Search

The main contribution of this paper is to investigate the correlation between Tan [delta] diagnostic measurements at 0.1 Hz (Very Low Frequency-VLF) and VLF breakdown performance for Medium Voltage (MV) cable samples through a laboratory test program. The cable samples used are a set of 15 kV, Cross-linked Polyethylene (XLPE), unjacketed cables removed from the field, the same service area, and having experienced similar operating conditions for almost four decades. The test program includes Tan [delta] measurements at different voltage levels and a subsequent VLF extended step-withstand test. The VLF step test allows the evaluation of risk of failure during VLF Tan [delta] testing and assessment of the ultimate performance of the cables. The Tan [delta] diagnostic measurements are represented by the Tan [delta] value and Tip-up, which are considered the classical metrics. However, the paper also suggests the use of a new additional diagnostic feature that takes into account the scatter in the Tan [delta] measurements for a particular test voltage level. Index Terms--Dissipation factor, Tan [delta], VLF breakdown, power cables.

In addition to after-laying of new-installed high voltage (HV) power cables the use of on-site non-destructive on-site testing and diagnosis of service aged power cables is becoming an important issue to determine the actual condition of the cable systems and to determine the future performances. In this paper based on field experience an overview is presented on on-site testing and partial discharge diagnosis of HV power cables with regard to on-site testing methods: energizing, diagnostic aspects, possibilities and implications for new and service aged power cables. Index Terms--High voltage power cables, on-site testing, ac over-voltages, partial discharges, diagnosis, condition assessment.

This paper describes important aspects of partial discharge (PD) diagnostics of distribution power cables. PD parameter were discussed under consideration of attenuation and dispersive effects of cable characteristics. Field experiences with PD diagnosis on paper insulated cables (PILC) and cables with cross linked polyethylen insulation (XLPE) by energizing with Damped AC Voltage demonstrate relevant demands and the effective outcome for asset management decision support. The main difficulty is to evaluate the risc of PD occurrences on the reliability of the cable system. If an sufficient amount of PD diagnostic data for the cable components is available statistical methods can be used for determing threshold levels and relevant condition indexes for the asset management. Index Terms--Power cables, partial discharges, PD pulse attenuation, dispersion, knowledge rules, asset management.

During the past decade the PD probing in the ultra-high frequency (UHF) range has successfully been proven for on-site PD diagnostics of GIS cable terminations in service. Therefore it was decided to apply this non-conventional method also for condition assessment of the insulation integrity of outdoor cable terminations. In order to evaluate the minimum detectable PD level the paper deals with comparative PD studies using the IEC and the UHF method. Moreover, experimental studies on the attenuation of PD pulses traveling through power cables were performed in order to assess the spatial selectivity of the UHF method applied.

The basis for computing PD calibration reflectograms in shielded power cable is presented. The computed reflectograms include the effects of cable attenuation, initial pulse width, cable length, and PD detection bandwidth. The authors have developed a program based on the algorithms presented in this paper which they are making freely available to the technical community. Index Terms--PD, partial discharge, calibration, solid dielectric cable, shielded power cable.

Parallel single-core (single-conductor) cables are employed in the backbone of building distribution systems. As power consumption in buildings grows continuously, overheating problems associated with such a cable installation have become a concern. This paper investigates the current distribution among parallel single-core cables installed on metal tray in a multiphase distribution system. A general prediction method of current distribution is introduced and is validated experimentally. To analyze the current distribution under different cable arrangements, empirical formulas of cable impedance are presented. The current distribution associated with the local practice of parallel cable installations is evaluated, and recommendations for the design and installation are presented. Index Terms--Cable, current distribution, metal tray.

The interiors of electrical conduits located on rooftops in full sunlight become considerably hotter than those located in shaded areas. Differentials between these conduit interior temperatures and outside air temperatures (the latter always measured in the shade) can easily reach 39[degrees]C (70[degrees]F) for conduits lying directly on a dark roof. As the height of the conduit above the roof increases, this temperature differential decreases, to perhaps 15[degrees]C (27[degrees]F) at a height of 0.9 m (36 in) above the roof. Lighter-colored roofs, although they keep the interior of the buildings cooler, actually reflect more heat onto conduits located more than a few centimeters above the roof. This makes these conduit interiors hotter as compared to conduits located above dark-colored roofs. In practice, the actual temperatures inside conduits are seldom taken into account when electrical ampacity calculations are made. This can lead to serious overheating and even failure of electrical cables inside the conduits. Index Terms--Ampacity corrections, building wire, conduits, derating, National Electrical Code (NEC), solar effects, THH, wire and cable.

