High Voltage Conductor Research Articles

On-line monitoring and diagnoses of power transformer bushings

Power transformers have been in service for many years under different conditions. Statistical studies have shown that failures of bushings are one of the main causes for long duration outages of transformers. The development of an instrument for supervising the conditions of transformers bushings is, therefore, of special interest. In this contribution two methods are introduced for monitoring of bushings. In the first method, using summation voltage of transformer bushings from bushing taps with and without neutral point voltage are considered. In the second method a new sensor is used which can give voltage signal as a signal reference from the high voltage conductor in each bushing. Comparing the signal reference with using tap voltage signal can evaluate the condition of transformer bushing. In addition a software for monitoring and diagnostic of transformer bushing is presented.

Patient Alert™ to detect ICD lead failure: efficacy, limitations, and implications for future algorithms

An algorithm that alerts implantable cardioverter-defibrillator (ICD) patients, in case of abnormal lead impedance (Patient Alerttrade mark, Medtronic), may help to recognize lead dysfunction. We aimed to determine the utility of Patient Alert for ICD lead-failure detection in a prospective study. Three hundred and sixty ICD patients were followed for 22+/-14 months. Patient Alert was active for pacing impedance <200 and >2000-3000 Omega, and high-voltage conductor impedance <10-20 and >200 Omega. Ten alert events and a total of 29 severe system complications occurred. Patient Alert detected three of 10 ICD lead failures, with a positive predictive value (PPV) of 77.8% for any severe system complication. Retrospective analysis identified 23 patients with a sensing integrity counter (SIC) >300 and revealed an additional four prior undetected lead defects. SIC detected ICD lead failure with 92.9% sensitivity and a PPV of 59.1%. Eight of nine patients with a false-positive SIC had an integrated bipolar lead. Patient Alert combined with SIC detected all ICD lead failures and 71.4% of all severe lead complications. Patient Alert, based on daily lead-impedance measurement, detected one-third of all ICD lead failures. Combined use with continuous lead integrity monitoring (SIC) increased sensitivity to 100%. Integrated bipolar leads may yield a false-positive SIC. Incorporating SIC and automated pace/sense threshold measurement may improve Patient Alert sensitivity for severe lead complications.

Non-Contact Determination of the Phase Sequence and Voltage Level of Overhead Conductors in Air Insulated Substations

This paper describes how the phase sequence and voltage level (132 kV, 275 kV or 400 kV) of single-circuit overhead conductors can be calculated from measurements made by passive, non-contact sensors situated on a moving platform at ground level.The investigation relies on sensing the electric field along the profile of the conductors through the use of passive sensors. The fabrication of the passive sensor is described together with an analysis of its performance. The variation of the vertical component of electric field strength along the lateral profile beneath single-circuit conductors has been studied using finite element modeling software, ANSYS. The results of this simulation have led to a proposed method of determining the magnitude and phase sequence information from overhead conductors via analysis of the induced voltages on the sensors.The paper concludes with an investigation made in a 400 kV substation in the UK. Analysis of the experimental results shows that the proposed technique can successfully evaluate the phase sequence, voltage level, the spacing between phases and the orientation of high-voltage overhead conductors.

The Development and Practical Use of A New 24 kV Dry Air Insulated Switchgear

We have developed a new environmentally fitted 24kV cubicle-type gas insulated switchgear (C-GIS) applying our dry air insulation technology and the electromagnetic actuation technology. Firstly, we clarified the relationship between the breakdown field strength at the tip/edge of high-voltage electrode in dry air and the field utilization factor expressing non-uniformity of the insulation gap. Based on the relationship, we designed the most suitable configuration and arrangement of the parts such as high-voltage conductors, disconnecting blades and some mechanical parts in a gas vessel. We succeeded in reducing both the number of insulation barriers and their size, compared with the former product. To reduce them, we produced some sample gaps simulated a practical insulation gap in the C-GIS and investigated its breakdown voltage dependence on the barrier height. Secondly, to apply the electromagnetic actuators for the operation mechanisms of the vacuum circuit breaker, we developed a new coupled analysis method that estimates the movement of a plunger inside the electromagnetic actuator and the electric current flowing through a closing/opening coil. Based on the analysis method, we could reduce both the number of the parts and close/open energy 45% and 80%, respectively, compared with the former spring-charged mechanism.

