Search

The reliability of low-voltage inverter-fed motors is highly dependent on the inception of partial discharges. The effect of impulsive waveform parameters must be investigated to predict the repetitive partial discharge inception voltage (RPDIV) and define test procedures that can indicate properly the behavior in service of the insulation system. This paper focuses on the RPDIV of magnet wires using twisted pairs subjected to repetitive unipolar impulsive voltage waveforms. The effects of supply frequency (5 to 200 kHz) at pressure levels that are typical for aircraft (20 to 100 kPa) is examined. Results show that RPDIV steadily decreases with frequency up to 100 kHz where it reaches a plateau. This behavior is explained as an effect of the oscillations that inevitably exist in the applied voltage waveform. Therefore, a conservative estimate of the RPDIV could be achieved by raising the supply frequency well above the operation frequency. In the experiments, the RPDIV is decreasing linearly with pressure. If this behavior could be confirmed for other insulation systems, the design of systems working at pressures typical of aircraft would result relatively easy. [ABSTRACT FROM AUTHOR]

This work assesses the initial and crucial part of electrical treeing degradation, the inception stage, focusing on its dependence on applied voltage waveform and frequency. Tests have been performed on needle-plane configuration samples in solids and gels. A physical model has been formulated through an adaptation of an established theory for solids in which electrical tree inception is related to damage-producing injection currents. The voltage rise time appeared to be the most important parameter influencing the tree inception in the gel, while in the solid material the frequency is more relevant. The analysis leads to the conclusion that tree inception in gels is due to a single high-energy event, in contrast to what is commonly known for solids where damage accumulation takes place. A tree inception model is proposed for the gel, in which initiation is driven by a pressure wave generated by the electric field and the space charge injected into the sample. The model fits the experimental data and may be used to predict the tree initiation for different waveforms and voltage values. [ABSTRACT FROM AUTHOR]

We have investigated the long term stability of nanofluids exposed to strong divergent fields. The nanofluids were made of conductive nanoparticles (magnetite) dissolved in a base transformer mineral oil. The results show that, due to dielectrophoretic forces, nanoparticles aggregation takes place under DC fields with modalities associated with the polarity of the applied voltage. Under AC fields, aggregation is still possible, but the fields needed are above streamer inception voltage. Comsol simulations and simplified analytical models are provided to investigate the nanoparticle concentration dynamics. The models confirm the role of dielectrophoretic forces as a driver for nanoparticle aggregation. [ABSTRACT FROM PUBLISHER]

This paper reviews results of partial discharge measurements and accelerated life tests performed on models of random and form wound insulation systems subjected to impulse voltage waveforms. The goal is to highlight how the features of the supply voltage affect the partial discharge activity and how this, eventually, reflects on the endurance of the insulation system. The most salient results are that, for both types of insulation systems, short rise times trigger PD of large magnitude, which are able to erode the insulation system faster than the partial discharges incepted using waveforms with longer rise times. In particular, failure times estimated by tests under sinusoidal voltages can be overly optimistic in assessing the long-term behavior of the insulation system subjected to impulse voltage waveforms. Frequency also is very important, as it controls the interplay between physical and chemical degradation rates. As a result, above partial discharge inception voltage the frequency acceleration rule does not hold, and can lead therefore to excessively optimistic results. [ABSTRACT FROM AUTHOR]

In this work, we compare the dielectric withstand performance of nanofluids prepared using Shell Diala D as a base fluid, and magnetite, graphene oxide and silicone dioxide as nanoadditives. The ac withstand capability of the nanofluids was investigated as well as partial discharge inception voltage, partial discharge and repetition rate under ac, dc positive and dc negative voltages. The results indicate that, for all nanofluids, nanoparticle concentrations around 0.2 g/l enhance dielectric withstand properties under quasi uniform fields. Under divergent fields, partial discharge characteristics are improved under ac conditions. Under dc conditions silica nanofluid performs better than mineral oil, but the other two nanofluids do not perform well. [ABSTRACT FROM AUTHOR]

