Single-phase Line Research Articles

High-efficiency single-phase motor

A three-phase induction motor was supplied from a single-phase public utility using a new and unique reconnection of the machine windings and three power capacitors to provide balanced currents and voltages in all of the windings and the corresponding three-phase high efficiency. Zero-crossing solid-state relays changed the capacitor values in response to load changes so that the single-phase efficiency was within 3% of the three-phase efficiency for all shaft loads between 20% and 120%. The single-phase power line power factor was near unity for a wide range of powers. This method is applicable to both high efficiency and standard three-phase motors without motor modifications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Calculation of the response of unshielded distribution lines to direct lightning strikes Part I. Multiconductor travelling wave analysis

This paper describes a comprehensive computer program to calculate the response to lightning strikes of a single-phase or three-phase unshielded distribution line with an earthed neutral conductor. The program uses a new implementation of a multiconductor travelling wave technique so that voltage and current waves on all phase conductors and the neutral are calculated. This new method is an improvement over previous methods which involved a modified single-conductor travelling wave calculation. In this new multiconductor travelling wave analysis, a set of equations describing the relationship between the incident and reflected waves for each node type is derived. The distribution system is made up of a series of node types classified according to their respective modes of earthing and function. The function equations derived are then solved on a time iterative basis to include non-linearities necessary for the accurate modelling of the problem. This paper describes the formulation of the technique and features of the program. A companion paper (Electr. Power Syst. Res., 22 (1991) 97 – 103) shows the validation by comparison of calculated results with some actual field measurements of the surge currents on a single-phase distribution line which has been specially instrumented.

Calculation of the response of unshielded distribution lines to direct lightning strikes Part II. Validation and studies

Part I of the paper describes the formulation and implementation of a new multiconductor dynamic travelling wave technique to calculate the response of unshielded distribution lines to direct lightning strikes. This paper presents a comparison of the results of calculations from this developed program with some actual field measurements of surge currents on a single-phase distribution line which has been specially instrumented. To offer validation, the calculated voltage and currents of two specific lightning incidents on the Leonard-Lee 13 kV distribution line are compared with some actual measured currents which were available. Voltages on a three-phase line with neutral wire are also calculated and the results obtained from this new implementation of the travelling wave technique are compared with a previous method which considered a single-wire travelling wave and coupling factor.

Studies on modeling corona attenuation of dynamic overvoltages

An experimental and theoretical study is presented on the corona characteristics of conductor bundles under dynamic overvoltages. Measurements have been made in the outdoor test cages of Institut de Recherche d'Hydro-Quebec on two bundles, under conditions of fair weather and heavy rain, for steady 60 Hz voltages as well as dynamic overvoltages. Based on the data on corona currents and losses obtained, a nonlinear resistance model of corona is proposed for attenuation studies. The Suliciu model for corona, originally developed for unipolar impulses, has been adapted for dynamic overvoltages. Both these corona models are used to study the influence of corona on the dynamic overvoltages developed during line energization and load shedding of a single-phase line. Among other findings, it is shown that the corona phenomenon stabilizes after the first half-cycle of the dynamic overvoltage. The corona losses of conductor bundles under fair weather conditions increase rapidly with the conductor surface voltage gradient; they approach losses under heavy rain at higher gradients.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Studies on Modeling Corona Attenuation of Dynamic Overvoltages

An experimental and theoretical study is presented on the corona characteristics of conductor bundles under dynamic overvoltages. Measurements have been made in the outdoor test cages of Institut de Recherche d'Hydro-Quebec on two bundles, under conditions of fair weather and heavy rain, for steady 60 Hz voltages as well as dynamic overvoltages. Based on the data on corona currents and losses obtained, a nonlinear resistance model of corona is proposed for attenuation studies. The Suliciu model for corona, originally developed for unipolar impulses, has been adapted for dynamic overvoltages. Both these corona models are used to study the influence of corona on the dynamic overvoltages developed during line energization and load shedding of a single-phase line. Among other findings, it is shown that the corona phenomenon stabilizes after the first half-cycle of the dynamic overvoltage. The corona losses of conductor bundles under fair weather conditions increase rapidly with the conductor surface voltage gradient; they approach losses under heavy rain at higher gradients. >

Scheme, based on travelling-waves, for the protection of major transmission lines

