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Reliability and power quality are two of the most discussed topics in the utility industry today. Many groups have performed power quality studies with varying results. One large industrial customer in northern New York State which experienced numerous process interruptions due to power system disturbances was the focus of this study. Monitoring methods, results, inadequacies of standards, and unique mitigation techniques used to conquer their problems are discussed in this paper.

Many utilities still have paper-insulated pipe type cables in service. In the near future they may have to replace some of these systems due to local increases in electric power demand or aged cable insulation. In many cases the steel pipes are well protected against corrosion and thus suitable for further use. For Retrofitting in such installations, XLPE-insulated cables offer several advantages. Felten & Guilleaume Energietechnik AG has developed a new three-core XLPE-insulated 64/110 kV cable with reduced insulation thickness (10 mm), that can be pulled into a pipe. In co-operation with VEW ENERGIE AG, the cable performance is being investigated in a field test, that started in October 1996. This long-term loading cycle test will last for three years. The test voltage, applied between conductor and earth, amounts to 127 kV. The temperature is measured with the help of an optical-fiber measurement system. This device is computer controlled and works as a remote monitoring system. Keywords: Retrofitting, power cables, cross linked polyethylene insulation, paper insulation, pipe cables, optical-fiber measurements, temperature measurement, cable ratings, power cable installation, trenchless technology

Power capacitors are widely used for regulating voltage and improving the power factor, and the type in most frequent use today are capacitors made of oil-impregnated paper film, a growing number of which will soon have been in operation in the field for 20 years, which has prompted us to make study of techniques for diagnosing deterioration in oil-impregnated paper film capacitors. It was found that thermal stress causes deterioration of the insulating paper, which increases the amount of dissolved CO and C[O.sub.2] in the oil, and lowers the partial discharge inception voltage, determining the useful lifetime of the capacitor. Based on this idea, techniques have been proposed for diagnosing deterioration, consisting of caution level and danger level, from actual stress in the field. Further, a trial calculation was made for the number of years and months it takes for a capacitor to reach the caution level, from an investigation of capacitors in service for years.

Disconnecting switch operations in gas insulated equipment cause transient voltages with risetimes as steep as 5 to 20 nanoseconds and magnitudes as high as 2.5 pu. There is very little information on the effect of these transients on oil-paper insulated equipment. There have been reports, however of transformer and bushing failures caused by these transients. The electrical breakdown characteristics of oil-paper insulation under steep front impulse were studied in this project, which was co-sponsored by the Canadian Electrical Association and B.C. Hydro. [V.sub.50] (50% breakdown probability voltage) breakdown data was obtained with steep front (10 ns/2500 [[micro]second]), lightning and switching impulse waveforms. Insulation breakdown voltage vs breakdown time (V-t) data and multiple impulse breakdown data were obtained with the steep front impulse waveform. The [V.sub.50] results showed that the breakdown strengths were lower for steep front impulses than for lightning impulses. The multiple impulse breakdown results showed that oil-paper insulation breakdown strength can be lower than 100 kV/mm. These results are alarming, since they suggest that oil-paper insulated equipment subjected to steep front transients will fail at voltages below the lightning impulse design level (BIL). The Volt-time data had a discontinuity. The breakdown process at risetimes below about 50 ns was different from the breakdown process at risetimes above 50 ns.

The electric characteristics and insulation design strength of a liquid-nitrogen-impregnated synthetic insulation was considered. It found to detect the impregnation of liquid nitrogen by measuring the electrostatic capacitance of the cable. [Epsilon] tan [Delta], an index of the dielectric loss, was 0.31% for cellulose paper and 0.18% for semisynthetic paper, PPLP and OPPL. It is found that the decline of the thickness dependence of the breakdown strength of the liquidnitrogen-impregnated insulating cable is steeper than that of the OF cables. It is possible to design the insulation strength of the 66 kV cable to be 10 kV/mm.

This paper briefly describes the special publication, 'Fault and Disturbance Data Requirements for Automated Computer Analysis', prepared by Working Group I 11 of the Relaying Practices and Consumer Interface Protection Subcommittee of the IEEE Power System Relaying Committee. The publication describes the analysis objectives and the data necessary to facilitate automated analysis. The address for ordering a copy from the IEEE is in the reference section.

