Showing papers on "AC power published in 1982"

Reactive Power Control In Electric Systems

Abstract: Theory of Load Compensation. Theory of Steady--State Reactive Power Control in Electric Transmission Systems. Reactive Power Compensation and the Dynamic Performance of Transmission Systems. Principles of Static Compensators. Design of Thyristor Controllers. An Example of a Modern Static Compensator. Series Capacitors. Synchronous Condensers. Reactive Compensation and the Electric Arc Furnace. Harmonics. Reactive Power Coordination. Selected Bibliography. Index.

Harmonic Power Flow Studies Part I - Formulation and Solution

Abstract: The conventional Newton-Raphson power flow study has been reformulated to permit the inclusion of nonlinear loads. These loads give rise to harmonic signals which propagate throughout the power system. The reformulation is based on the reduction to zero of the mismatch active power and reactive voltamperes, the imbalance current at harmonic frequencies, and the mismatch apparent Voltamperes. Conclusions on the existence of positive, negative, and zero sequence signals are made for harmonic frequencies. The harmonic power flow study formulation is illustrated for a three phase full wave bridge rectifier. A companion paper presents a discussion of the actual computer implementation and several practical examples.

Steady-State Security Regions of Power Systems

Abstract: A steady-state security region is a set of real and reactive power injections (load demands and power generations) for which the power flow equations and the security constraints imposed by equipment operating limits are satisfied. The problem of determining steady-state security regions is formulated as one of finding sufficient conditions for the existence of solutions to the power flow map within the security constraint set. Explicit limits on real and reactive power injections at each bus are obtained, such that if each injection lies within the corresponding limits, the system is guaranteed to operate with security constraints satisfied.

Optimal Power Flow Based Upon P-Q Decomposition

Abstract: The optimal power flow problem is formulated based upon the decoupling principle well recognized in bulk power transmission loadflow. This principle is exploited by decomposing the OPF formulation into a P-Problem (P-?real power model) and a Q-Problem (Q-V reactive power model); which simplifies the formulation, improves computation time and permits a certain flexibility in the types of calculations desired (i.e., P-Problem, Q-Problem or both).

Reactive Power Considerations in Automatic Contingency Selection

Abstract: On-line steady-state security analysis requires the evaluation of the effects of a large number of possible contingencies on a power system. Almost all contingency analysis programs have had to rely on a list of selected contingencies to be studied. The brute force approach of testing all contingencies every time an evaluation of the system performance is needed, becomes prohibitive due to its computational burden. A particularly attractive technique is to utilize a fast, approximate method to select the few contingencies that actually affect the security of the power system and then analyze only these cases in more detail. The contingency ranking and selection methods presented in the literature have all ranked outage cases on the basis of transmission line overloads. This limits the usefulness of these technqiues as contingencies that cause only voltage problems are totally overlooked. This paper shows that there is little correlation between the contingencies that produce line overloads and those that result in unacceptable voltage profiles, further establishing the need for a contingency selection method that is also voltage sensitive. Such a method, using the first iteration of an AC power flow, is presented. It is shown that the method meets both the speed and accuracy requirements for on-line use.

Dynamic Load Models Derived from Data Acquired During System Transients

Abstract: For several years power system load responses have been recorded during system transients by means of a remote data acquisition system developed by Ontario Hydro. Using these data, models for the loads are developed in the paper and parameters for the models are obtained. Conventional static load models are shown to represent adequately the characteristics of a residential/commercial feeder load. For large rotating industrial loads two models are developed. The first is a transfer function model which relates the small signal power and reactive power outputs to input changes in voltage and frequency. The second is an induction motor model with shunt static load. Recorded voltage is considered as an input to the model and the output real and reactive power are compared with the measured output. The weighted squared error between the measured output and the model output is minimized by obtaining optimum model parameters. Recorded and simulated responses of the paper mill loads are compared.

Developments in Optimal Power Flow

Abstract: This paper presents an advanced power flow methodology for optimally dispatching all active and reactive power in a power system. Two major obstacles impede the success of most optimization algorithms: (1) computational inefficiences associated with large system and (2) the problems associated with handling functional inequality, constraints. In view of these basic problems, techniques are presented to improve the solution algorithm, the handling of penalty functions, and the power solution optimization methodologies. Additionally, new algorithms are provided for the determination of an optimal step length and for scaling of control variable gradients. These improvements and innovations computing techniques have been incorporated into a computer program and demonstrated on practical size power systems.

