Partial Discharge Detection System Research Articles

A 65-kV insulated gate bipolar transistor switch applied in damped AC voltages partial discharge detection system

Damped AC voltages detection system (DAC) is a productive way to detect the faults in power cables. To solve the problems of large volume, complicated structure and electromagnetic interference in existing switches, this paper developed a compact solid state switch based on electromagnetic trigger, which is suitable for DAC test system. Synchronous electromagnetic trigger of 32 Insulated Gate Bipolar Transistors (IGBTs) in series was realized by the topological structure of single line based on pulse width modulation control technology. In this way, external extension was easily achieved. Electromagnetic trigger and resistor-capacitor-diode snubber circuit were optimized to reduce the switch turn-on time and circular layout. Epoxy encapsulating was chosen to enhance the level of partial discharge initial voltage (PDIV). The combination of synchronous trigger and power supply is proposed to reduce the switch volume. Moreover, we have overcome the drawback of the electromagnetic interference and improved the detection sensitivity of DAC by using capacitor storage energy to maintain IGBT gate driving voltage. The experimental results demonstrated that the solid-state switch, with compact size, whose turn-on time was less than 400 ns and PDIV was more than 65 kV, was able to meet the actual demands of 35 kV DAC test system.

Partial discharge detection technology based on the fibre Bragg grating

ABSTRACTIn this study, the application conditions and influential factors of fibre Bragg grating sensors used for partial discharge detection are analysed by discussing basic mechanics of fibre Bragg grating sensors. A partial discharge detection system based on a fibre Bragg grating sensor is designed and used for detection of free metal particle discharge and suspended metal electrode discharge in oil. The detection results are compared with that of a system based on a piezoelectric sensor in comparison tests. The comparison includes the detection sensitivity, anti-vibration ability, and ability against strong electromagnetic interference in substations. The test results show that the system based on the fibre Bragg grating sensor can effectively detect typical discharges; its sensitivity is similar to that of the system based on the piezoelectric sensor. The fibre Bragg grating system is more easily interfered by vibrations, but has greater anti-electromagnetic interference ability than the piezoelectric system.

Monitoring Stator Insulation in Critical Motors: Choosing Diagnostic Tests

The petrochemical industry has increasing interest in the condition monitoring of stator winding insulation during service. The factory acceptance specifications developed from the American Petroleum Institute (API) standards often require a partial discharge (PD) and/or power factor tip-up (PFTU) test for brand new windings as a factory acceptance test before installation. Petrochemical industry users often employ PD detection systems for the condition assessment of critical motors, but the use of the PFTU test as a periodic evaluation technique is less popular. Specialized resources are needed to perform these tests at the factory and in the field, imposing different technical demands and requiring expert data interpretation to ensure value for the end user. PD and PFTU may serve as complementary techniques and are most useful when data are trended through the machine winding service life. Both types of measurement depend on stator winding geometry, insulating materials, insulation system construction, and operating environment. This article explains the PFTU and PD tests as applied to both factory acceptance testing and field testing on installed machines, including setup and execution of measurements, and explores technical considerations to define an appropriate test regime to monitor insulation condition. Examples of PD and PFTU test data from factory acceptance of new stator windings and on-site measurements of installed machines are discussed.

A Wavelet Spatial Correlation Algorithm to Partial Discharge Denoising Based on MDL Criterion

The partial discharge (PD) detection systems are often vulnerable to strong external interferences, and sometimes the PD signals are submerged in noises (white noise for example) completely. So the signals acquired must be preprocessed to obtain the reliable PD information. While there are many methods for white noise denoising, mostly are not very suitable for partial discharge. The wavelet transform (WT) coefficient of PD and white noises have different spread characteristics in different WT scales. Based on the Information Theory, The Minimum Information Description Length (MDL) criterion is a optimization strategy, a small amount of signal parameter is requried to the PD signals representation, the paper proposes a wavelet spatial correlation algorithm to partial discharge denoising based on MDL criterion: optimal wavelet function is selected based on MDL, then have the white noise reduced in WT, the algorithm has wonderful virtues such as free from any parameters estimation about noise, free from presetting threshhold and threshold chooseing behavior, so the algorithm is highly adaptive. Large amount of experimental results illustrate that the method presented in this paper are efficient and feasible and outperforms other general method of PD noise reduction.