It is well known that cellulose materials used to insulate transformer windings gradually degrade during service due to a combination of thermal, mechanical, and electrical stresses. As a result the mechanical characteristics of the paper change during use and may affect the useful life of the transformer. It has generally been assumed that the electrical characteristics remain relatively constant throughout the aging process. If, however, thermal aging changes the electrical characteristics, it may be possible to gauge the thermal age of a transformer by externally monitoring these electrical characteristics over time. In this work, samples of oil impregnated thermally upgraded Kraft insulating paper are subjected to accelerated thermal aging. The relative dielectric constant and loss tangent are investigated by monitoring changes in capacitance and conductance as a function of frequency and thermal aging. This paper presents data showing that the thermal aging process produces changes in the electrical characteristics of the insulating system paper. An example is presented comparing the admittance versus frequency for a model of a 765 kV 500 MVA auto transformer. This demonstrates that the effect of aging can theoretically be observed from the terminals of the transformer. Keywords Transformers, Thermal Aging, Capacitance, Dielectric Constant, Impedance, Conductance, Loss Tangent

This paper presents a new technique for calculating the magnetic field shielding effectiveness of then conductive sheets of materials. The sheets are modeled as meshes of passive shielding wire filaments. Using this technique, complex three dimensional sources and shield configurations can be easily modeled. A computer program was developed to perform the calculations, and a comprehensive set of experiments was performed to verify the technique. Calculations and measurements are compared in the paper. The calculation method provides a numerical and experimentally verified technique for evaluating the shielding effectiveness of thin conductive sheets for power system magnetic field shielding applications. A predictive method such as this is becoming increasingly important as conductive materials are increasingly becoming accepted as effective shielding materials. Keywords: Shielding, Magnetic Fields

As modern equipment is more sensitive to power quality phenomena, transients introduced by capacitor switching become an increasing concern. The paper addresses the identification of switched capacitor position such that on-line or post-fault measures can be taken. The position is given in terms of proportional line impedance seen from the load bus. Perturbation methods are used to find an asymptotic expression for capacitor position as a function of the transient frequency. This paper presents analytical and simulation results for a standard radial distribution system. Keywords: Power Distribution Systems, Power Quality, Capacitor Switching, Capacitor Position Identification

This paper describes the analysis of thermally accelerated aged insulation samples to investigate the degradation processes observed in the insulation of aged transformers. Accelerated ageing experiments were performed on paper wrapped insulated conductors in the presence of air and nitrogen environments over a temperature range of 115 to 145 degrees C. Effects of oxidation on the ageing of oil-paper insulation were investigated and results are presented in this paper. The conditions of aged insulation samples was investigated by a number of diagnostic techniques: (a) measurements of interfacial polarization spectra by the return voltage method (b) measurement of molecular weight and its distribution by gel permeation chromatography, (c) surface analysis by X-ray photo-electron spectroscopy and (c) a study of the oxidation of the oil by a UV-visible spectroscopy. Results from these measurements are presented in this paper and are used to analyse the degradation process with special emphasis on oxidation. Keywords: Transformer insulation, ageing, oil-paper, interfacial polarization spectra, return voltage, gel permeation chromatography, condition monitoring

The introduction of microprocessor technology enabled multiple protection functions to be integrated into a common protection platform which has advantages when applied to generator protection. This paper provides an insight into industry application experience in using multifunction generator protection systems on various sizes and types of generators. Included are discussions on application and performance differences between multifunction protection systems and single function static and electromechanical relaying devices. Also included is a summary of the various types of tests performed on the multifunction protection systems by the user. The paper additionally addresses the need for application of redundancy and backup protection when applying multifunction generator protection systems on large or important generators. Keywords: Multifunctional Protection System, Generator Protective Relay, Redundant, Tripping, Signal Processing

This paper presents a time domain model for the representation of powers in linear and nonlinear electrical circuits. The model can account, in a physical (or engineering) sense, for 'active and reactive powers' as functions of time. The model is based on the time domain decomposition of the instantaneous power p(t) into two components: p(t)+r(t). Where, a(t) represents the instantaneous power consumed by the (linear or nonlinear) load. The information regarding the store/restore process is contained in r(t). In contrast with the traditional frequency domain model in which powers are defined orthogonal (i.e. S(super 2) = P(super 2) + Q(super 2) + D(super 2) + ) and therefore they do not interact with each other, the proposed model permits the interaction of active and reactive powers at every instant. Using the model of the paper we can obtain the instantaneous power needed for compensation of both, wave shape and power factor. Keywords: Definitions of Powers, Nonlinear Circuits

