Elektrodynamika aparatów elektrycznych

Abstract

Technical electrodynamics is concemed with the interaction between magnetic and electric fields on electrical devices, and with the analysis of electrodynamic forces in particular. This monograph presents the electrodynamics of selected electrical devices and apparatus - switching devices, driving electromagnets of apparatus, current limiting devices. Calculations of electrodynamic forces are important as a current flowing through a switching device during a short circuit may be hundreds times higher than its rated current, so electrodynamic forces can be tens of thousands higher than those under rated operational conditions. It may result, among others, in electrodynamic contact repulsion, and contact sticking making the further operation of a switching device impossible. Moreover, calculations of electrodynamic forces are necessary to determine the cross section of current conductors, span length, and to select the way of fastening current paths, and also to determine the number and the strength of supporting structures and fastening elements. The second and partly the third chapters cover the survey of formulas and methods for calculating electrodynamic forces on contacts and current paths of switching devices. For this case, the analysis of electrodynamic forces applies mostly to the pass current duty of switching devices. The knowledge of magnetic fields and electrodynamic forces is,Atecessary to analyze the phenomenon of arc e xtinguishing resulting. from arc motion on the contact-extinguishing system of a switching device during its commutating duty. The arc motion speed, which is dependent, among others, on the electrodynamic force effecting this motion, influences the course of arc voltage, arcing time, and energy released in arc, so influences also the electrical endurance and reliability of a switching device. The analysis of arc motion speed makes it possible to evaluate contact materials, arc runners, and extinguishing chambers, and also approximately the switching capacity of an extinguishing system. Therefore, the great part of Chapter 3, and Chapter 4 of this monograph describe electrodynamic forces acting on the root and the column of an arc that bums between contacts and on arc runners. The given examples for calculation of electrodynamic forces and for simulation of arc motion agree with the results of experimental investigations carried out with use of an ultra-high-speed film camera. Chapter 5 presents the broad theoretical description of electrodynamic forces acting on an arc root on ferromagnetic plate of extinguishing chamber being different in shape, without and with a cut-out. The calculations of arc motion trajectory made by the mirror reflection method, and measurement results verifying these calculations, taken as examples from the literature, have been collated by the author with the results of his own calculations based on the finite-element and boundary-element methods. The author's research has shown that such arc stop finał places can exist that are different from those given in the literature. Chapter 6 illustrates the possibilities of practical application of theoretical considerations gi ven in the foregoing chapters. Chapter 7 covers the analysis of forces developed by DC and AC electromagnet drives broadly used on electrical apparatus. Considering methods for calculating electromagnets described in the literature, the example analyses are given carried out with the author's computer programs and the commercial ones. The results of computer simulating the operation of a selected AC electromagnet in relation to an angle, at which a coil supply voltage is switched on, are compared with mcasurement results derived with use of an automated computerized test system. The finał chapter of this monograph presents new, high-class constructional solutions of electrical apparatus developed by scientists and designers competently employing the existence of electrodynamic forces. Designing such apparatus becomes easier with use of the descriptions of electrodynamic forces which were earlier elaborated and afterwards suitably developed.