High voltage equipment designed for DC applications is stressed differently from ac equipment. Most notably, the load conditions of the equipment play a major role in determining the electric field distribution in insulation under dc, due to the temperature dependence of conductivity. Additionally, polarization and space charge phenomena impose a time dependent behavior on the stress distribution. This has major consequences for the way in which degradation of the insulation under dc stress takes place. The nature of the stresses under dc may lead to accelerated degradation processes which could result in early breakdown of the insulation. This paper provides an overview of the stress conditions specific for dc application and highlights via which routes they may lead to failure. The stress distributions in converter transformers and dc cable systems will serve as typical examples. [ABSTRACT FROM AUTHOR]

The dependence of endurance test results on repetitive square wave voltage waveform parameters is investigated in this paper focusing on crossed pair specimens made of polyamide-imide enameled wires. Endurance tests carried out on crossed pairs above partial discharge inception voltage using both sinusoidal and square wave voltages show that lifetimes can be influenced significantly by voltage waveform parameters (rise time and frequency). Partial discharge statistics, recorded from test beginning to breakdown, are used to explain the remarkable differences associated with voltage waveform parameters. According to this study, the influence of voltage waveform parameters should be carefully considered in order to obtain effective evaluation of inverter-fed motor insulation systems. [ABSTRACT FROM AUTHOR]

This paper focuses on the influence of repetitive square wave voltage rise time on partial discharge pulse characteristics in the ultra-high frequency range. Paerial Discharge (PD) tests on single-point contact crossed pairs were carried out using repetitive square wave voltages with a wide range of rise times, from 200 ns to 400 μs, including also 50 Hz sinusoidal voltage waveforms. Experimental results show that rise time has a significant influence on magnitude and frequency spectrum of PD pulses. Voltages of shorter rise times generate larger PD pulses with a predominance of high frequency components in the energy spectrum. Interpretations are presented for this phenomenon. [ABSTRACT FROM AUTHOR]

This paper focuses on the limits of partial discharge apparent charge estimation and calibration using an unified approach. The fundamental problems that prevent accurate apparent charge estimates (resonances, attenuation and partial discharge pulse splitting) are tackled through this approach, highlighting the physical limitations that prevent partial discharge charge to be measured properly. The feasibility of calibration of Ultra-Wide Bandwidth measurement systems, something that is not treated in the IEC 60270 standard, is also discussed. [ABSTRACT FROM AUTHOR]

A novel method for measurement and interpretation of PD phenomena in inverter-fed motors is discussed in this paper. The interpretation of PD measurements is carried out resorting to the direct-quadrature (dq) transform of the three voltages at motor terminals at the instant a PD event occurs. New tools (the dq loci, dq Hq and dq Hn patterns) are proposed to infer PD activity in a statistical way, similar to that used under AC supply. The method has been validated through tests on motorettes. In addition, measurements on low-voltage inverter-fed motors subjected to repetitive surges till breakdown are reported to support the capability of the method to infer onsetting faults. Measurements are performed through a reliable and lightweight (thus suitable for, e.g., automotive or avionics applications) antenna coupler characterized by excellent signal-to-nose ratio. [ABSTRACT FROM AUTHOR]

In order to improve partial discharge (PD) detection and location in extruded power cables, Ultra-Wide Bandwidth detectors (UWB) can be preferred to wide- and narrow- band systems. As UWB systems aim to get the broadest frequency content in PD pulses, it is important to evaluate the frequency attenuation as a function of distance propagated of the cable under test, trying to achieve optimum signal-to-noise ratio (SNR) and large detection sensitivity. Some conventional techniques able to calculate attenuation and dispersion of PD pulses are considered and a fast approximate model is developed in this paper, trying to provide a simple tool to estimate the maximum PD detection length in polymeric cable, in relation to bandwidth measurement system and required sensitivity. [ABSTRACT FROM AUTHOR]

An investigation on partial discharge (PD) propagation in power cables is carried out in this paper with the aim of inferring limits for PD detection as a function of the distance between PD source and detector. Although this problem has not an exact solution unless noise levels are not specified, useful information concerning detectability and error in estimates are provided in this paper for both medium and high voltage polymeric cables. The issue of calibrator characteristics with respect to sensitivity detection is also tackled. [ABSTRACT FROM AUTHOR]