Static Reactive Compensation for Power Transmission Systems

Abstract: This paper concerns the application of static reactive compensators (SVCs) to Power transmission systems. Emphasis is placed on stability, and it is shown that SVCs can provide significant benefits in terms of increased transient stabilty liisand improved damping for synchronizing power flow oscillations. The paper includes descriptions Of static VAR compensators, with technical and economic comparisons of different compensators. An SVC system study model is presented which includes provision for modulating reactive compensation in response to a variety of system functions. Study procedures are illustrated which relate sYstem stability objectives to general specifications of SVCs, indluding their locations, regulating slopes, peak reactive power requirements, and modulation control.

The Quality of U.S. Commercial AC Power

Abstract: From May 1977 through September 1979, the Bell System conducted a study of commercial ac power disturbances ? To determine their nature and extent ? To devise statistical ways of predicting their occurrence ? To reduce or eliminate computer downtime through selection of appropriate, cost-effective power-conditioning equipment for use throughout the System. For a total of 270 months, field data was gathered from 24 Bell System data-processing sites. A statistical model, a Polya probability density function, best fit the overall observed data. It allowed predictions to be made as to the rate and duration of the various electrical disturbances distributed across the sites. However, statistical cluster tests of the data indicated that the overall model could not be used to predict disturbance activity at any specific site because of the high variability among the data from site to site. A modified Polya function, applied to observed data from specific sites, yielded more accurate predictions of the rate at which power disturbances will occur at various probability levels. A simple "look-up" table was devised to eliminate the need for tedious calculations. This table makes it possible to determine, based on the measured average number of disturbances occurring at a specific site each month, the maximum number of each kind of disturbance to be expected per year at a number of probability levels. The study indicated that different types of power-conditioning equipment yield varying reductions in the percentages of power disturbances.

Compact expandable electronic signal processing apparatus

Abstract: An electronic signal processing apparatus, such as, a personal computer, is basically composed of a power section for providing DC operating power from an AC power source and a main signal processing section operative by the DC operating power for performing the minimal necessary functions. The power and main signal processing sections are mechanically connected for relative sliding movements between closely adjacent positions minimizing the overall dimensions of the apparatus and spread-apart positions in which a space is defined between the power and main signal processing sections for accommodating at least one additional signal processing or handling section by which the functional capabilities of the apparatus are expanded.

Distribution System Integrated Voltage and Reactive Power Control

Abstract: Automated distribution systems offer new opportunities for improved control of voltage and reactive power at the distribution substation and feeder level. Digital processor algorithms which can have the objective functions of controlling voltage and reactive power and minimizing feeder losses in an integrated fashion according to specified priorities are described. Simulation results using a representative simplified distribution feeder configuration are presented based on the algorithms developed in connection with the PROBE [1] substation and feeder automation research project. This work is being advanced as a part of the development of the Integrated Distribution Control and Protection System engineering prototype for EPRI in Project RP 1472-1.

Coordinated load commutated inverter protection system

Abstract: A fault protective system for a load commutated inverter motor drive including an AC to DC source side converter coupled from an AC source to a DC to AC load side converter via a DC link circuit and wherein the load side converter supplies AC power of varying magnitude and frequency to the synchronous motor load. A pair of microcomputers interlinked by a common digital memory respectively control the inverters and interface with hardware type sensor means for detecting the occurrence of a plurality of different types of faults. Additionally, a number of stored instructional sets or programs are respectively included in both microcomputers to detect by software means another plurality of faults. The detection of a fault on either side of the link circuit is communicated to the respective computer which subsequently communicates with the other microcomputer to effect a coordinated protective action in response to thyristor cell failures, circuit failures, and abnormal operating conditions. Cell failure faluts include those instances where a thyristor cell actually fails due to an open or short circuit as well as those cases where a cell fails to commutate properly due to firing strategy problems. Cirucit failures include open and short circuits both in the supply line and the motor leads, while abnormal operating conditions involve such things as low line voltage or excessive motor voltage.

Self-powered, self-regulated, electronic ac control system

Abstract: A system of controlling the operation of an AC load with a switch placed in series with the load, which switch is itself operated by dc control logic powered by power loss experienced by the switch which the logic controls. Numerous elements in the control system perform multiple functions allowing the control logic to remain alive during both the on and off mode of the switch without power being provided to the logic by separate conductors to the AC power source, such that the control system is completely self powered and self regulated by simply placing the system, with two wires, into a series loop with the AC power source and the load.