The paper gives details of development work on a protective scheme based on the travelling waves present on major transmission lines after the incidence of faults. The basic principle of the scheme is outlined. Analytical treatment, based on an ideal single-phase line, is included to indicate how the initial travelling wave propagated from a fault and a later wave resulting from a reflection at the fault position may be identified. The time interval, between the arrivals of these two waves at the transducers which would energise the protective scheme, is proportional to the distance to the fault. Its position may therefore be determined with acceptable accuracy. Indication is given of the differences resulting from faults both on and external to a protected line, and discriminatory checks which could be incorporated are outlined. The application of the scheme to 3-phase lines is considered and a further discriminatory check is described. To demonstrate the potential of the proposed scheme, its responses to a number of fault conditions are provided.

Three-Phase Induction Generator for Single-Phase Line

Hydroelectric generators of less than 20 kW can be served only by a single-phase line in remote areas. For high efficiency and low cost, a three-phase induction generator should be used. This three-phase generator can operate with balanced voltages and currents when the ``phase-splitting'' circuit uses two capacitors connected to two different single-phase voltage sources.

Three-Phase Induction Generator for Single-Phase Line

Hydroelectric generators of less than 20 kilowatts can be in remote areas served only by a single-phase line. For high efficiency and low cost, a three-phase induction generator should be used. This three-phase generator can operate with balanced voltages and currents when the ``phase-splitting'' circuit uses two capacitors connetted to two different single-phase voltage sources.

Travelling-Wave Techniques Applied to the Protection of Teed Circuits:- Multi-Phase/Multi-circuit Sytstem

In a preceding paper [1], the authors had described new techniques based on the h.f. travelling-wave information contained in the post fault voltage and current signals. In an attempt to present the underlying principles without undue complications, the study was limited to a lossless, frequency independent single phase line model.

Audible Noise and Corona Loss Performance of 9-Conductor Bundle for UHV Transmission Lines

This paper summarizes the test results of a single-phase line of the 9 x 30.8 mm conductor bundle, supported in a symmetrical 1.22 m diameter circle. Statistical analyses of long-term audible noise and corona loss data for a variety of weather conditions and at line-to-ground test voltages of 815, 890 and 975 kV are presented, including the corona effects as function of rain rate. Extrapolations of single-phase test results to evaluate the audible noise and corona loss performance of an assumed three-phase line are also discussed.

Calculation of Induction and Magnetic Field Effects of Three Phase Overhead Lines Above Homogeneous Earth

The paper addresses the problem of induction effects of a three phase transmission line on a parallel circuit, in the presence of homogeneous earth. It is based on the simple expression' Z?= K?ln(D/D') of a mutual impedance (where D? is complex) which approximates well earth return effects as calculated by Carson2. This expression is used to derive equations for the magnetic field intensity IT of a single phase line, and for both Z?and H?of three phase lines related to a parallel conductor with ground return.

A Nonlinear Circuit Model for Transmission Lines in Corona

A phenomenological transmission line corona model is proposed in this paper which accommodates the diverse aspects of steady-state and transient power and energy losses and change in capacitance. Single phase line sections have been represented by a nonlinear model circuit which changes its state depending on the present and the previous values of the voltage. Propagation with corona is simulated by cascading identical model circuits and the nonlinear transmission line equations are solved by a finite difference method. The charge-potential characteristics of line sections and the nonlinear propagation characteristics of voltage surges computed numerically from our model conform with available experimental data in the literature.

Rectifier Considerations in the Design of Salient Pole Synchronous Machines

A review is made of existing methods for calculating the transient field current during three phase and single phase line to line terminal short circuits, since this current determines the ratings of rectifiers in the field supply. An equation, of improved accuracy is given for the three phase fault. Measurements and calculations are shown for laminated and solid pole machines. It is shown that the latter construction gives sufficiently different field currents and decrements to affect rectifier ratings but the new equation can be empirically modified to account for this. A method is given for calculating the inverse voltage of rectifiers during the fault when a rotating exciter is employed. The effect of thyristor waveforms upon bearing currents and frame to ground potential is demonstrated by calculations and measurements.

