Single-phase Circuits Research Articles

A Novel Method of Suppressing the Inrush Current of Transformers Using a Series-Connected Voltage-Source PWM Converter

This paper proposes a novel method of suppressing the inrush current of transformers. A small-rated voltage-source PWM converter is connected in series to the transformers through a matching transformer. As the connected PWM converter performs a resistor for the source current, no inrush phenomena occurs. The required-ratings of the PWM converter, which performs the damping resistor for the inrush phenomena, is one-four-hundredth as compared to that of the main transformers in single-phase circuits. In three-phase circuits, it is one-nine-hundredth. The basic principle of the proposed method is discussed. Digital computer simulation is implemented to confirm the validity and excellent practicability of the proposed method using the PSCAD/EMTDC. A prototype experimental-model is constructed and tested. The experimental results demonstrate that the proposed method can perfectly suppress the inrush phenomena.

An Improved Time Domain Arc Furnace Model for Harmonic Analysis

In this paper, an arc model is presented to carry out harmonic analysis of an AC three-phase arc furnace with a single-phase circuit. This model is based on the V-I characteristic of the arc and takes into account the effect of the arcs unbalance over the zero sequence harmonics. The model is implanted in EMTDC and tuned with field data. Simulations are performed in continuous work using Monte Carlo method to obtain arc length. Simulations results obtained with this model are compared for the main harmonics with actual data and simulation data obtained with other models. The comparison is carried out with the probability density functions of the harmonics.

A Novel Harmonic Compensator for Consumer Electronic Equipment Using the Correlation Function

This paper proposes a novel harmonic compensator for consumer electronic equipment that act as harmonic voltage sources in single-phase circuits, using the correlation function. The distribution transformer is equipped with an additional winding on the secondary side, and a single-phase voltage-source PWM inverter is connected to the added winding, acting as a shunt active filter. The leakage inductor on the secondary side winding behaves as though connected in series to the consumer electronic equipment. The shunt active filter can thus be used to compensate harmonic currents on the source side without an inductor series-connected to the harmonic voltage source. The basic principle of the proposed compensation method is discussed in detail. Digital computer simulation is implemented to verify the validity of the proposed compensation method. Experimental results demonstrate the novelty and excellent practicability of the proposed harmonic compensator with the proposed harmonic current detection method using the correlation function.

Insuring adequate spacing between underground distribution conductors in conduit and gas lines

The effects of faults occurring on secondary cables in a plastic conduit energized at 240 V were evaluated under simulated field conditions. Secondary cables were intentionally faulted inside polyvinyl chloride (PVC) and polyethylene (PE) conduits. The test setup represents a typical, residential single-phase circuit consisting of a padmount transformer with a length of secondary cable. The fault characteristics (voltage and current waveforms) and temperatures on the exterior of the conduit near the fault were recorded. The condition of the conduit after the fault was also assessed.

Spectral analysis of instantaneous powers in single-phase and three-phase systems with use of p-q-r theory

Three linearly independent instantaneous powers have been defined in the time domain in three-phase four-wire systems with the use of p-q-r theory. Any three-phase circuit can be transformed into three single-phase circuits by the p-q-r transformation. Thus the instantaneous powers in any three-phase systems can be analyzed as the same way of instantaneous power in single-phase systems. This paper analyzes the instantaneous powers spectrally in the frequency domain for single-phase systems and three-phase systems. Each instantaneous power in three-phase systems has its own spectral pattern that is characterized by the spectral distribution of the system voltages and currents. The instantaneous power in single-phase systems has its own spectral pattern different from that of three-phase systems. From the spectral analysis of the instantaneous powers, powers are newly defined in the frequency domain. The definition of the powers is consistent through single-phase systems and three-phase systems and agrees well with the traditional definition of powers in sinusoidal single-phase systems. Based on the defined powers, some useful power quality factors are defined to evaluate power qualities for various circuit conditions.

Insuring Adequate Spacing between Underground Distribution Conductors in Conduit and Gas Lines

The effects of faults occurring on secondary cables in a plastic conduit energized at 240 V were evaluated under simulated field conditions. Secondary cables were intentionally faulted inside polyvinyl chloride (PVC) and polyethylene (PE) conduits. The test setup represents a typical, residential single-phase circuit consisting of a padmount transformer with a length of secondary cable. The fault characteristics (voltage and current waveforms) and temperatures on the exterior of the conduit near the fault were recorded. The condition of the conduit after the fault was also assessed.