Seismic Interaction between Flexible Conductors and Electrical Substation Equipment

High-voltage flexible conductors are employed to interconnect equipment items in electrical substations located on seismically active regions to carry the electricity from one equipment item to another. They have sufficient slack to allow the conductor to accommodate the relative displacements of the adjacent interconnected equipment under seismic loading. However, additional forces due to the dynamic response of the conductor during severe shaking, and its interaction with the interconnected equipment, could cause additional unpredicted forces resulting in damage or failure of the equipment. This paper presents the results of a project to investigate the dynamic behavior of these conductors and their interaction with the interconnect equipment. The project included performing quasi-static and dynamic tests on one of the most commonly used configurations of these conductors in substations throughout the province of British Columbia in Canada. The results of this investigation demonstrated that there can be significant dynamic force amplification due to dynamic interaction of the flexible conductors with the equipment, and showed that the dynamic effect of these conductors must be considered when evaluating the seismic demand of interconnected equipment.

Corona and breakdown characteristics between sphere electrode with a protrusion and plane electrode under negative pulse voltage in N/sub 2/ gas

Corona and breakdown characteristics for a configuration of a sphere with a needle and a plane in N/sub 2/ gas are studied. The protrusion was used to simulate a metallic particle attached to a high voltage conductor surface in power apparatus. The corona and breakdown characteristics depend on the vertical distance between the needle tip and the bottom sphere. It was observed that the breakdown path changed from needle-to-plane to sphere-to-plane while increasing the vertical distance of the needle from the plane. Although corona was generated at the needle-tip at first and developed in the direction of the plane, both the needle-plane and the sphere-plane breakdown occurred at some short vertical distances. The sphere-plane breakdown in that distance was triggered by corona from the needle.

Electrode Area Effect on Breakdown Field Strength of Vacuum Gaps under Non-Uniform Field

This paper has discussed area effect on breakdown field strength in vacuum gaps under non-uniform field. To identify whether the common area effect can be found between uniform and non-uniform field gaps or not, 50 % breakdown field strength (E50) vs. electrode area more than 90 % of maximum fields strength on cathode (S90) was compared among four kinds of plate-plate gaps, three kinds of ring-plate gaps, and two kinds of sphere-plate gaps. As a result, E50 vs. S90 for plate-plate gaps shows different characteristics from the other kinds of gap arrangements when radial curvature of edge is large and gap length is short. We discussed the reason and how to conduct the insulation design for actual high voltage conductors, consist of some curved surfaces and plane surfaces.

Real-time digital processing of GPS measurements for transmission engineering

The Global Positioning System (GPS) is a state-of-the-art timing and positioning system based on 24 or more satellites launched and maintained by the US government. Power engineering applications based on GPS include phasor measurement, positioning applications, such as surveying and mapping, and potentially in deriving real-time data on transmission lines that will allow them to be loaded to a dynamic (thermal or security) limit. Inherent errors in GPS technologies are discussed, and the differential GPS method is described for accuracy enhancement. Further digital-processing needs are necessary for meeting the accuracy requirements of certain specific applications. The focus of this paper is on the digital signal processing (DSP) of differential-GPS (DGPS) measurements. The paper describes a methodology for further improving DGPS altitude measurements for the purpose of accurate determination of high-voltage overhead conductor sag. The Haar wavelet transforms (HWT) and least-squares parameter estimation (LSPE) techniques are considered.

A new method for real-time monitoring of high-voltage transmission-line conductor sag

The amount of power flowing through a high-voltage transmission line is proportional to its voltage and the current flowing through it. To increase power flow without modifying the line to support increased voltage, the current must be increased. There is a limit to this, however, since increasing the current causes the conductor temperature to increase and, hence, the conductors to elongate and sag. In this paper, a method to simply and inexpensively measure the amount of conductor sag and, through simple calculation, the average conductor core temperature is described, and the results of a field test are summarized. The method involves attaching two ends of a grounded wire of high electrical resistance to an appropriate location on each of two transmission-line towers and measuring the current induced on the wire by the nearby transmission-line conductors. Information from this measurement is a critical input to any method for dynamically rating transmission lines.

