Monograph 14

The analysis of propagation of the current and power of higher harmonics in the electrical net that contains non-linear receivers

Firczyk W.


The primary objective of the paper is to present an analysis of propagation of currents and powers of higher harmonics in the electrical net, to which linear and non-linear receivers are attached. The non- linear receiver is a current source of higher harmonics. Higher harmonics from this source are flowing to the electrical net. The propagation of higher harmonic currents, generated in non-linear receivers, depends on the powers of specific receivers supplied from an analysed system (linear and non-linear receivers) and also on the impedance of the electric line.
The currents of higher harmonics that flow in the line that supplies the non-linear receiver are not equal to currents of higher harmonics of this receiver's current source (for the real conditions). In some cases the harmonics of the same order, generated in different sources, can neutralise each other. The propagation of higher harmonics' currents is connected to the propagation of active powers of these harmonics. The analysis of the powers in an electric circuitry, that contains a non-linear receiver supplied by the source with nonsinusoidal electromotive power and inner impedance (different from "0"), presents that the active power delivered to the receiver from the source is related to the first harmonic. This power is being converted inside the receiver partly into effective work and in part is used for creating the current sources of higher harmonics. The higher is the level of nonlinearity the larger part of the power (that is delivered to the non-linear receiver), is used for creating the current sources of higher harmonics (the effective power will be decreased). In the event that there is more than one non-linear receiver, the distribution of the active powers of higher harmonics is very complicated. The same as in the example of currents, the distribution depends on the powers of the receivers, the level of their nonlinearity and the impedance of the electric line. The dissertation is also an analysis of various methods of adding up the currents of specific harmonics and the total currents flowing through the main points of the net. The currents of individual harmonics-their effective values were added using geometric and algebraic methods.
Also their temporary values were totalled  and their effective values were calculated. Calculating the values of the currents was processed in conjunction with the use of the simplified formula presented in the references. In all the cases the results were differing. It seems probable that for non-linear receivers of the same character, we can use the geometric method to calculate the approximate value of the current. The geometric method has to take into consideration all the harmonics or the adding method according to the simplified.