Unsymmetrical short circuits on water-wheel generators under capacitive loading

WATER-WHEEL GENERATORS without damper windings under capacitive load may have abnormally high voltages developed across their terminals at limes of unsymmetrical short circuits. These voltages are due to 2 causes. First, the difference in permeance of the magnetic circuit in the direct and quadrature axes produces, under unsymmetrical short circuits, distorted voltages which have high peak values even if there is no capacitance connected to the machine. Second, the capacitance of the line and the reactance of the machine resonate or partially resonate and produce still greater distortion of the voltages on the sound phase. The phenomenon associated with single-phase short circuits with no connected capacitive load, has been analyzed by Doherty and Nickle.
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The present paper is concerned with the effect of the capacitive load and an analysis of the factors involved in this phenomenon. Consideration is given to the system conditions under which these harmful voltages may arise and the remedial measures which may be applied for their elimination.