadband operation and directional radiation pattern using electromagnetic simulations. A cylindrical radome transparent to electromagnetic waves was designed without perturbing the radiation characteristics of the optimized UHF antenna. The 130 mm diameter fabricated sensor has directional radiation pattern, UHF bandwidth of 0.5 - 3 GHz and compact radome of 150 mm diameter. PD signals gathered for three defects in gas insulated test cells indicate better detection capability and sensitivity for the proposed UHF sensor than the reference sensor.The improved performance of the proposed sensor suggest that it could be used for PD detection in HV equipment such as gas insulated switch gear and transmission line.

Partial Discharge Detection and Diagnosis of Transformer Bushing Based on UHF Method

Bushings are essential components in a power transformer where incipient partial discharge (PD) activities and its detection and diagnosis cannot be ignorant. In this paper, an oil-impregnated paper (OIP) bushing is modeled to investigate that the oil gaps between the flange and condenser body in a typical OIP bushing provide a feasible path to trace the electromagnetic signal. As a non-destructive method, UHF (Ultra High Frequency) is proposed to detect 4 typical inside and outside PD defects of 110 kV bushings. To analyze the parameters of different defects, not only phase-resolved partial discharge (PRPD) is presented, but also 16 detailed time-domain and frequency-domain parameters of UHF signal are involved. Then feature extraction and selection are conducted through comparative principal component analysis (PCA) and extremely randomized trees (ET) algorithms. It is revealed that the selected features are representative and ET greatly reduces the amount of data whilst ensuring high accuracy. Fault diagnosis for bushing is finally achieved via support vector machine (SVM) with the selected features. The presented work of bushing PD detection based on UHF sensors provides a complete solution for the bushing diagnosis in potential field application and maintenance.

Study on the Propagation Characteristics of Partial Discharge Electromagnetic Waves in Gas Insulated Line

Defects in the gas insulated line can cause partial discharge, and the electromagnetic wave is generated. The finite difference time domain method is used to research the propagation of electromagnetic wave in gas insulated line structures. The electric field strength of time-domain waveform is selected as characteristic factor for analysis. By changing the gas insulated line model, the attenuation of electromagnetic wave through double insulator, L-type corner, T-type corner, straight tube and different GIL sizes is studied. In the straight tube structure, the amplitude attenuation of electromagnetic wave is linear and the attenuation band is between 1 GHz and 1.7 GHz. In the insulator, basin insulator has more serious influence on signal isolation than disc insulator. After passing through the insulator, the signal attenuation is obvious in the frequency band above 1 GHz. The amplitude of electromagnetic wave decreases more seriously through the corner structure, and the attenuation is at the whole frequency band. In different sizes of gas insulated line, the larger diameters of shell and conductor, the larger electromagnetic wave will be, and the faster attenuation will be; the length of gas insulated line cavity has little effect on electromagnetic wave. The theoretical research is expected to help to arrange the position of ultra-high frequency sensor reasonably.

A Meticulous Method for the Measurement of Partial Discharges in Gas Insulated Switchgears

This Paper presents the application of modern & meticulous procedure for the measuring Partial Discharge on the GIS (Gas Insulated Switchgear). The conventional method was by the usage of analog filters and the comparison between the induced and circulating currents, here we made use of the ultra-high frequency sensors which detects the ultra-high frequency signals that were produced during the abnormal condition. The UHF sensors are placed on the Gas Insulated Switchgears at the suitable designed location. The detected signal is digitized and transmitted to the control panel via the high speed fiber optic cables. It is processed and the cause for the partial discharge is known. At site it is done along with the high voltage measurement of the GIS. The final measured value is measured in Pico coulombs.

