Showing papers on "Power factor published in 1971"

A New Method to Eliminate AC Harmonic Currents by Magnetic Flux Compensation-Considerations on Basic Design

Abstract: A new method of eliminating ac harmonic current is proposed, which is based on the principle of the magnetic flux compensation in a transformer core. By means of the new method, abnormal harmonics as well as normal harmonics can effectively be dealt with. Considerations on the basic design of the new method are given.

Power train using multiple power sources

Abstract: A POWER TRAIN IS DESCRIBED WHICH IS COMPRISED OF A PRIME MOVER, TWO POWER CONVERTERS, AN EPICYCLIC GEAR TRAIN, AN ENERGY STORAGE DEVICE AND ASSOCIATED CONTROL SYSTEMS. IN THE PREFERRED EMBODIMENT, THE PRIME MOVER, AN INTERNAL COMBUSTION ENGINE, TYPICALLY SUPPLIES POWER TO THE GEAR TRAIN WHICH APPORTIONS MECHANICAL POWER TO ONE OF THE POWER CONVERTERS-AN ELECTRICAL GENERATOR-OR TO THE OUTPUT SHAFT OF THE POWER TRAIN. POWER FROM THE GENERATOR IS DELIVERED TO EITHER OR BOTH THE ENERGY STORAGE DEVICE, A BATTERY, AND THE SECOND POWER CONVERTER, AN ELECTRICAL MOTOR-GENERATOR WHICH IS DYNAMICALLY COUPLED TO THE OUTPUT SHAFT. THE POWER TRAIN MAY BE OPERATED IN ONE OF TWO MODES, IN THE FIRST THE INTERNAL COMBUSTION ENGINE RUNS AT CONSTANT SPEED AND RELATIVELY CONSTANT LOW POWER. ENGINE OPERATION OF THIS NATURE ALLOWS THE USE OF SMALL DISPLACEMENT ENGINES BURNING LEAN FUEL-AIR MIXTURES, THEREBY REDUCING ENGINE EXHAUST EMISSIONS. ENGINE POWER OUTPUT CONTROL IN THE FIRST MODE IS ACCOMPLISHED BY CHANGING THE LOADING OF THE GENERATOR ON THE ENGINE IN A FEEDBACK CONTROL MANNER. THE MOTOR-GENERATOR IS CONTROLLED BY THE OPERATOR WHO USES A SYSTEM WHICH CONTROLS THE FLOW OF POWER FROM THE GENERATOR AND OR BATTERY COMBINATION TO THE MOTOR OR THE FLOW OF POWER FROM THE MOTOR-GENERATOR TO THE BATTERY. IN THE SECOND MODE OF OPERATION, ALL ENGINE POWER IS MECHANICALLY DIRECTED TO THE OUTPUT SHAFT AND THE ENGINE OPERATES IN A VARIABLE THROTTLE MANNER. AS IN THE FIRST MODE, OUTPUT SHAFT PEAK POWER DEMANDS ARE SATISFIED BY DRAWING POWER FROM THE BATTERY AND THEREFORE THE ENGINE THROTTLE EXCURSIONS ARE MINIMIZED. EXCESS ENGINE POWER AND REGENERATIVE POWER DUE TO EXTERNAL FORCES ACTING ON THE OUTPUT SHAFT CAN BE TRANSFORMED IN THE SECOND POWER CONVERTER FOR STORAGE IN THE ENERGY STORAGE DEVICE. IN EITHER MODE, IT IS POSSIBLE TO VARY THE POWER SETTINGS OF THE ENGINE SLOWLY TO REFLECT THE MEAN POWER DEMAND ON THE POWER TRAIN. TYPICALLY THE STATE OF BATTERY CHARGE WOULD BE USED AS THE CONTROL VARIABLE.