A new technique for partial discharge (PD) source location in cable systems is presented in this paper. Such technique, here referred to as amplitude-frequency (AF) mapping, is based on the influence of attenuation and dispersion phenomena on PD pulse time and frequency characteristics. A comparative evaluation with other two well-known location techniques, i.e., time-domain reflectometry (TDR) and arrival time analysis (ATA) is presented through working cases. The results indicate that while TDR is appropriate for short cable systems, for longer cable systems, location by AF mapping can be obtained directly from PD testing, without additional efforts. The location thus achieved is, in most cases, accurate enough to allow maintenance practices to be carried out effectively. In some cases, ATA can be necessary to refine location and resolve ambiguities. [ABSTRACT FROM AUTHOR]

This paper presents a technique for outdoor ceramic insulator pollution assessment based on partial discharge detection and analysis. Laboratory tests and data coming from a monitoring activity carried out on some insulators of transmission lines are reported. They support the effectiveness of partial discharge detection and analysis as a tool to carry out condition-based maintenance of insulators of overhead lines. In particular, it can be seen that partial discharge analysis highlights the mechanisms bringing insulators to flashover (dry band arc activity) and is, therefore, well suited to predict increasing pollution and imminent flashover. As a consequence, algorithms are proposed to provide a quantitative evaluation of pollution severity. [ABSTRACT FROM AUTHOR]

This paper deals with the effect of supply frequency on partial discharge phenomena. Results of measurements performed on artificial and practical test objects are compared with computer simulations based on physical models. This comparative analysis points out and explains the differences in partial discharge phenomena observed in tests performed at different frequencies (from 0.1 to 300 Hz). The consequences associated to the use of different supply frequencies in practical applications are, eventually, outlined. [ABSTRACT FROM AUTHOR]

Inter-time (i.e., the time that separates a PD event from the next one) distribution analysis has been recently proposed as a tool to infer the presence of trees in solid insulation systems. In this paper, inter-time distribution analysis is improved to infer more accurately trees at an early growth stage. Measurements from both artificial specimens as well as practical objects are presented to support the effectiveness of this tool. Moreover, considerations on inter-time analysis robustness with respect to both noise interference and other partial discharge sources are reported. [ABSTRACT FROM AUTHOR]

An experimental investigation of the behavior of partial discharges occurring in insulation cavities as a function of light irradiation conditions is presented in this paper. Partial discharge inception voltage (PDIV) measurements were performed for different irradiation conditions of the test objects (visible light, of variable intensity, ultra violet (UV) light or absence of irradiation), defect geometry and conductivity of insulating material. It is shown that changes of such factors involve con siderable alteration of partial discharge inception features, in terms of both inception voltage and delay time. Depending on applied field, defect geometry, insulating material characteristics and irradiation condition, in fact, partial discharge inception voltage may be influenced prevailingly by background radiation, as generally stated in literature, or by field-assisted electron detrapping from material. cavity interface. [ABSTRACT FROM AUTHOR]

Applications of a new methodology, aimed at the identification of defects occurring in insulation systems of HV apparatus and based on partial discharge (PD) measurements, are presented in this paper. This methodology relies upon the digital acquisition of a large amount of PD pulses and separates the acquired pulses into homogeneous sub-classes. Signal processing tools recognize the presence of noise among the different classes. Identification of basic PD source typologies (i.e., internal, corona and surface discharges) is then achieved, resorting to fuzzy algorithms. The proposed procedure is applied to measurements performed on different HV apparatus, such as cables, transformers and rotating machines. The purpose of this paper is to show that the identification process is robust, regarding the measuring circuit, and flexible, so that it can constitute an advanced tool for condition based maintenance, guiding maintenance experts in making decisions on the condition of the insulation system under test. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) measurements constitute one of the most promising tools for electrical insulation diagnosis. This paper describes bow a procedure based on PD measurements can provide early detection of electrical trees in polymeric insulation systems. Such an application relies upon a new methodology, which provides enhanced tools for the identification of PD generating defects. Tree inference is carried out stepwise Acquired signals are primarily separated according to their waveform, thus achieving data sets related to a specific PD typology. Then, fuzzy algorithms are applied to PD height and phase derived quantities belonging to these homogeneous data sets, in order to assign a membership degree to specific output categories. If the data set is relevant to an internal defect, a further analysis is performed in order to establish whether or not this defect is a treed region. The algorithm described in this paper was developed resorting to tests performed on artificial test specimens and electrical apparatus. In particulars the rules to detect the presence of electrical trees were derived from experiments carried out on needle-plane objects, constituted by slabs of cross-linked polyethylene (XLPE) where a needle is inserted and partially extracted in order to generate a cavity in front of the needle tip. Tests were also performed on cables having artificial defects, as well as on other insulation systems, such as high frequency transformers Applications of the proposed approach to MV cables and to HV transformers show that electrical trees can be detected successfully before final breakdown. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the effectiveness of inference method for the diagnosis of solid insulation systems, based on Partial Discharge measurements. Theoretical background; Methodology; Results and discussion.

