Voltage Sensitive Loads Research Articles

Improved representation of generator and load dynamics in the study of voltage limited power system operations

The implementation and significance of modeling improvements in operational planning studies of a voltage limited network interface in the AEP System are presented. The modeling improvements are with respect to conventional load flow based modeling and consist of significant elements relevant to system voltage performance documented in the literature. These elements include voltage sensitive dynamic load models; distribution system equivalents that include load tap changer (LTC) regulation of load voltage; generator field current limiting action; and generator voltage regulator reactive line drop compensation. Both dynamic and steady-state aspects of voltage stability performance of the AEP voltage limited network interface are addressed. The implications of conventional load flow modeling in operational planning studies are discussed with reference to the results of the generator and load modeling improvements.

Optimal capacitor placement, replacement and control in large-scale unbalanced distribution systems: modeling and a new formulation

This paper undertakes the problem of optimal capacitor placement, replacement and control in large-scale unbalanced, radial or loop distribution networks. The problem is how to optimally determine the locations to install (or replace, or remove) capacitors, the types and sizes of capacitors to be installed (or replaced) and, during each load level, the control schemes for each capacitor in the nodes of a general three-phase unbalanced distribution system such that a desired objective function is minimized while the load constraints, network constraints and operational constraints (e.g. the voltage profile) at different load levels are satisfied. The objective function considered consists of two terms: cost for energy loss; and cost related to capacitor purchase, capacitor installation, capacitor replacement and capacitor removal. Comprehensive modelings of different components are presented which include primary power networks, three-phase transformers (different winding connections, off-nominal tap ratio, core and copper losses), cogenerators, voltage sensitive load models for single-phase, two-phase and three-phase loads, shunt capacitors and reactors. The new problem is formulated as a combinatorial optimization problem with a nondifferentiable objective function. The configuration space essential in the design of a annealing-based solution methodology for the new problem is derived.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

EFFECTS OF VOLTAGE SENSITIVE LOADS ON THE VOLTAGE STABILITY OF COMPENSATED EHV-TRANSMISSION LINES

ABSTRACT In this paper, effects of voltage sensitive loads, namely, constant power, constant current and constant impedance type loads on the voltage collapse phenomenon of EHV transmission lines with different types of compensation schemes are studied and discussed. Exponential modelling is used for the three types of loads and exact long line equations are used in the analysis. It is seen that the power transfer capability of a long line for any type of compensation scheme is the highest for a constant impedance load, and the lowest for a constant power load. The power transfer capability for a constant current load has an intermediate value compared to those for constant impedance and constant power loads respectively. Further, the transformer tap control has an adverse effect on the voltage stability for constant current and constant impedance type loads. Improved power factor improves the voltage stability condition for all types of compensation schemes. In all compensation schemes, an increased degr...

Transient excitation boosting at Grand Coulee Third Power plant: power system application and field tests

Transient excitation boosting (TEB) has been installed on the Grand Coulee Third Power Plant hydrogenerators (three 600 MVA units and three 700 MVA units). The authors describe the application and implementation of transient excitation boosting based on direct detection of a critical disturbance. Using telemetry, a signal is sent to inject a decaying pulse into the excitation systems of large generators with very powerful static exciters. This open-loop control improves interarea transient stability. TEB is initiated for outages of the 3100 MW Pacific HVDC intertie, and results in a decaying pulse input to the generator voltage regulators. TEB temporarily raises Pacific Northwest transmission voltages which increases voltage-sensitive loads. The increased load brakes Northwest generators which are accelerating because of the loss of HVDC intertie power. Transient stability of the parallel Pacific AC intertie is thus improved. Power system-wide commissioning tests were conducted on May 7, 1991. The tests are described and test results compared with simulation results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distribution automation applications software for the Athens Utilities Board

The development of a distribution automation applications software package for assessing system reconfiguration opportunities and volt/VAR control on automated radial distributions feeders is discussed. The package, called SYSRAP (System Reconfiguration Analysis Program), was developed as part of the Athens Automation and Control Experiment (AACE), a large-scale distribution automation research project being conducted on the Athens Utilities Board in Athens, Tennessee. The program runs on a personal computer, executes power flow and short-circuit analyses for detailed feeder models in tens of seconds, uses highly detailed feeder models including voltage-sensitive loads, and is adept at reorganizing the database to reflect switching operations and changes in the status of volt/VAR control equipment. >

Measuring and analyzing the impact of voltage and capacitor control with high speed data acquisition (distribution system)

Experimental results on the effects of capacitor switching on feeder operating variables as measured in the substation by a high-speed data acquisition system are presented. Consistent with the modeling of feeder loads as constant power, the switching in of a capacitor bank to improve power factor results in decreased reactive power injection and increased phase voltage. However, a reduction in real power injection reflecting reduced line losses is not observable at the substation. Similarly, the switching out of a capacitor bank results in increased reactive power, decreased phase voltages, and decreased real power. Analysis of the experimental results, using voltage-sensitive load models shows that while feeder losses are reduced following feeder power factor correction, the attendant improvement in voltage profile results in an increase in load that exceeds the amount of loss reduction. Consequently, distribution system operators using supervisory control and data acquisition systems will not be able to observe the loss reduction associated with capacitor switching to improve power factor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stability Analysis of a Modulated AC/DC System Using the Eigenvalue Sensitivity Approach

This paper develops an optimal control strategy for improved dynamic performance of integrated ac/dc systems, based on power modulation techniques. The basic feature of the method is the minimization of the adverse reactive power interactions between the controls and voltage sensitive loads, which tend to reduce the effectiveness of the modulation process. A method for stability analysis, based on linearization techniques and eigenvalue sensitivities, is developed and applied to a typical ac/dc system with non-linearly voltage dependent load. The dynamic performance of the system, both with dc power modulation and power system stabilizer, is evaluated for various operating conditions, different load characteristics and different excitation systems. Finally, a dynamic simulation program is developed and used to obtain the exact transient response of the ac/dc system in the time domain. The simulation results presented in the paper verify the responses predicted from the linear eigenvalue sensitivity analysis.

A New Device For Improving the Quality of Distribution Feeder Power to Digital Computer and Other Voltage Sensitive Loads

A New Device For Improving the Quality of Distribution Feeder Power to Digital Computer and Other Voltage Sensitive Loads

A New Device for Improving the Quality of Distribution Feeder Power to Digital Computer and Other Voltage-Sensitive Loads

A new power conditioning device is described for improving the quality of distribution feeder power supplied to large digital computer loads. The improved quality results from the synthesis of three-phase 60 Hz voltage waveforms which remain essentially constant in magnitude and shape over a large range of input voltage excursions in both the positive direction (surges) and the negative direction (sags).