Evaluation of Partial Discharge in Power Transformers by Acoustic Emission Method and Propagation Modeling of Acoustic Signal

Transformers are one of the most important and costly components of any power system. Proper monitoring of the health of a transformer is thus inevitable. Online monitoring of partial discharges (PD) is one of the ways by which the risk of catastrophic failure of a power apparatus can be reduced. Common insulation in power transformers are pressboard and oil. Unconventional PD measurement was developed for several decades ago as a form of PD detection system. In these PD measurement systems that are named unconventional method PD is analyzed by indirect features of this phenomenon, which includes electrical, acoustic, UHF, optical, and chemical methods. The main advantage of unconventional method is the ability of this method in order to decrease the amount of signal to noise ratio for on-site or on-line measurement. A study of the correlation between acoustic emission signals generated by PD and electrical PD charges is inevitable. By developing the speed of measuring devices like digital signal processor (DSP) the possibility of evaluation and calculation of acoustic signals in very short time have been increased. The aim of this paper is evaluation of acoustic signals for two different kind of pressboard (new and aged) with two types of sensors (75 kHz and 150 kHz peak frequency) and simulation of Acoustic Emission (AE) signals propagation which are produced due to PD inside a sample transformer tank by using Finite Element Method (FEM). 

Study of partial discharge characteristics at repetitive square voltages based on UHF method

Due to overvoltage produced by inverter output, inverter-fed motor insulation systems often experience fast electrical aging process, especially when partial discharge (PD) is incepted. Before putting into use, the PD detection should be performed on inverter-fed motors at repetitive square voltages to avoid the PD caused insulation deterioration when the motors are collected to inverters having specific characteristics. However, unlike PD tests at AC/DC voltages proposed in IEC 60270, the PD detection at repetitive square voltages is much more complex because of serious interference generated by impulse generator. To solve the problem, ultra-high frequency (UHF) method seems recommendable for its preferable signal-to-noise ratio (SNR). The chief aim of this study is to investigate PD pulse and statistical characteristics of turn-to-turn insulation for inverter-fed traction motors. A square-shaped Archimedes antenna, specially designed for the PD detection at repetitive square voltages of fast rise times, was used to perform PD tests on turn-to-turn insulation models. Time and frequency analysis results indicate that energy component of generator disturbance and PD pulses are mainly distributed in the 0–0.5 GHz and 0.6–1.5 GHz range, respectively. Based on the results, suitable filter was designed for power disturbance suppression. Additionally, resorting to the sensor unit (i.e. antenna and filter) and the PD test system, the PD statistical features at square voltages of different frequencies were obtained. Experimental results show that higher frequency will give rise, statistically, to PD of lower magnitudes distributing at smaller phases. A reasonable interpretation of this phenomenon was presented. Lastly, according to the PD statistical features, some suggestions for the PD detection system design, generator parameter optimization and the PD pulse extracting were given. The results of this work would be beneficial to the increase of the sensitivity when performing the PD detection on insulation systems for inverter-fed motors at repetitive square voltages and thus, improving the reliability of inverter-fed motors.

Partial discharge detection as a tool to infer pollution severity of polymeric insulators

This paper deals with the analysis of partial discharge characteristics of silicone rubber insulators, with the aim to develop a better diagnostic tool to identify the pollution severity of outdoor insulators. In this work, laboratory-based pollution performance tests are carried out on silicone rubber insulators under ac voltage at different pollution levels and relative humidity conditions, using sodium chloride as a contaminant. Partial discharge (PD) is acquired through an innovative PD detection system which is able to collect PD waveforms beside PD patterns. Time domain and frequency domain characteristics of PD pulses at different surface pollution conditions are studied. Statistical parameters of PD patterns are also evaluated in order to achieve a quantitative assessment of pollution severity of polymeric insulators. The results on silicone rubber insulators show that the pollution severity of outdoor polymeric insulators could be identified from the partial discharge pattern analysis.

몰드변압기의 부분방전 검출기술에 관한 연구

Transformer failures are mostly due to partial discharges (PDs) caused by the deteriorated insulation. It is, therefore, important to monitor PD occurrence in insulation system and prevent their deterioration. The presented paper deals with a PD detection method by a capacitive probe, which easily apply to cast - resin dry - type transformers. The PD detection system consists of a capacitive probe and a low noise amplifier having the frequency bandwidth of 500 <TEX>$Hz{\sim}30$</TEX> MHz. In the experimental set-up, sensitivity of the system is 7.16 mV/pC.

