A method of calculating current-limiter and fuse-clearing times in A-C systems

When a fault occurs on an aircraft a-c system with voltage-regulated alternators, the short-circuit current goes through a transient period depending on the alternator-regulator characteristic. This transient period has been found to vary from several milliseconds to perhaps 300 milliseconds and, consequently, may have a considerable effect on fuse or current-limiter clearing times. This paper presents a method of calculating current-limiter or fuse-clearing times which includes the effect of this transient period. Results of calculations from this method are compared with laboratory tests demonstrating that the method has a reasonable degree of accuracy.