Front Cover

For a specific susceptibility of end-user equipment, the impact of disturbances can be mitigated by design modifications of circuit layout, grounding system design, overvoltage protection, filters, use of steel conduit, use of additional transformers, etc. The effectiveness of these design options on power quality can be analyzed with specialized analysis software. These analysis methods should be able to model systems with three phase wires, four wires (three phase and a neutral/or ground wire), five wires (three phase wires, a neutral wire, and a ground wire), single and double phase circuits, grounding and bonding points, grounding systems, etc. This article presents a method with these capabilities. An additional feature of the method is that the power system component models are physically based, i.e., the model retains the physical construction of the component as opposed to being represented with an abstract mathematical equivalent. A physically based model and analysis procedure provides the means to expose the interrelationship between the physical parameters (i.e., grounding system design, size of neutral, etc.) and power quality. Typical results are presented in this article. In addition, the model is utilized for a statistical assessment of the effects of specific designs on power quality.

On a hysteresis model for transient analysis

The letter describes an approach to a representation of transient behavior due to switching off complex nonlinear circuits. For this purpose the widely known Jiles model (JM) was implemented into the Alternative-Transient-Program (ATP). Calculations have been made on simplified transformer single-phase and three-phase circuits.

Energy flow and power phenomena in electrical circuits: illusions and reality

Common opinions respective to the nature of the reactive power, energy flow and oscillations, as well as the notion of the apparent power in single- and in three-phase systems are discussed in this paper. It is shown that some interpretations of powers and energy flow in linear, single-phase circuits are often generalized for more complex situations where these interpretations are not longer valid. Consequently, power phenomena in electrical systems are often misinterpreted. This relates to the reactive power which occurs in three-phase systems without energy oscillation between the supply source and the load, as well as it occurs in time-variant systems without energy storage capability. Also, it was demonstrated in the paper that the arithmetic and geometric apparent powers, commonly used in three-phase systems, do not characterize the supply loading correctly when the load is unbalanced.

Passive filter design for harmonic reactive power compensation in single-phase circuits supplying nonlinear loads

The proliferation of different types of nonlinear loads into a distribution system has the potential to increase the harmonic levels in the system. The effect of attenuation on reducing the net current harmonics is reported for different nonlinear loads. Calculation of nonlinear load susceptances at different harmonic frequencies is presented. The design procedure of a reactance one-port compensator capable of reducing the voltage and current harmonics produced by nonlinear loads supplied from a source having internal inductive impedance is offered. The reactance one-port compensator application to a secondary distribution system loaded with different load types is presented. The analysis uses the electromagnetic transient program (EMTP) to model different loads as well as the distribution system. Finally, physical experiments have been conducted to verify the results obtained by simulation.

Modeling the warm-up phase of a high-pressure-lamps lighting network

This work presents a study of the dynamic regime of a lamp-network interaction corresponding to the warm-up phase of a high-pressure mercury discharge lamp. The lamp's behavior is described by a variable pressure model using the local thermodynamic equilibrium (LTE) concept. Indeed, this model covers the most interesting phase of the network dynamic regime, where discharge lamps appreciably impose their nonlinearity. We first analyze the electrical behavior of the discharge lamp in a single phase circuit, taking into account the ballast saturation. Then a micronetwork is studied and are show the influence of the discharge's evolution on currents in phases and neutral conductors. Finally, from the results of the physical model, we set up a simple parametric modeling which reproduces the electrical behavior of the lamp during its warm-up phase. Such an approach can be useful for electrical engineers working on the discharge supply circuits at industrial frequency (50-60 Hz).

Active Filter Applying Discrete Tracking Control

This paper presents a unique active filter system which operates with direct digital control (DDC). The system synthesizes the almost identical current with the total harmonic currents generated from the load. The current is injected to the a. c. source line by inverse phase. Although the control is based on simple digital calculations, it is proved that the a. c. source line current can be nearly sinusoidal current on a computer simulations as well as a bench mark test in a single phase circuit with nonlinear load.

