Patent GB-190812498-A (GB)
Title: Improvements relating to the Control of Electric Motors.
Filed: 1908-06-10
Granted: 1909-06-10
Abstract: 12,498. Mavor, H. A., and Mavor & Coulson. June 10. Motor control systems; switches.-Electric motors that require to be started, stopped, or reversed while subject to full load are so controlled that, prior to operating the controlling-switches to effect a change of running conditions, the current supplied to the motor or motors is reduced or stopped by varying the excitation of the generator. The controlling switches of the motor or motors cannot be operated until the generator field is sufficiently reduced, neither can the generator field be restored until the controlling switches have established the required connexions for the changed running conditions. The invention is specially applicable to a plant for marine propulsion having motors of the type described in Specification No. 8851, A.D. 1907, [A bridgment Class Dynamo-electric generators &c.], supplied from a generator arranged to be driven according to Specification No. 9950, A.D. 1907. The Specification describes its adaptation to three such pholyphase motors, the excitation of the turbo-alternator being varied by a controller driven by an auxiliary motor and arranged to interrupt the field circuit after the insertion of resistance in the manner described in Specification No. 28,040, A.D. 1907, [Abridgment Class Dynamo - electric generators &c.]. The controllers for the main motors are driven by separate auxiliary motors, and the circuits of the rheostat motor and of the main controller motors are interlocked in such a manner that, by the aid of multiple - way switches and circuit-breakers, the main controller motors are unable to operate until the generator feld circuit is broken, and only when all the main motor controllers have established the predetermined new connexions is the rheostat motor able to operate to close the generator field circuit and restore its excitation. The field of the turbo-alternator a is supplied by an exciter j, the electromotive force of which is governed by a rheostat k and controller o driven by an auxiliary motor q. The controller o moves always in a clockwise direction over the rheostat contacts, and carries two additional insulated bridging-pieces which co-operate with segments y, y<1>, y<2> and z, z<1>. The controllers x<4> of the main motors e are driven by auxiliary motors w. The four auxiliary motors are supplied with current through a switch i and bus-bars h. Hand-operated multiple-way switches u<1> co-operate with switches v connected with the controller spindles x<4> to determine the positions of the main motor controllers. Circuit-breakers u connected in series with the switches u<1>, v control the auxiliary motors by means of contacts r, s, t. In the Figure, the apparatus is shown in its position of rest. The operation of the system is as follows :-The order " stand "by engines" being given, the turbo-alternator a and exciter j are started. The exciter-field controller being in the position shown, the alternator field builds up. The switch i is next closed, sending current between the bus-bars h through switches 11<a>, 11 and relays u in parallel tb raise the circuitbreakers. The controllers x' are all in the 'off' position, and the turbo-alternator is fully excited. On the order "slow speed ahead," all the handswitches u<1> are placed on the contacts 12, opening the circuit of the relays u and closing a circuit between the bus - bars h through contacts s in parallel to segments y<1>, y, and the auxiliary motor q, which operates the controller o until it reaches the contact n, thus interrupting the exciter field circuit. In this position the circuit of the motor q is interrupted, current being diverted through segment y<2> to contacts t and motors w in parallel to operate the controllers x'. When these reach the position required, the switches v will engage with contacts 12<a> establishing a circuit between the busbars h through relays u and switches u<1>, v. The contacts at tare severed by the operation of the circuit - breakers, and the motors w stop. At the same time the contacts r are bridged. When each controller has established its required connexion and all the relays u have operated, the circuit of the motor q is again closed through the segment z (which is connected to the segment y), the segment z<1>, and contacts r in series. The controller o is thus operated to restore the generator excitation. The circuit of the motor q is automatically opened when the controller o reaches the full field position as shown.