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Accelerated lifetime tests on EPR specimens were performed with the aim to investigate the endurance under impulsive electric stress at room and 90 /spl deg/C temperature. The results outline that relationship of the electric field on the number of applied pulses, at 63% of probability of breakdown, can be described by the well-known inverse power model.

An objective formulation of the impulse testing procedure is proposed based on models for winding response as well as fault models. Experimental validation of the fault models for breakdown and partial discharge (PD) is provided. A new adaptive filtering approach is proposed for analysis during impulse tests. The procedure is validated with experimental investigation on a 10 section lumped parameter network.

The paper presents a very efficient method for synthesis of convolutional compactors capable of tolerating a number of unknown states in a single time frame while providing very high compaction ratios.

The use of high energy spark discharges to measure the impulse response of rooms will be discussed. Special emphasis will be placed on reverberation measurements, but other measurements will be included. Equipment designed at Rensselaer to simplify and speed this process will be described. This equipment is extremely compact and easily transported enabling field measurements by one person. The methods employed by other researchers will be explained, along with their advantages and disadvantages. Results of actual measurements will be presented and compared to those using more conventional techniques.

After two types of inflation uncertainty are derived within a time-varying parameter model with GARCH specification, the relationship between inflation uncertainty and interest rates for safe assets is investigated. The results support the existence of a "flight to quality" effect. © 2004 Elsevier B.V. All rights reserved.

Experimental results on fault simulations during impulse tests across windings and other specifically designed networks are reported. Both breakdown and partial discharge studies are conducted with digital acquisition of fault records. ? 2005 IEEE.

Impulse testing has been an integral part of predictive maintenance of electrical motors for many years. The influence that extensive impulse testing has on a motor is investigated in this paper. The questions investigated are the following: can impulse testing damage healthy or deteriorated insulation? Can weak turn-to-turn insulation be diagnosed with DC resistance, inductance, Megger or HiPot tests? Are motors with weak insulation, as proven by impulse testing, able to operate after failing the test? Are motors that show a turn-turn short capable of continued operation? These questions have been investigated by putting two low voltage motors through exhaustive testing rigors, until a failure was induced. Following the failure, additional testing allowed further investigation designed to determine the possible deteriorating effects on turn-turn insulation due to impulse testing beyond the motor's dielectric breakdown.

Impulse tests are performed on power transformers to assess their insulation integrity. During these tests, impulse voltages are applied, and the resulting voltage and current waveforms are recorded. After postprocessing of these data, the presence of faults in the winding should be detected. Different methods and models have been developed for pattern recognition of transformer winding current and classification of impulse faults, . The drawback of these methods is the representation of a fault as a short circuit with constant conductance. In this paper, the breakdown and arc were modeled to represent a more realistic fault during impulse tests. Using this model, it is possible to generate more realistic data, which are necessary to develop more reliable fault-detecting algorithms and, as a result, better pattern recognition and classification of impulse test waveforms. The model has its roots in the classical Mayr equation, and it is simulated with TACS and MODELS modules in EMTP. The simulation results verify the ability of the suggested method to represent disk-to-disk breakdown and arc fault during impulse testing.

Transfer function analysis is being developed for both impulse testing and monitoring of power transformers and offers advantages of fault identification and location. Based on Bergeron's method, a three-phase circuit equivalent to a power transformer is introduced in this paper. Sliding grounding insulation faults found at different locations in the winding are analyzed and simulated. The results reveal that changes in the transfer function help locate the fault and show the potential contribution to insulation fault monitoring and location.

Impulse testing has been an integral part of predictive maintenance of electrical motors for many years. The influence that extensive impulse testing has on a motor is investigated in this paper. The questions investigated are the following: can impulse testing damage healthy or deteriorated insulation? Can weak turn-to-turn insulation be diagnosed with DC resistance, Megger or HiPot tests? Are motors with weak insulation, as proven by impulse testing, able to operate after failing the test? Are motors that show a turn-turn short capable of continued operation? These questions have been investigated by putting a low voltage motor through exhaustive testing rigors, until a failure was induced. Following the failure, additional testing allowed further investigation designed to determine the possible deteriorating effects on turn-turn insulation due to impulse testing beyond the motor's dielectric breakdown.