PD Signal Attenuation in 550-kV GIS: Impact of Different Barriers on the Propagation of Electromagnetic Waves

Accurate modeling of partial discharge (PD) within gas-insulated switchgear (GIS) has become of paramount significance to improve the utilization of ultrahigh frequency (UHF) sensors within such capital assets. Providing better insight on how electromagnetic (EM) waves propagate within GIS systems provides valuable information that can be used to determine the optimal allocation of UHF sensors. Thus far, most existing models are not considering the full complexity of the GIS systems due to the many associated challenges and the high computational demand of such system modeling. In this work, a GIS system is modeled using the Maxwell solver of COMSOL multiphysics. CIGRE sensitivity verification recommendations (CSVR) are used to inject UHF signals using an internal sensor. Then, two external sensors, placed on the outer belt of dielectric spacers, are used to capture the radiated EM waves. The electric field distribution at selected frequencies is presented and discussed under two operating conditions for disconnecting switches. The modeled GIS contains many barriers, including two bends, multiple sudden changes in the outer to inner diameters ratios, six dielectric spacers, and two disconnecting switches. Time-domain simulation results are also presented to provide an insight into the attenuation properties of EM waves due to the different barriers. Finally, a comparison between simulated and measured results has been carried out to verify the modeling accuracy. The results show that GIS systems form complex structures for the EM waves, and fully understanding the wave propagation can be tedious.

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.

Multi-Resolution Generalized S-Transform Denoising for Precise Localization of Partial Discharge in Substations

Denoising is a crucial step in the localization of partial discharge (PD) in a substation. In this paper, a novel multi-resolution generalized S-transform (GST) denoising algorithm for precise localization of PD in substations is proposed. The algorithm denoises the PD signal received by the ultra-high frequency (UHF) sensor in two steps. First, the GST with the high frequency resolution is used to analyze the PD signal, and a GST filter is designed to filter out periodic narrowband noises. Then, the S-transform (a particular case of GST) is applied to analyze the PD signal, and the white Gaussian noise is suppressed according to the statistical characteristic difference between the noise and effective signal. Finally, the denoised PD signal is obtained and applied to PD localization. The simulations results show that the proposed algorithm can effectively suppress noise and can extract accurate time delay data from the denoised PD signal. The experiment results show that, compared with the wavelet transform, the localization error of the proposed algorithm is the smallest, which is 1.59m. The proposed algorithm can realize the precise localization of PD.

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.

Study of the Influence of Winding and Sensor Design on Ultra-High Frequency Partial Discharge Signals in Power Transformers.

Ultra-high frequency (UHF) partial discharge (PD) measurements in power transformers are becoming popular because of the advantages of the method. Therefore, it is necessary to improve the basic understanding of the propagation of signals inside the transformer tank and the factors that influence the sensitivity of the measurement. Since the winding represents a major obstacle to the propagation of the UHF signals, it is necessary to study the effect of winding design on signal propagation. Previous research activities have studied these effects using simplified models, and it is essential to consider the complexity of propagation in a complete transformer tank. Additionally, the quality of UHF PD measurements depends, to a large extent, on the sensitivity of the UHF sensors. In this contribution, a simulation model consisting of a simple, grounded enclosure with multiple winding designs is used to study the propagation characteristics of UHF signals when an artificial PD source is placed inside the winding. After analysis of the results, the winding designs are incorporated in an existing and validated simulation model of a 420 kV power transformer and analyzed to observe the influence in a more complex structure. Two commonly used sensor designs are also used in the simulation model to receive the signals. In all cases, the propagation and signal characteristics are analyzed and compared to determine the influence of the winding and sensor design on the UHF signals. It is found that the level of detail of winding design has a significant impact on the propagation characteristics. However, the attenuation characteristics of the UHF signals received by the two sensor designs are similar, with the electric field distribution around the sensor being the key difference.

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.

Characteristics of AC PDs on epoxy insulation surface excited by different impulse voltages in SF6 gas

In this paper the behavior of partial discharges (PDs) on epoxy insulation under AC and impulse superimposed voltages are experimentally investigated in SF 6 gas. The lightning impulse (LI) and the switching impulse (SI) voltages with different polarity are superimposed on different phases of the AC voltage. PDs are measured by three sensors, a 50 Ω measurement impedance, an ultra-high frequency sensor and a photomultiplier tube. The max PD amplitude, PD pulse number and PD duration under AC voltage after an impulse voltage are summarized and analyzed. The effect of the impulse superposition phase, the impulse type and the impulse polarity on the characteristics of AC PDs are discussed. Results show that after a positive impulse voltage was applied on the positive semi-wave of AC voltage (0 to 180°), PDs in the negative half cycle of the AC voltage can be remarkably excited. A negative impulse voltage was applied on the negative semi-wave (180 to 360°), AC PDs can be initiated in the positive half cycle of AC voltage. PDs excited by a LI voltage is severe than excited by a SI. PDs excited by a positive impulse is intense than excited by a negative impulse.

