On-line Partial Discharge Detection Research Articles

A PRPD-Based UHF Filtering and Noise Reduction Algorithm for GIS Partial Discharge.

The online detection of partial discharge (PD) in gas-insulated switchgear (GIS) is a crucial and powerful tool for maintaining their reliability. However, extracting weak discharge signals from strong disturbances is a significant challenge. The presence of noise can hamper the identification and localization of PD types, making the extraction of pure PD signals the focus of current research. This paper proposes a PRPD-based PD filtering algorithm that analyzes interference using the output information from PRPD and sets threshold parameters for noise reduction processing. This method is mainly used for secondary noise reduction at a later stage, without analyzing the noise source, to achieve effective signal acquisition while retaining the characteristics of the PD signals, thereby improving the system's sensitivity and the signal's purity.

An Innovative Fluorescent Fiber Sensor Based on Ce/Tb Co-Doped Silica Fiber for Partial Discharge Detection

A novel fluorescent fiber sensor based on cerium (Ce) and terbium (Tb) co-doped silica fiber (CTDSF) for partial discharge (PD) detection is proposed. The luminescence mechanism and PD detection principle of CTDSF are theoretically investigated. The CTDSF is fabricated using the rod-in-tube technique combined with the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser-heated drawing method. The intense emission peak of Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions located at 542 nm ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> - <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> transition) is excited at 302 nm, which indicates the energy transfer between Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. Moreover, the excitation peak region near 302 nm is well aligned with the PD light emission spectrum. Subsequently, the PD time domain signals of the needle-plate defect are experimentally measured by utilizing the CTDSF sensor, high-frequency current transformer, and plastic scintillation fiber (PSF). And the experimental results demonstrate that the CTDSF sensor can detect PD signals and has an excellent PD detection linear response with a sensitivity of 0.22 ns∙V/pC. Furthermore, the sensitivity of the CTDSF sensor is approximately 2.4 times dramatically higher than that of the PSF sensor. The CTDSF sensor integrated with the all-fiber system is predicted to have a wide range of potential applications for online PD detection.

Comparison of On-Line Partial Discharge Detection Techniques for High Voltage Power Cable Joints and Terminations

Cable joints and terminations play a vital role in providing dependable electrical connection, mechanical support and physical safeguard. These provide electrical stress control to shielded power cables. Despite their usefulness, they suffer from partial discharges (PD) because of enhanced voltage stress, moisture ingress and poor workmanship (during installation). Therefore, it is necessary to undertake on-line PD detection to determine their state. Some of these techniques are capacitive coupler (CC); acoustic emission (AE); and high frequency current transducer (HFCT). This article presents a literature review of these techniques based on the cost, availability, and applicability. The comparative analysis is also provided on location of their sensors, quantification and detection ability. The CC technique involves the quantification of the coupler sensor input measured in mV/pC by realizing the time of flight between two sensors for which the results are used to estimate location of the PD. Meanwhile, the AE technique has an advantage of high immunity to electrical noise, with a caveat that acoustic signals are highly attenuated within the cable joints. Additionally, the combination of the acoustic sensors and PD electrical couplers can be used to discriminate PDs from electrical noise. The HFCT has two methods – with demonising (HFCT-WiD) and without demonising (HFCT-WoD). The HFCT-WiD technique can significantly reduce the sensor’s detection sensitivity due to its high value of noise to signal ratio (NSR). Comparatively, the HFCT has the best results of quantification and detection ability for PDs among all three techniques investigated. However, in places where electrical noise is severe, PD activities may be detected effectively with AE technique. Further work is needed to statistically map these methods and establish their correlation with experimental data.