The transport alternating current (AC) losses of the three coils used in the fault current limiters (FCL) application are measured. The results have shown that two bifilar pancake coils have different AC loss characteristics.

The I-V characteristics and over-current behaviors of a 1-m single-layer test YBCO cable are examined. Numerical simulations are performed in order to clarify the over-current characteristics, hot-spot existence and effect of magnetic coupling.

The fault current limiting characteristics are examined according to the fault angle in the integrated three-phase flux-lock type superconducting fault current limiter (SFCL) in the fault type such as the single-line-to-ground fault, the double-line-to-ground fault and the triple-line-to-ground fault. The results have confirmed that the SFCL has a same current limiting rate irrespective of a fault angle in the same fault type.

The design and test results of a 6.6 kV-class superconducting fault current limiter (FCL) coil wound with YBCO tapes. The fault current limiting performance of the FCL is evaluated through over-current tests by using a capacitor bank.

A new topology of the active superconducting DC fault current limiter (DC-SFCL) applied in the hybrid AC.DC power supply systems is described. The simulation models of the DC-SFCL and the hybrid AC/DC power supply system are created by using MATLAB SIMULINK and the simulation tests are performed to evaluate the system performance.

Superconducting Fault Current Limiters (SCFCLs) have improved the reliability and stability of power systems, which consists of a transformer type inductive SCFCL with a ZnO device and a resistor in parallel. The contribution share of the voltage drop suppression and the acceleration energy consumption to the improvement of the power system stability are clarified with conditions like generator output and fault clearing time.

The propagation modes of ultrasound waves in an electrical cable are analyzed in an attempt to assess its behavior as an acoustic transmission channel. A theoretical model for propagation of elastic waves in electric power cables is presented.

The current limiting properties of different kinds of Mg[B.sub.2] wires at 50 Hz in the temperature range of 20-30 K are examined. Findings reveal fast transition to the normal state during the first half of the first cycle and a limiting effect during the subsequent six cycles.

High voltage testing of a three-phase 5-meter prototype high temperature superconducting (HTS) cable is discussed. Findings reveal an inception voltage in excess of the required 15.6 kVrms.

The bending of High Temperature Superconducting (HTS) power cables and the force exerted by the bending process on the HTS tapes is examined. Findings reveal that it is possible to reduce the mechanical stress in the HTS tape by increasing the tape thickness as the friction force acting on an HTS tape is dependent on the width of the tape.

The development of 22.9 kV High Temperature Superconducting (HTS) cable for practical distribution system in South Korea is discussed. Findings reveal that the use of 22.9 kV HTS cable will reduce 154 kV substation and cable construction costs.

The performance of a short-circuit test on non-inductively wound solenoid type superconducting fault current limiter (SFCL) is discussed. Results suggest that a shorter difference between the outer and inner tape is essential for more elaborate simulation.

In order to determine the pressure rise due to fault arcs in electrical installations, the portion of energy heating the surrounding gas of the fault arc has to be known. The ratio of the portion of energy to the electrical energy, the thermal transfer coefficient, well known in literature as [k.sub.p]-factor, is adopted here. This paper presents a theoretical approach to calculate the thermal transfer coefficient [k.sub.p] and to determine the pressure rise in an electrical installation. It is based on the solution of the fundamental hydro- and thermodynamic conservation equations taking into account melting and evaporation of metals as well as chemical reactions with the surrounding gas of the fault arc. The results for closed arc chambers show that factors such as the kinds of insulating gas and of electrode material, the size of the test vessel, and the gas density considerably influence the thermal transfer coefficient and thus the pressure rise. Furthermore it is demonstrated, with an example of a short-circuit in a compact medium-voltage station with heavy metal evaporation, that the mathematical approach is a reliable tool to assess the development of pressure. Index Terms--Chemical reaction, electrical installation, energy balance, fault arc, hydro- and thermodynamics, melting and evaporation, pressure, relative purity, theoretical approach, thermal transfer coefficient.

In this paper, a fuzzy logic-based algorithm to identify the type of faults in radial, unbalanced distribution system has been developed. The proposed technique is able to accurately identify the phase(s) involved in all ten types of shunt faults that may occur in an electric power distribution system under different fault types, fault resistance, fault inception angle, system topology and loading levels. The proposed method needs only three line current measurements available at the substation and can perform the fault classification task in about half-cycle period. All the test results show that the proposed fault identifier is well suited for identifying fault types in radial, unbalanced distribution system. Index Terms--Distribution system, fault identification, fuzzy logic.

