Showing papers on "AC power published in 1975"

A new power flow model and solution methodߞIncluding load and generator characteristics and effects of system control devices

Abstract: A new power flow model has been developed for the steady state behavior of large complex power systems, it allows the study of power flow under abnormal conditions as well as normal conditions. It is also shown how Newton's method can be efficiently applied to the model to provide exact and practicable solutions for a new steady state following the disturbance. Advanced applications are introduced which show how the steady state model can be combined with a dynamic simulation program.

Overvoltage phenomena associated with virtual current chopping in three phase circuits

Abstract: Switching of three phase load currents with low power factors, such as encountered in arc furnace installations can result in a series of reignitions and clearings. Depending on the switch performance and system parameters the switching transients may involve one, two, or three phases. The effect of virtual current chopping which can lead to line to line overvoltages is described. The phenomena are explained for simplified conditions, more complex situations are handled by digital computer studies.

No-break ac power supply

Abstract: An uninterruptable power supply supplies a regulated output by utilizing a ferroresonant transformer. Two independent inputs are connected to the transformer; one input is connected to a commercial AC line signal source, the other input is connected to a battery energized static inverter circuit. The AC line source normally supplies the output power. A phase control system monitors the phase of the regulated output signal and constrains the static inverter to run in phase with the output. The phase and magnitude of the AC line signal are monitored. If the magnitude of the AC line drops significantly, the static inverter is constrained to operate in phase with the AC line signal wherein the inverter and AC line both share to contribute power to the output load. If the AC line signal fails, the static inverter operates independently and supplies all of the output power to the load.

Naturally commutated cycloconverter with controlled input displacement power factor

Abstract: A naturally commutated cycloconverter having at the input a source of higher frequency than at its output is used as a static reactive power generator to correct displacement angle in an alternating current power system when coupled thereto at the output. Reactive power correction is obtained with such "high frequency link" by automatically controlling the output voltage of the cycloconverter so as to deviate by a required amount from the AC power system voltage. At the same time, a circulating current is established between the positive and negative banks of thyristors of the cycloconverter of such a magnitude as to compensate for the variations of the lagging quadrature component of the input current of the cycloconverter caused by output current variations, thereby permitting optimization of the high frequency link. The concept of generating controllable reactive power with a naturally commutated cycloconverter is used (1) with one cycloconverter as a controllable source of reactive power coupled to a power system; (2) with two cycloconverters tying a power system with a load, or two power systems together. In either instance, the output voltage of the cycloconverter is controlled for automatic compensation in the line power factor, and concurrently a circulating current is established in the single or in the two cycloconverters for automatic correction against variations in the lagging current at the cycloconverter input when the load conditions at the output thereof vary.

Static controller for power factor correction and adaptive filtering

Abstract: A polyphase cycloconverter operating in regenerative mode is connected between a voltage distribution system and a single phase high frequency resonant tank and controlled to produce essentially no real power flow to the resonant tank and a variable amount of leading (or lagging) reactive power. The static reactive power controller has fast response and can function as an electronically variable capacitor for power factor regulation, VAR control and adaptive filtering.

Phase sequence detector for three-phase ac power system

Abstract: The phase sequence of the phase currents supplied by a three-phase AC power supply to a phase-sensitive load (such as a three-phase AC motor) is monitored by developing three phase-displaced, rectangular shaped logic signals, respectively representing the three phase currents, and applying these logic signals to respective ones of the J, C and K inputs of a J-K flip-flop. When the load is correctly connected to the power supply, the phase relationship of the three logic signals will be appropriate to trigger the flip-flop to its set operating state. Any other sequence actuates the flip-flop to its reset state which, in turn, disconnects the load from the power supply.

Reactive power compensator

Abstract: Reactive current compensating apparatus for a multiphase electric power circuit comprises separately variable reactive impedance elements coupled to the power circuit in multiphase relation through phase shifting means such as a tertiary transformer winding When phase voltage supplied to the compensating impedance leads or lags the line-to-neutral voltage of the power circuit the compensating effect in respect to negative phase sequence line current components is enhanced as compared to direct conductive connection of compensating impedance to the power circuit

Remote switching system

Abstract: A remote switching system in which operation of a load is controlled by signals generated at a remote location and transmitted along an existing AC power line. The system includes a signal transmitter which can be plugged into an AC line socket, and which can operate to place a transient control signal on the AC power line. The system also includes a receiver which is connectable in series with a load to be remotely controlled, and which closes a switching circuit between the AC power line and the load when a switching signal on the power line is detected. The control signals are imposed on the AC line voltage by the transmitter only during an early time in a half-cycle of the power line voltage, before noise transient signals generally appear on the half-cycle, and the receiver is sensitive to control signals only during a corresponding portion of each half-cycle, thereby greatly reducing susceptibility of the switching system to noise on the power line. The receiver is sufficiently compact to fit within a switch box used in conventional household wiring, so that the receiver switch circuit can be connected in parallel with an existing load switch for alternative operation of the load from a remote location. The receiver is constructed to provide a heat transmission path from the internal receiver circuit components which produce heat during operation, to the external load switch and switch box surfaces, from which the heat can be dissipated into the ambient environment.

