Patent GB-190811512-A (GB)
Title: Improvements in or relating to Switch Arrangements for Starting Electric Motors.
Filed: 1908-05-27
Granted: 1908-11-12
Abstract: 11,512. Siemens Bros. Dynamo Works, Payne, B. G., and Schupp, E. May 27. Switches.-Switches, for use in starting electric motors, of the type having two arms one of which is moved to the fuil running position before the second, or rheostat arm proper, can begin to cut out resistance, are provided with an escapement device having an adjustable balance wheel to regulate the rate of cutting-out the resistance. The operating-device and the rheostat arm are mutually interlocked, so that the latter cannot move till the former is disengaged, and the operating - device cannot be re-engaged till the rheostat arm is back in the off position. The speed of operation of the rheostat arm may be made dependent on the current flowing in the armature circuit. As shown in Figs. 1 and 2, the main switch arm c is fast on an axle ex, which is biassed by a spiral spring c<a> towards the 'off' position. The rheostat arm c<1>, loose on the axle c<x>, is connected to the arm c by a spiral spring c<3>. The rheostat arm carries a pawl< >f<2>, which engages a ratchet-wheel f<1>, fast to an escapement-wheel f revoluble on the axle c<x>. The escapement - anchor g pivoted at g<1> has pallets g<x> so spaced as to give two steps-one short and the other long-on each of the contacts b of the resistance bx. A depending arm g' has a notch engaging a pin h<1> on a flange h connected with a balance wheel i. The Glance wheel is mounted between centres i<3> on the base and in a frame a<3>, and is. connected to one end of a spiral spring i<2>, the other end of which is fixed to the base a<1>. The movement of the rheostat arm is thus regulated in a series of steps governed by the oscillation of the balance wheel i produced by the escapement mechanism, but is free to move from the running' to the off' position by reason of the ratchet connexion f<2>, f <1>. The main switch arm is operated through a sliding sleeve d<3> having a crank d<10> and a flange d9 carrying screw pins d<8>. This sleeve is mounted in a bush d<4>, clamped in a frame a<2> by a flange d<6> co-operating with a nut d<5>. A hand-wheel d engages the screw pins d<8>, and normally occupies the dotted position shown in Fig. 2. A yoke d<7> embraces the sleeve d<3> beneath the flange d<5>, and carries pins e, e<1> projecting through the frame a<2>. Springs e<2> tend to press this yoke, and hence the operating-gear, into the dotted position. The arm c<1> carries a portion of a disk c<4> having radial edges. To start the motor, the hand-wheel d is first brought to the extreme left-hand position, and pressed into the full line position of Fig. 2. A pin d<1> in the crank d<10> then lies just behind the flange on the main arm c, and the pin e' just in front of the edge c<5> of the disk c<4>. The hand-wheel is rotated to the right, carrying the arm c with it, until an armature c<6> engages a no-volt release magnet k, the arm c<1> being meanwhile held against rotation by the engagement of the pin e' with the edge c<5> of the disk c<4>. Before the full running position of the arm is reached, however, a small switch l is operated by contact with the arm c, to close the circuit of the motor field through contacts l<1>, l<1> and the no-volt magnet k. The latter, being energized, then holds the arm c. The switch l is also held against the action of the spring l<x> by the arm c. The hand-wheel is then released, removing the stop pin e', and the arm c', under the tension of the spring c<3>, begins to cut out resistance from the armature circuit in the usual way, its speed being governed through the escapement mechanism. After its first movement, thedisk c<4> comes under the pin e', and the handwheel is thus rendered inoperative, leaving the control of the motor subject solely to the governing-mechanism. The circuit of the motor armature may be interrupted by lifting the armature m<1> of the overload magnet m by hand, thus shortcircuiting the magnet' k at the contacts m' and allowing the arms c, c' to return to the off position under the influence of the spring c<2>. The switch l is immediately returned, to its initial position by means of the spring l<x>, closing a discharge circuit for the motor field through an extra resistance c<7>, rheostat b<x>, and the motor armature. The starting-switch may be operated from a distance, as by a solenoid the core of which may act upon a chain wound round a pulley on the spindle c<x>. The speed of the rheostat arm c<1> is dependent on the weight of the fly-wheel i and the tension of the spring i<2>, either of which may be varied to effect an adjustment. Figs. 2 and 3 show a further method. A stop pin is provided on the fly-wheel, and a flat spring il is adjustably clamned to the frame a<3>, as shown, to serve as a buffer. According to the position of this spring, the amplitude and hence the speed of oscillation of the fly-wheel may be varied. The current in the armature circuit may be used to regulate the rate of cutting out the resistance b<x>. A solenoid r, Fig. 5, is connected on the armature circuit, and a core r<1> suspended therein by springs r<3> from a fixed bracket r'. A spring finger r6, on the head of the core rod rx; will then take up different positions dependent on the intensity of the armature current. Adjustment of the collar r' on the rod rx determines the actual position for a given current. In place of the stop pin j mentioned above, a number of stepped notches r<5> may be provided for the finger r<6> to engage. This arrangement results in an increase of amplitude of fly-wheel swing as the current in the armature circuit' increases, so increasing the interval between successive steps of the rheostat arm c<t>. The device may be arranged to act as an overload release, by providing contacts to short-circuit the magnet k should the core r<1> be drawn down beyond a given limit.