Double-circuit Line Research Articles

Analysis of the faults involving adjacent conductors of a six-phase transmission line together with a modelling of the phase conversion transformer

Abstract In a bulk power transmission system the amount of power transfer can be increased by converting the widely used three-phase double-circuit lines into six-phase single-circuit lines instead of upgrading the transmission voltage. In this conversion process only a phase conversion transformer at each end of the line is required while the existing conductors, towers and corridors of three-phase lines can be used intact. However, this conversion will have an effect on the system fault currents and fault levels. The well-known symmetrical component method is suitable for fault analysis in a three-phase system, but it has been found unsuitable for analysing the practical faults on a six-phase line and for modelling the phase conversion transformer. This paper illustrates the way the phase conversion transformer has been incorporated in the six-phase line fault modelling and also presents a new application of the straightforward loop current method by using it to determine the currents and fault MVA corresponding to the common and practical faults on a 132 kV six-phase line. The same method has also been applied to the fault analysis of a 132 kV and a 230 kV three-phase line and the results are compared with those for the six-phase line.

Nonoptimum compensation schemes for single pole reclosing on EHV double circuit transmission lines

Optimum reactor compensation configurations for implementing single pole reclosing on EHV (extra-high-voltage), double-circuit lines have been previously investigated. However, for some applications, optimum schemes may not be practical due to constraints such as reactor physical size, operating constraints and existing equipment. The performance of nonoptimum schemes is considered using an EGAT (Electricity Generating Authority of Thailand) 328 km, 500 kV, double-circuit line as an example. Several compensation schemes were considered, and their performance was examined with both circuits in service and with one circuit out for maintenance. The analysis indicated that some schemes with reactor values considerably off optimum still provided reasonable performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Travelling-wave-based protection of double-circuit lines

Double-circuit current comparison protection (DCCCP) is an algorithm for travelling-wave-based protection of a double-circuit high-voltage line. It uses the balance between the two circuits to distingush between an internal fault and an external disturbance. To prevent incorrect trips superimposed currents are used, and the relay has to be blocked after detecting an external disturbance. The setting of relay parameters is discussed, as well as its performance. The tripping time is between 100 and 200 μs for the majority of faults. For faults around voltage zero, the tripping time is between 1 and 3 ms, depending on the amplitude of the short-circuit current. Faults close to the remote line terminal are not detected at all. Some direct lightning strokes will lead to an incorrect trip. To overcome the disadvantages of DCCCP, it is combined with travelling-wave-based differential protection in a protective scheme. Differential protection is a somewhat slower but very reliable backup. Its parameter setting is discussed, as well as its performance. The tripping time is between 1 and 3 ms. The protective scheme further contains fast reclosure, breaker-failure detection and adaptive setting for the backup relays.

Design modification and layout of utility substations for six phase transmission

Evaluations performed on the New York State Electric and Gas Corporation's 115-kV Goudey-Oakdale line and Goudey and Oakdale substations to assess the capability of the existing equipment operate as part of a six-phase demonstration project are described. The design modifications that will be made to meet the goals of the commercial demonstration and to allow integration into the existing three phase operating grid are also described. Reconfiguration of an existing double-circuit line to a single-circuit six-phase line requires installation of phase configuration transformers at the end of the line terminals and the associated switching, metering, and protection equipment. In addition, the phase conductors from the terminals of the transformers must be transposed for connection to the transmission line to achieve the desired 60 degrees vectorial separation angle between adjacent phase conductors. Concepts of substation compaction that have been pursued when attempting substation modifications for six-phase reconfiguration are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Safety procedures for working on de-energized EHV lines sharing common right of way

