Showing papers on "AC power published in 1969"

Real Time Control of System Voltage and Reactive Power

Abstract: This paper presents a centralized optimizing computational algorithm for the on-line control of voltage and reactive power. The body of the paper is divided into two parts.

A Method for Optimum Scheduling of Power and Voltage Magnitude

Abstract: A general formulation of the economic dispatch problem is presented, based on the Lagrange multipliers approach. The necessary conditions are established and upon these conditions an algorithm is developed for real power and voltage magnitude dispatch (i.e., reactive power dispatch). Feasible solutions are always attained during the optimizing procedure. Basically the coordination equations have the same form of the Jacobian matrix for which efficient solution methods have already been developed. Very small additional work beside the necessary calculations for a load flow solution by Newton's method is required. All the equality constraints dual variables (Lagrangian multipliers) are calculated in the iterative procedure, but once the optimal solution is attained (within a specified precision) the additional dual variables of the Kuhn-Tucker theorem for the effective inequality constraints can be calculated. The feasibility of the method is shown by means of a sample system.

Divided-winding-rotor synchronous generator. A comparison of simulated 30 MW conventional- and divided-winding-rotor turbogenerators

Abstract: Experiment with a 5kVA machine showed the feasibility of a new form of turbogenerator using a rotor winding of two sections, in X formation, controlling the torque and reactive requirements separately.The performance of a conventionally wound rotor turbogenerator (c.w.r.) of 30MW size, described by Shackshaft, is compared with that of a divided-winding-rotor (d.w.r.) arrangement (CEGB patent application 2240/65) of the same machine.The analogue simulation shows that the d.w.r. can control power and reactive output satisfactorily, without altering the rotor position in relation to the generator air-gap flux. Fully rated stator current at leading power factor can be obtained continuously from no load to full load.The speed of response of the d.w.r.-generator reactive power to a step change of infinite-busbar voltage is, on average, twice that of the c.w.r. Turbogenerator stability is improved, and is shown to be independent of reactive generation or absorption, being affected only by active-power generation.Transient-stability comparisons are made by simulating 3-phase short-circuit faults close up to the high-voltage busbar, with low- and high-impedance connections to the infinite busbar.The c.w.r. simulation at full load with full excitation withstands a fault duration of 0.45s, which comes down, with reducing excitation, to 0.32s when Qu = − 0.225 p.u. and rotor angle = 70°; 0.2s when Qu = − 0.6 p.u. and rotor angle = 100°; and less than 0.1 s when Qu = − 0.9 p.u. and rotor angle = 120°.Comparable d.w.r. simulation of load and excitation conditions all require a fault duration exceeding 0.4s to cause instability. Even the Qu = − 2.3 p.u. condition is simulated without deterioration of control, and requires 0.4s fault duration to cause instability.The high-impedance connection to the infinite-busbar simulation shows, in general, that the maximum fault duration for each type of generator is reduced by 0.1s.

A Solid-State Supply for Induction Heating and Melting

Abstract: The paper describes a practical solid-state phase and frequency converter. Three-phase input power is converted to single-phase power of higher variable frequency output power, without the use of a dc link. A brief description of the circuit is given, followed by simplified theoretical considerations and actual experimental results.

Ac powered dc motor including semiconductor rectifiers

Abstract: In a DC motor which includes semiconductor rectifiers within it for converting AC power into DC power for driving the motor, an improved arrangement for supporting the rectifiers and brush holders.

Use of power and energy concepts in the analysis of multivariable feedback controllers

Abstract: The general linear-feedback multivariable-regulator problem is considered in terms of the injection of power into the controlled system by the controller. The concepts of power, energy, power decomposition, active power and reactive power are studied in this context and shown to give a physical insight into the techniques of modal control and spin-space mapping. An analogy is established between the energy exchanges of a system and its controller, and the energy-interchange effects in quantum mechanics.

Solid-state ac power control apparatus

Abstract: A solid-state AC power control circuit intended for use with digital computers and which can increase or decrease, and turn on or turn off the AC power supplied to a work load in response to the application of computer generated electrical signals to the proper input terminal. The amount of power change is determined by certain characteristics of the signals and the RC time constant of a memory circuit in the device. In addition to input terminals for receiving power increase and decrease input signals, two other input terminals are provided for allowing the controlled power to be turned full off or back on to a preset level by the computer without disturbing the memory circuit.