The paper describes a general methodology for the fitting of measured or calculated frequency domain responses with rational function approximations. This is achieved by replacing a set of starting poles with an improved set of poles via a scaling procedure. A previous paper [5] has described the application of the method to smooth functions using real starting poles. This paper extends the method to functions with a high number of resonance peaks by allowing complex starting poles. Fundamental properties of the method are discussed and details of its practical implementation are described. The method is demonstrated to be very suitable for fitting network equivalents and transformer responses. The computer code is in the public domain, available from the first author.

The paper presents a statistical approach to the high-voltage substation lightning performance estimation. The method involves the monthly distribution of the lightning discharges to the lines, determined according to the line geometry and thunder activity, as well as the monthly probability distribution of the substation configurations. The mean time between failure of the power transformer insulations is estimated for a 400 kV / 110 kV transformer substation. The paper provides the analysis of the results obtained for various dispositions, number and place of positioning the surge arresters, as well as the power transformer basic insulation level. The improved procedure of the lightning performance estimation can contribute to a more economical substation design. Keywords: HV substation, Lightning, Transformer insulation failure

Array-based logic is a novel technology based on algebraic-geometrical formulations where logical truth-values are considered as physical measurements. The preliminary study on which this paper is based shows how array-based logic can be applied to an existing substation control system resulting in a mathematically consistent and complete description of a substation interlocking scheme for steady-state security assessment. This study also showed that building a complete system rule-base in array-based logic is resembling the design of electrical networks: knowledge descriptions for each component are joined in agreement with the system topology. The knowledge description for each component, a 'primitive', is a logical description of the legality of each component state. The technology of array-based logic described in this paper is now incorporated in functioning expert system shells for personal computers. Because of the potentials of this technology a number of suggestions made by the preliminary study are presently being investigated in a research project. Keywords: array-based logic, automatic substation control, switching, interlocking, steady-state security assessment, electric power systems, rule-base, relations, complex system representation, expert system.

A Le-Blanc transformer is a special winding connection transformer for the single-phase power supply of electrified railway and it has been installed in the electrified railway of Taiwan(Tairail) for more than twenty years. It is well-known that the main electrical protection of large capacity transformers is differential protection. As the special winding connection and current relationship of Le-Blanc, differential relays are not easy to apply directly without using the special turn ratio current transformers. Therefore, the purpose of this paper is to design a differential protective scheme that is built by normal turn ratio current transformers connected for Le-Blanc transformers. According to the phasor combination method, a two-relay differential protective scheme that combines the primary line currents to match the secondary line current phases of Le-Blanc is proposed in this paper. For evaluating the performance of the proposed scheme, a practical design example using the parameters of a Tairail's Le-Blanc transformer and some scaled down data of the field test system in our laboratory are also presented in this paper. Keywords: Le-Blanc connection, electrified railway, differential protection, phasor combination method

The paper proposes an extended complex Kalman filter and employs it for the estimation of power system frequency in the presence of random noise and distortions. From the discrete values of the 3-phase voltage signals of a power system, a complex voltage vector is formed using the well known [Alpha][Beta]-transform. A nonlinear state space formulation is then obtained for this complex signal and an extended Kalman filtering approach is used to compute the true state of the model iteratively with significant noise and harmonic distortions. As the frequency is modeled as a state, the estimation of the state vector yields the unknown power system frequency. Several computer simulations test results are presented in the paper to highlight the usefulness of this approach in estimating near nominal and off-nominal power system frequencies. Keywords-Power system frequency, Frequency estimation, Extended Kalman filter, Nonlinear filter

The paper describes the design and field testing of a source based relay suitable for the protection of wind farms with fixed-speed induction generators. The relay provides short-circuit protection for the medium voltage (MV) power collection circuit and the MV and low voltage (LV) windings of each generator transformer. The use of the relay allows a reduction in the construction cost of a wind farm, since MV fuses are no longer required to protect the generator transformers. The paper discusses how the protection algorithm was designed based on the electrical behaviour of induction generators operating in a wind farm. The relay was evaluated at a wind farm in Wales and also in the laboratory using data from a wind farm simulator and a transient recorder. The latter, installed at the wind farm, recorded the voltage and current signals measured during local disturbances. The recorded or simulated data was subsequently replayed into a relay simulator which graphically describes the operating behaviour of the protection. Keywords: Source Based Protection, Wind Farms, Field Testing, Multi-Function Relay

