Negative-sequence currents for line-to-line faults

THE RECENT REVISION of the American Standards Association Standard for Rotating Electrical Machinery, C50, short-circuit clause specifies requirements for synchronous generators during 3-phase, line-to-ground, and line-to-line short circuits. A generator operating at rated kilovolt-amperes and power factor, with fixed excitation at 5-per-cent overvoltage, must be able to withstand a 3-phase short circuit at its terminals. For line-to-ground short circuits, the maximum instantaneous current must not exceed that obtained under a 3-phase short circuit.