Three-phase Network Research Articles

System Analysis and Application Concerning with Single Phase Spot Network (SNW)

Household use of microcomputer-based equipment now requires that the power supply to dwellings be highly reliable without momentary failures. Three-phase power supply networks have previously been used to distribute single-phase loads to dwellings. Single-phase networks have a better cost performance compared with the three-phase network system. However, due to the complicated current analysis in the case of faults and to the difficulty in developing relays based on the analytical results, single-phase networks have not yet been put into practical use. We have now succeeded in developing a single-phase network using the following five processes: (1) System analysis (2) Verification using a simulated circuit (3) Determination of the relay characteristics based on the analytical results (4) Development of a static single-phase network relay to satisfy with the complicated voltage-current relationship (5) Actual field test This system has been operating since 1983.

System analysis and application concerning with single phase spot network (SNW)

Household use of microcomputer-based equipment now requires that the power supply to dwellings be highly reliable without momentary failures. Three-phase power supply networks have previously been used to distribute single-phase loads to dwellings. Single-phase networks have a better cost performance compared with the three-phase network system. However, due to the complicated current analysis in the case of faults and to the difficulty in developing relays based on the analytical results, single-phase networks have not yet been put into practical use. We have now succeeded in developing a single-phase network using the following five processes: (1) System analysis (2) Verification using a simulated circuit (3) Determination of the relay characteristics based on the analytical results (4) Development of a static single-phase network relay to satisfy with the complicated voltage-current relationship (5) Actual field test This system has been operating since 1983.

Sparsity Enhancement in Mutuality Coupled Networks

Mutual coupling in three-phase or zero-sequence networks often results in severe sparsity degredation in network analyses based on the nodal admittance matrix. Retention of mid-line nodes in the zero-sequence nodal admittance matrix results in sparsity enhancement and computational improvements. These improvements come about from the breaking up of large mutually coupled groups. Examples based on both small and large test cases are used to illustrate the principles involved. These results indicate that even though, for a system of realistic size, retaining mid-line nodes approximately doubles the size of the nodal admittance matrix, the net computational requirements can sometimes be reduced to a third or less of those of the original system.

Synchronous Machine and Torsional Dynamics Simulation in the Computation of Electromagnetic Transients

This paper presents the development of a new time domain simulation program for the computation of machine and network transients over a wide frequency spectrum. The program uses the extensive capability for the detailed representation of, and the computation of electromagnetic transients on, the power system network available in the BPA Electromagnetic Transients Program (EMTP). The model of the synchronous generator, in which both the electrical and the mechanical shaft torsional dynamics are represented, possesses a large degree of generality. The model is interfaced with the EMTP network and a newly developed and computationally efficient numerical integration scheme is used to compute the machine transients. The option for representing arbitrary excitation systems has been implemented. The program's capability to simulate a three-phase network with an arbitrary number of synchronous machines - generators or motors -and their auxiliary control equipment, allows the evaluation of network - machine - control systems interactions. The application of the program to investigate the subsynchronous resonance phenomenon in a realistic-sized system is given. Other typical applications include transmission line reclosure, independent pole switching, load rejection or unit tripping, loss of synchronism and multi-machine interaction problems. The program, in use for some time by a number of utilities, has been incorporated as a standard feature of the EMTP.

Direct Coupling of Solar Cell Arrays to Electric Power Networks

Results of the investigation of the performance of solar cells when directly coupled to a conventional three-phase power network are presented. This approach dissociates the electricity production problem from the electric energy storage problem. Extensive studies of the required power inverter are performed. Preliminary simulation results indicate that ac power outputs of better than 90 percent of the optimum cell power output can be easily achieved by means of a suitably controlled inverter, thereby justify