Stabilization and Optimal Control Signals for a Power System

Abstract: The stabilization of power systems with excitation control using speed or power signals has been very well developed,1-6 while the application of optimal control to power system stability study is relatively new.7 Both are based on linear models. In this paper, a comparison is made of these two techniques. Signals derived from a lower order linear model are tested on a high order non-linear system modelled as a single machine-infinite bus as well as multi-machine systems.

Combining inverters for harmonic reduction

Abstract: A plurality of polyphase inverters are connected in circuit to substantially common polyphase loads through a polyphase reactor. Windings from each phase of each inverter are provided on the reactor to cancel the component of flux of the fundamental frequency within the reactor and to have the reactor substantially absorb the NP+/-1 harmonics where N is the number of inverters and P is the number of phases. For two three-phase inverters this substantially cancels the fifth and seventh harmonic voltages within the reactor applying a true 12-step voltage wave to each of the two common three-phase loads with nothing smaller than the 11th harmonic voltage supplied to each load. The two inverters are phase displaced by 360 DEG /2NP which normally at a 30 DEG phase angle would be a voltage loss of 3 1/2 percent applied to the load yet this reactor connection applies 100 percent voltage to the loads and the load power factor is reflected directly to each inverter. The loads may be DC isolated, permitting series connection of the inputs of the inverters from a single high voltage DC supply.

Optimisation of Turbo-Generator Transient Performance by Differential Dynamic Programming

Abstract: Methods which have been proposed for increasing the margin of stability in large generators generally act by controlling the generator electrical power output. A more direct control of the stability can be achieved by regulating the power input to the turbine. Simultaneous control of the field excitation and the turbine

Optimum Network Switching in Power Systems

Abstract: Power system stability can be improved by sudden changes in the electric power network such as the insertion of braking resistors, generator dropping or load shedding A unified treatment of optimum switching is presented by considering the switching instants to be elements of a generalized control vector Dynamic optimization is then applied to determine optimum switching instants

Protection means for preventing overvoltage and undervoltage conditions in power circuits

Abstract: An electrical power system includes power conversion apparatus for receiving electric power from a source and supplying the electric power in converted form to a load and control apparatus for automatically stopping the operation of the power conversion apparatus in response to the departure of a selected operating parameter, such as input voltage to the power conversion apparatus, from a preestablished range having upper and lower limits. A signal representative of the operating parameter is sensed and utilized to produce an out-of-range signal only when the operating parameter departs from the preestablished range, the out-of-range signal being utilized in turn to stop the operation of the power conversion apparatus.

Automatic voltage control apparatus for electrostatic precipitators

Abstract: A thyristor power supply control circuit for an electrostatic precipitator which operates to tend to drive up the volts applied to the precipitator load and step it back by increments in response to sparking, the sparking being detected as a change from predominantly capacitive load circuit to a predominantly inductive load circuit and the change being instanced by current tending to flow after a.c. supply voltage zeros. Arcing within the precipitator is detected as such an inductive condition existing in two successive supply half cycles and leads to suppression of the arc by collapsing the precipitator volts for a suitable interval.

Power control and phase angle correcting apparatus

Abstract: Apparatus for controlling power and for compensating for a low power factor due to a relatively large varying inductive load. A number of branches having an inverse parallel connected pair of thyristors and a capacitor connected in series are connected in parallel. These parallel branches are connected in series between an alternating current source and the load. At least one thyristor of one of the inverse parallel connected pairs of thyristors is gated on at some time during each half cycle of the alternating current supply voltage in order to control the power flow to the load. One thyristor of one or more of the inverse parallel pairs of thyristors is gated on at appropriate times during each half cycle in order to place one or more of the capacitors, which are in parallel with each other, in series between the source and the load.

