US735151A - Centrifugal starting-switch for induction-motors. - Google Patents

Description

H. G. REIST.

OENTRIFUGAL STARTING SWITCH FOR INDUGTION MOTORS. APPLICATION FILED MAY 26, 1902.

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No. 735,151. PATENTED AUG. 4, 1903. H. G. REIST.

4 GENI'RIFUGAL STARTING SWITCH FOR INDUCTION MOTORS.

APPLICATION FILED MAY 26 1902.

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WiTHEssEs. I INVEHTOR V HENRY .REisT.

W BY ATTY.

UNITED STATES Patented August 4, 190

PATENT OFFICE.

HENRY e. REIST, OF sO HENE'oTADv, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC OOMPANY, A CORPORATION OF EW YORK.

CENTRIFUGAL STARTING-SWITCH FOR INDUCTION-MOTORS.

SPEGIFICATION forming part of Letters Patent No. 735,151, dated August 4, 1903.

Application filed May 26,1902. Serialllo. 108,920. (.Nomodel.)

T0 aZZ whom it may concern..-

Be it known that I, HENRY G. REIsT, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Centrifugal Starting- Switches for Induction-Motors, of which the following is a specification.

My invention relates to motor-starting devices, and more particularly to starting devices for alternating-current electric motors in which the secondary member is provided with a closed-circuited'induced winding having a resistance in circuit with the said winding for the purpose of producing a good start-.

ing torque, the said resistance being gradually cut out of circuit step by step as the speed increases.

The object of my invention is to provide such a motor with an efficient centrifugallyactuated starting device which will constitute an improvement on the device shown and described in the patent to L. Bell, No. 505,505, granted September26, 1893. To this end I employ in the preferred embodiment of my invention a plurality of independent switches mounted on the secondary member of the motor and arranged to be actuated independently and at difierent times by centrifugal force for the purpose of cutting out the starting resistance step by step as the speed increases.

My invention further comprises a novel switch construction, which will be more fully explained hereinafter and set forth in the claims.

In the accompanying drawings, Figure 1 is an elevation of a motor to which my invention has been applied, the casing of said motor being partially broken away. Fig. 2 is an end view of the armature or rotor of said motor, on a larger scale, showing the manner in which the starting device is mounted thereon. Fig. 3 is a perspective detail View of one windingw is mounted; C, the armature-shaft, and S the spider which supports the armature-ring, the said spider being keyed to the said shaft at 70. Fastened to the spider S by means of the bolts g is an additional frame H, upon which the starting-switches D, D, D, and D are mounted. Carried within the armature and bolted to the ringB thereof by means of the bolts b are the resistance-grids 6o 0", which are electrically connected together and to the fixed contact-pieces n, 'n, and n of the starting-switches by means of the links m, m, and m and also the connections 1), as shown in Fig. 2. In the three-phase winding shown there are three each of contact-pieces n, n, and 71?, those in each set being mounted one behind the other, as shown in Fig. 3, and fastened to the frame H by means of bolts g. Attached to or integrally formed with the contact-pieces n, n, and 91. respectively, are the switch-contact faces f, f, and f with which the movable elements of the switches D,D,D and D coact. Since these movable elements are similarly constructed, the construction of 75 but one will be described-namely, that of switch D. In Fig. 2 I have shown said switch in its normally open position against the stop d, which is carried by the frame H, while in Fig. 3 Ihave shown in a perspective view the said switch in its closed position. Pivoted on the pin 10 which is carried by the frame H, is

a bell-crank lever, the arms of which make an obtuse angle with each other. One arm, t,

of said bell-crank lever carries the switchbrushes or main and auxiliary contact-makers a and a, which coact with the relatively fixed contacts f. Connected by means of the pin p 'to the other arm, t, of the bell-crank lever is a spring 6, which is fastened at its opposite end by means of an adjustable screwand-nut connection to the relatively fixed stud p, which projects from the frame H. The adjustable connection between the spring 6 and the stud p is clearly shown in Fig. 3 and comprises a nut 0, to which the spring is fastened, and ascre'w'or bolt 0, which operates in both the stud p and the nut o, no thread being cut on the part of the screw which passes through stud p. The tension on the luu spring is changed by this means, and thereby the force required to move said switch from its normally open position may be varied. The auxiliary contact-pieces a, carrying the carbon button a are made of resilient material and are mounted so as to make contact with the relatively fixed contact-facesfprior to and to break contact later than the main contact-brushes a. The brushes a, Fig. 3, are formed of laminated conducting-strips removably mounted on the outer end of the arm t, it being understood that the arm if, on which the brushes a and the removable auxiliary contact-pieces a are mounted, is formed of one piece of conducting material, so that when the brushes a or a are in contact with the contact-faces f a short circuit between these faces is made. The switches D and D have separate studs p for the springs 6, While the switches D and D use the same stud p for their springs e; but this variation in construction doesnot affect the operations of either of said switches.

