Large Single-phase Loads Research Articles

A novel control scheme for simultaneous elimination of imbalance, disturbance and voltage harmonic in power systems

In recent years, the increasing application of nonlinear and unbalanced electronic equipment and large single phase loads have made voltage imbalance a serious problem in power distribution systems. A novel approach has been proposed to eliminate voltage imbalance and disturbances. The main strategy of this scheme is based on series active filter. By improving control circuit toward existing schemes and proposing a new strategy to control the voltage amplitude, simultaneous elimination of voltage imbalance, faults, voltage harmonics and also compensation of voltage drop in transmission lines become possible. Eventually, the voltage on the load side is a perfectly balanced three phase voltage with specific proper amplitude. The proposed scheme has been simulated in a test network and the results show high capability of this scheme for the complete elimination of imbalance without phase shift.

Study on Voltage Unbalance Improvement Using SFCL in Power Feed Network With Electric Railway System

An electric railway system uses a single-phase source that is supplied through a Scott transformer from a three-phase transmission system. In addition, the electric railway system has rapidly changing load characteristics in time. An unbalance is generated owing to the rapidly changing large single-phase loads. Subsequently, the unbalanced load causes an unbalanced transmission line. A voltage unbalance in the source influences the power equipment by causing a reduction in the power generation capacity of the generator and a decrease in the output of the other facilities in the transmission line. In addition, many flexible ac transmission systems are applied to transmission lines to compensate for and control electric power. A voltage unbalance causes a control error in these systems. We propose the application of a superconducting fault current limiter to improve the voltage unbalance in a transmission system linked to a Scott transformer. In addition, we analyzed the effects of the proposed method using transient simulations.

A fault-induced transient analysis of unbalanced distribution systems with harmonic distortion

Abstract This paper presents a new method to calculate a fault-induced transient in an unbalanced three-phase distribution system, subjected to a shunt fault and/or a series fault, using the three-phase bus impendance matrix. The method is also applicable to multiple faults which involve a shunt fault and an open conductor. The imbalance caused by large single-phase loads, untransposed feeders, conductor bundles, etc., is reflected in the polyphase bus impedance matrix. Consequently, line removals, additions, impedance changes, conductor and phase openings can be simulated by modifying the base-case impedance matrix in the complex frequency domain. Thus, the proposed method makes it possible to analyze any type of single or multiple fault-induced transient occurring anywhere in the system.

Three-phase modeling for transient stability of large scale unbalanced distribution systems

The authors propose a generalized method to analyze the transient stability by using the three-phase bus admittance matrix algorithm for any network configuration. The method takes into account the unbalance created by large single-phase loads, untransposed feeders, conductor bundles, and cables. Consequently, the effects of unsymmetrical shunt and/or series faults, as well as the addition or removal of single-phase feeders, can be simulated anywhere in the network. Also presented is a novel, general systematic technique of studying transient stability of unbalanced distribution systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A generalized computer technique for the development of the three-phase impedance matrix for unbalanced power systems

Abstract This paper presents the development of the three-phase bus impedance and bus admittance matrices for unbalanced power systems. The imbalance conditioned by large single-phase loads, untransposed feeders, bundled conductors, etc., is reflected in the polyphase impedance or admittance matrix. The method utilizes the phase frame representation of network elements. Consequently, line removals or additions, impedance changes, conductor and phase openings can be simulated easily by modifying the bus impedance matrix. Thus, the proposed method makes it possible to analyze any type of single- or three-phase loads and unequal mutual coupling between the phases for large-scale power systems.