Part I. Presents a study that investigated noise rejection tools for advanced partial discharge (PD) inference in on-field measurements. Background on problems in the measurement of PD phenomena; Analysis of two kinds of noise using ultra wide band digitizers; Results and implications.

Illustrates a model that enables the estimation of life of polymeric insulation subjected to direct current stress, both in the presence and in the absence of voltage polarity inversions. Derivation of model parameters; Characteristics of the general life model; Probabilistic framework of the model.

Focuses on a study on digital acquisition, classification and analysis of the stochastic features of random pulse signals generated by partial discharge (PD) phenomena. Description of the measuring system; Details of PD pulse classification and clustering; Evaluation of classification effectiveness; Results and discussion.

In this paper, the PD properties of an ester oil/PB and a mineral oil/PB system undergoing a moisture transient are investigated using a needle-plane electrode under natural cooling. The temperature, moisture concentration and water activity of the oil are continuously monitored. Moreover, an improved moisture diffusion model is developed by using COMSOL Multiphysics to verify the experimental results. The measurement results show that there is a sharp reduction of partial discharge inception voltage (PDIV) or a sudden increase of PD intensity in the process of natural cooling for both ester oil and mineral oil system. However, the PDs extinguish gradually after the occurrence of the minimum of PDIV. For the cooling mode selected in this study, the minimum of PDIV for the ester oil system appears in the third hour after cooling begins, while it is about in the second hour for the mineral oil system. In addition, the simulation results are consistent with the experimental data. [ABSTRACT FROM AUTHOR]

In this paper, a comparative study including measurement and modeling of partial discharge for various void geometries (cylinder, block, and prisms) at very low frequency (VLF) and power frequency (PF) voltage is presented. Results from experiments and simulations are presented with phase-resolved discharge patterns and integrated parameters (maximum/average discharge magnitudes, and repetition rates). Dynamic simulation, achieved using a combination of finite element analysis and Matlab, matches the experimental results. Differences of discharge characteristics between VLF and PF may be attributed to the physical mechanisms in the modeling including cavity surface conductivity and space charge decay rate. Compared with discharge activities at PF, the VLF excitation in general exhibits relatively lower discharge magnitude and repetition rate. Also, the inception voltage is found to be lower at VLF. [ABSTRACT FROM AUTHOR]

We are pleased to announce that the February 2018 issue of the IEEE Transactions on Dielectrics and Electrical Insulation (TDEI) will be a special issue on High Voltage Direct Current (HVDC) Transmission System Insulation topics. [ABSTRACT FROM PUBLISHER]

A reply to a discussion on the effect of supply voltage frequency on testing of insulation system is presented.

