Showing papers on "AC power published in 1984"

Instantaneous Reactive Power Compensators Comprising Switching Devices without Energy Storage Components

Abstract: The conventional reactive power in single-phase or three- phase circuits has been defined on the basis of the average value concept for sinusoidal voltage and current waveforms in steady states. The instantaneous reactive power in three-phase circuits is defined on the basis of the instantaneous value concept for arbitrary voltage and current waveforms, including transient states. A new instantaneous reactive power compensator comprising switching devices is proposed which requires practically no energy storage components.

Fuel-cost minimisation for both real-and reactive-power dispatches

Abstract: The fuel cost formula is developed for optimal real-and reactive-power dispatch for the economic operation of power systems The problem is decomposed into a P-optimisation and a Q-optimisation module, where both modules use the same fuel cost objective function resulting in the optimal load flow The control variables are generator real-power outputs for the real-power module; and generator reactive-power outputs, shunt capacitors/reactors and transformer tap settings for the reactive-power module The constraints are the operating limits of the control variables, power-line flows and busbar voltages The optimisation problem is solved using the gradient projection method (GPM) for the quadratic objective function and linear constraints The GPM allows the use of functional constraints without the need of penalty functions or Lagrange multipliers among other advantages Mathematical models are developed to represent the sensitivity relationships between dependent and control variables for both real- and reactive-power optimisation modules; and thus eliminate the use of B-coefficients Results of two test systems are presented and compared with conventional methods

Hinge clamp for securing a sensor module on a power transmission line

Abstract: Self contained radio transmitting state estimator modules are mounted on power conductors on both sides of power transformers in electrical substations and on power conductors at various places along electrical transmission lines. They are electrically isolated from ground and all other conductors. These modules are capable of measuring current, voltage, frequency and power factor (or the fourier components thereof) the temperature of the conductor, and the temperature of the ambient air. The modules transmit these parameters to local receivers. The receivers are connected by an appropriate data transmission link, to a power control center which allows determination of the state of the power system. Appropriate control signals are transmitted back to the electrical switchgear of the system to bring it to the appropriate optimum state. Direct local control may also be effected, for example, the prevention of overloading a transformer. A "donut" state estimator module comprises a novel hot stick operated hinge clamp and a novel voltage sensor which measures the current between an isolated capacitor plate and ground. The donut measures the fourier components of voltage and current over a number of cycles and transmits the components to the local receiver. The local receiver derives the desired electrical measurements such as voltage, current, power factor, power, and reactive power and transmits them to local or remote control stations. Up to 15 donut modules may transmit on a single channel to a single local receiver. Each transmits at intervals which are an integral number. The intervals between transmissions of all donuts do not have a common factor and the average interval is the desired transmission rate. Each donut uses the zero crossover of current of its conductor to establish its transmission interval. The system is self-calibrating using known reference signals within the donut module.

Probabilistic Load Flow Considering Dependence Between Input Nodal Powers

Abstract: This paper presents a new method for obtaining a probabilistic load flow solution when dependence between the input nodal powers is considered. Such dependence is modeled in order to account for the criteria used to balance the system active power and also the correlation between loads due-mainly to environmental and social factors. The proposed technique is applied to a typical power system and the results discussed.

Passive signal coupler between power distribution systems for the transmission of data signals over the power lines

Abstract: A passive signal coupler transfers data signals being transmitted over AC power lines from a first AC power distribution system to a second AC power distribution system. Each leg of the passive signal coupler coupled to a phase of the power line voltage includes a series LC circuit, tuned to the data signal carrier frequency. Each leg coupled to the first power system is terminated in a first winding of a transformer. Each leg coupled to the second power system is terminated in a second winding of the transformer.

Control system for a voltage-type inverter

Abstract: In a control system for a voltage-type inverter which comprises a bridge connection of electric valves each comprising a reverse parallel connection of a semiconductor switching element and a diode, and converts a DC power to an AC power by means of PWM control, a voltage detection device is provided to detect an output voltage of the inverter. A voltage correction circuits corrects the pulse width of the pulse width modulation signal in accordance with the comparison of the detected voltage and the PWM signal. A drive circuit, which provides a dead time during which the switching elements of the electric valves connected in series with each other are concurrently non-conductive, uses the corrected PWM signal for driving the switching element.