High current carrying cables used in power transmission lines create strong magnetic fields in their vicinity. For ac lines at 50-60 Hz, the magnetic field is quasi-static and hence uncoupled from the electric field. Shielding of such low frequency magnetic fields is a challenge. In this paper, finite element modeling is used to study the effect of various shield geometries and shield materials around a current carrying wire. Two-dimensional analysis is sufficient: for this problem because the cables are very long compared to the wire diameters. Shielding effectiveness, defined as the difference in the magnetic field intensity with and without the shield, is presented. It is concluded that a partial shield is the optimal design for shielding the region below the cable. To achieve this, the shield gap must be oriented above the high current wire. Index Terms - Finite element modeling, magnetic fields, power lines, shielding.

The paper presents an original analytical procedure which enables a quick and, for practical purposes sufficiently accurate evaluation of the significant parts of the ground fault current, for a fault at any of the towers of a transmission line of an arbitrary number of spans. The advantages of the method are the simplicity and accuracy of the formulae for solving uniform ladder circuits of any size (from one up to an infinite number of pis) and any terminal conditions. The formulae are obtained by applying the 'general equations of the line represented by discrete parameters' on a specific electrical circuit formed by a transmission line ground wire during ground faults. The presented method is suitable for analyses aimed at evaluating the maximum substation grounding system fault current, at selecting the ground wire capable of withstanding the fault currents and at the prediction of step and touch voltages near transmission towers.

The space charge in full size 250 kV DC cables was measured using the pulse-electroacoustic method. Measurements of two types of newly developed DC XLPE cables with 20-mm insulation were taken under a DC voltage of 500 kV with the conductor temperature at room temperature and at 85 [degree] C. A qualitative analysis of the space-charge distribution and a quantitative analysis of the electric fields in the vicinity of semicon interfaces were conducted. It was shown that the field in the vicinity of the inner semicon tends to increase by 10-40% when the polarity of the applied voltage was reversed, in the case when the conductor was kept at 85 [degrees] C. However, the distortion of the electric field was significantly less than that expected in conventional XLPE cables. As the result, the subjected DC cables are considered to have stable DC characteristics from the viewpoint of space charge-behavior.

Investigations on the growth properties of sulfide tree in cable insulation, subjected to dc electric fields, are described in this paper. Measurements of electric strength and conductivity are correlated to tree growth, observed by optical and electron microscopy, during accelerated aging tests performed in sea water with hydrogen sulfide. It is shown that both electric strength and dc conductivity are very sensitive to the length and concentration of sulfide trees, and that the magnitude of the electric field affects tree shape and growth rate significantly.

A one-dimensional model for field control in cable terminations is analyzed mathematically both for linear and nonlinear field grading materials. For an applied ac voltage, the concept of the penetration length allows for a useful characterization of the voltage profile, even for materials where both the conductivity and the permittivity are field dependent. For lightning impulse events an analytical solution for purely resistive field control is presented, allowing for an arbitrarily strong nonlinearity of the conductivity. The model results yield a useful input for more detailed finite element calculations. The results show that conclusions for nonlinear field control based on linear calculations in general are misleading.

More than 160 years of history go with the use of polymers in the cable industry. Polyethylene of low and high density and crosslinked polyethylene gradually succeeded paper and polyvinylchloride. This review discusses some aspects of the aging processes of polyethylene under working conditions. Electrical and water treeing are considered, dependent upon the morphology and the induced characteristics of the insulating material.

Two performance parameters of a cable or connector shield are its surface transfer impedance [Z.sub.T] and its surface transfer admittance [Y.sub.T]. A new method for measuring these properties is presented. The use of two different terminations for the cable or connector under test (CUT) allows to determine both [Z.sub.T] and [Y.sub.T]. Through characterization of the inner and outer transmission lines of the triaxial cell, using time domain reflectrometry, [Z.sub.T] and [Y.sub.T] can be determined in amplitude as well as in phase. The phase is obtained by de-embedding the measured S-parameters up to the CUT. The de-embedding of the measurements also allows to extend the frequency range up to 3 GHz. To illustrate this method a solid shield with a circular aperture and a coaxial cable with a braided shield have been measured and compared, respectively, with theoretical predictions and published results.

