Page:Elementary lectures on electric discharges, waves and impulses, and other transients (Steinmetz 1911).djvu/16

ELEMENTARY LECTURES ON ELECTRIC
DISCHARGES, WAVES AND IMPULSES,
AND OTHER TRANSIENTS.

LECTURE I.

NATURE AND ORIGIN OF TRANSIENTS.

1. Electrical engineering deals with electric energy and its flow, that is, electric power. Two classes of phenomena are met: permanent and transient, phenomena. To illustrate: Let G in Fig. 1 be a direct-current generator, which over a circuit A connects to a load L, as a number of lamps, etc. In the generator G, the line A, and the load L, a current $i$ flows, and voltages $e$

Fig. 1.

exist, which are constant, or permanent, as long as the conditions of the circuit remain the same. If we connect in some more lights, or disconnect some of the load, we get a different current $i'$, and possibly different voltages $e'$; but again $i'$ and $e'$ are permanent, that is, remain the same as long as the circuit remains unchanged.

Let, however, in Fig. 2, a direct-current generator G be connected to an electrostatic condenser C. Before the switch S is closed, and therefore also in the moment of closing the switch, no current flows in the line A. Immediately after the switch S is closed, current begins to flow over line A into the condenser C, charging this condenser up to the voltage given by the generator. When the