All 3-core cables require fillers to fill the space between insulated cores and the belt insulation or a sheath. The equations given in IEC 287 and in the Neher-McGrath paper for the internal thermal resistance of 3-core cables were developed for paper insulated cables. For such cables, it was assumed that the insulation and filler materials have the same thermal resistivities. In reality, in 3-core cables a variety of materials are used as fillers. The majority of these will have a higher thermal resistivity than the insulation. In the previous paper, a new formula was developed to compute the value of the internal thermal resistance of belted cables taking into account the thermal resistivity of the filler. In this paper, screened cables are considered and a new formula for the computation of the internal thermal resistance of such cables is presented. The effect of filler resistivity on cable ampacity is also discussed

The paper presents a simple method for the characterization of the current-to-voltage (I-V) transducers that are based on current transformers. It is performed by reducing to a minimum the unbalance voltage that arises when the transducer output is compared with the voltage drop caused by the transducer input current across a precision noninductive shunt. Experimental data relevant to different types of passive and active I-V transducers are reported and discussed in the paper. Keywords: Calibration;Transducers;Current Transformers; Testing.

Recently the return voltage measurements have been proposed for the diagnostics on the high voltage equipment characterising the dielectric properties of insulation systems. The application of return voltage method at the diagnostics of the HV current transformers are presented in this paper. The return voltage characteristics such as maximum of return voltage, the initial slope of return voltage and the time to peak value dependencies on charging time are discussed. These characteristics vary depending on the ageing changes of the insulation. That indicate for a possible applicability of the technique for assessing the state of transformer insulation. The investigations of temperature influence on the rerum voltage characteristics were aimed to determine the state of the insulation under operating conditions. The theoretical analysis of the results allows to calculate the temperature of insulation that corresponds to the thermal breakdown of insulation. Keywords: current transformer - oil-paper insulation - ageing - diagnostics - return voltage

Cables crossing other heat sources either perpendicularly or at oblique angles will experience a rise in conductor temperature which should result in ampacity derating. In the first part of the paper a mathematical model for calculation of derating factors was presented. In this paper, a practical numerical example is considered with a pipe-type cable crossing a 10 kV distribution circuit. The numerical analysis presented here confirms experimental findings reported in the literature that the cable crossing may elevate conductor temperature by as much as 20 [degrees] C.

The Unified Power Flow Controller (UPFC) is a novel power transmission controller. The UPFC provides a full dynamic control of transmission parameters, voltage, line impedance and phase angle. This paper presents a useful tool for power utilities engineers to evaluate the application of the UPFC, its impact on their power system and what would be the shunt and series ratings. This paper gives sets of equations for a system including the UPFC and an equivalent two bus power network. A numerical method tested with Matlab has been successfully validated with analog model and EMTP. The Matlab code given in the paper allows to perform fast parametric studies for the application of the UPFC. Keywords: FACTS, UPFC, Matlab

This paper describes a series of development tests carried out when developing a GIS (Gas Insulated Substation) fault location system using pressure wave sensors for a GIS with a main bus in which each gas section per bay is connected by gas piping. This paper also refers to the basic construction of the software of the fault location system actually applied to a GIS with a rated voltage of less than 168kV. Keywords: GIS, Fault location system, Sensor, Pressure wave

Wavelets introduce new classes of basis functions for time-frequency signal analysis and have properties particularly suited to the transient components and discontinuities evident in power system disturbances. Wavelet analysis involves representing signals in terms of simpler, fixed building blocks at different scales and positions. This paper examines the analysis and subsequent compression properties of the discrete wavelet and wavelet packet transforms and evaluates both transforms using an actual power system disturbance from a digital fault recorder. The paper presents comparative compression results using the wavelet and discrete cosine transforms and examines the application of wavelet compression in power monitoring to mitigate against data communications overheads. Keywords: Wavelets, Fourier transforms, disturbances, data compression

