Measuring system for partial discharge

High-speed Nuclear Quality Pulse Height Analyzer for Synchrotron-based Applications J-F. Beche, J. J. Bucher, L. Fabris, V. J. Riot Abstract--A high throughput Pulse Height Analyzer system for synchrotron-based applications requiring high resolution, high processing speed and low dead time has been developed. The system is comprised of a 120ns 12-bit nuclear quality Analog to Digital converter with a self-adaptive fast peak detector- stretcher and a custom-made fast histogramming memory module that records and processes the digitized data. The histogramming module is packaged in a VME or VXI compatible interface. Data is transferred through a fast optical link from the memory interface to a computer. A dedicated data acquisition program matches the hardware characteristics of the histogramming memory module. The data acquisition system allows for two data collection modes: “standard” data acquisition mode where the data is accumulated and read in synchronization with an external trigger and “live” data acquisition mode where the system operates as a standard Pulse Height Analyzer. The acquisition, standard or live, can be performed on several channels simultaneously. A two-channel prototype has been demonstrated at the Stanford Synchrotron Radiation Laboratory accelerator in conjunction with an X-ray Fluorescence Absorption Spectroscopy experiment. A detailed description of the entire system is given and experimental data is shown. I. S UMMARY A fast high resolution and low dead time Pulse Height Analyzer (PHA) system for Synchrotron-based applications has been developed. This module is an addition to and completes the previously designed custom electronics for XAFS applications [1, 2]. The PHA system receives analog information from a low dead time pulse processing front-end section. The low dead time PHA system is comprised of a fast high resolution Analog to Digital Converter (ADC), a fast histogramming memory and a VME or VXI compatible interface. The VME-based system consists of one complete data acquisition channel. The VXI-based PHA system addresses the problem of simultaneous data acquisition from multiple channels. Both systems were tested at the Stanford Synchrotron Radiation Laboratory in conjunction with an X- ray Fluorescence Absorption Spectroscopy experiment. The block diagram of a single acquisition channel is shown in Fig. This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Science Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. J-F Beche, J. J. Bucher, L. Fabris and V. J. Riot are with E. O. Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (telephone: 510- 495-2327, e-mail: JFBeche@lbl.gov). The analog input section is built around a fast self-adaptive peak detector-stretcher described in [1]. The peak detector- stretcher includes all the necessary logic to provide pileup rejection and gating functions. The stretched signal is fed to a commercial ADC chosen to maximize throughput without compromising the differential non-linearity (DNL). This ADC is an 8Msps unit, providing 14 bit of resolution with no missing code over the full temperature range, and with an intrinsic DNL of ½ LSB. In order to improve the DNL (not adequate for nuclear spectroscopy applications), only the first 12 most significant bits are used. A 6-bit sliding scale correction [3] lowers the DNL to less than 1%. Including delays, the conversion time of the ADC is 120ns. The electronic pulse-processing amplifier, in its fastest version, shapes the energy events coming from the detector with a 250ns peaking time fourth-order, pseudo-gaussian shaping function. The conversion time of the ADC does not add to the dead time associated with the pulse-shaping amplifier. Data collection is either gated by an external synchronization signal such as an accelerator beam clock or a precise clock signal to time-stamp the data collection and measure count rates. After an analog to digital conversion has taken place, the ADC board control logic sends a request to the histogramming memory module. When the histogramming memory controller acknowledges the request, it uses the ADC data to increment by one the content of the corresponding address memory location. The entire operation lasts 130ns, which is less than the dead time of the pulse- processing amplifier. Therefore, the histogramming operation does not increase the overall event-by-event processing time of the entire system. The histogramming memory module is packaged in a VME or VXI compatible interface and is built around a dual-port static random access memory. One port is dedicated to data accumulation while the second port is mapped to the VME or VXI address and data buses. The transfer to the computer is controlled by either the synchronization signal in the form of an interrupt signal sent to the VME or VXI controller, or by the computer accessing the memory at regular time intervals. The former corresponds to the “standard” acquisition mode and the latter to the “live” mode. In standard mode the content of the histogramming memory must be erased (zeroed) before collecting any new data set.

We constructed an on-line partial discharge (PD) monitoring system (PDOM) with a CT sensor, an analogue-digital converter, and a tablet PC. A sampling frequency for data acquisition is 100 MHz, and we exchange on-site PD data through a cloud system. We successfully measured PDs in the early stage of insulation deterioration of a cross-linked polyethylene (XLPE) cable in a field site. Additionally, following PD detection by using a PDOM, we can locate a PD position by using a PD locator (PDL) system. By locating a PD, we can estimate the actual PD magnitude considering attenuation factor of a high frequency pulse. We show how the PDL system works on a XLPE cable network with time synchronization between two positions by using an injection current pulse. The locating accuracy of the PDL system is evaluated.