In the framework of developing defect-based life models, in which breakdown is explicitly associated with partial discharge (PD)-induced damage growth from a defect, ageing tests and PD measurements were carried out in the laboratory on polyethylene (PE) layered specimens containing artificial cavities. PD activity was monitored continuously during aging. A quasi-deterministic series of stages can be observed in the behavior of the main PD parameters (i.e. discharge repetition rate and amplitude). The evolution of the parameters reflects the physicalchemical changes taking place at the dielectric/cavity interface during the aging process. PD activity shows similar time behavior under constant cavity gas volume and constant cavity gas pressure conditions, suggesting that the variation of PD parameters may not be attributed to the variation of the gas pressure. It is speculated that the change of PD activity is related to the composition of the cavity gas, as well as to the properties of dielectric/cavity interface. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for the diagnosis of HVDC systems based on partial discharge analysis. In particular, the characteristics of partial discharge phenomena from different test objects are highlighted, with the aim of providing tools enabling automatic identification of the type of PD, as well as noise and disturbance rejection, for on-line and/or off-line PD testing of HVDC equipments. The results show that, using a fuzzy identification system based on higher-order moments of the PD magnitude and inter-time distributions, corona phenomena can be identified easily, whereas it is sometimes difficult to distinguish between internal and surface partial discharge sources. For this purpose, the characteristics of internal and surface partial discharge phenomena as a function of influence variables as humidity and temperature are reported. By exploiting these characteristics through on-line/off-line PD monitoring systems, accurate identification of the PD phenomena affecting an electrical apparatus can be attained. [ABSTRACT FROM AUTHOR]

This paper reports and discusses qualification and type test procedures for random wound motors as specified in IEC Technical Specification 60034-18-41. Since laboratory tests dealing with off-line partial discharges measurements followed by life tests showed that motors qualified as good can fail in very short times, an extensive investigation on the causes of such discrepancy and, in particular, on the differences existing between the stresses applied during off-line tests and in service is described. In addition, the results of partial discharge measurements performed on crossed pairs are presented, highlighting how the differences in the applied voltage waveform can influence the Repetitive Partial Discharge Inception Voltage. Suggestions to improve the off-line test procedure and related equipment are eventually discussed. [ABSTRACT FROM PUBLISHER]

Experiments on the breakdown characteristics of a long air gap containing a floating conductor under switching impulse are carried out to address issues in live-line work engineering. The effects of gap distance, floating conductor structure, wavefront time, and high altitude on breakdown voltage are investigated, respectively. The results show that a floating conductor with sharp protrusions reduces the breakdown voltage and produces the lowest breakdown voltage area (LBA). The maximum reduction rate of the breakdown voltage and the position of the LBA vary with the gap distance. The position of the LBA is also related to the floating conductor structure. The results indicate that different floating conductor structures with similar electric field distortions have a similar effect on the breakdown voltage. For the effect of wavefront time on breakdown characteristics, the results show that the breakdown voltage under switching impulse with a long wavefront time is higher than that under a standard switching impulse. For the effect of high altitude, the results show that the LBA at high altitude is different from that at low altitude, and the high-altitude breakdown voltage corrected using the International Electrotechnical Commission (IEC) altitude correction method is not exactly the same as the actual experimental results. [ABSTRACT FROM AUTHOR]

This paper deals with the analysis of leakage current and phase angle characteristics of porcelain and silicone rubber insulator in order 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 porcelain and silicone rubber insulator under ac voltage at different pollution levels and relative humidity conditions with sodium chloride as a contaminant. Multi Resolution Signal Decomposition (MRSD) using Discrete Wavelet Transform (DWT) is employed to understand the time-frequency characteristics of the leakage current signal. Fast Fourier Transform (FFT) spectral analysis is adopted to calculate the phase angle values of the applied voltage and leakage current signals. Reported results on porcelain and silicone rubber insulators show that the pollution severity of outdoor insulators could be identified from the DWT STD-MRA (Standard Deviation Multi Resolution Analysis) Distortion Ratio pattern analysis of leakage current signals. [ABSTRACT FROM AUTHOR]

The aim of this paper is to infer partial discharge (PD) detection limits in extruded cables as a function of the distance between PD source and detection point. The investigation is carried out for different types of detectors, from IEC 60270-compliant to ultra-wide bandwidth systems. For this purpose, a medium voltage cable has been modeled as a transmission line with frequency-dependent parameters accounting for skin effect, dielectric and semicon characteristics. Pulse propagation through the cable has been predicted for very tong distances. Different filters have been used to simulate different detectors, emphasizing the behavior of these systems, particularly the features of sensitivity, noise rejection, PD source separation and PD source localization. [ABSTRACT FROM AUTHOR]