In this paper, a three-dimensional algorithm for the insulation design of the high-voltage equipment is presented. In general, the insulation design consists of two steps. One is the electric field calculation. The other is the correction of the shape of the electrode or the insulator to be designed. The main point of this paper is the introduction of the rational B-spline to improve the shape control for the insulation design. In former researches, the correction of a shape is made by direct control with the nodes on the shape. This required many design variables and causes the discontinuous curvature of a designed shape. These problems can be dealt by the indirect control which is one of the useful properties of the rational B-spline. The use of rational B-spline results in the reduction in the number of design variables and guarantees the smooth curvature of the designed shape. The proposed algorithm is applied to the design of the shape of the shield ring which is installed in the joint of transmission lines and the insulator and has been designed by the method of trial and error. The combination method of Charge Simulation Method(CSM) and surface Charge Simulation Method(SCSM) is used to calculate the three-dimensional electric fields produced by this system. Key Word: Three dimensional algorithm, Insulation design, Combination method, Indirect control, Rational B-spline, Shield ring

This paper presents a new approach to solve the distribution feeder reconfiguration problem for loss reduction and service restoration. By using the proposed algorithm, a more efficient network configuration can be obtained to reduce loss. Three switching indices were defined in this paper. Branch voltage-drops and line constants were used with all the electrical constraints. Meshed networks were considered instead of the radial topology by closing all the tie switches. By considering only the largest switching index in each loop, this algorithm can reduce the number of feasible states drastically. The switching index can also be used for service restoration. Many tests have been run to show its effectiveness.

This paper presents a high-pulse shunt compensation scheme based on the 3-level GTO-inverter which requires minimal magnetic interface. The scheme utilizes small inductors, rather than phase-shifting transformers, for combining several 3-level inverters to a high-pulse static synchronous compensator. The resulting arrangement has an output harmonic profile comparable to a 48-pulse inverter. A suitable control scheme is developed for the proposed compensator which provides smooth var control for the network. Simulation studies are presented in the paper, which demonstrate that the proposed design could decrease the complexity of advanced compensation schemes. Keywords: STATCOM, three-level GTO-inverters, FACTS, Harmonic elimination, Phase-shifting transformer.

This paper presents a comparative analysis of the effects of expulsion and current-limiting fuse (CLF) operations in distribution systems on power quality and system protection. This analysis included field tests of both types of fuses on a distribution system in Florida. To further analyze fuse effects on the voltage dip duration and spread of the overvoltages created during the fuse operations throughout the system, computer simulations were also performed. Unique digital fuse models were developed for use with the EMTP/ATP program. This paper shows that CLFs improve power quality by supporting system voltage during faults, reducing the voltage dip duration, and do not affect load operation. Additionally, CLFs reduce the fault let-through [I.sup.2]t. Key words: Fuse, Current-Limiting Fuse, Modeling, EMTP, ATP, Distribution Systems, Power Quality

This paper presents the details of a prototype of an intelligent alarm processor called the Advanced Alarm Processor (AAP). The AAP uses model-based reasoning methods to synthesize and suppress power system alarms in the on-line environment. These model-based reasoning and processing methods are a new approach to intelligent alarm processing. The transformer model presented in this paper is a subset of the complete AAP which also processes power system, communications, protection, and substation alarms. The transformer module is used to demonstrate the reasoning and message-handling methods. Finally, the utility of the AAP is demonstrated through tests in which raw Energy Management System (EMS) input alarms are processed by the prototype to produce higher-level messages.

The operational reliability of high voltage power equipment depends mainly on the quality of electrical insulation. The main characteristics determining insulating structure (IS) quality are: - flashover voltage distribution (FOV); - volt-time curve (VTC); It is currently thought that FOV follows the normal symmetrical law of distribution, while the VTC are inversely proportional to the degree function (so-called 'hyperbolic type'). However, a series of IS discharge characteristics exist which differ significantly from the norm, both in flashover voltage quantity and in form. This paper discusses some results of IS investigations by the author in this area, based on research carried out in the 1980's in Russia at the HV Center of Siberian Research Institute of Energetic (Novosibirsk) [1]. Paper has only the most unquestionable and systematical part (basically experimental). The rest of results, into a good deal in higher extents interesting, also there are, but in connection with the limited sizes of one paper cannot be published right away as the logical streaking of heaved theme, viz: 'To question about the mechanism of the formation of anomalous characteristics...' and 'The paths of streaking, and the prospects of application in Power Systems...'