Partial Discharge (PD) characteristics of typical defects in oil-paper insulation under AC, DC and AC-DC combined voltages have been studied extensively. However, there is still limited material available for the pattern recognition of partial discharge under actual stress withstood by valve side windings in converter transformers. In this paper, the PD of needle-plane defect is measured under actual stress in converter transformers. The stress is DC voltage superimposed harmonics, which has been analyzed in PSCAD at first. Then DC voltage superimposed both single harmonic and multiple harmonics, including simulated actual stress and approximate square waveform, have been applied on electrode. PD parameters and patterns are acquired by detector using pulse current method. The test results indicate that the inception voltage and pulse repetition rate of PD have no direct relationship with harmonic order due to the accumulation of space charges injected by DC voltage. PD amplitude shows a growing trend and phase distributions of PD expand with the increase of harmonic order. PD patterns are also closely related to the waveform of applied voltage. PD amplitude rises with the increase of voltage change rate, and the majority of PD pulses occur in the phase range which has a higher voltage change rate. Experimental results show that harmonic order exerts a great effect on PD characteristics of needle-plane defect under DC superimposed harmonic waveforms. The findings of the current study are useful in further research on the pattern recognition of PD and diagnose in converter transformers.

Internal insulation defects of oil-immersed transformers are common because of flaws in both manufacturing and transportation process. Partial discharge (PD) activity caused by insulation defects may occur at rated voltage condition, leading to deterioration of material, which results in breakdown of insulation. Feature parameters of PD are closely related to the performance of insulation materials. Therefore, the parameter changes under long-term AC voltage due to the decrease in electrical properties of material. It is effective to acquire insulation condition of materials by analyzing changes in the parameters of PD. The present thesis studied partial discharge in insulation defect of oil-paper insulation under long-term AC voltage. The PD tests were performed on specimens of 1 mm thickness which was placed between the needle-to-plane electrodes in an oil cup. The specimen was impregnated with oil in vacuum with treatment of hot air drying in order to remove moisture. Feature parameters of PD, such as phase-resolved partial discharge analysis and equivalent time-frequency, were recorded during the test process. When the feature parameters of PD are significantly changed, some specimens were removed. The surface appearance of these specimens was studied by scanning electron microscope. The measurement provides a theoretical basis for the analysis of the changes in the feature parameters of PD, which is helpful for the estimation of remaining life of insulation material. Test results indicate that as the AC voltage applied, cellulose depolymerisation continuously happened at the surface of paper. Cellulose in some area is carbonized by PD, and particulates are created. As the PD developed, the discharge magnitude is increased at the beginning while decreased rapidly just before breakdown of the paper, and the distribution phase of discharges is almost unchanged.

Partial discharge(PD) test for simulated insulation defects of used hydro generator stator winding was conducted to analyze the PD Parameters. Simulated insulation defects are classified by 5 types corona, slot, internal, multi and aging defect. Phase resolved partial discharge, statistical parameter (skewness, kurtosis), PD magnitude as a function of the test voltage(Q-V curve) and PD magnitude change under test voltage for 2 minutes are used as PD parameters. The analysis of PD parameters by 4 types are proved to be useful methods. In particular, PD parameter characteristics of aging defect could help to assess the aging condition of stator winding because aging defect has more weak insulation strength than other insulation defects : PD distribution is wide and flat, PD rises rapidly near and Q-V curve rises sharply and then gently drops.

Noise has been a major problem in Partial Discharge (PD) measurement, hampering its effectiveness as a means of assessing insulation condition and of diagnosing faults in power plant insulation. The problem has become more evident in recent years as efforts are made to adopt on-line PD-detection for practical plant insulation condition monitoring. The majority of PD detection systems use Ultra High Frequency (UHF), High Frequency Current Transformer (HFCT), Acoustic Emission (AE) sensors or IEC60270 standard electrical contact systems. Despite great advances which have been achieved in hardware instrumentation over the past years, various forms of noise still affect PD measurements, irrespective of the type of measurement system employed. This paper presents the experience which the authors have accumulated in recent years dealing with noise in PD measurement using the four, aforementioned, measurement systems. Following a brief comparison of the requirement for signal analysis of the four PD measurement systems, the paper addresses the source of noise that often appears in practical applications. Denoising techniques such as the traditional digital filters, matched filters, discrete wavelet transforms and the second generation wavelet transforms will then be introduced and contrasted in terms of their distinct features, advantages and disadvantages. The most effective technique will then be proposed for the four PD measurement systems discussed. Real world data will be used to support the conclusions of the paper.

