Exciter Instability

1. The form of equation for exciter voltage and current is the same as the well known equation for the electric circuit containing resistance, inductance and capacity. Hence the same form of oscillations and transients are involved, the only difference being that in the present case the duration of the transients is much longer. 2. Instability may occur when the exciter is operating on the straight part of the saturation curve, if in addition some combination of the following conditions exists: (a) very low residual voltage-say 1 per cent or so. (b) a relatively large voltage drop in the armature. (c) large inductance in the load circuit, as always exists in the alternator field. (d) alternator transient of greater duration than the exciter transient. (e) excessive series field strength. 3. Instability may be classed, for convenience, under two headings: (a) voltage ``creeping,´´ and (b) ``double-energy´´ transients. The former may be caused by slight speed transients of the exciter; or by temperature transients causing corresponding resistance transients in the shunt field circuit; or by hysteresis effects which may be caused by small undulations in the exciter voltage. The ``double energy´´ transients, such as oscillations and reversal of excitation, may be initiated by a shock, such as a short circuit on the alternator, or sudden, relatively large change circuit in constants, for instance a large change in resistance in the shunt field circuit. 4. The exciter can be stabilized against voltage ``creeping,´´ (a) by special design to increase the angle ?? Fig.