This paper deals with the application of the Ultra-High-Frequency method (UHF-method) for the detection of partial discharges (p.d.) in gas-insulated substations (GIS). First a review of the GIS-relevant part of the theory of electromagnetic wave propagation in the UHF-range (300 MHz - 3 GHz) is given. New information considering the attenuation due to reflections of UHF-signals at spacers is presented. For the used sensors to pick up the UHF-signals inside the GIS a new description as antenna valid in the UHF-range is introduced. The second part of this paper presents measurements with the UHF-method to compare the sensitivity to the conventional p.d. detection method according to IEC-270. Practical conclusions are drawn from these new results for the application of the UHF-method for on-site testing and online-p.d. monitoring of GIS. Keywords: Gas-insulated substation, SF6, Partial discharges, Ultra high frequency, UHF-method, Monitoring.

The equations given in IEC 287 and in the Neher-McGrath paper for the internal thermal resistance of 3-core cables were developed for paper insulated cables. For such cables, it was assumed that the insulation and filler materials have the same thermal resistivities. In reality, in 3-core cables a variety of materials are used as fillers. The majority of these will have a higher thermal resistivity than the insulation. In this paper, a new formula is developed to compute the value of this thermal resistance taking into account the thermal resistivity of the filler. The effect of filler resistivity on cable ampacity is also discussed.

This paper describes an analytical solution to use a generic 2D finite difference method to accurately calculate the Quasi 3D spatial distribution, components, and total core losses in transformer cores. The solution takes into account 1) Magnetic anisotropy and nonlinearity of the core material, 2) All components of iron losses of the core material; including losses in directions other than the rolling direction, and 3) joint model & localized losses due to the distorted flux distribution in the joint regions (due to core gaps) across the corestack. With above attributes considered in the analysis, one is able to use the results to 1) calculate very accurately the total core losses of a transformer at the design stage every time; for all core materials, at all operating inductions, for all core geometries, and for both 50 Hz and 60 Hz, 2) Understand the contribution of cross losses. harmonics, and joints to the total losses of a core, 3) Evaluate the impact of various joint attributes, such as, type of joint, number of steps, number of laminations per step, size of gaps, and lamination thickness on the total performance of the core, and 4) Improve the core loss performance of transformers by optimizing core design and core material parameters. This paper presents the analysis as applied to 3-phase, 3-limb cores. Other 1-phase and 3-phase core geometries will be the subject of a subsequent paper. The paper also presents the results of the extensive experimental/test verification performed on a number of model cores in the lab as well as on a large number of actual commercial transformer cores with excellent agreements. The results of this analysis have been used in developing the new design practice at ABB worldwide to calculate core losses of stacked power and distribution transformers with consistent accuracy. Keywords: loss, transformer core, no-load, finite difference method, anisotropy, nonlinearity, core joints, magnetic flux, reluctivity

In an attempt to determine the magnitude of the effects of a number of core production attributes; such as core quality, joint stacking, clamping pressure, etc. on the performance of stacked cores, a comprehensive experimental and analytical study has been conducted, These effects were studied for different core material grades, and for both single and three phase cores. The two performance parameters studied are core losses and core exciting current. This paper presents the results of the experimental part of the study. Results of the theoretical study will be reported in a subsequent paper. The experimental models used in the study were designed such that they depict the performance of full size cores. In addition, some tests were made on full size cores to verify the effect of core yoke clamping on core loss. The results presented in this paper have already been used by ABB transformer plants world-wide to improve core performance as well as improve the accuracy of core loss and core exciting current calculations at the design stage. Keywords: Transformer, Core, Clamp, Building Factor, Core Loss

This paper describes how an EMTP based simulator can be used in conjunction with a relay test set to type-test a protection relay operating within a circulating current differential protection scheme. The combination of a simulator and a test-set is designed to replace a high power synthetic test plant that has been used for more than 30 years for type and approval testing of differential protection relays. The paper will include results that describe the operating performance of the new test system, on both internal and external faults, and these will be compared with experimental results obtained from an identical set of tests on the synthetic test plant. Keywords:- Circulating current differential protection, current transformer behaviour, digital modelling of current transformers, differential protection test system, synthetic test plant.