Circulating-current loss within Roebel-bar stator windings in hydroelectric alternators

Abstract: Circulating currents are produced within stator windings of Roebel bars by endregion leakage fields, causing voltages to arise between the strands or subconductors. A method for calculating the endregion fields arising from both rotor and stator is given, and values of voltage for a simplified bar representation are obtained. The impedance of a Roebel bar to a circulating current is discussed, and values of circulating current are obtained for one machine. It is shown that the circulating currents in each bar are substantially independent of those in other bars, but that the reactance within each bar is of the same order as the resistance. The circulating-current loss is a small component of the total loss in the machine considered (10% of the stator I2R loss), but varies with the load and the power factor. Its significance is that two-thirds of it occurs in the top layer of the stator winding, increasing the temperature rise there by 13%. The theoretical analysis from which the above conclusions are drawn is confirmed by search-coil measuremnets which show an average agreement within 18%.

Three-phase power controller

Abstract: A three-phase power controller for controlling three-phase power to a non-unity power factor load is disclosed, which employes a separate bidirectional gate in series with each of the lines to the three-phase load for gating the load current to the load. Each bidirectional gate includes a master gate and a slave gate slaved to the master gate. A synchronous control circuit supplies a sequence of gating on signals to the respective gates. The synchronous control circuit includes a zero-crossing sensor for sensing the alternating potential supplied across each set of power supply terminals and a particular half-cycle sensor for sensing the particular half-cycle of each of the alternating potential applied across each respective set of power supply terminals. Light emitting diodes and photo detectors are employed in various ones of the gating control channels to provide high voltage isolation between the gates and the circuits generating the gate control signals.

Phase angle regulator for high frequency inverter

Abstract: In a static inverter, phase angle error detection circuitry is used to control the operating frequency of the inverter as a function of the phase displacement between the alternating current supplied to a tank load and the alternating voltage across that load, thereby regulating the power factor of the load circuit.

Series Capacitor Switching to Quench Electromechanical Transients in Power Systems

Abstract: A method of quenching transient oscillations of a generator feeding a load over long lines was implemented in the laboratory. A disturbance that caused instability was repeated with this control, and the system remained stable.

Capacitor bank for ac networks

Abstract: A capacitor bank for alternating current networks has a number of parallel branches each of which is connected by antiparallel-connected thyristors to the network. There is a control device for each thyristor which, when the bank is fully loaded, connects the thyristors in one conducting direction or the other in synchronism with the maximum of the network voltage in such direction. Each branch of the bank can be recharged by the full load during each half-period of the network voltage. Upon the occurrence of reduced load on the bank, the control devices emit current pulses to connect the thyristor switches in one direction or the other of the maxima of the network voltage in such direction for recharging. These latter pulses are emitted at a frequency which is substantially less thaN the network frequency.

Digital Analysis of Excitation Control for Interconnected Power Systems

Abstract: Excitation control by stabilizing signal taken from several locations in the system, together with the proper transfer function, has been investigated to satisfy the system stability from an overall performance view point, rather than one machine against an infinite bus. Several stabilizing signals have been tried from which the following signals have been found to have a great affect in increasing the damping: (1) a signal from the change of network voltage and taken from the far end, and (2) a signal from the change in the machine terminal frequency through a compensating network having a transfer function containing three zeros and three poles. The location of such signals greatly effects the system stability, and it is found that the signal taken from the change of frequency at a remote point of the network and applied to the voltage regulator of the machine under consideration has more effect in stabilizing the system. The station working with a leading power factor makes the stability rather critical, and stabilizing such stations greatly improves the system stability.

345 MVA Fully Water-Cooled Synchronous Condenser for Dumont Station Part I. Application Considerations

Abstract: A brief historical review of the use of static capacitors and synchronous condensers for regulating power system voltage is made. Comparative costs are shown which demonstrate that the large synchronous condenser has a place on the large EHV power system. Application of the 345 mva fully water-cooled synchronous condenser on the American Electric Power System is described.

