Fig. 2,241.—Quick break fuse. The fuse wire is connected between the fixed terminal A and the movable arm B, and is held under tension by the spring which exerts pressure on the movable arm in a direction tending to separate A and B. In operation, when the fuse blows, the movable arm quickly moves to the position B´, thus attenuating the arc and accelerating its extinguishment.
Ques. What metal is used for fuse wires?
Ans. Various metals. Ordinary fuse wire is made of lead or an alloy of lead and tin.
Ques. What is the objection to aluminum?
Ans. It becomes coated with oxide or sulphide, which acts as a tube tending to retain the metal inside and prevent rupture.
Ques. What is the objection to copper?
Ans. Its high fusing point.
Current Limiting Inductances.—The great increase in capacity of power stations, for supplying the demands of densely populated centers and large manufacturing districts, together with the decrease in the reactance of modern alternators and transformers due to improvement in design to obtain better regulation, has presented a problem in apparatus protection not contemplated in the earlier days of alternating current distribution. This problem is entirely separate and distinct from that of eliminating the tendency toward short circuit, incident to the high voltages now common in transmission lines. It accepts that all short circuits must occasionally occur and considers only the protection of the connected apparatus against the mechanical forces due to the magnetic stresses of such enormous currents.