Power Supplies for Electroslag Furnaces: A Preliminary Comparison

This paper reviews the relative merits of the five main types of power supplies that can be used for electroslag melting. These are: ac single-phase line frequency, ac three-phase line frequency, dc electrode positive, dc electrode negative, and ac low frequency. The comparisons are based mainly on operating experience with furnaces producing industrial-sized ingots [over 12 in. (30.5 cm) in diameter] in a wide variety of ferrous and nickel-based alloys. The power supplies are compared on the basis of the following 14 industrially important indices: power cost per ton, power supply capital cost, electrode costs, total furnace capital cost, melt setup cost, desulphurization in ferrous alloys, molten metal pool depth, absence of inherent stirring, applicability to slab melting, molten slag starting, melt mode flexibility, supply line balance, supply line flicker, and power supply reliability. In general, the survey shows each of the possible melt modes their advantages, disadvantages, and the fact that none of them can be recommended as a universal solution for all applications. It is, however, apparent from the comparisons that ac single-phase line frequency has the broadest potential application.

Decoupling of Transmission Lines to Radio-Influence Voltages

Theoretically, the R-C decoupler network has been shown to provide both better attenuation and impedance-matching characteristics. Reactive elements alone (L-C) may give sufficient attenuation, but their low-loss characteristic is likely to alter the RI performance of the source side, returning part of the energy of some impinging pulses while passing others so that pulse fronts, tails, and amplitudes are transformed. Two sets of field tests were made to determine whether several sections of transmission line could be satisfactorily decoupled or isolated to RI, using the R-C decoupler network with the resistance shunted, for 60-cps purposes, by a relatively high inductance. Although questions regarding correct line termination and line attenuation at higher frequencies have not been answered, use of properly designed RI filters or decouplers has been shown to provide a high degree of RI isolation between sections of line. The tests were intentionally made on a single-phase line with no ground wire. Extensive field investigations would involve 3-phase conductors, plus one or two ground wires. All these conductors must be decoupled to get proper results during simultaneous testing of different line sections. From previous tests at Tidd, it has been found that heating the conductors-so as to produce in them a few degrees of temperature rise above ambient-greatly alters the RI and corona loss obtained during fog, drizzle, and damp weather in general. Current for heating cannot be drawn through the resistors of R-C decouplers.

Equivalent Circuit of 3 Phase Induction Motors operated Single Phase Line

Equivalent Circuit of 3 Phase Induction Motors operated Single Phase Line

Lightning Experience on 132-Kv Transmission Lines of the American Gas and Electric Company System 1930-1931

This paper, which is a continuation of a four-year operating record of an extensive 132-kv transmission system under lightning conditions, presents and discusses the record for 1930 and 1931. Operating experience is given on: 1. Yearly line outages due to lightning for all lines. 2. Severity and frequency of lightning storms over the system for a three-year period. 3. Frequency of double circuit outages. 4. Extent of line and station apparatus damage. 5. Effect of tower footing resistance in reducing lightning outages. 6. Reduction in tower footing resistances by the use of driven ground rods and counterpoises. 7. Effect on lightning outages by overinsulation. 8. Relative frequency of single-phase, two-phase and three-phase line faults. 9. Location of lightning flashovers on the line in reference to top, middle and bottom conductors. Conclusions are drawn from the results of the operating experience on these lines.

Artificial Transmission Lines With Distributed Constants

Artificial transmission lines have been very valuable in developing the theory of transmission of power. This theory has been developed in great detail for steady state conditions, and it is now important to extend it to cover transient conditions. This can best be done upon artificial transmission lines but the usual lumpy type of line introduces parasitic reflections caused by the discrete units of inductance, and therefore are of very limited use for this purpose. Attempts have been made from time to time to produce artificial lines with distributed constants, but the results were either unsatisfactory or expensive and bulky. A method, originally proposed by Pupin, has been developed by which small compact and cheap artificial transmission line coils can be designed and built to represent any desired configuration of circuit. These involve tinfoil wound in with the wire between the different layers, insulated from the winding by the usual form of condenser dielectric paper. One of the most difficult parts is to arrive at a coil with the proper constants. Formulas have been derived for doing this which will calculate the result given by the coil within the limits of manufacturing error, and which can be used in a straightforward manner similar to the design of other electrical apparatus. Either single or polyphase lines may be represented, and a single-phase line representing the average configuration of a 110,000-volt line approximately 1000 miles (1600 km.