Metallic particle motion and breakdown characteristics in GIS with 0.1‐Hz VLF (very low frequency) high voltage applied

AbstractVLF (Very Low Frequency) high voltage with frequency of 0.1 Hz will be utilized for an on‐site test of XLPE underground cables, instead of conventional dc high voltage test. Since XLPE cables are connected to GIS (Gas Insulated Switchgears) in substations, the influence of VLF voltage application to GIS insulation should be investigated. One of the most important characteristics for GIS insulation lies in the metallic particle contamination and its behavior, which may induce breakdown in GIS.From the above viewpoint, this paper discusses the metallic particle behavior and breakdown characteristics under VLF voltage application in GIS. Experimental results revealed that (1) Particle motion under VLF condition was similar to that under dc condition, while specific in the transient behavior at the polarity reversal. (2) Breakdown was induced by particles located in the vicinity of high voltage conductor at the instance of crossing the gap or in the firefly conditions. (3) Breakdown voltage in positive half cycle was higher than that in negative half cycle at the lower gas pressure, while lower at the higher gas pressure, which was attributed to the particle behavior and the breakdown mechanism of SF6 gas.Consequently, metallic particles in GIS under VLF voltage application exhibited the specific behavior associated with the slow change of instantaneous voltage and polarity, and resulted in the complex pressure dependence of breakdown characteristics. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 33–40, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.1166

Algorithm to predict dry-band arcing in fiber-optic cables

Utilities frequently use ADSS (all dielectric self-supporting) fiber-optic cables installed on transmission lines 3-6 m below the high voltage conductors. Dry-band arcing occurs on the fiber-optic cables when the cables are polluted and wet. This has been assumed to cause cable failures. An equivalent circuit has been developed to represent the polluted fiber-optic cable in the high voltage environment. The objective of this paper is to present a novel numerical method that can be used to predict dry-band arcing in fiber-optic cables. KCL (Kirchoff's current law) is used to derive node point equations for the equivalent circuit. Forward elimination and backward substitution of node voltage is used to solve the equations. The effect of pollution, tower arrangement, and conductor sag is analyzed. The numerical method has speed advantages over circuit simulation methods. This method includes conductor sag, nonuniform pollution, and variable capacitance. This algorithm can be used to predict dry band arcing in fiber-optic cables.

Ice accretions on high–voltage conductors and insulators and related phenomena

This paper proposes to survey a good part of the research work accomplished to date on the atmospheric icing of conductors and insulators in the presence of high voltage, with emphasis laid on the studies carried out at the University of Quebec in Chicoutimi. The review covers laboratory testing and mathematical modelling. The role of several electrical parameters, such as electric field strength and polarity, corona discharge, water droplet charge and ionic wind velocity, on the structure and amount of ice accretion on high–voltage conductors, is discussed. Concerning the icing of insulators, the initiation of electrical discharge on the ice surface, the formation of local arcs along the air gaps and their development to a flashover arc along the insulators are discussed. Basic experiments on the role of several major parameters relating to ice accretion, insulator characteristics and voltage type and polarity, on the maximum withstand voltage of short insulators, are also discussed. Finally, several measures for improving the withstand voltage of insulators are briefly recalled.

Modelling of corona at a high-voltage conductor under double exponential and oscillatory impulses

An alternating-current corona model is adapted to allow its application to fast transient overvoltages in coaxial geometries. An initial study of data for positive and negative lightning and switching impulses shows good agreement between the model and experiment. Application is then made to a negative corona under oscillatory impulses with frequencies of 33 and 125 kHz. The model is used to aid interpretation of the complex experimental results, and gain an insight into the underlying physical phenomena. A semi-quantitative adaptation is then made to successfully simulate experimental data. The model is shown to be applicable to all voltage types including direct, alternating and impulse voltages.

A novel transducer to replace current and voltage transformers in high-voltage measurements

A transducer which combines both current and voltage sensors in a single integrated unit is described. The principle of operation is based on Poynting's theorem which defines the rate of how of electromagnetic energy in terms of the electric and magnetic field intensities at a point in space. Current is measured by sensing the tangential component of the magnetic held, and voltage is measured by sensing the radial component of the electric field in a well-defined region around the high-voltage conductor. Signals from the two sensors are processed by simple electronic circuits to give an output suitable for direct connection to modern analog and digital meters, relays and computers for continuous on-line monitoring and protection. The new transducer overcomes the limitations of conventional current and voltage transformers. It is also ideally suitable for incorporation as a module in gas-insulated systems. Typical applications of the transducer in high-voltage power systems are also discussed.