The continuous monitoring of power system devices is an important step toward keeping such capital assets safe. Partial discharge (PD)-based measurement tools provide a reliable and accurate condition assessment of power system insulations. It is very common that voids or cavities exist in every solid dielectric insulation medium. In this article, different voids are modeled and analyzed using an advanced finite element (FE)-based computational algorithm. The proposed approach can be used to measure PD in cavities and voids regardless of their shape and size. The frequentative scripting approach with finite element modeling (FEM) provides the results which satisfy all PD conditions. PD behavior has been studied and analyzed through PD statistical features obtained from the simulated PD signal. A comparative study between simulated and experimental results is also performed to validate the accuracy of the proposed modeling approach. To further improve the accuracy of the model, the influence and optimization of certain free parameters required for modeling has been carried out. The article shows how PD is greatly influenced by the shape and size of voids in dielectric insulators. The research realized in this article further provides the PD statistical features and its variation with respect to void shape and size. These features are utilized for the assessment of insulation quality. The variation in PD parameters with respect to voltage level is also presented and discussed.

emisji wnz. Abstract. The article presents the results of research and analysis which include an assessment of influence of selected microclimate parameters on the issue of partial discharges (PD) in high power drives in the energy sector. The author presented the results of their own research, which was made in industrial conditions in a long period of time. The study included measurement of environmental parameters such as the air temperature, radiant temperature, air velocity, humidity and the relative moisture of air. It also measured the parameters of PD like: PD intensity, amplitude of PD and the PD pulses. (The Analysis 0f the Influence of Environmental Conditions on the Measurement of Emission Partial Discharges in Electrical Machines).

The High-frequency power transformer (HFPT) is a new type of intelligent distribution equipment. It is easy to fail under high frequency voltage, the main cause of which is partial discharge (PD). A comprehensive test system is established to study the impacts of the frequency on PD characteristics. The PD inception voltage (PDIV), PD times, and PD mean amplitude of polyimide film are measured under the frequency 1∼50 kHz. The adaptive algorithm is established to decompose and reduce the noise so as to acquire the pure PD signal and achieve the effective characteristics. Also the insulation lifetime is recorded to illustrate the relationship between PD and aging state. Furthermore, the frequency-dependent characteristics of several typical PD parameters are elucidated in details using the method of equivalent microcircuit which can explain the PD activities under high frequency voltage. The experimental results show that with the increase of frequency, PD mean amplitude and times of polyimide film see downward trends after first increase while the PDIV keeps roughly constant with frequency variation. Through the analysis, the frequency-induced space charge accumulation effect plays a dominant role in the above physical changes under high frequency, whereas, the frequency stress changes the insulation permeability as well as the tangential E-field vector, which executes a prominent impact on the PD development under low frequency. It is worth noting that the lifetime is greatly shortened as the frequency increase which is different form the trend of PD characters, showing that there is no direct relationship between PD and the insulation lifetime.

Statistical modeling procedures are presented for representing various conditions in different types of samples and equipment at, or near, the onset of partial discharge (PD). Using multiple-regression techniques it was possible to establish trends in PD behavior in terms of the repetition rate. The latter parameter was chosen as being sensitive to changes near inception, and it is measurable by conventional instrumentation (for example a multichannel pulse-height analyzer). The statistical repetition rate models also can be related to the probability of inception. The probabilistic definition derived complies with the simpler criteria often used in partial-discharge testing. Application of the methods is described by statistical models determined for five examples that include resin-insulated and oil-impregnated systems. Computer analysis showed that a high proportion of the variability of discharge behavior near inception could be estimated from the models: in particular, the effect of voltage in combination with increase in time, insulation thickness, and temperature changes. In addition, the models indicated that characteristic PD patterns are identifiable for resin voids and oil wedges. It is concluded that adoption of statistical techniques could result in the specification of PD inception in terms of probability, thus reducing the difficulties in interpreting the results from commercial tests. >

Partial discharge (PD) is a common phenomenon that occurs in insulation of high voltage equipment such as transformers and has a damaging effect to the insulation. In this paper, the application of descriptive data mining on PD occurring in insulating systems is shown. Experiments were set up to create three basic types of PD: corona, surface discharges and internal discharges. PD data were analysed using phase resolved analysis and pulse height analysis. Descriptive data mining was applied on the collected data using decision tree with genetic algorithm (GA) to mine the rules/relationships that can be used to differentiate the PD. These extracted rules are useful as input to predictive data mining such as fuzzy logics.