Detection of super-high-frequency partial discharge by using neural networks

A system has been developed for the detection of super-high-frequency (SHF) partial discharge (PD) at frequencies up to 6 GHz. The system consists of three antennas for capturing PDs and a fast digital oscilloscope for sampling data. One of the antennas is a disk-cone antenna with frequency range below 710 MHz. The other two half TEM horn antennas have been designed and constructed for the frequency range 716 MHz - 5 GHz. To extend the frequency range up to 6 GHz, a methodology has been developed by compensating amplitude-response to frequency-magnitude. The compensation is realised by using multilayer feed-forward neural networks to equalise on amplitude-response. A direct sampling method is used to log the captured PD data. This PD detection system has been implemented to measure PDs at a 400 kV electrical substation (Strathaven, Scottish Power Ltd).

Investigation of suppressing PD white noise by compound information of complex wavelet transform

AbstractAccording to the distinct properties between the complex wavelet coefficients of partial discharge (PD) signals and white noises, this paper presents the specific compound information (CI) of WTRIn series for complex wavelet transform (CWT), which are utilized to suppress white noises. Through the simulation case, the influence of n‐index value on denoising effect is discussed and the optimal CI of corresponding to different PD waveforms is analyzed by the simulation investigation. The parameters of variable tendency parameter (VTP), normalized correlation coefficient (NCC), and signal‐to‐noise ratio (SNR) are defined to synthetically evaluate the denoising effect. The db4 complex wavelet is constructed to suppress the white noise in ultra high frequency (UHF) PD detection system. The results indicate that the denoising effect of the CI for CWT is better than the simple information (SI) for CWT and the CI of WTRIn series have the optimal denoising effect to suppress white noise for UHF PD signals. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Pulse Analysis Algorithms for Distinguishing Discharge Sources using Different Types of Sensors

It is very important to discriminate noises such as air corona in measuring on-site partial discharges (PD). Therefore, in order to investigate the possibility of separating PD and noises through the pulse wave shape analysis (PWA), pulse wave shapes measured by a resistive sensor and a high frequency current transformer (HFCT) have been analyzed and PWA were performed. For the purpose, the high frequency partial discharge (HFPD) detection and PWA system has been developed. Also void discharges and air corona were adopted as the artificial defect and noises, respectively. For the PWA algorithm, two kinds of methods such as TF-KK (Kurtosis of time domain and frequency domain) and MMR-S (the ratio of max/min value and the summation of the captured data) were compared. As a result, the developed system in this study showed good ability of distinguishing small void discharges from very large noises such as big air corona and ground floating discharges, which implies that the developed HFPD diagnostic system with the PWA algorithm has been proved to have very good performance of eliminating noises.

An improved optically based PD detection system for continuous on-line monitoring of HV cables

An optically-based remote sensing technique using a laser source, polarization scrambler, standard single mode fibers, fiber polarizer, electro-optic (EO) modulator and optical receiver, for continuous on-line monitoring of partial discharges (PD) in high voltage cable joints is proposed. Both the fiber polarizer and EO modulator, which are placed near cable joints, are passive without any power requirements. An EO modulator with no electrical bias, which operates close to the half-intensity point, was used and proved to have much better light transmission performance and higher measurement sensitivity than the bias modulator approach investigated earlier. Various multiplexing techniques including optical switches and a fused fiber coupler have been investigated in order to implement multi-channel monitoring so that one laser source can be used to provide light to several fibers. The revised PD optical remote sensing technique has been applied to practical PD measurements on both 132 kV cable joint at the University of Southampton in the UK and 400 kV cable joints at Sudkabel GmbH in Germany. Obtained results have verified the principle and demonstrated the effectiveness of the developed technique.

Characteristics of PD pulses in electrical trees and interfaces in extruded cables

The characteristics of partial discharge (PD) occurring within electrical trees in extruded cable insulation, and also at model interfaces between a cable and its accessories, have been investigated. A wideband PD detection system was used that enabled the true shape of the PD pulses to be measured. The rise- and fall-times, pulse width, amplitude and frequency of the pulses were recorded as electrical trees grew through the insulation, and also as the tracking progressed along a model cable/accessory interface. The PD pulse characteristics in electrical trees varied with time of voltage application and also with the electrical stress in the insulation. Differences in the PD characteristics of electrical trees in the bulk of a polymer and at interfaces between polymers were observed.