McGraw-Hill's handbook of electrical construction calculations

Procedures: basic calculations wiring methods branch circuits feeders services transformer circuits voltage drop lighting motor circuits electric heating sample calculations sizing branch-circuit conductors branch-circuit calculations makeup of feeder circuit feeder sizing neutral size in 3-phase feeders sizing parallel feeder sizing components for 3-wire, single-phase circuits currents in 3-phase circuits calculating branch-circuit and feeder components selecting feeder protection sizing grounding and bonding conductors underground service calculations size of nipples conduit fill for mixed wire sizes calculating size of pull-boxes number of wires in wireway protecting 2-wire transformer circuit transformer secondary feeder a typical transformer circuit a puzzler on wireway fill range circuits motor circuit calculations circuit for a wounded-rotor motor calculations for a motor feeder protecting motor starter coil circuit protecting contactor oil circuit.

Unity-power-factor PWM converter with DC ripple compensation

The generation of harmonics and their subsequent propagation into power lines is a topic of increasing concern to power-supply authorities. To prevent obstacles in the power system, a unity-power-factor PWM converter will be applied at ac-dc power conversion plants. However, the PWM converter, especially at single-phase circuit, has some serious defects, including low-frequency ripple current that flows into the dc line and gives rise to a low-frequency ripple voltage that appears on the dc output. In usual cases, it is necessary to connect a very large capacitor or a passive L-C resonant circuit to the dc line for reduction of low-frequency ripple voltage. However, when batteries are connected to the dc output, most of the dc ripple current flows into the battery even if the above circuits are used, because the impedance of the battery is very low compared to that of the circuits. The low-frequency ripple current causes power loss on the battery and the temperature rises. It is well known that the life of a battery is deeply influenced by the temperature. The ripple current, therefore, should be reduced as low as possible. To accomplish reduction of the low-frequency ripple current, a novel topology for the PWM rectifier is presented in this paper. The main circuit is constituted by adding only a pair of switching devices to the conventional PWM converter circuit. With a simple control technique, the ripple energy on the dc line is converted into stored energy on the input ac capacitors through additional switches. The theoretical characteristics are obtained by using the state-space averaging method. The effect of ripple reduction is confirmed by experiments using a breadboard setup. © 1998 Scripta Technica, Electr Eng Jpn, 123(1): 51–62, 1998

A Study on the Operation Limits on the Unity-Power-Factor PWM Converter with DC Ripple Compensation

The generation of harmonics and their subsequent propagation into power line is a topic of increasing concern to power supply authorities. To prevent the obstacles on the power system, Unity-Power-Factor PWM converter is going to apply to AC-DC power conversion circuit. However, PWM converter, especially at single phase circuit, has some serious defects, that is low frequency ripple current which flows into the battery connected to the DC output or low frequency ripple voltage which appears on the DC output capacitor. Especially, in case of the batteries are connected with the DC output, the low frequency ripple current flows into the battery and cause power loss on the battery. The power loss cause high temperature of the battery and shortens the life of it. To accomplish the reduction of the low frequency ripple current, the authors have been proposed a novel topology of the PWM rectifier and reported its operation principles. In this paper, the operation limit influenced by the circuit parameters, especially capacitance of the input capacitor, is discussed. It is shown that the operation limit can be estimated based on the calculation of the ripple energy that is stored in the input capacitors. By adopting the ripple energy expression on both the input capacitor and the DC output, the limitation for the DC ripple reduction can be clearly expressed. The calculated results agree well with that of the experimental results. The proposed calculation technique is useful for the practical design of the proposed PWM converter.

Transient Analysis of Salient Pole Synchronous Machine in Space Complex Vector

This paper provides circuit equations of salient pole synchronous machine and its analytical solutions. The author expressed cross section of synchronous machine as complex plane and named it space complex plane. Voltages, currents and magnetic fluxes expressed in this complex plane, were named space voltages, space currents, and space magnetic fluxes respectively.To distinguish ordinary complex quantities, such as complex currents of single-phase circuit, from space complex vectors, such as space complex currents, The author named them time complex vectors temporarily in this paper.Using these space complex vectors and time complex vectors, The author analyzed salient pole synchronous machine.For instance, calculated results of transient phenomena of 3-phase sudden short circuits of salient pole synchronous machine are showed in this paper.

