Patent GB-190520099-A (GB)
Title: Improvements in or relating to Electric Alternating Current Switches.
Inventor: CRAWLEY CHARLES WILLIAM SCOTT
Filed: 1905-10-04
Granted: 1906-10-04
Abstract: 20,099. Crawley, C. W. S. Oct. 4. Switches.-Sparking in switches-for alternating-current work is prevented by locking the switch in such a way that it can open or close only at or near the instant of minimum current or voltage. On the alternator shaft b, Fig. 1, or upon some shaft running in synchronism, sub-synchronism, or multi-synchronism therewith, is a. loosely-mounted contact c<1> separated from the shaft, by an insulator c<3>, and also a contact-arm b<3>, which once in every revolution makes contact with the contact c, which is connected through a galvanometer d or the like to one end of a resistance in the.main lead. If the contact b<4> be adjusted upon the shaft, a position can be found in which the galvanometer reads zero, i.e. that at the instant contact is made the cycle is at minimum potential or current. As shown in Figs. 2 and 3, the arm or base-plate a carrying the switch is pivoted upon the dynamo shaft b, and the contact c' is fixed on the sleeve a<1> by the setscrew c<4>, the arm b<4>, Fig. 1, being replaced by a stud b<4> mounted in the periphery of the spirallygrooved disk b<3>. The switch arm f is extended beyond its pivot f<1>, and. carries a pin f<4> which engages in the grooves in the disk so that the switch cannot be opened or closed except as the pin f<4> passes in or out through the channels b<7>, b<8>, and, if the parts are arranged so that this always happens as the contacts b<4>, c' come together, the switch can be open and closed only at the predetermined time arranged for when the contact-arm was adjusted. To ensure more sudden break, the arm f may be provided with a depending part f<8>, Fig. 9, so arranged as to make contact with the spring f<10> just before' the main switch opens ; as the main switch opens immediately afterwards, the spring< >f<10> carries the whole current for a short time, until the continued movement causes the spring to flick past the arm f<8>. Or the spring may be mounted on the extension and the rigid stud fixed to the frame, as shown in Fig. 10, which also shows a modification to avoid controlling a heavy main switch directly by the disk b<3>. In this case, the disk controls a small -bell-crank switch arm f<11> mounted on the same pivot as the main switch f and held closed by a catch f<7> against the spring f<2>. Immediately on the main switch being opened, the current is taken by the auxiliary switch, but continued movement causes the tail f<14> to release the catch f<7>, and thus allow the bell-crank switch to open at the predetermined instant. The off-set f<15> provides means for returning the switch again. If desired, the shaft of a motor running in synchronisms with the current to be broken may take the place of the main-shaft, but in this case it is preferable to fix the switch and, for adjustment, to revolve the stator; the motor circuit and the galvanometer circuit, or either of these, may be energized by one or more transformers, phase changes being allowed for when adjusting, and two galvanometers, as shown in Fig. 17, may be arranged with one galvanometer circuit energized by a transformer secondary so as to govern the make as well as the break ; or a single galvanometer with additional contacts in its circuit may be employed. Instead of the grooved disk, any equivalent device may be used ; for example, Fig. 20 shows a cam-wheel b<3> fixed to the dynamo shaft. On the main switch f being opened, the bar k and with it the swinging link k<3> are moved to the left, and the cam thereupon rocks the lever k<3> and off-set k<4> so as to move the sector f<11> step by step till the spring f<10> breaks circuit. The sector is held in position by a detent f<18>, until, on the returning of the switch f, the projection f<*1> releases it. The device may be used in combination with any automatic contact maker or breaker, and the' switch may be held closed or open by a catch and pulled into the other position by-a a spring, the catch being released by absence of current in the galvanometer circuit;