Ground continuity monitoring system

Abstract: In a system which delivers electrical power to remotely located electrical equipment, such as mining equipment, through power conductors in a cable extending from a main source of power to the equipment, the cable including at least two power conductors connected to the electrical input terminals of the equipment and a ground conductor connected to the frame of the equipment, there is added a ground conductor monitoring circuit including power circuit isolating means connected to one of the power conductors of the cable and the ground conductor thereof to provide across a pair of connecting terminals a series circuit including the cable ground conductor isolated from the main power circuit at a given frequency substantially different from the main power source frequency. These connecting terminals are preferably connected across the secondary winding of a transformer having a center tapped primary winding driven by push-pull connected transistors or the like fed by the oppositely phased outputs of a signal generator circuit at said given frequency. The push-pull transistor circuit includes a load resistance on one side of the load terminals thereof constituting one arm of a D.C. bridge circuit, and the load terminals and the primary winding of the transformer constituting the adjacent arm of the D.C. bridge circuit. Control means at the output of the bridge circuit is responsive to the output of the bridge circuit indicating that the impedance reflected into the primary winding exceeds a given value by disconnecting the main power source from the cable power conductors.

Cycle converter power supply for microwave heating

Abstract: A cycle converter power supply circuit comprising four silicon controlled rectifiers (SCR''s), electronic semiconductor switches, used to program current flow through four separate legs of a transformer in a manner to produce an alternating current at a frequency considerably in excess of the prime power. A bridge rectifier circuit in the secondary of the transformer permits the power to be converted to a direct current flow similar in character to what would be achieved through rectification of the prime power. Since the voltage conversion is accomplished at a higher frequency than the prime power, the core area of the transformer can be reduced roughly by the square root of the switching frequency.

The Derivation and Application of Design Equations for Ferroresonant Voltage Regulators and Regulated Rectifiers

Abstract: Design equations for the most commonly used ferro- resonant regulators and regulated rectifiers are derived. Expressions relating the physical size of the components and the short circuit characteristic of the circuit to the output power, frequency, input power factor, and voltage levels are developed. From these expres- sions, design equations that optimize the design are obtained and specific component values are recommended. For regulated rectifiers, the design of the filter and the effect of the filter on the design of the basic regulator are discussed. The effect of deviating from the recommended values and the effects of nonlinearities not considered in the derivations are discussed. Design examples and data are presented.

Phase shift detector

Abstract: A reverse power flow relay having high load current sensitivity over a wide power factor range receives input signals representative of the voltage on and the current in a power line, shifts the phase of the voltage signal 90 DEG , and has a first high-gain operational amplifier for deriving rectangular positive voltage pulses from the phase-shifted signal, a differentiator for deriving a sharp voltage pulse at the leading edge of each rectangular voltage pulse when the voltage input signal crosses the zero axis, a second high-gain operational amplifier for deriving first rectangular positive current pulses from the current input signal, an inverter for deriving second rectangular positive current pulses shifted 180 DEG in phase from the first rectangular current pulses, a NAND gate logic circuit for providing a first output when the sharp voltage pulses coincide with the first rectangular current pulses, thereby indicating forward power flow, and for providing a second output when the sharp voltage pulses coincide with the second rectangular current pulses, thereby indicating reverse power flow, and a latch circuit operated by the NAND gate logic circuit.

Apparatus for ensuring dc power supply from either ac or rechargeable dc source

Abstract: A power supply apparatus for supplying DC power to an electric appliance such as a radio receiver, a television receiver and the like is adapted to be connected selectively to an AC power source or a rechargeable battery for producing DC power, the connection being changeable manually and also automatically when the AC power is interrupted.

Closed-Loop Optimal Excitation Control for Power System Stability

Abstract: An optimal excitation control for the stability of synchronous machines is found in a closed form using Pontryagin's minimum principle. While the optimal control is bang bang, in practice it is necessary to compromise with normal voltage regulator action to produce a sub-optimal control. The time required for stabilization is slightly increased by this. The results obtained for the single machine- infinite bus case indicate that such control provides major benefits in removing transients.