A new definition of instantaneous active-reactive current and power in three-phase circuits, and its application

Conventionally, the active, reactive, and apparent power in three-phase circuits has been defined by extending the concept based on the RMS values of voltage and current with respect to time in single-phase circuits. Applying the definition based on single-phase circuits to three-phase systems with nonsinusoidal conditions has resulted in many options in the description of power properties, as well as their interpretation and compensation, and this has led to a controversy as to which method should be chosen, and how power quantities should be defined. This paper proposes a new definition of the instantaneous active-reactive current and power based on instantaneous space vectors in polar coordinates for three-phase circuits. The instantaneous active-reactive power and current are defined in the voltage-current vector plane without any special fictitious power. The new definition proposed here leads to the same formulas as the conventional ones, which is a great advantage of the new definition. Comparing it to the p-q theory, we discuss the new definition in detail. It is shown that, using the new definition, one is able to calculate the instantaneous active-reactive power and current directly from the voltage and current space vectors. The new definition thus offers a lucid concept of electric power in three-phase circuits. Using digital simulation, an application example is shown to confirm the validity and practicability of the new definition. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 83–91, 1997

Unity-Power-Factor PWM Converter with DC Ripple Compensation.

The generation of harmonics and their subsequent propagation into power line is a topic of increasing concern to power supply authorities. To prevent obstacles on the power system, Unity-Power-Factor PWM converter is going to apply to AC-DC power conversion plant. However, PWM converter, especially at single phase circuit, has some serious defects, that is low frequency ripple current which flows into the DC line and low frequency ripple voltage which appears on the DC output In usual case, it is necessary to connect a very large capacitor or a passive L-C resonant circuit to the DC line for the reduction of low frequency ripple voltage. However, in case of the Batteries are connected with the DC output, most of the DC ripple current flows into the Battery even if previous circuits are used because the impedance of the Battery is very low compared with that of previous circuit. The low frequency ripple current cause power loss on the Battery and the temperature has risen. It is well known that the life of the Battery is deeply influenced by the temperature. The ripple current, therefore, should be reduced to as possible as low.To accomplish the reduction of the low frequency ripple current, a novel topology of the PWM rectifier is presented in this paper. The main circuit is constituted by adding only a pair of switching devices to conventional PWM converter circuit. With simple control technique, the ripple energy on the DC line is converted into the stored energy on the input AC capacitors though the additional switches. The theoretical characteristics are obtained by using statespace-averaging-method. The effect of the ripple reduction is confirmed by experiments using a bread board set-up.

A New Definition of Instantaneous Active-Reactive Current and Power Based on Instantaneous Space Vectors on Polar Coodinates in Three-Phase Circuits.

Conventionally, the active, reactive and apparent powers in three-phase circuits have been defined by extending the concept based on the RMS values of voltage and current with respect to time in single-phase circuits. Applying the definition based on single-phase circuits to three-phase systems with non-sinusoidal conditions has resulted in many options in the methods of power properties description, interpretation and compensation, and this has led to a controversy on which method should be chosen, or on how power quantities should be defined. This paper proposes a new definition of the instantaneous active-reactive current and power based on instantaneous space vectors on polar coordinates in three-phase circuits. The instantaneous active-reactive power and current are defined in the voltage-current vector plane without any special fictitious power. The new definition proposed here leads to the same formulas as the conventional ones. The authors claim that this is a great advantage of the new definition. Comparing it to the p-q theory, we discuss the new definition in detail. It is shown that using the new definition one is able to calculate the instantaneous active-reactive power and current directly from the voltage and current space vectors. The new definition, thus, offers a lucid concept of electric power in three-phase circuits. Using digital simulation, an application example is shown to confirm the validity and practicability of the new definition.

Transient Analysis of Cylindrical Synchronous Machine Taking Damper Winding Currents into Consideration.

This paper provides complex circuit equations of cylindrical synchronous machine taking damper winding currents into consideration and its analytical solutions. I expressed cross section of synchronous machine as complex plane and named it space complex plane. I named voltages, currents and magnetic fluxes in this complex plane, space voltages, space currents, and space magnetic fluxes respectively.To distinguish ordinary complex quantities, such as complex currents of single-phase circuit, from space complex quantities, such as space complex currents, I named it time complex quantity temporarily in this paper.Using these space complex quantities and time complex quantities, I analyzed cylindrical synchronous machise.For instance, calculated results of transient phenomena of 3-phase sudden short circuits and step change of field voltages of cylindrical synchronous machine are showed in this paper.