A Novel Embedded Sensor for Partial Discharge Detection in Inverter-Fed Machines

This article presents a novel ring-shaped hybrid fractal antenna for detection of partial discharge (PD) in inverter-fed machines. PD is known as a source of degradation and lifetime reduction in the machines winding insulation. PD activity is becoming a major concern in high performance drives, especially due to the increased use of repetitive impulse voltage with short rise-time (high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ) from pulsewidth modulation-controlled inverters. The proposed hybrid fractal antenna is designed and experimentally demonstrated to show a high sensitivity in the ultrahigh-frequency bandwidth of interest for PD detection as well as an ability to discriminate PD signals from other sources of high-frequency disturbances. Additionally, the proposed PD sensing solution features a unique ring-shape geometry that facilitates its physical integration into a live machine, making it suitable as a noninvasive solution for online condition monitoring and PD detection of any inverter-fed electrical machine.

Study of Ultra High Frequency Measurement Techniques for Online Monitoring of Partial Discharges in High Voltage Systems

Partial Discharge (PD) activity is a pre-cursor for insulation degradation which may eventually lead to catastrophic failure of the electrical equipment with severe social and economic consequences. It is therefore imperative that PD is detected at its early stages to permit repair or replacement, prior to total failure. The bulky non-planar construction of existing ultra-high frequency (UHF) sensors coupled with the lack of proper feeding techniques and the ultrawide signal bandwidth of PD signals which necessitates the use of digital storage oscilloscope have restricted field deployment of UHF technique for online PD detection. In this work, we present a compact ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.58 \boldsymbol {\lambda } $ </tex-math></inline-formula> ) wideband (0.5-3 GHz) dual arm Archimedean slot spiral with coplanar waveguide feed for PD detection, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda } $ </tex-math></inline-formula> is the wavelength at center frequency. Numerical simulations of the antenna were compared with the measurements of the fabricated antenna. The fabricated wideband antenna was used to detect PD emissions from a mineral oil test cell connected to 10 kVA 50 Hz transformer. We also present different UHF signal measurement techniques ranging from PD pulse detection to reconstruction of the bandlimited PD signal in the digital domain for online structural health monitoring of high voltage systems. The proposed UHF PD measurement techniques are low cost compared to the conventional approach and indicate the feasibility of an embedded system for online PD monitoring using the fabricated UHF sensor.

Research on UHF PD detection method based on improved DBN

With the development of power grid technology and the widespread application of gas insulator switchgear (GIS) equipment, the power supply reliability of the power system has been greatly improved, but the problem of partial discharge (PD) faults in GIS has always been prominent, seriously affecting the safe and stable operation of the power grid. How to quickly determine the type and cause of GIS discharge is the key to online PD detection. In this paper, in order to deal with the very complicated data processing of ultra-high frequency (UHF) PD, the time-consuming and low efficiency of manually judging the type of PD, a classification model of UHF PD system based on deep confidence network (DBN) is established and an automatic classification method for UHF PD based on improved DBN is proposed; the activation function Sigmoid is improved to effectively prevent the occurrence of the gradient disappearance problem; the optimized DBN parameters are used to train and classify data of different PD types. The classification accuracy rate of the test results reached 96.7%, realizing the rapid classification evaluation of UHF PD types.

Denoising of Heavily Contaminated Partial Discharge Signals in High-Voltage Cables Using Maximal Overlap Discrete Wavelet Transform

Online detection of partial discharges (PD) is imperative for condition monitoring of high voltage equipment as well as power cables. However, heavily contaminated sites often burden the signals with various types of noise that can be challenging to remove (denoise). This paper proposes an algorithm based on the maximal overlap discrete wavelet transform (MODWT) to denoise PD signals originating from defects in power cables contaminated with various levels of noises. The three most common noise types, namely, Gaussian white noise (GWN), discrete spectral interference (DSI), and stochastic pulse shaped interference (SPI) are considered. The algorithm is applied to an experimentally acquired void-produced partial discharge in a power cable. The MODWT-based algorithm achieved a good improvement in the signal-to-noise ratio (SNR) and in the normalized correlation coefficient (NCC) for the three types of noises. The MODWT-based algorithm performance was also compared to that of the empirical Bayesian wavelet transform (EBWT) algorithm, in which the former showed superior results in denoising SPI and DSI, as well as comparable results in denoising GWN. Finally, the algorithm performance was tested on a PD signal contaminated with the three type of noises simultaneously in which the results were also superior.