Power control system

Abstract: A relatively low power level electrical signal is utilized for controlling the switching action of a plurality of relay networks in a power control system so as to control the AC power being supplied to a load A plurality of switch branches are provided each including an AC power switch having a pair of power terminals and a control electrode arranged to carry a relatively high power level signal through its power terminals Energization of the power switch is effected by the application of a relatively low power level signal to its control electrode through a switch such as a pair of relay contacts which need have only a relatively low power-handling capacity in comparison with the power level to be supplied across the power terminals of the AC power switch A selectively energizable relay coil is serially connected to the power terminals and is operatively coupled to a pair of relay contacts in a succeeding switch brand, which in turn, are coupled to the control electrode of another similar AC power switch, and, upon closure energize this another power control switch so that the AC power signal flows through its power terminals in order to energize a load coupled thereto The relay contacts coupled to the control electrode need only be sufficient to carry a relatively low power level signal in order to energize the another AC power switch, while the load power signal flowing through the power terminals may be at least an order of magnitude greater than that supplied to the control electrode for rendering the another power switch conductive

Modes of Operation of Three-Phase Inverters

Abstract: Three-phase inverters have different modes of operation, while the load power factor angle varies over a 3600 range. A method of analysis is described which makes it possible to find these modes of operation. The method is based on the use of Park vectors. These vectors-generally used in the analysis of three-phase ac machines-are composed of the instantaneous values of a three-phase system. Voltage and current vectors of a three-phase inverter are used to find the current distribution of the inverter. An analysis is given of all the possible conditions of an inverter connected to an active load that can produce any load power factor from zero leading to zero lagging. Some special modes of operation are discussed in detail. Ranges of load power factor angles having different types of commutations are obtained. A control method is shown which makes it possible to obtain effective voltage regulation at the full range of load power factor at a reduced commutation frequency.

Solid-state power electronics in the U.S.A.

Abstract: This article focuses on the conversion and control of large blocks of electric energy by solid-state power devices such as silicon rectifier diodes and thyristors. Power conversion fulfills the important requirement of delivering a desired type of electric energy when the available form is unsuitable. Examples include the energization of dc machines, dc fields, and batteries when the available source is single-phase or polyphase alternating current. Another example relates to variable-speed drives for Induction and synchronous motors when the power source is either dc or fixed-frequency ac. Power control is concerned with varying the level of power delivered to a load, as in on-off switching, or varying the output voltage of a rectifier.

Artificial Commutation of Converters Through Injection Technique

Abstract: The conventional converter consumes reactive power by virtue of the lagging power factor inherent in normal operation. Operation at leading power factor requires commutation in the region (?+ u) > ?. This can be achieved through artificial commutation by reversing the valve-to-valve voltage during the commutation period. In a two-converter station the vars so generated can be supplied to a conventional converter operating in parallel on the ac side and, ideally, the station capacitive reactance can be reduced to that required for satisfactory harmonic filtering.

Dc detection circuit

Abstract: A DC detection circuit in an AC power circuit for detecting DC and for protecting AC loads from the deleterious application of a DC current. The DC detection circuit is particularly applicable to an emergency lighting system having both AC and DC power sources and AC and DC lighting facilities for detecting the application of DC and for disconnecting the AC lighting facilities to prevent their damage and for lighting the DC lighting facilities.

Mechanically variable high reactive power inductor for testing capacitive loads,such as high voltage electrical power transmission cables

Abstract: A mechanically variable high reactive power inductor is described for testing capacitive loads, such as high voltage electrical power transmission cables or large capacitors. The inductor is formed of upper and lower separable core segments magnetically coupled to electrical windings. The cores are separated in an accurate stable manner to change the inductance of the inductor to tune the inductor into resonance with the capacitance of the load being tested to obtain effectively a series resonance condition therewith. The upper core segment is suspended from lead screws which are jointly operated by a control capable of varying speed to establish accurate gap control for improved high voltage testing capability.

New approach for economic load scheduling

Abstract: Economic load scheduling, carried out by loss-formula coefficients, has been shown in the literature to be inaccurate. A new approach is presented here which employs a simple principle of moments (as employed in the calculation of a.c. distributors) and based on the removal of loops from the power-system network. The method provides comprehensive economic dispatch information regarding the active power output of a plant and its voltages and power factors at regular intervals. This approach is particularly suitable for monitoring and controlling power systems by digital computers operating online to achieve optimum economy. Included illustrative examples show the inaccuracy of the B coefficient approach (even for a base case), and indicate the improved accuracy achieved by the new method even for negative loads; the savings in operating costs relative to that computed by the B coefficient method being from 1% to 3%, in relatively small power systems, with the expectation of greater savings in larger systems.