This paper presents the results of a continuing investigation into effect of water on water absorption and density of crosslinked polyethylene (XLPE). The experimental set up was made for the following XLPE cable insulations: steam and dry cured with water tree retardant crosslinked polyethylene (TR-XLPE) and without water tree retardant crosslinked polyethylene (natural XLPE). During tests, the tap water was injected (1) into the cable conductor with cable ends closed, (2) into the cable conductor with cable ends opened, and (3) into the metallic screen with cable ends opened. The XLPE cable insulation together with the water present in the cable was subjected to electrical stress and heating. The results were analyzed theoretically and experimentally. The aim of this paper is to present the results of the influence of the water on water absorption and density of various kinds of XLPE cable insulation in different service conditions.

This paper describes the design, computational aspects and implementation of an iterative technique for measuring power system frequency. The technique provides accurate estimates to a resolution of 0.01-0.02 Hz for near-nominal, nominal and off-nominal frequencies in about 20 ms. Computation requirements are modest and the technique has been implemented on a modern digital signal processor. The proposed technique was extensively tested using voltage signals obtained from a dynamic frequency source and from a power system. Some test results are presented in the paper. Keywords: Power system frequency, Frequency measurement, Frequency relaying, Microprocessor-based relays.

Working Group F-8 'Digital Simulator Performance Requirements for Relay Testing' of the Relay Input Sources Subcommittee, Power System Relaying Committee, was formed in 1992 with the following assignment: 'Investigate performance characteristics of digital simulators when generating Electromagnetic Transient Program (EMTP) and Digital Fault Recorder (DFR) based relay test waveforms. Write performance requirements specifications and prepare a paper describing the importance of the simulator performance characteristics.' This paper presents the work accomplished by the working group in fulfilling its assignment. Keywords: Digital Simulator, Relay Test, Protection, EMTP, Digital Fault Recorder, Model Power System

This paper describes an apparatus and method for increasing the electrical clearances of energized conductors from their grounded supporting structures, ground and other underlying objects. More specifically, this includes a number of insulators which help form an outwardly extending conductor loop, called 'Upgrade-Loop' to increase the clearance between the electrical conductor and its support structure. Upgrade-Loops may be installed on existing transmission towers without any modification to the structures. They may even be installed live line, if necessary. Upgrade-Loops can be implemented on existing power lines such that they would raise the conductors, thus increasing conductor clearance to ground and other underlying objects. This paper also describes Upgrade-Loops applications which include: 1) upgrading voltage for increasing the power transfer capability of a line, 2) improving line performance for system overvoltages and contaminated environments and 3) simplifying line compaction for increased loadability while reducing ground level electric and magnetic fields. Keywords: Upgrade-Loops, Voltage Upgrade, Electrical Clearances, Line Compaction, Electric and Magnetic Field Reduction, Resistive Loss Reduction, Increased Loadability, Live-Line Work.

This paper presents a new arc furnace model which copes with the two main voltage disturbances normally associated with arc furnaces: voltage fluctuations and harmonics. The model is based on the stochastic nature of the electric arc current-voltage characteristic. The model has been estimated from measurements made in two actual electric plants. Although a single-phase model has been normally proposed, this paper develops a three-phase model in order to fully represent the unbalances that are present in real plants and which play a central role in the behavior of compensation devices such as SVCs. The model has been implemented using the SIMULINK environment in order to facilitate later simulation of advanced disturbance control systems. Finally, the simulation results are compared with actual data in order to validate the accuracy of the model. KEYWORDS: Arc furnace, Voltage fluctuation, Harmonic, System identification.

This paper deals with analysis of the detailed dynamics of the TCSC. The system considered is a system of one machine connected to an infinite bus through a thyristor controlled series compensated transmission line. This system can be described as periodic state equations. This paper provides analysis of the periodic state equations using the state variable approach. Transient characteristics as well as steady state characteristics of the TCSC are presented using the analytical equations for three operating modes of the TCSC. The simulations are performed using the MATLAB program.

The presented paper describes the model for the study of a power transformer as the termination of a transmission line with a traveling wave. When the traveling wave running on the transmission line reaches the transformer, it is partly reflected and partly transmitted through the transformer. The voltages on input and output transformer terminals depend on the shape of the traveling wave and on the relation between the transmission line surge impedance and the input and transfer impedance of the transformer. As the transformer impedance is frequency dependent, the responses of the transformer to the traveling waves can not be determined without knowledge of these dependencies. The model described in this paper is based on measurement of transformer impedance. It considers the frequency dependence of transformer impedance and enables the calculation of voltage on both input and output terminals of the transformer for any shape of the traveling wave on the line connected to the transformer.

