Reactive power in circuits with sampled resistive load

Milan Stork – Daniel Mayer

   The process of power transmission lines, from source to load is a well-known, if the voltages and currents vary harmonically. With the lines is transmitted active power that is dissipated in load (this power exits from the system) and reactive power (this power oscillates between the source and the load). Note that it would be more appropriate designation the external power and the internal power. Such systems are known as cyclo-dissipative. The active power is dissipated in the load and the reactive power oscillates between the source and the load. Physically, reactive power is delivered to reactive elements of load. Transmitting reactive power increases Joule's losses and voltage drops on lines. Reactive power can be compensated in a known manner. Compensation reduces the effective value of the current in the line. To the case of periodic but non-sinusoidal voltages and currents has been devoted many publications, conferences, etc. during the past 100 years. But despite much effort, this problem has not yet been fully solved. In the present article, we show that in a system with a harmonic source of voltage even in the case of a linear pure resistive load a reactive power can be generated and can be compensated. A necessary, but not sufficient, condition is that the resistive load is time-varying. The presented study deals with a periodically sampled resistive load.

Keywords: reactive power, non-sinusoidal voltages, time-varying resistive load

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