Device for parallel supply into an AC or three-phase network

Abstract: In order to synchronise a final control element (an invertor (2) supplied, for example, from a solar generator (1) or an externally driven synchronous machine) to a network (11) to be supplied, both the magnitudes (¦Uw¦, ¦Un¦) and the directions of the corresponding voltage vectors are determined by means of coordinate converters (21, 31) and vector analysers (22, 32) from the final control element output voltage (Uw) and the network voltage (Un). The difference (¦Un¦-¦Uw¦) of the magnitudes is supplied via a magnitude controller (30) to the amplitude control input (3) of the final control element. A vector rotator (25) forms the angle between the vectors, which angle can be controlled to zero by a phase controller (33) acting on the frequency control input (4) of the final control element (2). In order to keep the final control element in synchronism with the network after closing the synchronising switch (14), and to control the exchange of real power and reactive power at the fundamental frequency between the mains and the final control element, the real component and the reactive component are determined from the measured current value (Iw) by means of a coordinate converter (41) and a vector rotator (42) and are each supplied to a controller (43, 44). The output signal of the real current controller is also connected to the phase controller input, and the output signal of the reactive power controller (43) is additionally connected to the magnitude controller input. This results in a universal apparatus which facilitates both network synchronisation and maintenance of a network-synchronous parallel operation of the final control element, while also facilitating the transition to an externally synchronised supply into a passive consumer network (isolated operation).

Application of Induction Generators in Power Systems

Abstract: A study of the application of induction generators in power systems, conducted under EPRI sponsorship is sunmarized in this paper Included are the results of investigations of induction machine dynamic performance, effect of machine parameters, modeling requirements, and voltage support requirements for stability under disturbance conditions of varying severity Application scenarios are identified and quantitative results are presented in normalized form so that approximate evaluations can be made of var control requirements for specific situations

An AC to DC converter with high quality input waveforms

Abstract: An ac to dc converter which draws sinusoidal and in phase current waveforms from the ac power source is described. Harmonic and power factor measurements obtained from an FET converter operating at 45 kHz for a single phase and a three phase connection are presented. A stability analysis and design methodology is given.

Apparatus and method for communicating digital information on AC power lines

Abstract: A carrier current transceiver includes a transmitter section and a receiver section coupled to an AC power line. In the transmit mode, input data in the form of a logical "0" enables a carrier frequency signal to excite a tuned cavity. The tuned circuit includes a first winding of transformer, a capacitor and a damping resistor. A second winding of the transformer is capacitively coupled to the AC power line to produce a stepped down carrier current signal to represent a transmitted logical "0". A logical "1" is represented by absence of the carrier current signal. In the receive mode, a small carrier current signal representing a logical "0" is received via the AC line and is stepped up by the transformer and capacitively coupled to an input of the receiver section. Outband frequencies are removed by means of a second tuned circuit and the resulting signal is amplified by self-biased CMOS inverter circuitry and then is limited by a diode limiter circuit before being input to a phase locked loop data recovery circuit that produces a logical "0" if the carrier frequency is applied for a predetermined period. The damping resistor critically damps large oscillations produced in the first tuned circuit by large noise impulses on the AC line to prevent such oscillations from enduring long enough to be detected as logical "0"s by the phase locked loop data recovery circuit.

Controller for alternating current elevator

Abstract: An apparatus for controlling an AC powered elevator by rectifying a commercial AC power source into a direct current through a rectifier, converting the direct current into a variable frequency AC power through a main inverter, driving the AC motor by the thus converted AC power to operate the cage of the elevator, and sending the regenerated electric power back to the commercial AC power source via a regeneration inverter connected to the DC side of the main inverter when regeneration braking is applied to the electric motor. If the main inverter becomes defective, the main inverter is separated from the electric motor, the AC side of the regeneration inverter is connected to the motor, and the motor is operated by relying upon the regeneration inverter.

A quantitative analysis of induction motor performance improvement by SCR voltage control

Abstract: Minimum input power and maximum efficiency operation occur at characteristic slip values which can be realized for any induction motor operating at part load by properly adjusting the amplitude of the applied stator terminal voltages. It is shown that these two criterion yield perceptibly different results when the motor is driven from an SCR voltage controller. In addition, it is demonstrated that a constant power factor controller results in an operating regime which is substantially poorer than operation at either minimum input power or maximum efficiency. It is further shown that minimum stator current and minimum power factor angle criterion yield results which are closer to the ideal than the constant power factor controller.

Voltage Versus Reactive Current Model For Dispatch and Control

Abstract: This paper derives a reactive current model for voltage/reactive dispatch and control which the authors believe is more suitable for corrective action than conventional reactive power models. The new model is based on the concept of real and reactive current which reduces the influence of the scalar bus voltages on the sensitivity coefficients of the model. Load versus voltage characteristics are incorporated in the model. Model coefficients for a thirty bus test case are compared with those obtained from the B" coefficients of the decoupled load flow. A simplified method for calculating the new model coefficients is also presented.