Unbalanced Faults on a Three-Phase Network by a Generalized Treatment

Unbalanced Faults on a Three-Phase Network by a Generalized Treatment

The Triple-Harmonic Equivalent Circuit in Three-Phase Power Transformer Banks

The importance of triple-harmonic voltages and currents in electrical power systems is generally recognized by engineers associated with the power and telephone industries. It is desirable to have some convenient method of representation and calculation of the triple-frequency effects in three-phase power systems. The path of the third-harmonic current is different fromn that of the fundamental current and for this reason the circuit can be considered as separate and, distinct. The characteristics of the triplefrequency circuit as determined by laboratory experiment are given in this paper. Methods of measurement of the required quantities for accurate solution of the triple-frequency circuit are described. The results of an experimental investigation of the equivalent triple-frequency circuit as proposed by H. S. Osborne in 1915 are set forth. A typical simple three-phase power network has been set up and the measured currents compared with computed values. Oscillograms are presented of voltages and currents with typical transformer connections demonstrating the principles of operation of the circuit both for normal and abnormal excitation conditions. The effects of various types of connected loads are discussed, with particular attention given to the condition of triple-frequency resonance. It is shown that triple-frequency resonance occurs when the external capacitive reactance of the circuit is equal to the triple-frequency no-load impedance of the transformer. Resonance produces large triple-frequency currents and serious distortion of the line-to-neutral voltage of the system.

Equivalent single-phase networks for calculating short-circuit currents due to grounds on three-phase star grounded systems

This paper presents a method for calculating the steady state value of the short-circuit current in a fault to ground on a power system operated with grounded neutral, and the distribution of this current throughout the system. Constant impedances and electromotive forces in the system, and electrically short lines, are assumed, and line capacitance is neglected. If, at the time the fault to ground occurs, the distribution of the load current in the system is known, the total current in any portion of the system under the short circuit condition may be calculated by means of this method. By “total current” is meant here the sum of that part of the fault current which appears in the branch considered, and the normal current in the branch due to the loads. The latter current, of course, does not appear in the fault. Formulas and equivalent circuits for the usual three-phase transformer and generator connections used in practise, are given. The use of such circuits permits the calculation of the fault current and its distribution in the power system from an equivalent single-phase network. Since currents in a three-phase network under balanced conditions may also be calculated from a single-phase network, it is accordingly possible to calculate, entirely on a single-phase two-wire basis, the total current in any branch of a star grounded network for a ground on any phase. The setting up of equivalent 2-wire single-phase networks similar to those for the three-phase case is not generally possible where the number of phases exceeds three. The value of the method lies in its enabling one to calculate on a single-phase two-wire basis the short circuit current (steady state) due to a ground on a three-phase grounded neutral system, as regards both magnitude and distribution and taking into account all system loads. In the usual approximate method of making short-circuit calculations, a single-phase-to-neutral network is substituted for the actual network. While this method involves less labor than that proposed in the paper, the results obtained by it are inexact, the effect of non-grounded loads being usually ignored. The method of the paper involves much less work than that required by three-phase calculations giving equal accuracy. An illustrative example is given.

Equivalent Single-Phase Networks for Calculating Short-Circuit Currents Due to Grounds on Three-Phase Star Grounded Systems

This paper presents a method for calculating the steady state value of the short-circuit current in a fault to ground on a power system operated with grounded neutral, and the distribution of this current throughout the system. Constant impedances and electromotive forces in the system, and electrically short lines, are assumed, and line capacitance is neglected. If, at the time the fault to ground occurs, the distribution of the load current in the system is known, the total current in any portion of the system under the short circuit condition may be calculated by means of this method. By ``total current'' is meant here the sum of that part of the fault current which appears in the branch considered, and the normal current in the branch due to the loads. The latter current, of course, does not appear in the fault. Formulas and equivalent circuits for the usual three-phase transformer and generator connections used in practise, are given. The use of such circuits permits the calculation of the fault current and its distribution in the power system from an equivalent single-phase network. Since currents in a three-phase network under balanced conditions may also be calculated from a single-phase network, it is accordingly possible to calculate, entirely on a single-phase two-wire basis, the total current in any branch of a star grounded network for a ground on any phase.