This paper reports a pulse technique for measuring the shielding effectiveness (SE) of enclosures, without the use of an anechoic chamber or an open area test site (OATS). Experimental results are presented and compared to those of the conventional frequency domain method using an anechoic chamber. The results obtained from the pulse method are in good agreement with those of the frequency domain method. The pulse method is demonstrated to be a practical means of measuring enclosure SE, as well as an independent means for cross-checking outcomes from other measurement schemes, because it does not require site calibration.

Combined conditioning and a test method suitable for estimation of dielectric strength of commercial vacuum interrupters (VI) has been offered. Comparison with the conventional "up and down" method has been provided. The method has been successfully applied for a range of commercial vacuum interrupters.

Power transformers installed in the 1960s and 1970s were protected by surge arresters with gaps and silicon carbide valve elements. Many of these arresters are still in service but the population is declining. By 1980, gapless zinc oxide arresters were being installed in all new installations. There are two reliability issues involving surge arresters: adequacy of protection and consequential damage resulting from in-service failure.

In this paper an attempt has been made to find a correlation between the characteristics of gaseous decomposition products of insulation dissolved in insulating fluid and residual life of high-voltage impulse capacitors (HVIC) according to the results of life tests. It is shown that the most informative parameter, characterizing insulation condition, is the ratio of concentration of CO/sub 2//CO. A scheme is proposed of HVIC diagnostics in service according to results of the chromatographic analysis of gases dissolved in oil.

Various tests were performed on glass cap insulators under laboratory conditions. Laboratory methods were selected for a systematic insulator diagnosis on porcelain cap and long rod insulators. Electromechanical parameters of the aged insulators may be reduced to half the original value, to far below the required values. The power frequency wet test proved the ageing for other type of insulator strings too. The monitoring of leakage current impulses helps to follow the procedure. The selection of these impulses detects the mechanical defects of the insulators.

The authors evaluated the impulse breakdown characteristics of several commercially available insulating liquids under a highly divergent field for the purpose of characterizing and screening potential candidate insulating liquids for use in high-voltage cables. The ASTM D-3300 needle-to-sphere impulse test was used as the basis for the evaluation. In addition, it was hoped that the impulse data on the oils could be correlated with those of the corresponding oil-paper composites, thus providing an effective tool for predicting cable performance in actual service conditions. The needle-to-sphere impulse breakdown appears to show some dependence on differences in oil composition. The needle-to-sphere impulse breakdown voltage shows a significant dependence on oil viscosity and temperature. >

Experimental measurements of the effect of mist formation in vapor-mist dielectrics on impulse breakdown are presented. The water breakdown voltages are shown to increase as the temperature falls to the boiling point. This is an effect of the mist formation. The mist formation is also shown for benzene, hexane, ethyl alcohol, methyl alcohol, Freon R-11, R-113, R-11-R-113 mixture, R-113-R-114 mixture, and R-113-R-12 mixture mist. The electrical strength of the mist depends on the mass increase of clusters. >

Time series data for blood hemoglobin and plasma protein observed in 31 chronic hemodialysis patients for periods of three to seven years were analyzed by Akaike's method of multivariate autoregressive modeling. The results of the analysis were rather uniform among the patients and suggested that this approach can consistently identify the dynamic system of individual patients. >

A comprehensive study has been carried out in SF/sub 6//CCl/sub 2/F/sub 2//CO/sub 2/ mixtures to measure 50% breakdown voltages V/sub 50/ using both positive and negative polarity lightning impulse (1.2/50 mu s) voltages under nonuniform fields (5-mm rod, 230-mm plane electrode) over a pressure range of 0.1 to 0.5 MPa for a gap spacing of 20 mm. The sum of SF/sub 6/ and CCl/sub 2/F/sub 2/ concentrations in the mixture was always maintained in the range of 21 to 40%, the rest being CO/sub 2/. Among the different sets of SF/sub 6//CCl/sub 2/F/sub 2//CO/sub 2/ mixtures studied, two ternary mixtures, namely 20% SF/sub 6//20% CCl/sub 2/F/sub 2//60% CO/sub 2/ and 30% SF/sub 6//10% CCl/sub 2/F/sub 2//60% CO/sub 2/, were found superior to SF/sub 6/. From the known gas content in the mixtures and from the measured breakdown voltages, a cost/benefit analysis has been carried out for the various mixtures investigated. A striking feature of this analysis is that the most promising ternary gas mixture, namely 30% SF/sub 6//10% CCl/sub 2/-F/sub 2//60% CO/sub 2/, costs only 33% as much as pure SF/sub 6/, giving 100% to 170% positive breakdown strength, and 90 to 100% negative breakdown strength as compared to that of pure SF/sub 6/. >