Wearable Textile UHF-RFID Sensors: A Systematic Review.

Textile radio-frequency identification operating in ultra-high frequency (UHF-RFID) sensors based on different scenarios are becoming attractive with the forthcoming internet of things (IoT) era and aging society. Compared with conventional UHF-RFID sensors, textile UHF-RFID sensors offer the common textile features, light weight, washability and comfort. Due to the short time and low level of development, researches on the integration of textile UHF-RFID techniques and textile sensing techniques are not flourishing. This paper is motivated by this situation to identify the current research status. In this paper, we provide a systematic review of the fundamentals of textile UHF-RFID sensors techniques, materials, the brief history and the state-of-the-art of the scenario-based development through detailed summary and analysis on the achievements from the starting year of 2004 to the present time. Moreover, according to the analysis, we give a proposal of the future prospects in several aspects, including the new materials and manufacturing processes, machine learning technology, scenario-based applications and unavoidable reliability.

Study on the mixing and separation of UHF signals with multiple insulation defects in GIS

In order to explore the mixing characteristics of ultra-high frequency (UHF) partial discharge (PD) signals in GIS, simulation tools and Antenna Theory concerning the electromagnetic field (XFDTD) have been adopted in investigating the mixed features of UHF signals in GIS environment. Simulation results and theoretical analysis in this paper demonstrate that convolution is the basic relationship between PD current signal and the single UHF PD signal; the PD mixing signals are the linear and instantaneous mixture of single PD signals and they are also the linear and convolution mixture of PD current signals. The reverse process of those mixing modes are also been discussed based on blind sources separation and find out that it is an over complete blind source separation problem to gain single UHF PD signal from mixed one. Moreover, it can be approximated to conventional blind source separation when the layout of ultra-high frequency sensors is compact.

Partial Discharge Measurements in a High Voltage Gas Insulated Transmission Line Insulated with CO2

This paper uses practical experimentation to analyse the effect of replacing SF6 with pure CO2 in conventional gas insulated transmission line sections by studying partial discharge measurements taken with applied voltages up to 242 kV (rms). The results can also help in understanding the properties of new alternative gas mixtures which can be utilised with a ratio of up to and over 95% CO2. The experiments undertaken involved filling a gas insulated line demonstrator with 3 bars of CO2 and applying voltages up to 242 kV in both clean conditions and particle-contaminated enclosure conditions. The results demonstrate that CO2 can be used to insulate gas equipment without breakdown at high voltage, however, a higher gas-filling pressure may be needed to reduce the partial discharge found in the tests presented in this paper. Another aspect of the work showed that partial discharge (PD) measurements from internal ultra-high frequency (UHF) sensors compared with a direct measurement from a capacitive divider both clearly showed the effect of contaminating particles in CO2. However, the PD divider measurements also showed considerable external PD on the outside of the gas compartment, leading to the conclusion that UHF sensors are still regarded as having the highest sensitivity and noise immunity for gas insulated switchgear (GIS) or gas insulated transmission line (GIL) systems including when the equipment is insulated with CO2.

Detection and Localization of Partial Discharge in Transformer Oil and Winding using UHF Method

Transformers are important part in power transmission. One of the serious faults that is seen in transformers is electrical insulation failure. Insulation failure is usually initiated by partial discharges (PD). Due to high voltage stress, the fluid insulation in electrical system or a small solid portion can get dielectric breakdown, this is known as partial discharge and this does not create a space between the conductors. The accurate location of PD is an effective method for assessing the existing electrical insulation condition and preventing future accidents. PD is detected by many methods, but for onsite detection of PD, one of the efficient methods is sensing the electromagnetic waves radiated by the discharge source with a frequency range that can go up to 3GHz. In this technique Ultra High Frequency (UHF) sensors are mounted on the transformer tank to measure these waves. This provides a suitable solution for on-site detection of insulation failure in power transformers.

