No abstract

A description is given of polyphase electric systems and their classification, with special reference to the three-phase system. The computation of a three-phase symmetrical system is described, with special reference to the power of the symmetrical system. Distortions of the sinusoidal form occurring in three-phase networks essentially change the characteristics of the network. It is shown how the phase and line values in networks with distorted sinusoids are computed. At the end, an example is given of how higher harmonics in a certain power supply network are computed by using software simulation, and another example from practice where the results of measuring higher harmonics in a 10 kV power distribution network are shown.

: SI unit of ampere is defined by means of magnetic force between two parallel conductors through which current flows. However, no mention is made of electric force in the opposite direction, which also exists between conductors. For that reason the existing definition is confusing for students, because it leads them to assume that by means of it ampere is also practically realized in laboratory. An analysis of forces shows that under certain conditions the electric force is much smaller than the magnetic force, but that fact still changes the physical picture of the propounded definition. The electric force can be compensated, which should be stated in textbooks when it comes to the definition of ampere, or else mention that ampere is practically realized by the current balance.

What the calculation of the mean and effective current (voltage) values of complex waveforms amounts to is dealing with integrals, and that poses some difficulties to most engineers. In today’s practice the problem makes itself manifest in a series of different waveforms, which makes the process of its solving all the more complicated. However, if the mean and effective values of typical forms are known, the process can be greatly simplified, and that’s what the present article is about.

In this work the dynamic properties of thyristors are considered. The property of the p-n barrier is briefl y reviewed and the principle of thyristor turn-on by means of a two-transistor model explained, along with an illustrative graphic interpretation of the basic equation. Described next are the dynamic properties of thyristors with a more detailed analysis of the du/dt and di/dt effects and the dynamic turn-on process.