GB389107A - A method of limiting interruptions of service in electrical transmission and distribution systems, and a construction of fuses therefor - Google Patents

Abstract

389,107. Protective cut-out arrangements. SCHWEITZER & CONRAD, Inc., 4435, Ravenswood Avenue, Chicago, U.S.A. -(Assignees of Conrad, N. J.; 1099, Pelham Road, Winnetka, Illinois, U.S.A.) June 10, 1931, No. 10612. Convention date, July 24, 1930. [Class 38 (v).] A distribution system, such as shown in Fig. 1, having circuits 3, 5, 7, 9 of .successively decreasing power rating is protected by fuses 12 .. 16 which are so correlated as regards their time-overload characteristic that upon the occurrence of a fault those fuses further from the fault will not operate before periods of time greater than required to permit operation of fuses nearer to the fault. In some cases there may also be automatic circuitbreakers also included in the system, for example a step-down transformer may have a fuse located on its high tension side-and a circuit-breaker on the low tension side, in such cases the time-overload characteristic of the fuses is also correlated to that of the circuit breakers. The time-overload characteristic of the.fuse is controlled by varying the length of the fusible element while maintaining the required rated current carrying capacity by appropriate choice of cross-section. In addition, the characteristic may be varied by complete or partial submergence of the element in carbon tetrachloride or granulated cork. The fuses require to be such that when fusion starts, the arc should be extinguished before other fuses start to operate. Several forms of fuses are described, all generally similar to that shown in Fig. 4. A glass sleeve 38 has a ferrule 36 closed by a cap 39, and supports through a spider 74 a fuse terminal 40, to which a fusible link 43 and a strain wire 44 are attached. The lower ends of the link and wire are attached to a terminal 42 which is urged downwards by a spring 45, and supports by means of pins 62 a liquid director 58. A fibre tube 86 is supported by a ring 80 and is secured yieldingly therein by means such as screws 89 and washers 90. Upon rupture of the fuse, the liquid director and terminal 42 are drawn downwards and liquid is forced into .the tube 86. If the pressure generated is sufficient, it is released progressively by forcing off the cap 39, then the spider 74 and then ejecting the tube 86 by rupture of the washers 90. The size and shape of the tube 86 and director 58 may be varied, as also the manner of yieldingly securing the tube 86. The level of the liquid in the sleeve 38 may be adjusted, in some cases it completely surrounds the fusible element, and in some cases the tube 86 or the space above it may be packed with granulated cork.