Double-circuit lines or lines sharing common right of way are becoming a common feature of the transmission system because of several right-of-way constraints, such as the desire to effectively utilize the transmission corridors and/or to conserve forest areas. The authors analyze some of the typical situations being encountered and recommend some safety procedures for the maintenance of the lines exposed to induction from a nearby energized circuit. It is recommended that deenergized lines should not be grounded at substation ends for maintenance purposes, as this would cause excessive circulating ground currents through earth switches. Hot-line maintenance techniques should be used for maintenance or deenergized circuits which are continuously exposed. Hot-line techniques should also be used for works in double-circuit portion of partially exposed line.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Insulation coordination, environmental and system analysis of existing double circuit line reconfigured to six-phase operation

Insulation coordination, environmental and system analysis of existing double circuit line reconfigured to six-phase operation

Performance of distance relay mho elements on MOV-protected series-compensated transmission lines

It is shown that the applicability of memory-polarized distance relay mho elements to the protection of MOV (metal oxide varistor) protected series-compensated lines is dependent on the system configuration, line loading, the location of the potential source, and the magnitude of memory polarization. For a configuration with compensation at one end of a line, the results indicate certain advantages in using the potential from the line side of the capacitor, and the use of a relatively large magnitude of memory polarization. The presence of a conducting MOV enhances the performance of the mho element both in terms of security on reverse faults and dependability on forward faults. The results obtained pertain to the proposed application in the Ontario Hydro system of a relatively large amount of compensation at one terminal in each circuit of a double-circuit line.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transformer winding selection associated with reconfiguration of existing double circuit line to six-phase operation

Conversion of an existing double circuit three-phase 115 kV overhead transmission line near Binghamton, New York to six-phase operation will provide a commercial demonstration of the feasibility of high phase order power transmission. An important part of this demonstration is specification of the phase/voltage conversion transformers and requirements to permit single pole switching of the line in a practical manner at minimum cost. The results of engineering studies which led to selection of two delta-wye three-phase transformers at each end, one of each pair with reversed polarity to obtain the 60 degrees shift between phases, are presented. >

Influence of AC-DC parallel interconnection on voltage stability of AC systems

The static and dynamic characteristics of power supply to each node in a hybrid ac-dc power system are analyzed by means of static and transient P-V curves. Three kinds of dc transmission control scheme are compared. DC transmission systems are more effective in delivering power to inverter nodes. The constant firing angle, constant current control techinque provides more power to inverter nodes than the conventional constant current, constant voltage and constant power, constant extinction angle techniques. Transient digital simulations indicate that dc interconnection improves voltage stability to both the opening of a dc interconnected line and one-line opening of ac double-circuit interconnected lines.

Corona discharge streamer model

Starting from the motion of a charged particle in the electric field set up by the conductor system of a power transmission line, the paper develops a model for the streamers released when the voltage stress at the surfaces of conductors leads to corona discharges from them. The frequency content of streamer pulses defines the frequency spectrum of radio noise-fields radiated from transmission lines in corona. This is a definition which is achieved for the first time in analytical form in the present paper. From the basis which the waveshape of a single streamer pulse in the time domain provides, multiple point discharges are interpreted as random uncorrelated noise sources in power spectral density form. Comparisons are made between this frequency domain function and previously published corona excitation functions derived from measurement. Further validation studies are reported in which noise-interfering fields found from the streamer model which the paper develops are correlated with the results of recent measurements on a 500 kV double-circuit line energised for test purposes to 522 kV.

HVDC conversion of HVAC lines to provide substantial power upgrading

The feasibility of conversion of AC lines to DC lines for a substantial power upgrading is analyzed, and it is shown that increases of 3.5 times or more are feasible. The main design objective is to permit the conversion to be carried out as a simple retrofit or maintenance operation, rather than a new construction operation, thereby reducing outage times and simplifying possible new licensing procedures. Both HV and EHV double-circuit and single-circuit AC lines of average characteristics have been used as an example for conversion to both bipolar and monopolar lines respectively. In addition to the substantial increase in power transfer capability, the conversion to DC also substantially reduces the per unit losses and enhances reliability through the improved lightning performance of the converted line. HVDC operation has proven advantages in optimizing operation of the total system. The data presented provide a reference framework to facilitate preliminary evaluations, although detailed conversion studies can only be made on a case by case basis. >