The implementation of basic access ISDN (integrated services digital network) using the standard Digital Subscriber Line (DSL) will convert the local loop to a digital transport facility. The author suggests procedures for determining whether a basic access loop is subject to service-affecting impulse noise and describes the technical parameters of instruments that would be used to make that determination. The standard DSL will be a robust technology that will be largely immune to the effects of impulse noise. It is recommended that loops carrying DSL signals be tested for impulse noise only when the other maintenance tests have failed to reveal the source of customer trouble. Specifically, it is not recommended that impulse noise testing be part of a routine loop-qualification procedure. Results of impulse noise studies suggest that an errored second objective be used to determine whether impulse noise will affect service on loops carrying DSL signals. The author proposes a measurement procedure that uses currently available impulse noise tests sets to estimate the errored second performance of a DSL on a given loop. >

A composite long rod insulator produced in the authors' laboratory is discussed. The insulator is made of porcelain and silicone rubber. Test results on the electrical and mechanical properties are reported. The insulator has many advantages, such as light weight, ease of manufacture, high mechanical strength, very good antipollution performance, no risk of internal puncture, and reduced need for service safeguarding. These advantages become more obvious in EHV and UHV lines. >

The effect of repetitive surges on the impulse strength of interturn insulation was studied for coils in three motor stators. In each stator, the coils were divided into several groups. Breakdown voltages of coils in one group were measured for 0.1- mu s risetime impulses and the average breakdown voltage of these unaged coils was determined. Coils in the other groups were first subjected to a number of surges with magnitudes 3 to 6.5 pu (1 pu is the peak-rated line-to-ground voltage of the machine), and then the impulse breakdown voltages for these aged coils were measured and compared with those for the unaged coils. There was an indication of surge aging of the turn insulation only for one stator. Surge magnitudes capable of causing detectable aging of turn insulation appear to be higher than those likely to occur at normally operating utility motors. It is suggested that there is a threshold value of surge magnitude for producing aging effects. >

A description is given of two generalized models of impulse breakdown, which provide a theoretical basis for the integration method. The first is a physical approach, in which the breakdown criterion is the critical size of the relevant physical process. The second is an energy approach, which proposes that breakdown follows when the energy delivered to an incipient and filamentary (prebreakdown) channel reaches a critical value. It is found that the two approaches give the integration method a reasonable theoretical basis consistent with generalized views of breakdown processes in gaseous, liquid, and solid insulants. >

Results are reported of investigations into the influence of the space charge associated with impulse corona on the growth and direction of the leader in a rod-plane of 1.72 m with a negative-polarity lightning impulse voltage applied to the rod. The charge oscillograms show three distinct steps of 2.5, 5.0, and 8.0 mu C, and these are attributed to the first corona and secondary discharges including leader development. In order to assess the effect of impulse corona space charge on the field distribution, field calculations with and without space charges were carried out using the charge simulation method. From the results of the calculations together with photographs taken of the discharge, attempts are made to explain the direction and growth of the leader in the gap. >

The authors present an overview of dielectric phenomena in the breakdown of non-pressure-assisted, impregnated-paper-insulated HVDC (high-voltage direct-current) cables. Dielectric breakdown stress results are presented and interpreted. The dielectric phenomena arising in a shrinkage void formed within a cable insulation made of impregnated paper layers are analyzed. >

The work models the performance of mobile particles in compressed-gas-insulated substations under an intentionally applied impulse voltage of reduced magnitude. The subsequent microdischarges are used to detect the presence of particles and identify their approximate sizes. A comprehensive computer model is described. It describes and interrelates the potential and field distributions on and around the particle, particle lifting and movement, timing of the initial microdischarge, and the complete pattern of the microdischarges as might be detected by an external monitoring circuit. >

The authors describe a space charge measurement technique for a long XLPE cable specimen. The length of the cable specimen has been limited in conventional methods, because of the problem of pulse propagation through the cable. The problem was overcome by using the pulsed electroacoustic method, and also by applying the pulse voltage at the outer shield where the piezoelectric device was fixed. A preliminary experiment carried out using a 3.2-mm-thick XLPE cable confirmed the validity of the method. >

Presents a functional level built-in self-test of digital filters. This BIST technique is based on predetermined patterns which are not dependent on the filter implementation. Many examples show that stuck-at fault coverage is about 98%. >