Pulsed voltage driver for capacitive load

Abstract: A voltage source of pulsed signals for charging or discharging a capacitive load is disclosed. The circuit includes two complementary transistors serially coupled along their output (collector and emitter) electrodes between the two voltage sources as a push-pull driver. Their input (base) electrodes are each coupled in parallel by a respectively associated serially aligned capacitor and resistor to an input terminal that is driven by a binary logic level circuit while their common coupled output (collector) electrodes are coupled to a capacitive load.

High stability current regulator controlling high current source with lesser stability

Abstract: Two current regulated power supplies are connected across a common load impedance. A first regulated power supply having high stability characteristics is connected in a conventional feedback manner to regulate current to the load. A second feedback power supply having lesser stability characteristics than the first but greater output current capabilities is connected to null the sum of opposing voltage drops, one across a current sensing resistor in series with the first power supply and the load and the other in series with the second power supply and the load. The ratio of the resistances of the latter two resistors controls the relative current contribution of the two power supplies to the total load current.

Transistor switches for high voltage applications

Abstract: A high voltage switch arrangement comprising switches each defined by cascaded transistors connected effectively in the arms of a bridge for switching a high voltage across a capacitive load so that an a.c. voltage is supplied through the load when the bridge is fed from a d.c. source and the switches operated sequentially.

Power supply aspects of semiconductor equipment

Abstract: This article presents data concerning the often ``unmentioned'' influences of semiconductors upon power sources, other equipment, and the user. The influence of methods of power control and the resulting harmonics is considered in detail, including some new data on the effect of unbalanced firing angles. Also presented is information relative to metering accuracy, radio, telephone, and control-circuit interference, lamp flicker, and semiconductor influence, including the characteristics of a new RFI-free switching device. In addition, aspects of regulatory agencies are considered, and detailed references for further in-depth study are given.

An electronic wattmeter for nonsinusoidal low power factor power measurements

Abstract: The development of an electronic wattmeter for use in power circuits with very low power factors and nonsinusoidal waveforms is reported. The wattmeter is constructed of commercially available components which include a high-accuracy electronic multiplier and appropriate amplifying, averaging, and compensating circuitry. It is a portable laboratory instrument with provisions for direct reading of both instantaneous and average power. A thermal standard has been used to calibrate the wattmeter over a wide range of current pulse magnitudes and pulsewidths and at power factors down to 0.01. Several applications of power measurements in typical solid-state power controller circuits are discussed.

Static network protective relay

Abstract: A static protective relay comprises a power directional unit for controlling a circuit breaker which couples a primary feeder or a source of supply of a 3-phase power distribution system to an alternating current secondary network through a network transformer. The power directional unit senses reverse power flow above a preselected threshold level from the network to the network transformer to energize a tripping coil of the circuit breaker. Included in the power directional unit is a voltage deriving circuit producing a voltage proportional to the system current through the circuit breaker, a modulator which modulates the voltage by a voltage proportional to the system voltage at the circuit breaker to obtain an output proportional to real power flow through the circuit breaker, and a detector which energizes the tripping coil upon the presence of a reverse power flow signal from the modulator. The power directional unit also includes a source of variable bias comprising circuitry for providing a bias signal which varies both in magnitude and in phase and is a function of the phase angle of the phase current. The variable bias is supplied as an input to the detector to provide a power directional unit exhibiting improved sensitivity to highly capacitive phase currents.

A Rapid Digital Computer Solution for Power System Network Load-Flow

Abstract: Introducing the Self-Adjusting Accelerator, a completely new digital computer method of solving a power system network load-flow is presented. With no sacrifice in accuracy, a mathematically rigorous solution (employing A B C D1 constants) is obtained using less computer time than any other nodal iterative method.

Computation of Eddy Currents, Shielding and Transient Forces in Power System Equipment by the Method of Images

Abstract: The magnetic effects of induced eddy currents in thin conducting sheets are analyzed by means of moving current images and by an electrical circuit analogy. The methods are applied to practical power system equipment problems such as shielding and the calculation of conductor short circuit forces.