Application of high-T/sub c/ superconductors in aluminum electrolysis plants

The electric power system in an aluminum electrolysis plant has several features that may advocate use of superconducting technology: high power, low voltage, system compactness, direct current, and substantial conductor cost and losses per meter. Two case studies where the cost of conventional busbar conductors is compared with the predicted cost of a future nitrogen-cooled high-amperage superconductor based on Ag/BSCCO tapes are carried out. To be an attractive alternative the investment and capitalized operational costs of a superconducting line should not exceed USD 70 per meter per kiloampere rating. Simplified estimates of cost and properties of a superconducting cable show that these requirements are very hard to satisfy, even if long lengths of Ag/BSCCO tapes with operating current densities as high as 50 kA/cm/sup 2/ become available. >

Visible-light spectroscopy of pulsed-power plasmas (invited)

We describe the investigations of the plasma behavior in three pulsed-power systems: a magnetically insulated ion diode, and plasma opening switch, and a gas-puffed Z pinch. Recently developed spectroscopic diagnostic techniques allow for measurements with relatively high spectral, temporal, and spatial resolutions. The particle velocity and density distributions within a few tens of microns from the dielectric-anode surface are observed using laser spectroscopy. Fluctuating electric fields in the plasma are inferred from anisotropic Stark broadening. For the plasma opening switch experiment, a novel gaseous plasma source was developed which is mounted inside the high-voltage inner conductor. The properties of this source, together with spectroscopic observations of the electron density and particle velocities of the injected plasma, are described. Emission line intensities during the switch operation are discussed. In the Z-pinch experiment, spectral emission-line profiles of various charge-state ions are studied during the implosion phase. Radial velocity distributions are observed from the line Doppler shifts and widths.

900 MHz radio signals operational control

The use of 900 MHz radio for supervisory control and data acquisition applications was investigated by the Houston Lighting and Power Company (HL&P). Multiple address system applications in the 928/952 MHz band were evaluated. The purpose of this application was to replace leased telephone lines with 928/952 MHz radio channels to achieve lower costs and improved operational reliability. A second application with distribution automation and control pilot test programs on the HL&P distribution system was explored. The purpose was reliable, cost-effective, bidirectional communications at a reasonable bit rate for control and monitoring of distribution feeders and related sectionalizing facilities. A third application of 900 MHz involving real-time monitoring of high-voltage transmission line conductors was investigated. In this instance, the radio provided a safe and reliable path for data collection between power donuts and master controller.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High negative voltage spheres in an unmagnetized plasma: fluid simulation

Because of the anticipated use of high-voltage power sources on future space platforms, there is an increased interest in elucidating the phenomena associated with the interactions of a high-voltage conductor and the ionospheric plasma at low-Earth-orbit altitudes. Currently there are ongoing rocket, laboratory and modelling programs, and an electrodynamic tether will be flown on the Space Shuttle. All of these programs involve the current collection characteristics of high-voltage spheres embedded in both magnetized and nonmagnetized thermal plasmas. In support of these efforts, the authors have solved the time-dependent nonlinear fluid equations for ions and electrons and the Poisson equation in order to study the response of a nonmagnetized plasma to 'negative' high-voltage spheres. Simulations were conducted for a range of voltages (-10 to -10000 V) and for plasma densities from 104 to 106 cm-3. The temporal evolution of the plasma was followed all the way to the steady state. In all simulations, there were certain qualitative similarities in the plasma response.

Techniques for computing the sheet winding transformers ohmic losses using numerical and analytical methods

The electromagnetic behavior of a sheet winding transformer is examined. Modeling each part of this transformer presents particular difficulties. The high-voltage coil consists of approximately 3000 elementary thin conductors. A solution based on the fact that the reaction field of the high-voltage thin elementary conductors does not influence macroscopically the distribution of the whole magnetic field is proposed. On the other hand, the variation of the magnetic field in the sheet winding is almost insignificant in the radial direction. The use of line elements for sheet windings allows an easier meshing. The results from sheet winding numerical modeling are compared to the experimental ones, and the results of two different high-voltage coil modelings between them.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical fibres for sensors

Silica-based optical fibres are eminently suitable for use as long-distance information transmission lines. They have a very low transmission loss, enormously large band-width and are relatively immune to environmental conditions. The features which make them potentially attractive for sensing applications are their small size and weight, chemically passive nature, freedom from electromagnetic interference and the absence of sparking hazard. Optical fibres can thus be used in situations where metal systems would be prohibited for reasons of safety. On the other hand, optical sources are not cheap. Optical fibre sensors clearly will not be introduced unless they can be justified on economic grounds and there is always a reluctance to introduce a radically new technology into existing industrial processes. Applications must therefore be sought where fibres provide a more economic solution or perform a function not easily undertaken by conventional methods. Examples are the distributed temperature sensor, where a single fibre can replace several hundred point sensors, and the current monitor, which is physically separated from the high-voltage conductor. These and other specific devices will be discussed and reviewed.