Current Harmonics, Voltage Distortion, and Powers Associated with Electric Vehicle Battery Chargers Distributed on the Residential Power System

Abstract: The harmonic performance of the networks of several types of electric vehicle (EV) battery chargers is documented. Cumulative effects at the substation level for random distributions of each of five different charger types are reported. Chargers with and without current- smoothing inductors and with and without controlled rectifiers for maintenance of constant current are included. Results are reported as magnitudes of expected harmonic current; active power; apparent, reactive, and distortive volt amperes; and power factor hour by hour over typical daily recharge cycles for the network of chargers. Results regarding comparisons among chargers demonstrate the desirability of including a current-smoothing inductor in the charging circuit and indicate that constant-current type chargers using controlled rectifiers generate significantly more harmonic current than the simple noncontrolled taper-current chargers. Typical third harmonic current values of 15 A per charger on the 120-V side and 20 A per phase on the 12.8-kV side for a network of chargers (at ten percent penetration of chargers into the residential distribution network) indicate the possibility for harmful effects to customer and utility equipment and for interference into communications circuits. The results reported here should be useful in both predicting harmful effects at various densities of EV chargers on the residential network and in designing chargers to minimize those effects. supported in part by the New England Electric System.

Optimal Reactive Power Allocation for Improved System Performance

Abstract: This paper presents a fast converging method for finding the optimal capacitor allocation in a power system for minimising power losses and for improving the quality of the supply system which is achieved by optimal allocation of all reactive power sources in the system in a co-ordinated way. The problem is formulated as a Mixed Integer Linear Programming problem and is solved by decomposing it into two smaller subproblems. The method has very fast convergence without zigzagging of the solution about the optimal point. The potential of the model has been demonstrated by its application to sample systems.

Three Phase Transmisssion System Modelling for Harmonic Penetration Studies

Abstract: Three phase modelling of an a.c. transmission system is presented for harmonic penetration studies. Circuit coupling and impedance unbalance are incorporated in a simulation programme which models an 86 bus equivalent of the New Zealand South Island system. A comparison of measured and simulated results at the current injection busbar is used to select system component models; then results of impedances and sequence voltages are presented for selected busbars when the system is subjected to current unbalance and circuit configuration changes.

Closed loop power factor control for power supply systems

Abstract: A power factor controller for alternating current/direct current drilling rigs is provided which utilizes a uniquely controlled, unloaded, over-excited generator to provide reactive power to maintain the rig's power factor within prescribed limits during peak demand operations.

Simulation study of DC transit systems with inverting substations

Abstract: The increasing use of chopper-controlled regeneratively braked stock in rapid transit and suburban railways has brought into focus the problems of limited energy receptivity in the DC supply network. While the use of on-board rheostatic braking or mechanical braking are established methods of dealing with non-receptivity, an alternative arrangement using inverting equipment at the DC substation has been introduced at some locations in Japan, Germany and Brazil. This paper describes a simulation-based study of a rapid-transit system with substation inverters, which was undertaken to establish operating limits and optimum design criteria which could be generally applicable. The paper deals with the choice of installed inverter capacity, inverter location, current commutation limits and inverter control. In addition the energy-saving consequences of using inverter equipment are discussed in detail. The implications of fitting inverters, with respect to the bulk AC supply system, in terms of voltage distortion, voltage regulation and reactive power demand, are considered for a range of typical values of short-circuit level.

Class E high-frequency high-efficiency dc/dc power converter

Abstract: A Class E switching-mode dc/dc power converter is obtained by adding a rectifier circuit at the output of a Class E dc/ac power inverter. It can operate at high efficiency at high switching frequencies. Further, the power switch is not subjected to high power dissipation or high second-breakdown stress while it is switching between the "on" and "off" states, even if the dc load on the power converter varies over a very wide range, e.g., from open-circuit to short-circuit. The high efficiency is achieved by shaping the waveforms of switch voltage and switch current so that the transitions of those two waveforms are displaced in time from each other. Then the power switch does not experience simultaneously high voltage and high current while switching. High efficiency and low stress on the switch are achieved under all load conditions by interposing a matching network between the output of the Class E dc/ac inverter and the input of the rectifier circuit. That matching network transforms the rectifier input impedance in such a way that the impedance presented to the output of the Class E dc/ac inverter is always in the range which generates switch voltage and current waveforms that yield low power dissipation and low second-breakdown stress during switching, for any value of dc load resistance at the output of the rectifier.

Optimal Voltage Dependent Continuous-Time Control of Reactive Power on Primary Feeders

Abstract: The availability of substation-based computers and the decreasing relative cost of installation, operation and control of switched capacitors encourage the use of more sophisticated and effective capacitive compensation schemes for loss minimization on radial distribution feeders. This paper sets forth a new voltage dependent model for the optimal control and design problems involving continuously controllable shunt capacitors on primary feeders. The new model obviates the need for a load-flow solution while allowing inclusion of the effects of voltage variation on the design and control phases of an optimal capacitive compensation scheme. The benefits and limitations of the model are reflected via numerical examples.