Results obtained from lightning impulse measurements on fiberglass crossarms alone and with three porcelain suspension insulators are examined. The ratio of critical flashover (CFO) voltage under wet and dry conditions for fiber-glass crossarm is fairly consistent, and for crossarm with porcelain suspension insulators it is equal to 0.94. The CFO voltage added by fiberglass crossarms 0-2 ft in length to that of porcelain suspension insulators is 130 kV/ft for dry conditions and 100 kV/ft for wet conditions. For fiberglass crossarms 2-4 ft in length, the CFO voltage added to that of the porcelain string under dry conditions is 150 kV/ft and under wet conditions is equal to 140 kV/ft. >

The authors report on experiments in which multipulse lightning currents were applied to varistors to simulate the effects of multistroke lightning currents. Multipulse currents cause more damage than standard single-impulse current tests. Seven out of eight varistors failed the multiple current test at 75% of maximum rated current. Of these, three were destroyed by short-circuit and were physically damaged, while another three exhibited gross changes in their I-V characteristics. Devices subjected to single impulse currents survived. The multipulse tests used are representative of the surges caused by multiple stroke lightning in the field, and it is concluded that the adequacy of the standard impulse tests currently specified for low voltage AC power circuits should be reassessed. >

An electrode arrangement in compressed SF/sub 6/ was studied to verify its applicability as a precise voltage chopping device under standard lightning impulse for testing purposes. The effect of irradiation of the chopping gap and the application of a low DC sweeping voltage on the gap breakdown voltage dispersion under a standard lightning impulse was also studied. The results obtained show that the effect of irradiation and the DC sweeping voltage for the configuration and pressure tested was practically negligible, leaving the electrode conditioning as the most important factor to be taken into account when considering the utilization of this electrode arrangement as a chopping gap for standard lightning impulse chopping at the crest. >

A brief review is presented of the historical development of the standards for high-voltage impulse measurements. Test procedures based on new standards for an impulse measuring system, consisting of an impulse divider and a digital recorder, are discussed. The practical implementation of the tests requires some additional testing equipment. Commercially available calibration and testing equipment that has a high degree of automation and thus assures that the accuracy of a measuring system can be maintained is described. >

The impulse breakdown mechanism of PPLP (polypropylene laminated paper) is investigated in detail, taking into consideration the effect of PP (polypropylene) film. It is found that, although both positive and negative streamers affect the impulse breakdown mechanism, each effect is very different. That is, the positive charges are trapped on the surface of PP film easily, while the negative charges tend to spread into the insulating material. Consequently, it is suggested that the most essential factor of the impulse breakdown mechanism is the positive charges. Comparison of a sheet of PPLP and a specimen made of Kraft papers and PP film suggests the importance of the effect of oil thin films between Kraft paper and PP film. >

In order to clarify the factors involved in breakdown under AC and lightning impulse voltages, the authors have developed a prebreakdown detection method, and have discovered a number of facts concerning the factors determining the breakdown of insulation in XLPE (cross-linked polyethylene) cables. Experimental results reveal that impurities in the insulation constitute the governing factor in breakdown under AC voltages, whereas breakdown under impulse voltages is predominantly governed by protrusions in the shielding layers. >

A methodology is presented to test susceptibility of digital ICs for impulsive phenomenon. This paper gives an explanation of the impulse immunity test strategy and the test methods developed. Some results will be discussed.

Full-scale impulse testing of various cable systems that were carried out under the DSTAR (Distribution System Testing, Application, and Research) program, of which the NRECA Rural Electric Research program has been a participant, is described. The primary objective of this phase of the DSTAR program is to evaluate the neutral performance of various cable types under impulse conditions. It also attempts to evaluate the efficacy of a number of neutral grounding schemes. >

The results of an experimental investigation of the lightning performance of selected electrode configurations as well as 115 kV and 230 kV substation structures are presented. The evaluation of the lightning performance of the air clearances for structures used in HV substations was based on the measured critical flashover voltage (CFO) values for standard 1.2/50 /spl mu/s lightning impulses with both positive and negative polarities. The measurements of CFO voltages were performed in the Mississippi State University High Voltage Laboratory. The method used for estimating the air clearance in HV substations is discussed. The results obtained enable the designer to optimize air clearances for a specific application. >

The quick progress in the development of electrical insulating materials allowed significant miniaturization of electric and electronic components. Today dielectric materials with very high performance are available. But there exists no long-term experience about the behavior of very small insulating distances (creepage distances). Especially under the influence of pollution. Because of this lack of information investigations of a large number of modern insulation materials were carried out. Small creepage distances on these materials were exposed to the influence of natural pollution. The insulating-characteristics of the polluted insulating distances were investigated under well defined climatic conditions. One essential result of these investigations is that the withstand capability of the small insulating distances is strongly influenced by the ability of insulating materials to adsorb water on the surface. This ability is the most important parameter for the insulation characteristics of small insulation distances.