The partial discharge measurements have been widely used in the field of insulation diagnostics. The presence of partial discharges inside the cable indicates the degradation of insulation material. This paper deals with the development of insulation diagnostic method based on the partial discharge (PD) measurements. The useful information about the partial discharge activity and insulation defects is extracted by the experimental results. Artificial cavity was introduced inside the medium voltage XLPE cable by using the traditional needleplane configuration. The statistical characteristics formulated with the help of PRPDA technique and ultra-wideband discharge characteristics by using HFCT sensor was studied and analyzed. Paper is related to study about the partial discharge phenomenon in detail. The aim is to interpret the variations in the partial discharge characteristics over the insulation ageing period in terms of physical phenomenon's taking place in PD sources. The results of this work are based on the partial discharge measurements for lifetime tests conducted over the medium voltage (MV) XLPE cable samples at high voltage laboratory.

Optimal selection of features of Partial Discharge (PD) signals recorded from defects in High Voltage (HV) cables will contribute not only to the improvement of PD pattern recognition accuracy and efficiency but also to PD parameter visualization in HV cable condition monitoring and diagnostics. This paper presents a novel Random Forest (RF)-based feature-selection algorithm for PD pattern recognition of HV cables. The algorithm is applied to feature selection of both PD signals and interference signals with the aim of obtaining the optimal features for data processing. First, the experimental data acquisition and feature extraction processes are introduced. PD signals were captured from faults created in a cable to obtain the raw PD data, and then, a set of 3500 transient PD pulses and a set of 3500 typical interference pulses were extracted, based on which 34 PD features were extracted for further processing. Furthermore, 119 two-dimensional features and 1082 three-dimensional features were generated. The paper then discusses the basic principle of the RF algorithm. Finally, RF-based feature selection was implemented to determine the optimal features for PD pattern recognition. The results were obtained and evaluated with the Back Propagation Neural Network and Support Vector Machine. Results show that the proposed RF-based method is effective for PD feature selection of HV cables with the potential for application to additional HV power apparatus.

It is well known that thermal and electrical stresses have a strong influence on the degradation of insulation, but the effect of the stress duration is not yet well analysed. On this account thermal, electrical, and a combination of thermo-electrical stresses were applied to a number of cast-resin samples, and their effects were evaluated via partial discharge measurements. Stress duration as well as time without stress was varied. This information will be used in a statistical method to recognise the influence of the duration of the applied stress on the partial discharge activity of every sample. The statistical method is the analysis of variance (ANOVA), which is useful when the frequency distribution of the measurements is a so-called normal distribution. All measurements were carried out following this distribution and thus the reliability of such tests is only dependent on the linear behaviour of the following variables: partial discharge inception and extinction voltage, number of discharge impulses, sum of the charges of all impulses, and average charge per impulse. The other variables are the stress duration and the time without stress. In order to recognise variations which only correspond to the same effect, tests must be ordered in groups with the same characteristics. Tests must also be performed in continuous and repetitive cycles under stress in order to avoid undesirable effects. The results of these experiments may form the basis for the identification of a relationship between one or more partial discharge parameters and the stress duration.

The problems of high voltage equipment usually come from the imperfection of solid insulation, which may be caused by poor workmanship during cable installation, leading to multi-void inside solid insulation and subsequently partial discharge when that cable is put in service. Therefore, this paper aims to investigate the discharge phenomena of multi-void inside solid insulation by creating artificial defects in epoxy resin and testing under AC and very low frequency voltage sources. The test object consists of a single void with different void diameters and multi-void created by injecting the air voids at atmospheric pressure into epoxy resin. The partial discharge inside a single void and multi-void is detected by using a conventional and unconventional sensor. The results of PD measurement are represented in the phase-resolved partial discharge (PRPD) and several partial discharge parameters, such as PD charge magnitude and PD repetition rate. In addition, the results are analyzed to observe the impact of the multi-void with different conditions such as variable void diameter, the thickness of epoxy resin, type of voltage source, and PD sensor. The test can specify trends toward breakdown and the severity of multi-void inside solid insulation.