Application of singular perturbation techniques to power system transient stability analysis

Abstract: This work extends Lyapunov techniques for power system transient stability analysis to system models incorporating voltage magnitude variation, real and reactive power loads, and flux decay effects. A method of estimating the domain of attraction of an asymptotically stable equilibrium in the resulting system of differential equations with algebraic constraints is examined.

Control of AC power to inductive loads

Abstract: A control system is provided for controlling the average power from an alternating voltage source (AC) to a load having inductive properties The system uses a synchronous switch shunted by a capacitor connected between the source (generator) and sink (load) to pulse duration modulate the AC voltage carrier wave A control signal generator circuit drives the synchronous switch such that the switch is closed at a variable time early in each half-wave of the AC voltage source carrier wave and such that the switch is opened at a subsequent later, variable time during that half-wave This is accomplished by sensing the voltage across the synchronous switch in order to inhibit closing of the switch early in the half-wave until the synchronous switch voltage (and thus the voltage on the capacitor) is substantially zero and then opening the synchronous switch at a point in time to give the desired volt-second area between closure and opening within each half-wave

Apparatus for measuring the potential of a transmission conductor

Abstract: Self contained radio transmitting state estimator modules are mounted on power conductors on both sides of power transformers in electrical substations and on power conductors at various places along electrical transmission lines. They are electrically isolated from ground and all other conductors. These modules are capable of measuring current, voltage, frequency and power factor (or the fourier components thereof) the temperature of the conductor, and the temperature of the ambient air. The modules transmit these parameters to local receivers. The receivers are connected by an appropriate data transmission link, to a power control center which allows determination of the state of the power system. Appropriate control signals are transmitted back to the electrical switchgear of the system to bring it to the appropriate optimum state. Direct local control may also be effected, for example, the prevention of overloading a transformer. A "donut" state estimator module comprises a novel hot stick operated hinge clamp and a novel voltage sensor which measures the current between an isolated capacitor plate and ground. The donut measures the fourier components of voltage and current over a number of cycles and transmits the components to the local receiver. The local receiver derives the desired electrical measurements such as voltage, current, power factor, power, and reactive power and transmits them to local or remote control stations. Up to 15 donut modules may transmit on a single channel to a single local receiver. Each transmits at intervals which are an integral number. The intervals between transmissions of all donuts do not have a common factor and the average interval is the desired transmission rate. Each donut uses the zero crossover of current of its conductor to establish its transmission interval. The system is self-calibrating using known reference signals within the donut module.

Uninterruptible ac power supply

Abstract: An uninterruptible ac power supply permits parallel operation between a commercial ac line and an inverter unit, greatly simplifies the monitoring of the commercial ac line and minimizes the transient of output voltage during the switching of mode. The uninterruptible ac power supply is comprised of an iron core divided with magnetic shunts into three sections and has an output winding, a winding for a commercial ac line and a winding for an inverter unit, one each wound on the aforementioned three sections of the iron core, the said three windings so disposed that the output winding is wound on one terminal section and the windings for the commercial ac line and the inverter unit are wound on the remaining two sections.

Ac uninterruptible power system

Abstract: A system to provide substantially uninterruptible AC power. Line voltage is applied to a load through a solid state electronic switch. A squarewave inverter powered by batteries in connected across the load. When line power is reduced to a predetermined level, the switch opens disconnecting the line, and after a short time delay of less than a millisecond, the inverter starts. Upon restoration of normal line power, the process is reversed; the inverter stops and after a like short time delay, the switch closes reconnecting the line.

Unity Power Factor off Line Switching Power Supplies

Abstract: A simple circuit is presented that performs the unity power factor function with low harmonic distortion of the input line current. The circuit is of the resistor emulation type. A description of circuit operation and design parameters are included as well as measured performance. An in depth description of the large signal computer model that was used to verify harmonic current content and control loop performance is presented.

Correction to "Application of a Thyristor Controlled var Compensator for Damping Subsynchronous Oscillations in Power Systems"

Abstract: This paper presents a new concept for controlling static VAr compensators (SVC) in power systems. It allows thyristor controlled VAr compensators to effectively damp subsynchronous resonance (SSR) oscillations besides controlling the system voltage. Eigenvalue analysis and digital time simulations for the IEEE SSR benchmark system are utilized to investigate the role of the main voltage regulator of the SVC in stabilizing the system and alleviating the SSR modal interactions that may be introduced by the auxiliary speed signal alone. Stability zones are identified to optimize the compensator parameters for economical application.