The response of Eskom's MV/LV distribution transformers to lightning transients is examined and the results presented. A high frequency transformer model has been derived utilising measurements based on impulse testing techniques for use in ATP for Windows and is used to simulate the transfer of surges from the MV to the LV side. The model reproduces the frequency dependant response of the transformer at its terminals and may be used together with any type of simulated load. Both varieties (i.e. Yznll and Dynll) of the Eskom standard distribution transformer are studied and their individual responses compared. The results have been verified by laboratory measurements.

The ISO Quality Standards, coupled with the publication of new technical standards, have led to an increased interest in the traceability of measurements. This paper presents a detailed description of the capabilities of NRC to provide simultaneous comparative measurements which is the reference method for qualifying impulse voltage measuring systems. This paper describes the measuring systems in use at NRC for calibrating client's measuring systems, either at NRC or at the client's site. Methods of making comparative measurement are reviewed and results from comparative measurements made using a variety of recording instruments are summarized. Recent measurements at NRC are reported to show the accuracy which can be achieved in comparative measurements. The uncertainty of one type of measuring system in use at NRC is estimated from international comparisons. Present work in IEEE and IEC is reviewed to predict the likely developments over the next few years.

The author has shown previously that a monochannel develops in transformer oil at the positive voltage pulse tail with an amplitude corresponding to the low gap breakdown probability (about 1-10%). A new method for investigating the impulse discharge mechanism, based on this phenomenon, is proposed. Three stages of discharge development are identified: discharge initiation and discharge zone formation; a stage of separation, movement and flashover of the gap by a monochannel; and monochannel transformation and complete breakdown. The characteristics of discharge development at these different stages are discussed.

Due to computational and convergence speed restraints, acoustic echo cancellers used for desktop handsfree units typically use an adaptive filter significantly shorter in length than the length of the enclosure/room impulse response it is attempting to model. A simple measurement based on this impulse response is proposed that gives the maximum obtainable depth of cancellation for a given filter length. By comparing this measurement with actual Echo Return Loss Enhancement measurements for different adaptive filter lengths, the optimum filter length for a given handsfree enclosure and transducers can be determined. >

Improvements of the "differential technique" of partial discharges (PD) measurements in hydrogenerators have led to noise-free PD spectra. These low-noise measurements have been obtained following the development and the implementation of the "HF grounding" technique for the couplers and of the "Time and Amplitude" (T&A) calibration technique for the PD detection systems. Following theoretical considerations on the behaviour of ungrounded coaxial lines, the "HF Grounding" technique is introduced and is shown to lead to an improved PD detection circuit having an improved response to PD impulses and an improved immunity against HF electrical noises. In order to achieve the required calibration accuracy for PD differential measurements, specially designed impulse injectors have been developed to feed the calibration impulses into the stator's windings through the phase buses. The necessary details to implement these techniques are mentioned and PD measurements obtained from hydrogenerators in various conditions are discussed. >

Impulse trees in insulators have been measured three-dimensionally to investigate their development mechanism. Since a usually observed tree is a projected one on the plane, the projected tree has pretend branches and the directions of its branches are not exact. In this paper, the impulse trees in the polymeric insulator (PMMA) have been measured three-dimensionally utilizing a CT (computer tomography) method. Successive impulse voltages have been applied. In each step, the tree has been measured and also the properties of the tree which cannot be obtained by the projected tree, such as the cross section. The volume and the distribution of the branches have been obtained for both polarities. >

New possibilities are open to the field of high voltage impulse tests. Nowadays the use of digital recorders, in high voltage laboratories, is quite common. This allows the use of a personal computer to make the evaluation of the tests results. However, due to the presence of disturbance, the software must include processing techniques that will allow better waveshapes to be obtained, to which the evaluation procedure given by the international standards can be directly applied. This paper deals with the use of frequency domain techniques to perform the processing. >