Ans. For pressures above 1,100 volts.
Ques. Describe the operating mechanism of a remote control, hand, and electrically operated switch.
Ans. For hand operation, the mechanism between the operating lever and switch proper, consists simply of a system of links and bell cranks. Various shapes of bell crank are used, to permit change in direction or position of the force applied to operate the switch.
Fig. 2,230.—Pacific oil switch with solenoid control, designed for 60,000 and 70,000 volt installations; it is capable of handling a 25,000 kw. generating station. The break is horizontal, made by the rotation of a flat member edgewise through the oil. The solenoid, at its extreme outer position, has a free start before commencing to move the control parts of the switch. As it approaches the extreme inner position, where the opening spring and the contacts begin to offer the greatest resistance, the magnetic action is, of course, most powerful, and the leverage by which it is applied moves to an increasing radius, by means of rollers working in the curved slots of the control shaft levers. These curved slots and rollers have the additional advantage of making the opening action very free and smooth. The tripping coil does not act on the latch directly, but gives a hammer blow that is positive. The latch proper is a roller having a powerful hold and easy release. Current can not be left on either the closing or opening coils, as they are automatically cut out by the movement of the switch.
Ques. Name two classes of electrically operated remote control switch.
Ans. Those operated by solenoids, and those operated by motors.
The solenoid type are closed by the action of a plunger solenoid, and opened either by another solenoid called a "tripping coil" or by gravity. Some examples of remote control are shown in the accompanying illustrations.