In Fig. 4 I have shown diagrammatically the electrical connections between the arma tore-windings w, (which are here shown in Y connection,) the resistances r, and the switchcontact faces f, f, and f respectively. As will be seen, the resistances are respectively connected in circuit with the windings of each phase and have their outer ends grounded on the armature-spider or connected together in some other way. The resistances are divided into sections, and each section is connected with its corresponding contact-face in one of the sets f, f, or f Normally the winding w is close-circuited through its Y connection at one end and through the resistances r and the ground connections at the other end. If a short-circuiting switch is placed across the contact-faces f part of the resistance r in each phase will be short-circuited. If a switch is placed across the contacts f, more of the resistances are short-circuited, and if a switch is closed across either of the sets of contacts f the entire resistance will be shortcircuited and the armature-windings closecircuited through the contacts f and said switch.

In operation under normal conditions when the motor is at rest the switches D, D, D and D are open and the movable member of the switches rest against the stops or studs d. When the main-line switch is closed, the rotary field produced in the stator induces current in the rotor, the said current flowing through the windings w, which are connected together in Y connection at one end and the resistance r and ground connection at the other end. As the speed increases the centrifugal force acting on the movable members of the starting switches becomes sufficiently great to overcome the tension on the spring e of the switch D which has been previously set to operate at a predetermined speed. As the arm t, carrying the contact-makers a and Ct, moves outward the resisting force of the spring 2 becomes relatively less and less, due

to the peculiar manner in which the switch is mountedthat is, consideringa line drawn through the stud p and the pin 19 anda second line drawn through the pins 10 and 12 As these lines approach parallelism the turning moment about the pin 19 due to the tension of the spring 6 is gradually reduced. Since the centrifugal force acting on the arm t and contact-makers a and a remains practically constant during the movement of said switch, it will be seen that the switch will close with a snap action against the relatively fixed contact-faces f and will remain closed even though the speed of the rotor drops considerably-that is to say, it requires less force to maintain said switch in its closed position than is required to start it from its open position with the arm 25 resting against the stop d. When the switch D has been closed,.equal amounts of the resistances r in each phase are short circuited and the rotor increases in speed. When the speed at which the switch D has been set to operate has been reached, the said switch closes suddenly, more resistance is short-circuited, and the rotor is further increased in speed. When a predetermined higher speed is reached, the switches D and D operate simultaneously, thereby short circuiting all the resistances r and allowing the rotor to rise to its maximum speed.

By the use of switches of the construction herein disclosed the motor will run with the resistance all out out, even under an overload sufficient to cause the'speed to drop materially.

One switch of the proper size to carry the current which is induced in the winding to when the motor is running at normal working speed would be sufficient to perform the function which is now performed by the switches D and D acting simultaneously. Two switches, however, have been used in the modification shown, since it allows a more symmetrical and evenly-balanced construction and allows the switch to be made lighter and more compact.

While I have shown and described my invention as applied to a three-phase induction-motor using four switches, I do not limit myself to any particular number of phases or any particular number of switches or to an alternating-current motor.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

1. In a motor-starting device, a plurality of switches operatively connected with the rotatable member, and means for adjusting said switches so that they will operate independently and successively as the speed of the rotatable member increases.

2. In a motor-starting device, a plurality of centrifugally-actuated switches carried by the rotary member of the motor and adjusted to operate successively as the speed of said member increases.

3. In an electric motor having a closed-circuited armature-winding, the combination with resistance in circuit with said winding, said resistance being divided into sections,

of a plurality of independent switches operatively connected with the armature, said switches being independently adjustable to operate automatically at any predetermined speed, and adapted to short-circuit the successive sections of said resistance as the speed increases.

4. In a multiphase electric motor having a closed-circuited armature-winding, the combination with resistance in each phase of said Winding, said resistance being divided into sections, of independent centrifugally-actuated switches operatively connected with the armature, said switches being adjusted to operate independently to short-circuit corresponding sections of said resistance in the several phases simultaneously at certain predetermined speeds and the successive sections of said resistances as the speed increases.

5. In a multiphase electric motor having a closed-circuited armature-Winding, the combination with resistance in each phase of said winding, of a single switch operatively connected with the armature and adapted to opcrate automatically to short-circuit the reoperatively connected with the armature and 1 adapted to short-circuit the resistance in the several phases simultaneously when a certain speed is reached, the said switch being so constructed and arranged that a greater force is required to start the switch from its normally open position than is required to maintain the switch in its closed position, and means for adjusting said switch so that it will operate at a different speed.

In witness whereof I have hereunto set my hand this 23d day of May, 1902.

HENRY REIST.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

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