Use of spatial phase difference method to detect microwaves associated with stator coil partial discharge in a generator

This paper presents a new system for detecting electromagnetic waves emitted from partial discharges (PD) due to material defects in high-voltage electric machinery and apparatus. PD is a symptom and/or a direct cause of the deterioration of insulation systems used in high-voltage stator coils. This system can detect PD by using the spatial phase information of the microwaves emitted from PD, which are voltage pulses of very short duration. We describe the properties of this system which is composed of two double-ridge-guide-horn antennas, two preamplifiers, a gigahertz interference receiver (GHz-2ch-down-converter) of original design, two A/D (analog to digital) converters, and a personal computer. We experimentally show that this system can be used for detection of the microwaves emitted by PD occurring in the stator coil. The result of this work is the development of a new noncontact PD detection system for generators, which can be operated by station personnel. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 16–26, 1997

Diagnostic methods for GIS‐insulated switchgear insulation using external antenna

AbstractA partial discharge detection system was developed using an external antenna that can be easily installed on the outside of the GIS. The antenna is fitted closely to the outer circumference of the insulation spacer, and it can detect electromagnetic radiation of the partial discharge with high sensitivity.To have high sensitivity even in noisy condition, three kinds of methods that can eliminate external noise effectively were verified. In addition, the locating method of defect based on distance attenuation was confirmed. Actually, the insulation monitoring system which employs the antenna is used in a substation that had already been installed. At present, it is operating satisfactorily.

Advanced digital instrumentation for partial-discharge measurement

A new computer based partial-discharge (PD) measuring system was successfully tested in the laboratory in long duration tests on dielectric materials and capacitors. The system measures each current pulse generated by partial discharge during a predetermined time. The pulses are digitized by a 200 megasample/s real-time waveform digitizer and stored in a fast memory unit. The data obtained are transferred to a personal computer for analysis. This system records a large number of pulses without dead time and produces statistical information related to amplitude, polarity, energy and charge content of the PD-generated current pulses. The operation, analysis and display of results are controlled by software. The software can easily be modified to obtain different evaluation methods. This gives flexibility to the new PD detection system and allows its use as a design tool. The operation of the system is automatic, and no human supervision is required. Long duration tests of ceramic capacitors were performed to validate the operation of the diagnostic system. One result indicates that the aging of the tested capacitors changes the charge distribution curve, which was obtained by the statistical analysis of current pulses. The distribution curve shifts towards higher levels of charge as the capacitors deteriorate. This result agrees with the experimental data reported in the literature. The system is particularly suitable for aging studies on dielectric materials under different test conditions.

Partial discharge. XIV. Acoustic partial discharge detection-practical application

For pt.XIII see ibid., vol.8, no.4 (July/August 1992). The finer points of acoustic partial discharge (PD) detection systems and their common applications are treated. The PD source, propagation path of the waves, the acoustic sensor, and system noise are described. The design of acoustic PD instrumentation, the location of discharges, and the detection and evaluation of signals are discussed. Applications to outdoor insulation, medium-voltage air-insulated switchgear, capacitors, transformers, and cables are covered. >

Partial discharge. XIII. Acoustic partial discharge detection-fundamental considerations

An overview of the basic acoustics theory required to understand the finer points of acoustic partial discharge (PD) detection systems is given. PD and acoustic test methods are discussed, and acoustic wave motion, impedance, and intensity are described. Wave propagation and signal absorption, and the velocity of sound are discussed. Acoustic characteristics of media gases, liquids, and solid materials are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

活線診断用高精度部分放電検出システムの開発

活線診断用高精度部分放電検出システムの開発

Fault Anticipator for Substation Equipment

Following an inordinate number of in-service failures of 230-kV current transformers, a need was perceived for some sort of early failure warning device for equipment in substations. The development and evaluation of an inexpensive partial discharge detection system for continuous on-line monitoring of substation equipment is described in this paper. The source of partial discharge activity, which nearly always precedes failure in high voltage equipment for times from minutes to months, may be unequivocally identified in a noisy substation environment, with no false alarms. Possible personnel hazard and damage to other equipment caused by an explosive failure can be avoided with appropriate operator action upon an alarm.