The Role and Benefits of Static Var Systems in High Voltage Power System Applications

Abstract: The specific role of Static Var Systems (SVS) as a form of dynamic reactive power compensation in high voltage ac power systems is described. A characteristic of the SVS which sets it apart from other forms of compensation is its extreme speed of response in adjusting its reactive power output to meet rapidly changing needs of the system. Examples [1] are given showing the benefits of SVS in suppressing load rejection overvoltages, increasing the transient stability power limit of a 500 kV radial transmission system, and in preventing a voltage collapse following a generator trip and subsequent increase in import power requirements. One example shows how the installation of a third 500 kV circuit could be avoided with the application of two SVS, with a significant savings in capital costs.

Control Design of an Active and Reactive Power HVDC Modulation System with Kalman Filtering

Abstract: This paper discusses results of an EPRI contract on control design for an ac/dc transmission system to increase power transfers limited by dynamic stability. The control is acbieved by modulating the rectifier dc current or power and the inverter dc voltage. Coordinated active and reactive power modulation is accomplished by Linear Quadratic (LQ) control design. Improved performance is realized by utilizing reactive power coupling between dc and ac networks to modulate dc and ac active power. For the demonstration system, power modulation with coordinated voltage modulation is shown to be about ten times more effective than power modulation alone. Control interactions between electromechanical modes of oscillation are eliminated by Kalman filtering. Filtering permits excellent control performance with a minimum of system measurements. Modern control technology is applied within realistic system constraints, such as measurements.

Exit sign lamp flashing system with self-checking provisions

Abstract: An emergency exit sign auxiliary lamp flashing system operates from self-contained rechargeable batteries upon failure of the electrical power from the AC power mains supplying power to the exit sign, including a charging circuit for recharging the batteries, with provisions for preventing overcharging and for disconnecting the load from the batteries before the battery voltage drops to a level which would impair its service life. Included is a solid state circuit which provides for automatically exercising and self-testing the proper functioning of the system to ensure its being serviceable when called upon to function during a power failure by periodically simulating the effect of a failure of AC power and verifying that the battery, lamp and flashing circuit operate normally or signalling a visual and/or audible alarm if they fail to operate properly.

DC To AC power inverter

Abstract: The DC to AC power inverter is of the class B, C, D or E type and includes a battery, at least one power SCR and associated capacitor circuitry, at least one input winding on a main transformer core and at least one output secondary winding on the transformer core. Such inverter requires a quiescent current to establish operating current for capacitor commutation charge and includes a feedback loading circuit for feeding current generated by the quiescent current back to the battery. The inverter also includes a self-detecting load demand circuit coupled to a line from said output winding for cyclically energizing the inverter, for sensing a minimum AC load and for holding said inverter in an energized state until less than a minimum AC load is sensed during an energizing cycle. Further the invention includes automatic power factor correction circuitry for supplying full time leading power factor correction to a load, with the automatic power factor correction circuitry being sensitive to light reactive loads.

Method and apparatus for controlling AC motor

Abstract: A method and apparatus for controlling an induction motor, in which an AC power source is connected to the induction motor through a switch and a frequency converter, and the motor speed is controlled by controlling the output frequency and output voltage of the frequency converter. In the starting operation, the induction motor in a free-running state is supplied with an initial voltage in a given frequency which is expected to make the absolute value of the motor current minimum or near minimum, and then the supply voltage is increased gradually from the initial voltage with its frequency being retained at the given voltage. When the output frequency of the frequency converter reaches a predetermined value, the output frequency and voltage thereof are increased gradually with the ratio therebetween being maintained at a given value.

A Simple Multiple Pulsewidth Modulated AC Chopper

Abstract: A simple multiple pulsewidth modulated (MPWM) ac chopper using power transistors for 3-? power control is discussed. 120° chopping period is used for main transistors so that the circuit can accommodate resistive and lagging or leading power factor loads. Only 1-? sensing is used for 3-? control. An alternate economical power and control schemes for 3-? MPWM ac choppers suitable only for resistive loads is also suggested. The experimental results for 12 choppings per cycle are given.

Asymmetrically Modulated AC Chopper

Abstract: The paper describes a current impulse-commutated ac triac chopper employed to obtain the optimum supply power factor correction for reactive loads. The resultant displacement and distortion factors of the supply and efficiency of the load are considered. Theoretical results are in excellent agreement with results obtained experimentally.