A study on grounding in the vicinity of the work site on 1000‐kV power transmission line. Part 1. Electrostatic induction and its protection

In order to clarify the grounding conditions for protecting workers on a de-energized circuit from induction from a live circuit and to determine the required current capacity of the grounding conductor for a 1,000 kV double-circuit power transmission line, the phenomena caused by electromagnetic induction resulting from a live circuit are discussed. The electromagnetic induction current Ig flowing through the body of a worker and the electromagnetic induction current IgO flowing through the grounding conductor can be analyzed by dividing the various power line conditions into three main factors, and using electromagnetic induction current calculations for a power line of infinite length. The zone where Ig does not exceed 1 mA is within 1 km of the grounding point on the de-energized circuit owing to the grounding resistance (0.1 Ω) of the substations at the ends of the line and the difference in the phase configurations on the line when the current I1 of the live circuit is a constant 1 kA through the line. Similarly the value of IgO is determined by the grounding resistance of the substations at the ends of the line and the difference in the phase configurations on the line. IgO is approximately 10 A per 1 kA of I1. The currents Ig and IgO produced by electromagnetic induction are additive, allowing Ig and IgO in the actual power line to be evaluated by summation.

Computation of secondary arc current on double-circuit EHV lines employing single-pole switching

Abstract Successful selective- (or single-) pole switching (SPS) of faulted EHV transmission lines depends on rapid secondary arc extinction. Two factors which govern the probability of secondary arc extinction are the effective value of the steady-state secondary arc current and the rate of rise of the recovery voltage. Successful application of SPS requires that the magnitude of the secondary arc current should be kept below a certain level. The purpose of this work is to present a method for the computation of the effective value of the secondary arc current on a double-circuit transmission line employing SPS. The model developed for the double-circuit line takes into account the mutual coupling between the two individual circuits. A typical 400 kV double-circuit line is considered and the effective value of the secondary arc current is evaluated for both transposed and untransposed configurations of the line. Then a comparison with the results available from simple network analysis is made.

Derivation of Correct Relaying Signals During Intersystem Faults for the Protection of Double-Circuit Lines

A digital distance relay is provided with voltage and current signals from one end only of the protected circuit, and is expected to assess the fault location on the basis of these locally derived signals. Many parameter of the power system exert an important influence on the calculation of fault impedances and fault location. An important aspect of designing a distance protection scheme is to select correct values of voltages and currents at relay location so that the calculated impedance during a fault condition is the positive-sequence impedance from the relay location up to the fault location.In power systems including double-circuit transmission lines (phases R1, S1, T1 - R2, S2, T2), the possibility of intersystem faults is given. Common distance relays are not always able to detect the fault, because the impedances are very complicated. The paper presented demonstrates how a suitable combination of voltages and currents leads to impedances for the faulted phases, which do not differ from the impedances seen by the three-phase fault. The unsymmetrical faults phase Rl to phase R2 to earth, phase S1 to phase T2, and phase S1 to phase T2 to earth are discussed. The impedances seen by the relays including the healthy phases are also discussed. For the calculation the zero-sequence mutual coupling of the double-circuit line and resistances at the fault location are taken into account.

Application of Power System Stabilizers for Enhancement of Overall System Stability

This paper provides a detailed account of analytical work carried out to determine the parameters of power system stabilizers (PSS) for the Darlington nuclear generating station presently under construction in eastern Ontario. The results presented are, however, of general interest and provide a comprehensive analysis of the effects of the different stabilizer parameters on the overall dynamic performance of the power system. They show how stabilizer settings may be selected so as to enhance the steady-state and transient stability of local plant modes as well as inter-area modes in large interconnected systems. In addition, it is shown that the selected parameters result in satisfactory performance during system islanding conditions, when large frequency excursions are experienced. Darlington GS, when completed by 1992, will comprise four 1100 MVA, 0.85 p.f., 1800 RPM turbine generators with "CANDU-PHW" reactors, moderated and cooled by heavy water. The station will be incorporated into the 500 kV network through three double-circuit lines. The units will be equipped with transformer-fed thyristor excitation systems and Delta-P-Omega type PSS [1, 2].