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.

Amplitude Distribution of Partial Discharge Signals on Tunnel-Installed High-Voltage Cables

For 110 kV and above tunnel-installed high-voltage (HV) cross-linked poly-ethylene (XLPE) cable systems, it is a normal procedure to adopt a cross-bonding scheme. The high-frequency current method is frequently used in the cross-bonded cable systems for on-site or online partial discharge (PD) detection by monitoring the signals on the cross-bonding wires. To further study the amplitude distribution characteristics of the PD signals, a parametric characteristic admittance model of a three-phase cable system in a tunnel is established based on Tylavsky’s formulas. The model is used to calculate the amplitude distribution formula of the PD pulse current on the cross-bonding wires. In addition, the influence of cable laying and tunnel environment on the amplitude distribution is also studied. Finally, the correctness of the model and the conclusion are verified by simulation experiments and on-site tests. The results show that the signal amplitude distribution is determined by the ratio of the characteristic admittances. As the distance between the cables and the distance from the inner wall of the tunnel increase, the amplitude difference gradually decreases.

Accurate on-line fault location and PD activity location results obtained with SCG – a long-term utility experience

In recent years, Alliander (one of the largest network owners in the Netherlands with almost 40,000 km of medium-voltage (MV) cable (polymer insulated lead covered and cross-linked polyethylene) installed a number of smart cable guard (SCG) systems to verify its effectiveness in preventing failures or, if there is a breakdown, to reduce the repair time (outage time). Alliander concluded that SCG is indeed a very effective tool for on-line detection and location of (intermittent) faults and partial discharges in MV power cables. These phenomena are located with an inaccuracy better than 1%, based on travelling waves. On average, each SCG system could have prevented about 6150 customer minutes lost per year. Preventive repair also allows seeing the cause of degradation, helping to develop counter measures. SCG can be used in all types of MV cable networks and replaces fault passage indicators as well. Based on this, Alliander will implement more SCG systems in the upcoming years.

Online Detection of Partial Discharges in Medium and High Voltage Cable Accessories by Acoustic Emissions

Online Detection of Partial Discharges in Medium and High Voltage Cable Accessories by Acoustic Emissions

UHF Moore Fractal Antennas for Online GIS PD Detection

A sensor for a Moore fractal antenna was designed to detect partial discharge (PD) in gas-insulated substations. This worked at an ultrahigh frequency. First, the multifrequency characteristics of this antenna were analyzed and ANSYS HFSS was used to simulate the Moore fractal antenna and the Hilbert fractal antenna for comparison. The results show that the Moore fractal antenna had good directivity and omnidirectional radiation features. We then developed physical models for them according to the simulation results. The two antennas were tested using a vector network analyzer. The results show that the Moore fractal antenna had more frequency bands than the Hilbert fractal antenna. The PD was tested in the laboratory and detected by the Moore fractal antenna and the Hilbert fractal antenna. A comparison of the measured results showed that the proposed antenna was promising for online PD detection applications.

A Novel Time Alignment Technique for Online PD Location in Covered Conductors

This letter presents a double-side measuring method for online partial-discharge (PD) detection and location in covered conductor (CC) lines. To synchronize both PD sampling units mounted on two separate sides, a novel time alignment technique is proposed and implemented using the combination of a pulse injector and a pulse detector. A laboratory experiment on a 10-kV CC line was conducted to verify the feasibility of this technique.