It has been observed that voltage waveforms generated by power electronic converters may affect significantly the reliability of electric motor insulation. Since partial discharges are considered to be the main cause of the reliability loss, new enamel insulations for magnet wires are being developed in order to withstand better stress amplification. The electrical characterization of these insulating materials is often carried out through aging tests which may provide estimation of life under different stress levels and conditions. However, deeper investigation of aging phenomena due to supply voltage waveforms is needed, especially regarding the relation between aging factors and stress conditions. This paper deals with this topic, showing experimental evidences of relation between partial discharge quantities (e.g., inception voltage, repetition frequency, amplitude) and electrical properties, associated with charge accumulation, which can be directly evaluated through space charge measurements. Characterization of insulating materials and comparison of materials candidate for application in power electronic waveform environment can be carried out resorting to the methodology proposed here. This approach can provide, therefore, a useful feedback to wire manufacturers regarding, e.g., the choice of additive nature and enamel components for magnet wires in power-electronic controlled motors. [ABSTRACT FROM AUTHOR]

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

Dealing with electrical rotating machines fed by voltage converters, understanding the effect of impulsive voltage parameters on partial discharge features is of great importance to select appropriate impulsive voltage to perform partial discharge inception voltage measurements. Similarly, the dependence of insulation endurance on voltage parameters might help to develop qualification tests providing more accurate evaluation of insulation performance. The effect of voltage duty cycle on partial discharge characteristics and endurance of inverter-fed motor insulation were investigated through a large number of tests performed on single-contact crossed enameled wires under bipolar repetitive impulse wave voltages. The partial discharge pattern, magnitude, repetition rate show that short impulsive voltage duration (i.e. small duty cycles), can induce asymmetric PD patterns and reduce the probability of PD inception at the falling flanks of impulsive voltages. Moreover, the endurance tests indicate that the duty cycle of the repetitive square wave voltage can affect the insulation endurance significantly. Repetitive square wave voltages with small duty cycles tend to overestimate endurance. Accordingly, when performing partial discharge inception voltage and endurance tests on insulation of inverter-fed motors, the influence of duty cycle should be carefully considered. [ABSTRACT FROM AUTHOR]

To ensure insulation system reliability of rotating machines driven by power electronics, accelerated tests under repetitive impulsive voltages should be performed on turn-to-turn insulation according to the standards provided by the International Electrotechnical Commission. The parameters of repetitive impulsive voltage can significantly influence insulation lifetime, and thus, voltage parameters should be carefully controlled during the accelerated tests. To increase endurance test efficiency when testing many insulation specimens in parallel, the rise time of impulsive voltage should be controlled at certain constant values after the breakdown of one or more specimens to obtain objective endurance test results. This study provides a description of a novel square wave voltage generator used for the insulation evaluation of rotating machines driven by power electronics. A single-channel generator with variable rise times used for one specimen and a multi-channel generator with a constant rise time used to test five specimens in parallel are presented based on a push-pull solid-state switch. In the multi-channel generator, the RC parameter of the high-voltage circuit can be adjusted automatically by resorting to controlling units and a circuit structure after the breakdown of one or more samples when performing endurance tests on parallel specimens to keep the rise time of impulsive voltage at constant values. The multi-channel generator can significantly increase the endurance evaluation efficiency of the insulation systems of rotating machines fed by power electronics. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to understand the pros and cons of aluminum conductors insulated with anodized aluminum for rotating machines used in aircraft. The investigation is focused on the breakdown voltage and partial discharge inception voltage of simple systems (crossed pairs, simplified coils). The results show that both breakdown voltage and partial discharge inception voltage are very sensitive to curvature radius and lower than those achieved using conventional copper conductors insulated with polymeric enamels. However, the operating temperature of the insulation (600 ?C) is extremely appealing. Therefore, it could be interesting to devise high temperature fillers and suitable manufacturing procedures to exploit this insulation system in specific applications, where the weight of the machine is the key factor for material selection. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]