Control circuit for compensating for power variations utilizing controlled multipliers or dividers

Abstract: An AC power supply powers several transducer circuits, in which input voltage variations cause variations in the output signals from the transducer circuits. A time division multiplier has an input connected to the AC power supply and a second input connected to a fixed DC voltage source. Variation in AC amplitude change the duty cycle of pulses generated by the multiplier. Semiconductor detector gates are driven by the multiplier pulses in order to demodulate and divide the output signals of the transducer circuits by a factor proportional to the duty cycle, thereby compensating for variations from the AC power supply.

Regulated series to multiple power converter

Abstract: A UNIT IS DESIGNED TO BE PLACED IN SERIES WITH A PLURALITY OF SERIES RUNWAY MARKER LIGHTS IN AN AIRPORT LIGHTNING SYSTEM, AND EMPLOYS A BIDIRECTIONAL THYRISTER RESPONSIVE TO LINE VOLTAGE OF A DETERMINABLE AMOUNT TO SHORT CIRCUIT THE UNIT IN EACH HALF-CYCLE OF THE ALTERNATING CURRENT POWER. THE UNIT INCLUDES CURRENT-RESPONSIVE POWER CONVERSION MEANS TO SUPPLY POWER SUITABLE FOR USE IN A FLASH LAMP. IN A SECOND EMBODIMENT, SILICON-CONTROLLED RECTIFIERS, ONE FOR EACH HALF-CYCLE OF THE AC POWER, ARE FIRED TO CAUSE SHORT CIRCUITING OF THE UNIT WHEN THE PREDETERMINED DESIRED MAXIMUM VOLTAGE IS REACHED. IN EACH EMBODIMENT, THE VOLTAGE-RESPONSIVE DEVICE INCLUDES A VOLTAGE DIVIDER ACROSS THE UNIT AND A BILATERAL AVALANCHE SWITCHING DEVICE.

Harmonic Analysis of AC-to-AC Frequency Converter

Abstract: Direct ac-to-ac frequency converters can be built using solid-state devices. This paper is primarily concerned with three-phase to single-phase converters where the output frequency is greater than the input frequency. In these converters, the input power factor and the harmonics of the input and the output currents vary with the output frequency. A digital simulation of an idealized three-phase to single-phase converter is used to predict the harmonic content of the input and the output currents. The results thus obtained can be used to design the input and the output filters to reduce the undesired harmonics.

Scr control for inductive power circuit

Abstract: A control switch circuit for providing gate pulses to an SCR switch in an AC power circuit which circuit includes a variable inductive load. The control circuit includes a magnetic amplifier with one control winding energized by a fixed reference voltage or by a variable control signal and with a second, oppositely wound control winding energized through a feedback circuit the input of which is provided by a current transformer connection to the power circuit. The output of the magnetic amplifier is a series of pulses which are connected to the gate of the SCR and which are shaped so as to provide a steep, high-voltage leading edge for precise timing and for saturation of the gate junction of the SCR in a minimum time period.

Inherent Constraints Control Convergence A New Method in the Long Look at Load Flow

Abstract: A new method has been devised to solve the well- known load-flow problem. It is based on the fact that the equations for real and reactive power at a bus have the same form as those for ordinary circles under the assumption that the voltages are fixed for all other buses. The real and reactive power losses are similarly expressed as circles. This enables one to find the least square solution to the common chords or radical axes to use as the new voltage solution. A sort routine and an extrapolation method is included to speed convergence.

Motor Starting with Capacitors

Abstract: A portion of the high-inrush incident to starting of large synchronous motors can be supplied by static capacitors because of the low power factor of the inrush kVA. However, care must be exercised in application of the static capacitors so as to avoid harmful resonant conditions, overvoltage due to self excitation of the motor and the proper selection or sizing of equipment for a specific application. An installation in a cement plant of large synchronous grinding mill motors employing static capacitors for motor starting is reviewed. Some of the considerations in application are shown and results of operation are also shown.

Power Failure Ride Through for an Inverter System Using Its Own Induction Motor Load as Energy Source

Abstract: The functioning of a system when energy in rotation motors are used to provide continuous operation during a momentary failure of ac input power is investigated. The system includes an ac power input, a dc rectifier, and an inverter which normally provides ac power to high-inertia induction motors. During a failure of the ac input, the frequency of the inverter is reduced so that the motors can transfer their rotational energy back to the dc bus through the inverter. When ac power returns, the system returns to its original condition.