Feasibility of DC Transmission with Forced communication to Remote Loads

Abstract: Previous researchers have analysed the forced commutated HVDC inverter and have concluded that it could be used to meet the reactive power at the inverter terminals. This investigation is a further technical appraisal involving a two terminal transmission scheme to a remote load with no ac generation at the load. Several possible inverter configurations are discussed.

Cogeneration Application of Induction Generators

Abstract: An induction generator an induction motor which is driven above its synchronous speed byasuitable prime mover and is provided with source sufficient reactive power for excitation. The simplicity, reliability, and low cost of the induction generator makeit well suited for many Industrial cogeneration applications. A brief review is presented of the basic theory ofinduction generators with a discussion of the major differences between induction and synchronous generators. The application of a 3000-kW induction generatoris compared to that of a comparably sized synchronous machine in a typical cogeneration scheme. The comparison focuses on relative costs, equipment, protective relaying, utility tie-in and synchronizing, maintenance, and operating procedures.

Semi-conductor motor control system

Abstract: A semi-conductor system for controlling three phase motors by voltage and/or frequency variations. An input circuit provides dc power, such as a three phase full wave input bridge with silicon control rectifiers to provide a voltage controlled dc power output. An output inverter bridge having six silicon rectifiers receives dc power and converts it to three phase ac power for operating an induction motor. A diverter network is connected between the dc power input circuit and the output inverter and is activated periodically for temporarily diverting the dc power from the inverter in order that the inverter rectifiers may be turned off. The diverter may include a tank circuit having a capacitor and an inductor connected across the dc power output through a diode and a silicon control rectifier is connected to the tank circuit for shunting the dc power from the inverter and applying a reverse voltage to the inverter. A harmonic suppression circuit is connected across the output of the converter and may include a capacitor connected between each of the three phase output lines of the inverter.

Power factor correcting network

Abstract: An electronic ballast for energizing one or more gaseous-discharge lamps and for regulating the power consumed thereby, the ballast including a power supply for providing a source of DC power between a pair of outputs, a pair of transistors connected as switches in series between the power-supply outputs, the transistors for selectively coupling to the juncture thereof positive and negative potentials, a voltage-conditioning and current-limiting network for energizing the lamp from the potential developed between the transistor juncture and a power-supply common, and a pulse generator for developing pulses for driving each of the transistors in turn whereby a potential is developed at the transistor juncture which alternates as positive-going and negative-going pulses each separated by a dead time, the pulse generator for monitoring the power consumption level of the lamp and responsive thereto operative to vary the frequency and/or the width of the transistor driving pulses whereby the lamp consumption is regulated. Also included is a third harmonic trap for coupling the power supply to the AC power line to improve the power factor.

Variable-voltage variable-frequency elevator control apparatus

Abstract: A variable-voltage variable-frequency elevator control apparatus is disclosed in which a circuit for the consumption of regenerated power produced during regenerative braking is provided on the DC side of the apparatus rather than on the AC side. During regenerative braking with an emergency generating unit in operation, regenerated power is consumed by the consumption circuit on the DC side of the circuit and is prevented from being returned to the emergency generating unit. This prevents the production of voltage notches commonly produced during regenerative braking by thyristor commutation in conventional circuits. Because no voltage notches are produced, a reduction in the size of the emergency generating unit can be achieved. In addition, since it consumes DC power rather than 3-phase AC power, the consumption circuit requires fewer elements than in conventional control apparatuses.

Effects of Voltage Control in Utility Interactive Dispersed Storage and Generation Systems

Abstract: When a small generator is connected to the distribution system, the voltage at the point of interconnection is determined largely by the system and not the generator. This paper examines the effect on the generator, on the load voltage and on the distribution system of a number of voltage control strategies. Synchronous generators with three kinds of exciter control are considered, as well as induction generators and constant extinction angle inverters, with and without capacitor compensation. Operation with a constant slightly lagging power factor is shown to have some advantages.

Method and apparatus for sampling output AC currents in a voltage-fed inverter power supply

Abstract: In a voltage-source inverter AC power supply, the AC currents are measured exclusively by sampling the DC current in the DC link between voltage-source and inverter. Each sample so derived is correlated to the status of the switches in the inverter at the instant of sampling, or before and after a change in the switching status of the inverter. This technique applies more generally to pulse-width modulation applications, but also to an adjustable voltage input (AVI) inverter motor drive.