Effect of conductor height and terrain on the steady-state induced voltage and transient current through a linesman's body on a de-energized line

In the first part of the paper, vertical conductor height and terrain are shown to have a strong effect on the magnitude of the induced voltage in the de-energized line of a 500 kV double-circuit overhead transmission line. Of the several factors influencing vertical conductor height, the tree effect is investigated in particular. The results of some basic experiments show that tall trees under power lines have the effect of decreasing the vertical conductor height owing to their electrostatic shielding function. It is concluded that tree and terrain effects must be considered when constructing the shunt admittance matrix for calculation of the induced voltage of EHV and UHV power lines which go through mountainous areas. In the second part of the paper, the waveforms of transient touch-currents experienced by linesmen have been analyzed using the modified Fourier transform method. The effects of trees, the terrain and the frequency dependence of line parameters on the transient touch-current have also been investigated. The results show that trees and terrain below the transmission line greatly increase the magnitude of the touch-current, but the use of frequency-dependent line parameters has very little effect on these results.

Analysis of half-wavelength transmission lines with simulation of corona losses

The growing interest in very-long-distance transmission (2-3000 km) and the state of the art of half-wavelength transmission lines are briefly discussed. A model for the numerical simulation of corona losses at high electric gradients is proposed. Then an analysis is made of the steady-state and transient operation of an 800 kV, 60 Hz, 2500 km double circuit line. Results show that corona losses drastically limit the sustained overvoltages, but also place a limit on transmissible power and can affect transient stability. Possible schemes for interconnection of two half-wavelength lines at intermediate switching stations are also examined in order to attain acceptable system reliability.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Similarity Criteria of EHF Physical Model of Long Distance Transmission Line with Plate Phases

Carson's equations for computation of frequency dependent parameters of overhead transmission line are modified. The earth is considered to be homogenous. The optimal required number of terms of Carson's series for applications on computer is determined. Accurate mathematical expressions for resistance and inductance of overhead transmission lines are obtained.Different arrangements of conductors for double circuit transmission lines are studied. The mutual inductance and potential coefficient (mutual capacitance) of such arrangements are computed. Double voltage class type double circuit transmission lines are suggested. The plate type double circuit lines are proposed for power transmission over long distances.This paper presents a mathematical analysis in order to determine the coefficients of similarity criteria of EHF physical model for the given long distance transmission line. The integral analogue method and PI-theorem are used. The independent parameters of EHF physical model are formulated. The scales of four independent parameters of the designed EHF physical model are obtained.

Effect of High Altitude on High Voltage AC Transmission Line Corona Phenomena

This paper summarizes the results of a research effort conducted by Bonneville Power Administration (BPA) to determine the effect of altitude on corona phenomena from high voltage transmission lines. A computer-controlled, reliable, unattended test station was installed at an altitude of 1935 m on a double-circuit 500-kV line near Basin, Montana, to continuously monitor audible noise (AN), radio noise (RI), and television interference (TVI). To obtain comparative data at a lower elevation, another test station was installed on a 500-kV line of similar design near Stayton, Oregon, at an altitude of 277 m. Comparison of the high altitude data with the lower elevation data and with predictions demonstrated that the correction factor of 1 dB/300 m developed in the 1950's and 1960's for radio noise is still valid and is also applicable for AN, TVI and, possibly, corona losses.

Efficient power transmission over short distance using controlled double-circuit lines

Abstract This paper presents a mathematical analysis which facilitates the calculation of voltages and currents in controlled double-circuit type transmission lines. In addition the active and reactive powers at both ends of the controlled as well as the ordinary transmission lines are computed. In the investigation the effect of the phase shift between the two voltage systems of the two circuits of the controlled line is considered.