Synchronous generator stability due to multiple faults on unbalanced power systems

Abstract This paper investigates the dynamic behavior of a synchronous generator connected to an unbalanced three-phase power system which is subjected to a shunt fault at one location and blown fuses or open conductors at another location. The method involves phase frame representation of the line. The imbalance created by large single-phase loads, untransposed lines, conductor bundles, etc., is reflected in polyphase impedance matrices. Consequently, line removals, additions, impedance changes, conductor and faulted phase openings can be simulated based on the boundary conditions. Thus, the proposed method makes it possible to study the synchronous generator stability due to any combination of single or multiple asymmetrical series and shunt faults occurring anywhere in the system and the results of several case studies are presented. A significant finding is that certain faults cause the generator to lose synchronism only after several cycles of the rotor angle swing curve. In such cases it is therefore no longer correct to judge the system's stability only on the ‘first swing cycle’ of the rotor angle.

Three-phase modeling of unbalanced distribution systems during open conductors and/or shunt fault conditions using the bus impedance matrix

Abstract This paper presents a digital simulation technique for unbalanced three-phase distribution systems subjected to a shunt or a series fault. The method is also applicable to multiple faults which involve a shunt fault at one location and blown fuses or open conductors at another. The method utilizes the phase frame representation of network elements. The imbalance conditioned by large single-phase loads, untransposed feeders, conductor bundles, etc., is reflected in the polyphase impedance matrix. Consequently, line removals, additions, impedance changes, conductor and phase openings can be simulated by modifying the base-case impedance matrix. Thus, the proposed method makes it possible to analyze any type of single or multiple fault occurring anywhere in the system.

Exact Calculation of Simultaneous Faults Involving Open Conductors and Line-to-Ground Short Circuits on Inherently Unbalanced Power Systems

The analysis of simultaneous faults, espec ially involving mutually coupled lines on inherently unbalanced power systems using the symmetrical components technique, may not be practically feasible because of the difficulties encountered in the assembly f sequence networks and their solution. To al-le- these problems, this paper presents an alternative method for digitally simulating a basically ubnlanced three-phase power system which is subjected to a shunt fault at one location and blown fuses or open conductors at another location. The method involves phase frame representation of network elements and the use of the distributed source solution technique in conjunction with the principle of superposition. e phase coordinate model of power system ele- is modified/enlarged to simulate inherent system imbalances as well as the unbalancing contributed by the change in network configuration. The unbalance conditioned by large single-phase loads, untransposed transmission lines, conductor bundles, etc. is re- flected in the polyphase admittance matrix. Consequently, line removals, additions, impedance changes, conductor and phase openings can be simulated quite easily by simply modifying the base case admittance matrix. Even the treatment of mutually coupled lines presents no computational problems, unlike the symmetrical component approach. Thus, the proposed method makes it possible to analyze simultaneous faults on basically unbalanced power systems with the same ease and simplicity as unsymmetrical faults on a balanced system with the aid of symmetrical components. The method is applicable to any combination of series and shunt faults occurring anywhere in the system.

Distributing large single-phase loads in limited-capacity 3-phase power systems

A LARGE single-phase load drawn from a limited-capacity 3-phase system will unbalance the 3-phase system. If analyzed by symmetrical components in the 3-phase system, equal and opposite positive- and negative-sequence currents are realized. This unbalance leads to excessive heating in the stator of the alternator, thus substantially reducing its over-all capacity. If uncorrected, the unbalance may also cause local hot spots in ordinary induction motors.

Distributing large single-phase loads in limited capacity 3-phase power systems

A conversion method has been developed to balance a 3-phase power system automatically, if a large single-phase load alters the system. Past control systems were useful for only a particular load condition, while this method is effective regardless of the magnitude, power factor, or change in the load.

A unit for balancing the voltages of three-phase aircraft inverters supplying large single-phase loads

A unit for balancing the voltages of three-phase aircraft inverters supplying large single-phase loads

A unit for balancing the voltages of three-phase aircraft inverters supplying large single-phase loads

A unit for balancing the voltages of three-phase aircraft inverters supplying large single-phase loads

A Unit for Balancing the Voltages of Three-Phase Aircraft Inverters Supplying Large Single-Phase Loads

A means of reflecting a singlephase load so it appears as a balanced three-phase load to the power supply is discussed in this paper. A balancer of this type, designed for use in aircraft, is described and its characteristics discussed.