No. 2, 2002


Ludek Schreier : Zero sequence in stator currents of induction machines, pp.119-138

Origin of the zero-sequence component in stator currents of the tree-phase electric machines is investigated. This component rises if the neutral of the stator winding is connected with the supply voltage. It is shown that the zero-sequence component causes not only a leakage magnetic flux, but also a flux passing through the air gap of the machine. Depending on the rotor winding configuration, unwanted torque pulsations and additional losses may arise. The theoretical conclusions are compared with results of experimental measurement.

Viktor Pekarek : Emission of electromagnetic waves through medium of matter waves, correlation between wavelengths and temperatures in radiation series of hydrogen, pp.139-149

The matter waves emitted by electrons of hydrogen atoms interfere with one another in an interatomic vacuum, giving rise to interference surges at frequencies identical with the frequencies of the hydrogen spectrum. In addition to the surges interpreted as quanta of energy Elight, there appear by-products of the interference, regarded as energy Eheat. On summing up the two components, the energy Etotal culminates at points displaced across the hydrogen spectrum in terms of the Wien Law. Associated with the energy maxima are the ratios Elight/Etotal = 0.66, recalling the well-known ratio R/Cv = 0.66, typical for a maximum conversion of thermal energy into mechanical work in an ideal gas. The affinity between gas thermodynamics and thermodynamics of radiation allows constructing the formula Elight/Etotal = 1 - 4(lT)2 that yields a complete correlation between the wavelengths and temperatures in the hydrogen spectrum. Inserting the ratio 0.66, the formula applies to the Wien constant lT = 0.288675 conjoint with maximum energy transfers in radiation processes. New aspects of the Wien Displacement Law are discussed.

Karel Zeman, Jiri Cibulka : Dynamic properties of traction drive with induction motor in transient regime consequent on interruption of energy supply, pp.151-163

The behaviour of a traction drive with an induction motor and voltage converter is analysed after a short-term interruption of energy supply. Special attention is devoted to the case when a generatoric run of the motor is used to charge up a converter capacitor, to avoid interrupting the working regime.

Ales Tondl : Three-mass self-excited systems with parametric excitation, pp.165-176

Two three-mass systems self-excited, e.g. by flow, are analysed. The self-excited vibration is quenched by means of parametric excitation using the spring stiffness variation. This contribution represents the first step to the analysis where the conditions for a full vibration quenching are sought. It is shown that for these systems two intervals of parametric excitation frequency can exist where the quenching effect can be achieved.

Leslaw Topor-Kaminski, Marian Pasko : Full n-terminal OTA with n-CCII, pp.177-187

Conception of realisation of n-terminal OTA using n CCII+, has been presented. The examples of FnTOTA applications for modelling controlled sources of multiterminal voltage and current operational amplifiers, as well as multiterminal current conveyor, have been given. Basing on FnTOTA, resistanceless circuit playing role of amplifier or potential divider, has been prepared. Its simulation in SPICE using the models of AD844 operational amplifiers with current feedback has been performed.

Josef Mrazek : Physics of very long air sparks and the lightning discharges, pp.189-204

The paper deals with physical processes in the discharge paths of very long air gaps and various kinds of lightning. The first chapters concern the ways of ionising of the discharge path and the conditions of maintaining of it in the ionised state. There are analysed the two most important forms of transition of the impact ionisation by particular electrons to the collective mechanism of ionisation by the hot electron gas. They are the initiation of the discharge in a divergent electric field and in a convergent electric field. The principles of the forming and keeping alive of the discharge channel are discussed as a co-operation of the elementary events, which ensure the balance of the system. A special attention is paid to the self-regulation of the channel by the changes of the space charge. There are given examples of practical application of the theoretical considerations. The theoretical conclusions are compared with the experimental work. The presented results can help to solve technical problems of extremely long gaps and of the lightning protection.

Nikolaos Athanasiadis : An innovative firing technique for a facts controller, pp.205-215

An innovative firing technique is used in this paper to simulate a common FACTS controller, the Static Var Compensator. The validation of the firing technique used in the paper demonstrates the effectiveness of the controller. The firing method is capable of establishing accurate firing similar to using the Phase Locked Loop method; consequently it can be used as an alternative to this method for the particular FACTS controller.

Lubomir Kocanda : Theoretical analysis of soft impact oscillator periodic motions with small number of impacts in the motion period, pp.217-228

Single degree of freedom (SDOF) system with piecewise constant characteristics in stiffness and viscous damping (Kelvin-Voigt model) is analysed. A mass vibrating across the boundary between media with different mechanical properties is excited by harmonic force. Analytically derived set of transcendental equations is solved by the quasi-Newton method. A stable crossing of a grazing boundary and existence of two stable periodic motion regimes is confirmed. Presented results for basic stable periodic motion with one impact in a motion period obtained by analytical solution and numerical simulations are in a good agreement.