Alternating current power supply employing programmed turn-on and turn-off

Abstract: A reliability of a high-power alternating power supply wherein a low-power alternating current is used to convert a high-power direct current to said high-power alternating current is improved, when driven by sources and when driving loads that are inductive or inductively coupled, by the use of a programmed turn-on and turnoff procedure wherein the energy supplied to a reactive load is gradually increased and diminished respectively.

Circuit for regulating peak values of an ac wave

Abstract: A peak-to-peak regulator is coupled in series between an AC power source and the primary of an AC transformer. Another winding on the same transformer is employed to detect when peak values of the AC wave exceed a predetermined value, and negative feedback in response thereto increases the impedance of the regulator. Positive feedback circuitry is included which detects an increase in voltage drop across the regulator and which in response thereto further enhances or aids the negative feedback. As a result, the current through the regulator is minimized for the duration of the peak of the AC wave which it regulates.

Improvements in electrical inverter stations

Abstract: 1,174,166. Inverters. ALLMANNA SVENSKA ELEKTRISKA A.B. 19 April, 1967 [20 April, 1966], No. 17927/67. Heading H2F. In an inverter in which the power factor is controlled by an adjustable bank of capacitors 17, a signal is derived indicative of the reactive power and is fed to a control device for the capacitor bank 17 and to the trigger circuits for the inverter 1 in such a way that a reduction in reactive power causes first an increase in the commutation margin of the rectifiers and then a decrease in the capacitance of the capacitor bank the arrangement being such as to ensure a minimum commutation margin. As described, the signal representing reactive power is derived by means of a Hall generator 14 supplied by potential and current transformers 16, 15 and developing a voltage across resistor 20 the polarity of which is dependent on the sign of the effective reactance in the network. When the load is reduced on the network 10, the capacitance of bank 17 tends to be excessive hence the signal from the Hall-generator 14 is such that when fed via control circuits 7, 8 (see Specification 985,674) the delay angle for the rectifiers 2 is decreased. The signal from the Hall-generator is also fed to an electromechanical control device 13 for the capacitor bank so as to reduce the capacitance, correct the power factor and hence cancel the signal from the Hall-generator. The delay angle for the rectifiers 2 is thus restored. When the original load conditions have been re-established, the capacitor bank will be to small and the reactive power in the network will therefore be inductive. A new output signal of opposite polarity will thus be obtained from the Hallgenerator 14 which is fed to control device 13 so as to reset the capacitance. Diode 21, however, prevents the signal from decreasing the commutation margin of the rectifiers 2 beyond a predetermined angle. The trigger circuits for rectifiers 2 include transistors 5 controlled by the combination of signals derived at 8 from the network 10 and at 7 from the current supplied by the D.C. transmission line 90. Fig. 2 (not shown), depicts a simplified arrangement of four inverters 1 connected in series across a three-wire high voltage direct current transmission line and having isolating switches in series with each side of the D.C. line and across each inverter. The Hall-generator 14 is replaced by a potential transformer feeding a rectifier and smoothing capacitor, the output being compared with a D.C. reference voltage.

115-kV Load-Flow Analysis Using a Simplified Loop Digital Program

Abstract: An IBM 7094 digital computer is used to solve a small load-flow problem by an iterative nodal technique. Using an IBM 1620 computer the same flow problem is solved using a simplified loop method approach. From comparison of these results, the simplified method appears acceptable for small single-loop systems not requiring greater than 7-percent accuracy.

Tolerable Limits of Voltage Fluctuations Produced by Magnets Pulsed Directly from Alternating Current Power Lines

Abstract: Switching magnets, for time sharing of beam lines, can be pulsed directly from the ac power line if it does not cause objectionable line voltage fluctuations (flicker). Switching circuits, which are less expensive and more reliable than conventional magnet power supplies are often all that are needed. Of particular interest for beam lines of the Zero Gradient Synchrotron (ZGS) was a test to determine the permissible attenuation of 1 cycle of the 60 Hz power line every 2 s. Other tests included multiple cycle attenuation at different repetition rates and square wave modulation of the ac power line. Thresholds of perception and the distribution of opinions on the flicker disturbance as functions of voltage attenuation were determined for viewing TV and reading by incandescent light. The results of these tests are reported and can be used to calculate the permissible magnitude of pulsed current in a given ac power system.