Solid state AC power relay

Abstract: A trigger type device employing a pair of oppositely poled SCR's or a triac, provides bidirectional control of AC power through a simple circuit comprising a pair of rectifying diodes and an opto-electronic coupler.

Method and apparatus for the static compensation of reactive power

Abstract: A method and apparatus for the static compensation of reactive power using controlled reactive power converters having control variables derived from the phase load currents in which the phase load currents are converted into a line frequency oscillation and two rotating current vectors derived from each of the line frequency components, with the current vector components then transformed into d-c quantities by addition to a system vector to form a co-rotating and counter-rotating vector, from the components of which control variables of the reactive power converter are formed.

Switching amplifier system

Abstract: A switching amplifier includes a pulse width modulator for converting a bipolar input signal, which may be a speech signal, into a train of unipolar pulses having durations which vary with the instantaneous absolute amplitude of the input signal. The pulses control the energizing of a series switch which supplies current to a switching bridge circuit. The switching arms of the bridge circuit are controlled by the polarity of the input signal. Another switch and several diodes are used to provide a path for output current when the series switch is open. The output current is filtered to remove fluctuations at the switching rate, and applied to a load. The amplified output voltage signal accurately follows the input signal, and the efficiency of conversion of DC power to AC output power can approach 100 percent, limited only by switching and filtering losses. A single polarity DC supply, such as a battery, is used to provide bipolar output current to an ungrounded load. High efficiency is maintained even with partially reactive loads, since the switching circuits return reactive power to the DC power supply.

The control and performance of a series connected multiterminal HVDC transmission system

Abstract: The feasibility of a series connection of stations in a multiterminal HVDC transmission system is demonstrated. Techniques were developed to control this system, and the operation of the system was studied on a large power system simulator. The performance of the system was shown to be similar to conventional point to point systems with most control functions being carried out by local controls. An overall system control is shown to be necessary only for optimizing load distributions. Given adequate tap changer ranges on the converter transformers the increase in valve damping and system reactive power requirements are shown to be moderate. The series connected multitermimal system is shown to have a number of advantages over the alternative parallel connected system for certain applications.

Effects of voltage and reactive power constraints on power system reliability

Abstract: The paper deals with a method for the reliability evaluation of a power generation and transmission system, when considering, together with the constraints on the active power capability of elements, the voltage constraint in network nodes. The approach suggested is an extension of a previous method for the reliability evaluation when considering only the active power capability constraints. The method is based on the approximate evaluation, by means of linear computation methods, of the reactive power flows and of the consequent voltage values in network nodes. This evaluation is performed starting from the approximate evaluation of the active power flow derived with the classic method of d.c. load-flow computation. The system performance, as a consequence of voltage constraints, is quantitatively evaluated by means of two indices: the first being the power disconnected in the nodes as a consequence of unacceptable voltage values or lack of reactive generation, the second being the irregularity of the voltage Service.

Induction heating appliance circuit that produces relatively high frequency signals directly from a relatively low frequency AC power input

Abstract: The invention includes a number of high frequency inverter circuits which develop high frequency signals, preferably in the 20 KHz to 50 KHz range, for use in a work coil, which exhibits inductance and generates a magnetic flux in response to a supplied current, or in a transformer primary winding to effect a magnetic flux output in the form of a transformer action The magnetic flux output from a work coil may be used, for example, to effect heating of a cooking utensil or the like, and the signal transmitted through a transformer may be used, for example, in electrical welding or the like Both current fed and voltage fed inverters, which use one or more high frequency switches, such as SCR's, as well as multiplexed and stacked inverters for efficient time sharing of components, are disclosed

Circuit arrangement including a number of converters, in particular direct converters, in y connection

Abstract: A circuit arrangement is disclosed comprising three direct converters which are fed from an a.c. voltage network. The converters are arranged in a Y configuration and are connected to a three-phase load. To increase the transmitted power and to vary the reactive power requirement, the circuit arrangement is provided with means for generating a control voltage for the control unit of at least one of the three converters such that the output voltage of this converter has a periodic waveform which includes essentially no fifth and seventh order harmonics. Additionally, the load-side conductor currents of the three converters are controlled with control signals having sinusoidal waveforms. A particular form used for the control voltage is a trapezoidal waveform.