From the editors' desk

The first article in this issue is "Special Requirements of High Frequency Current Transformers in the On-Line Detection of Partial Discharges in Power Cables," by Yang Xu, Xiao Gu, Bin Liu, and Baojun Hui of the State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, China; Zhigang Ren of the Beijing Electric Power Research Institute, Beijing, China; and Shaoxin Meng of the China Electrical Power Research Institute, Wuhan, China. The article discusses some special requirements of high frequency current transformers and the instrumentation in the on-line detection of partial discharge (PD) in cables. Four types of defects representing typical situations in the field were created in a 110-kV cable and joint for PD detection. Based on the frequency analysis of the PD signals, the upper frequency of a measuring instrument needs to be higher than 40 MHz and the lower frequency no less than 500 kHz. The lower frequency limit is recommended to avoid power line interference. Provided that the high frequency current transformer satisfies the bandwidth requirement, a high transfer impedance is preferred. A sensitivity better than 100 pC is expected in on-site PD detection and in high noise environments. The article compares eight PD measuring instruments based on high frequency current transformer detection with respect to lower and upper limit frequencies, sensitivity, PD pattern recognition functions, and PD signal attenuation. Among the existing functions, the PD pattern recognition function needs to be improved for on-line cable tests. In addition, the article concludes that there still is a need for an on-line calibration method based on high frequency current transformer sensors.

Special requirements of high frequency current transformers in the on-line detection of partial discharges in power cables

The insulation condition of power cables is closely associated with partial discharge (PD) [1]. Early signs of cable insulation failure such as from electrical treeing are revealed by PD detection [2], and insulation failure will eventually lead to breakdown [3]–[5]. For AC cross-linked polyethylene (XLPE) cables, online PD detection is used to determine potential defects in the cable, and high frequency current transformers (HFCT) are most commonly applied for convenient and noninvasive detection. Conventional PD measuring techniques have been specified in IEC 60270 [6], and cable factory tests are based on this method. When PD detection is conducted on cables in service, some special issues such as noise reduction and dynamic range have to be dealt with [7]. Complex electromagnetic interferences and noise may significantly affect detection results by reducing the detection sensitivity [8]. Some high frequency components of PD signals cannot be covered by the detection bandwidth of a measuring instrument because the upper limit frequency is not high enough [9]. One more challenge is that a long cable can cause significant attenuation of PD signals [10]–[12], which will decrease the signal amplitudes to be detected. Therefore, the PD measuring instruments for on-line detection for cables have to satisfy some additional requirements.

Guarding MV cables on-line: With travelling wave based temperature monitoring, fault location, PD location and PD related remaining life aspects

On-line partial discharge (PD) detection and location has proven to be a valuable tool for assessing the condition of medium-voltage (MV) power cables in service. A few advances are discussed in this paper. It is of importance to know all factors affecting PD activity in order to judge its severity. Cable temperature, more specifically its variation due to load cycling, is one key parameter. From the variation of the signal propagation velocity along the cable it is shown that the temperature can be monitored within one degree centigrade accuracy. The PD activity was found to respond upon temperature cycling caused by load variation. Moreover, data gathered from years of field experience has led to more insight in the predictability of upcoming faults based on (trends in) PD activity. It is possible now to identify the time between the moment partial discharges appear (or reach a certain level) and a final breakdown for different types of cable insulation. Occasionally, cable faults occur without being preceded by PD activity. For distribution network operators, a quick location of a MV cable fault, either a direct complete fault or a self-healing (or intermittent) fault, will contribute to reduce the outages both in duration and frequency. The earlier applied PD location technique is extended to capture also faults based on first arrival of the associated transients. This fault pinpointing is possible for any MV power cable type within 1% of the cable length, independent of the network grounding and whether a fault is a permanent one or a self-healing one. This paper presents the various techniques and results from test cases and a real captured field fault.

