COMBINED ELECTROMAGNETIC FACILITIES
(Ulyanovsk, technical university)
FOR CONTROL SYSTEMS IN POWER ENGINEERING
Power electromagnetic facilities namely controlled and saturated reactors (CR and SR) are used in power engineering for automatic control and adjusting. Reactors are realized on the bases of pivotal magnetic cores or magnetic cores of electric machine type with circle symmetry.
Being the means for reactive power adjusting reactors are necessary for compensation of excess charging power of electricity transmission lines (ETL) and advancement of their carrying capacity, limiting of commutation overvoltages and short circuit currents, reducing of voltage fluctuations, rational voltage and current distribution, etc. At present there is an increased requirement of controlled reactors for the ETL in Russia due to frequent active power underloading of lines.
At the same time CR and SR installation increases the amount of mounted equipment thus leading to the several negative consequences. For the sake of their eliminating the principles of constructing of effective reactive power consumption facilities with appointed and improved characteristics were formulated. A class of combined
CR, SR and controlled reactors-transformers (CRT) which are multipurpose system devices was developed in accordance with these principles. These devices simultaneously perform the functions of separate reactor and power transformer (transreactor), reactor and battery of capacitors (reacond), reactor and direct current source, etc. and are intended for improvement of operating modes of ETL, distributive networks 6...10 kV and above and industrial enterprises power supply systems.
It is concluded from devices comparison that combined facilities have better reliability and weight-size parameters then separate power facilities with the same functions. CRT operates in agreement with features of electrical power system: the power of reactor has to be minimum when the transformer loading is maximum and the power of reactor has to be maximum when the transformer loading is minimum.
Generalized mathematical model of considered devices, algorithm and its program realization were developed on the basis of Maxwell's field theory and finite elements method. By dint of created model an "anatomy" of combined facilities with adjusted inductivity were investigated and correlations between constructive and schemotechnical features of devices and their characteristics were established. Design decisions for device optimization were taken after the modeling procedure. Mathematical model takes into consideration a non-linearity of magnetic environment and an actual longitudinal geometry of the reactors with pulsed field and a cross geometry of the reactors with revolving field.
Generalized mathematical model of electromagnetic regimes of combined facilities working ("physiology") with adjusted inductivity and effects appearing when these devices are magnetisized, respective algorithm and its program realization were developed on the basis of electric and magnetic circuits non-linear theory. By means of this model normal working regimes of reactors, transient processes, asymmetrical regimes resulted from supply network, loading and devices asymmetry were investigated. The most dangerous operating regimes were determined. It was recommended to influence over processes nature by symmetrical and prior magnetization, etc. This model is valid for the devices of arbitrary magnetic core construction and takes into account the looses in steel as a function of magnetic induction.
The method for transformer type CRT design is proposed. It represents an execution of calculation in two stages: during first stage the calculation performed in nominal transformer regime which is defined by standards and within the second the calculation performed in nominal reactor regime which is based on the results of first stage. Methods for CRT design in these regimes as well as relevant computer program for principal sizes definition which correspond to the minimum cost of active part at certain values of idling and short circuit looses and other normalized parameters were created.
The design method for CR of electric machine type in symmetric magnetization regime is developed. In this regime the range of reactor adjusting is increased for 15...20 %, the fast-action in transient processes is raised, the losses in steel are reduced and the "shaking" vibrations are excluded. Algorithm and program realization of CR design method that uses as an optimization criteria minimum of calculated annual expenses, etc are developed. It is determined that at 2-poles working winding the best is utilization of 4-poles serial asynchronous motor. It provides higher yokes saturation and leads to more effective execution by reactor its functional destination.
Designed and produced reactive-capacitive facilities were installed on substations 10/0,4 kV. These devices provide reactive power adjustment, implementation of the functions of power transformer and electric power quality improvement. Microprocessor automatic control system for electric network voltage stabilization in the place of reactive-capacitive facility installation was developed, produced and tested.
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