Reactive current compensating apparatus for electric power systems

Abstract: A reactive current compensator for improving the power factor of a multiphase alternating current electric power circuit comprises a bank of fixed capacitors connected to multiphase line terminals in star circuit relation and two multiphase banks of fixed inductors connected to said terminals in parallel circuit relation, one inductor bank being star-connected and the other being ring connected, together with switching means responsive to a characteristic of power circuit current for controlling the magnitude of current in each phase of both inductor banks.

Clock drive apparatus

Abstract: Apparatus for driving a timing device from an external AC power source and, in the event that the AC power source fails, from an auxiliary DC source. The driving apparatus includes a pulse producing circuit which produces periodic pulses in response to timing pulses. A timing pulse circuit, including an oscillator which produces an oscillating voltage having a frequency substantially proportional to the AC power source frequency, applies the timing pulses to the pulse producing circuit. A DC power supply receives the voltage which is supplied by the AC power source and generates a DC energizing voltage to energize the various circuits of the apparatus, including the pulse producing circuit and the oscillator. In the event that the AC power source fails, the voltage produced by the auxiliary DC source is used to energize the various circuits of the apparatus. A storage device is included in the DC power supply for receiving and storing the generated DC energizing voltage so as to maintain a sufficient energizing voltage during the interim between the failure of the AC power source and the time that the auxiliary DC source reaches a satisfactory energizing level. A driving circuit responds to the periodic pulses produced by the pulse producing circuit to supply driving energy to the timing device. The timing device comprises a single clock or clock system or, in the alternative, a master clock which is used to drive and control one or more slave clocks.

Regulated high voltage ac power supply with regulated d.c. bias current

Abstract: A circuit for concurrently producing regulated high voltage a.c. current and bias d.c. current on one output line, where all regulation is accomplished in low voltge circuits, power supply being particularly useful as the power source for copier and duplicator corotrons. The basic wave shape is a rectangular wave which is amplified and regulated for application as the a.c. input to a corotron. The corotron itself is used as the rectifier for the d.c. bias current, with this current being variable in either the positive or negative direction by varying the symmetry of the a.c. rectangular wave. Since the part of the wave which has the shorter duration must have the higher amplitude, and current in the corotron increases with voltage, a feedback loop which controls the rectangular wave duty cycle will regulate the d.c. bias current as well.

System performance characteristics of superconducting alternators for electric utility power generation

Abstract: The application of superconductors in the field windings of large steam-turbine generators appears to offer a number of significant economic and operational advantages. The principal advantage offered by such machines appears to be a potentially large reduction in size, weight, and cost for a given power rating. In addition, superconducting alternators also appear to have a number of unique and potentially advantageous operational characteristics, most of which are a consequence of the relatively low per-unit synchronous reactance that is characteristic of these machines. This paper reviews the reasons for the low synchronous reactance attributable to the use of superconducting field winding, and compares the expected performance characteristics of a superconducting alternator in the 1000 MVA range with those of a conventional power system generator of comparable rating. Among the specific topics discussed are performance with regard to dynamic stability, transient stability, voltage regulation, and excitation control. The principal operational advantages of a superconducting alternator appear to be 1) the absence of a dynamic stability limit within its MVA capability, 2) significantly greater transient stability when operating at leading power factors, 3) superior voltage regulation, and 4) no degradation of dynamic stability due to automatic voltage regulator action. Consequently, superconducting alternators appear to be ideally matched to modern power system applications that require operation of generators at leading power factors.

System for energy storage and DC to AC conversion

Abstract: A system is disclosed for storing electrical energy and for converting DC power to AC power. The system includes a very large flywheel which is mounted in an evacuated housing and is driven by a plurality of wheels powered by DC electric motors which receive current from an input power source. An independent plurality of wheels coupled to AC generators selectively engage the rotating flywheel to withdraw energy from the rotating mass of the flywheel in the form of alternating current. Control systems are provided for adjusting the radial position of the drive and output wheels in dependence upon the speed of the flywheel. Additional control systems are provided to change the number of driving motors or output generators in contact with the flywheel depending upon the input power available or output power required.

Current control system for high frequency link cycloconverter

Abstract: In a system including an input cycloconverter which operates a high frequency resonant tank from a source of low frequency voltage supplied through a reactor, with or without an output cycloconverter, an input cycloconverter control circuit and method independently controls real and reactive power or real power and input power factor. The in-phase and quadrature components of input line current as well as the tank voltage are controlled, and for the main applications a simpler implementation has a limited range of phase angle settings close to 0° and to ±90°. The current control technique has the advantages of fast response and simplicity.