Data‐driven method using DNN for PD location in substations

Partial discharge (PD) detection and location based on ultra-high frequency (UHF) sensor array have been employed for the power equipment in the whole substation for assessing the insulating condition of electrical equipment and determining a precondition for further implementing insulation diagnosis. At present, one of the widely used localisation methods is time difference of arrival (TDOA) based, localisation result of which is extremely sensitive to time delay estimation and usually time-consuming to solve. Motivated by this, a data-driven method using the deep neural network (DNN) is proposed in this study to significantly speed up the solving process of non-linear TDOA equations and simultaneously guarantee the accuracy of results. It works with sequences of time delay measured from the UHF sensor array as the input of the network and with the corresponding coordinates of PD source as output to train the network. Simulation results demonstrate that the proposed method shows relatively higher accuracy and efficiency in PD location. In addition, many factors such as array shape, error type added to time delay, and detailed structure and parameters of network are taken into consideration for error analysis, laying foundation to more reliable localisation of PD.

Design and application of double layer bowtie antenna and single layer bowtie antenna as UHF sensors for partial discharge detection

The reliability of the power system cannot be achieved without good insulation quality of the high voltage apparatus. The Ultra-high frequency (UHF) method has been applied and proven to be accurate in detecting partial discharge (PD) signals emitted from the PD source in the form of electromagnetic waves. This paper discusses the design and application of double layer bowtie antenna and single layer bowtie antenna as UHF sensors for partial discharge detection in air insulation. The PD measurement results obtained by using the designed double layer bowtie antenna were compared with PD measurement results obtained by using the single layer bowtie antenna. The PD characteristics of induced EM waves detected by double layer bowtie antenna and single layer bowtie have been analysed. Based on the simulation results, the double layer bowtie antenna has a minimum return loss values of -31.54 dB and -33.43 dB, with corresponding resonance frequency values of 1.7 GHz and 2.7 GHz, with a total bandwidth of 602 MHz, and corresponding VSWR values of 1.04 and 1.05 while the measurement results by using Vector Network Analyser (VNA) shows that the designed double layer bowtie antenna has a minimum return loss of -20.2 dB, at a resonance frequency of 1.7 GHz, a bandwidth of 576 MHz and corresponding VSWR of 1.2. The single layer bowtie antenna has a bandwidth of 240 MHz, a minimum return loss of -24 dB, at a resonance frequency of 1.28 GHz, and a VSWR of 1.13 based on the simulation results while the single layer bowtie antenna has a bandwidth of 298 MHz, a minimum return loss of -23.32 dB, at a resonance frequency of 1.3 GHz, and a VSWR of 1.14 based on the measurement results by using VNA. The bowtie antennas were designed using the 3D-HFSS software with FR4-epoxy substrate type and later on were printed on the Printed Circuit Board (PCB). The PD measurement data were performed by using the applied voltage level of 7 kV. According to the antennas simulation results, antennas measurement results by VNA and PD measurement results, the double layer bowtie antenna has proven to be more sensitive than the single layer bowtie antenna.

A strong correlation between the bending rigidity and the length of single-walled carbon nanotubes

Continuous efforts to discover the novel carbon nanotube ultrahigh frequency resonators or sensors have being made since past two decades. The bending rigidity plays a key role in determining the frequency magnitude. Although it is previously justified that the bending rigidity has the almost linear dependence on the cubic of tube diameter, its dependence on another characteristic scale, i.e., the tube length is missing. Considering that the direct experimental observation faces significant challenge due to the low measurement precision by the inevitable thermodynamic fluctuation, we theoretically explored such size effect by means of three approaches respectively at different scale levels including quantum mechanics lattice dynamics calculations, molecular mechanics simulations and nonlocal continuum modeling for single-walled carbon nanotubes. The results from the different approaches give the consistent conclusion that there exists a strong correlation between the tube length and the bending rigidity, i.e., the rigidity increases with the tube length and converges to the value predicted by continuum theories. Moreover, we also find the nonlocal parameter reflecting the microscopic lattice effect in present continuum modeling almost independent of the chirality and linearly increases with the tube diameter with a scale factor 1.5. The comprehensive study may not only guide the design of ultrahigh frequency carbon nanotube devices but also provide insight to the bending nanomechanics of other devices made from nanotubes, nanobeams and nanowires.