This paper describes the analysis of accelerated aged insulation samples to investigate the degradation processes observed in the insulation from aged transformers. Short term accelerated ageing experiments were performed on paper wrapped insulated conductors and on pressboard samples. The condition of aged insulation samples was investigated by two relatively new diagnostic techniques: (a)measurements of interfacial polarization spectra by a DC method (b) measurements of molecular weight and its distribution by gel permeation chromatography. Several other electrical properties of the paper/pressboard samples were also studied. Possible correlations have been investigated among the different measured properties. The GPC results have been used to predict how molecular weights change with temperature and time.

An generalized outage table approach to analyzing reliability of bus schemes of power stations is proposed in the paper. The approach enables us to profoundly and fully study the influences of different bus schemes on reliability of power stations. The numerical examples given in the paper demonstrate that the proposed algorithm is very practical and efficient.

Among special insulation tests for DC converter transformer, polarity reversal test can be substituted by applied AC voltage test from a stress similarity in oil ducts. In order to investigate equivalent levels of other insulation tests to polarity reversal tests, dielectric strength of transformer at polarity reversals was examined by use of a model of typical oil/paper composite insulation. From comparison of polarity reversal and other insulation tests, it was found that dielectric strength of transformer insulation at polarity reversals is phenomenally similar to that under switching impulse stresses. Equivalent AC test voltage to polarity reversal test was also estimated from the experimental results. The breakdown characteristics of polarity reversal tests showed that partial discharges at polarity reversals impose less harmful stress on insulation barriers than those at usual AC or impulse tests. keyword - HVDC, Converter transformer, Polarity reversal, Oil/paper insulation, Partial discharge

This paper describes the application of two relatively new diagnostic techniques for the determination of insulation condition in aged transformers. The techniques are (a) measurements of interfacial polarization spectra by a DC method and (b) measurements of molecular weight and its distribution by gel permeation chromatography. Several other electrical properties of the cellulose polymer were also investigated. Samples were obtained from a retired power transformer and they were analysed by the developed techniques. Six distribution transformers were also tested with the interfacial polarization spectra measurement technique, and the molecular weight of paper/pressboard samples from these transformers were also measured by the gel permeation chromatography. The variation of the results through different locations in a power transformer is discussed in this paper. The possible correlation between different measured properties was investigated and discussed in this paper.

Failure events in substations often result in multiple outages of generators, lines and/or loads in power systems. The simulation of substation originated outages for practical substation configurations is difficult, due to the complex switching actions with disconnect switches and circuit breakers that can take place. A digital computer program has been developed at the Delft University of Technology, which simulates these complex switching actions following substation failures. The simulation algorithms, which deduce the contingencies before and after switching actions with their corresponding reliability indices, are described in detail in the paper. The paper reports on results obtained from analyzing six different busbar schemes with redundant components.

The main electrical protection of Le-Blanc connection transformers that supply the single-phase power to electric railway in Taiwan is the overcurrent protection. This paper presents a more complete protective scheme, the differential protection, for Le-Blanc by phasor combination method. The calculation procedure and the good mismatch results of a practical design example using the parameters of a Le-Blanc transformer of Taiwan Railway Bureau(Tairail) are described in this paper. In addition, using the normal current transformers and electromagnetic type transformer differential relays to completely construct the protective scheme is another merit of this algorithm. Keywords: Le-Blanc connection, Scott connection, electric railway, high-speed railway, differential protection, phasor combination method, current transformer(CT)

This paper provides a quantitative measurement of the benefit that a Unified Power Flow Controller (UPFC) can provide to increase firm power transfer between two large power systems. Included is a complete model for a UPFC control system that contains bus voltage control by the shunt inverter, real power transfer between the shunt and series inverters, and real and reactive power control for the transmission line into which the series inverter is inserted. A significant part of the model is representation of dynamic limits that coordinate injected current limits for the shunt inverter, power transfer limits between inverters, voltage injection limits for the series inverter, current limits for the series inverter, and line voltage limits for the transmission line. This paper contains a simple system simulation to demonstrate the coordinated dynamic control and illustrate issues that system planning engineers must consider in defining applications for a UPFC. KEYWORDS: Power Flow Control, Voltage Control, Static Synchronous Compensator, Unified Power Flow Controller, Voltage Sourced Inverters