Solution of load-flow problems in power systems by ϵ-coupling method

Abstract: The ϵ-coupling method has been applied to the solution of the load-flow problem in power systems in connection with the weak coupling between the subsystems for active and reactive power flows. The load-flow algorithm, based on this method, confirms the theoretical expectation of being considerably more efficient than the Newton-Raphson algorithm, as far as computing time and memory requirements are concerned, which are on the level of those required by the decoupled algorithms. The algorithm may be adapted to problems demanding efficient load-flow computations, such as security monitoring and optimal load-low problems.

Solid State Series Motor Drive

Abstract: This paper is concerned with the detailed study of the performance characteristics of solid state dc series motor drives under phase control and current control schemes. The drive systems with the control schemes are simulated on a digital computer. An efficient time saving method is employed for computation. Different modes of operation are considered. The performance characteristics, such as, speed-torque, input harmonic content and input power factor variations are obtained and compared for the two types of control schemes. The peak current and ripple content which affect the commutating capability of the motor are also investigated. Current control scheme looks promising over the commonly used phase control scheme. Experimental results demonstrate the feasibility and verify the basic principles of operation.

Variable temperature apparatus using a thermal conductivity measurement technique for the determination of superconducting ac power loss

Abstract: A variable temperature apparatus is described which uses a thermal conductivity measurement technique for the determination of superconducting ac power loss. The technique consists of measuring the increase in temperature of a thermally isolated sample carrying an alternating current. Accurate measurements over a relatively large temperature range are possible. Loss data on a 13 cm long, single filament NbTi superconductor are presented at various temperatures and currents.

Improvement in DC Motor Performance by Asymmetrical Triggering, Part I: One-Quadrant Drive

Abstract: The static Ward-Leonard drive suffers from two major disadvantages: 1) poor power factor when the phase-controlled converter supplying the motor is operated at a delayed triggering angle, and 2) the problems associated with discontinuous armature current when the machine is lightly loaded. If asymmetrical triggering technique is judiciously applied to a converter-controlled dc drive, it improves not only the power factor but also the overall performance of the drive. It reduces the ripple content of the armature current and the value of the extra inductance necessary to achieve current continuity for low-current operation.

Steady-State Analysis of Single-Phase AC Controller with Resistance Load

Abstract: A number of load waveforms, produced by switching elements in a single-phase supply to a resistance load, are analyzed. The power factor of the circuit is investigated and its relationship to power, distortion factor and fundamental power factor given. A number of particular switching modes are introduced to give leading power factors and certain harmonic elimination.

Phase shifter for controlling the power components and power factor of a cycloconverter

Abstract: A phase shifter circuit generates cycloconverter reference signals for independently and linearly controlling the real power and input power factor or real and reactive power in either polarity. Using the per phase line voltage as a reference phasor, its amplitude and phase are adjusted by a sine-cosine converter, analog multipliers and summing amplifiers. The phase shifter has an almost instantaneous response and can be controlled by polarity reversing dc control signals.

Method and apparatus for compensating reactive power

Abstract: An arrangement for compensating reactive power in a three phase network using two converters with the same no load d-c voltage in which the two converters are coupled in parallel on the d-c side and shorted by a common choke with the one converter operated with a delayed firing time and the other with an advanced firing time and a d-c current in the choke regulated to a constant value by influencing the firing angles of the two converters in opposite directions.

Static reactive power generating apparatus

Abstract: An AC/AC frequency changer operating under a one to one frequency ratio has its input coupled to a power system of same frequency and voltage, with an inductor connected between its output and input terminals. The output voltage is controlled so as to deviate by a predetermined amount from the input voltage so that reactive power flows from the output to the input which, owing to the inherent phase inversion in the frequency changer, causes reactive input current and reactive output current to be summed up directly at the input terminals. As a result, the frequency changer requires only a power rating which is half the reactive power which it can supply to the power system.

Harmonic Line Currents in Large Thyristor Six-Pulse Converters

Abstract: A guide to the generated line currents from six-pulse converters is presented. Included are the effects of commutating reactance, phase angle retard, partially inductive loads, and general comments on plant distribution layout, especially electrochemical plants. It is intended as a concise general guide to predicting the level of harmonics to be expected in a specific case, and as a guide in minimizing the occurrence of the more complex circuit effects of a total system. Harmonic currents in large thyristor converters, Megaverters ®, are found to be not significantly greater than in diode converters; however, more care must be given to plant layout of multiphase systems in order to benefit from the attempt at harmonic reduction.