Detection of online PD signals in XLPE cables using the Bhattacharyya distance

Partial discharge (PD) signal detection can be used for insulation monitoring of power system equipment. Online PD detection as a main task of insulation monitoring for different power system equipment is a difficult procedure when environmental noise is taken into account. This paper proposes a new scheme based on the Bhattacharyya distance approach with the main goal of detecting the PD signals in cross-linked polyethylene cables. The proposed method, as a preprocessing tool, can be used for detection of PD signals in a noisy environment. The simplicity and the accuracy of the Bhattacharyya distance approach are the 2 main advantages that grab the attention of the authors in introducing this technique for detection of PD signals in different high-voltage power devices. In order to remove noises between intervals of measurement of PD signals, other simple signal processing techniques should be used as postprocessing tools. Detection of PD signals in a noisy environment, i.e. �nding the times of PD occurrences, is the most important and difficult stage in online PD signal monitoring. The Bhattacharyya distance method is a simple approach that can be used for detection of short duration time signals such as PDs.

On-line partial discharge defected phase selection and localization in cross-bonded single core cables

In this paper, a practical rule-based guideline has been presented for on-line detection of partial discharge (PD) defected phase (i.e., phase selection) followed by discriminating PD defected cable section (i.e., localization) in cross-bonded single core cable networks. Both goals are met by relying on the proposed rules that take the advantages of an energy-based index, calculated/measured at different junctions of cable network. The whole process provides practicability needs, as it requires neither synchronized measurements at different junctions of a network nor any PD pulse detection. Moreover, the proposed procedure derives the required indices from the measurements out of the link boxes, which provides enough safety in practical applications. Simulating and investigating four popular cross-bonding schemes (including sectionalized and continuous by coaxial cable and single core cable) as well as various characteristics of PD sources, different source locations, and noisy condition have proven acceptable performance of the proposed method in both tasks of phase selection and localization.

Identification of partial discharges immersed in noise in large hydro-generators based on improved wavelet selection methods

Background noise is a major problem in online Partial Discharge (PD) detection. Particularly in large hidro-generator windings, PD pulses originated in locations far from the PD sensors are strongly attenuated due to the propagation characteristics of the pulses, and arrive to the sensors completely buried in the background noise. Therefore, it is of paramount importance to identify the PD signals whose power is at least around the same as that of noise, thus with a medium to high signal to noise ratio, to extend the PD predictive diagnosis to the innermost bars of the winding. The wavelet shrinkage technique provides the best results in eliminating this type of noise. For this purpose, it is essential to choose the most appropriate wavelet decomposition, defined by the topology of the decomposition tree, its number of levels and the selected wavelet functions. In this paper a new algorithm for the automatic selection of the number of decomposition levels is proposed, and two new methods for the selection of the wavelet decomposition filters applied to PD signals measured from two large hydro generators are advanced. In addition a new methodology to evaluate the performance of denoising methods, which takes into account the average results for all possible relative time shifts of the PD pulses and several noise threshold levels is described. One of the proposed methods presented much better results than do the traditional CBWS, EBWS and SNRBWS methods, with respect to both the denoising performance and the runtime.

On-line PD detection and localization in cross-bonded HV cable systems

This paper addresses the detection and localization of partial discharge (PD) in crossbonded (CB) high voltage (HV) cables. A great deal has been published in recent years on PD based cable insulation condition monitoring, diagnostics and localization in medium voltage (MV) and high voltage (HV) cables. The topic of pulse propagation and PD source localization in CB HV cable systems has yet to be significantly investigated. The main challenge to PD monitoring of CB HV cables is as a result of the interconnectedness of the sheaths of the three single phase cables. The cross-bonding of the sheaths makes it difficult to localize which of the three phases a PD signal has emanated from. Co-axial cables are used to connect cable sheaths to cable link boxes, for ease of installation and protection against moisture. A second challenge is, therefore, the coupling effect when a PD pulse propagates in HV cable joints and the co-axial cables, making PD detection and localization more complex. The paper presents experimental investigations into PD pulse coupling between the cable center conductor and the sheath and the behavior of PD pulse propagation in CB HV cables. It proposes a model to describe PD pulse propagation in a CB HV cable system to allow monitoring and localization, and also presents the knowledge rules required for PD localization in CB HV cable systems.