The transfer impedance [Z.sub.t] of a cable is often assumed to be a characteristic of the shield only. We investigate the limits of this assumption by calculations and measurements. The first test cable was formed by a solid copper tube ('shield') and a wire inside; several positions, also non-central, were chosen for the wire. The common mode current (between 10 Hz and 100 kHz) through the tube had as return path a single wire, which was placed at several positions, near and at some distance from the shield. A second cable with a braided shield was tested as well. The results show that both the differential mode and the common mode circuit have to be carefully defined for a particular [Z.sub.t]. Varying either circuit may alter [Z.sub.t] drastically. Consequently, the [Z.sub.t] of a particular cable measured in a triaxial setup, is a characteristic of that setup and cannot always be used in another setup as in for instance cable bundles.

This paper presents a closed form expression to compute the AC/DC resistance ratio of HPFF (High Pressure Fluid Filled) pipe-type cable in the presence of harmonics. Industry currently computes this factor, which is a significant part in assessing the current carrying capacity of a system, with the assumption that the currents are purely sinusoidal at 60 Hz. However, as levels of harmonics increase on power systems, concern for the effect of harmonics on system ampacities rises, and that effect has already been discussed for distribution systems. This paper develops a closed form hybrid of the resistance ratio equations presented by Neher and McGrath, and compares the results with measured data at 60 Hz. At present there is no measured data available for the resistance ratio at higher frequencies, so a two dimensional finite element model is developed to view the effect of frequency on the resistance ratio. A discussion is given on the effect of a specific harmonics scenario on the resistance ratio of a given system, and results are presented for some example systems. The paper also discusses the validity and characteristics of each method.

The paper suggests a mathematical model for the analysis of the performances of the grounding systems of distribution substations in underground cable networks with uncoated metal sheathed cables. The model derived has been utilized to evaluate the main grounding system performances and the potentials transferred to the consumers installations in the case of a ground fault in the source substation. Several typical cases have been analyzed as an illustration of the method.

The tensile stress of a cable is usually estimated by measurement of the force in some attached member. There are situations where it is important to know the actual stress in a cable and calculation may be difficult. The magnetic Barkhausen Noise (BN) method can be applied for stress measurement in ferromagnetic steel cables. The cable was led through the magnetizing and sensing coils and the induced noise was amplified and measured. 7-wire strands used in reinforced concrete, steel rope used by cranes and zinc-coated steel rope were the cables tested. The BN changed with applied tensile stress in all these materials. As tensile stress increased, magnitude of BN decreased and coercive force increased. The origin of this phenomenon was studied in relation to microstructure and XRD analysis. Based on the results utilization of BN for stress measurement is considered.

Two new concepts applicable to cylindrical generalized screens are introduced: standard responses and standard excitations. The standard responses allow the description of any current and charge distribution on the screen. For a given generalized screen's cross-section, they can be derived from the complex potential of a simple electrostatic problem. The standard excitations are electromagnetic (EM) field configurations suitable for a description of fields created by sources external to the screen. All standard excitations are explicitely computed in the case of a circular cylindrical shield. We present only three standard excitations for the case of the elliptical cylinder, and for the case of a rectangular cylinder. Index Terms--Cables, electromagnetic (EM) coupling, shielded multiconductor cable, shielding, standard excitation, standard response.

This paper deals with probabilistic modeling of the electromagnetic (EM) response of cables inside a complex cavity subjected to well overmoded EM penetration. Theoretical studies indicate that the field amplitudes and cable currents squared both should have a [Chi]-square distribution with two degrees of freedom, but our observations indicate that a log normal fit is empirically better unless the data, if experimentally obtained, is first passed through a carefully tailored trend-removing filter. If a cable model is driven by statistically simulated enclosure fields, similar extreme care must be taken with the numerical generation of these driving fields. The major innovation reported here is the development of an algorithm that models cable-drive fields simultaneously having a [Chi]-square power-flux distribution and the physically mandated local autocorrelation at a spatial point as frequency is swept or at a fixed frequency as the power flux sensor is moved around to map the cavity response. Nature is quite adept at creating a cable drive with these simultaneous attributes, but computer emulation had proved very exasperating. Our algorithm, as an unplanned bonus, also has the capability to transform random numbers from one distribution to another. For instance, one can input normally distributed power-flux values and obtain as the output [Chi] square or log normally distributed power-flux values. The reverse transformations are also allowed. Index Terms - Aperture leakage, cable coupling, [Chi]-square distribution, electric field, electromagnetic interference, electronic mode stirring, log-normal distribution, mode-stirred chambers, statistical electromagnetics.