US1685931A - Accelerating relay - Google Patents

Description

Oct. 2, 1928. 1,685,931

N; K. ANDERSEN ACCELERATING RELAY Filed Nov. 10. 1922 INVENTOR MW Niels K Andersen BY W ATTORNEY WITNESSES:

Patented Oct. 2, 1928.

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P NNSYLVANIA, Assmnon r winsrrirenous: nnzc'rnrce unxuracrnnms COMPANY; A CORPORATION. or PENNSYL- and apparatus theretorand'it particular relationto the .aeceleratibn and speed control I of electric motors:

' The object of my invention is provide a yst m and apparatus foijprevennng motors from drawing excessiv current under various operating conditions.

My invention comprises a relay having a rotatable armature and a field-magnet winding forfcontrolling thearmatuie in accordance with certaincurrent conditions obtain 1 ing in the circuit of the motor toebe (36ntrolled. The relay armature is] rovided with movable contact members which operate successively to control portions of the motorstaiting' resistor, The relay fieldmagnet windin is normally energized from a. source that a so supplies, e ergy. to the motor. When the motor'is' connected in circuit, the field-magnet winding of the relay is auto matically subjected to the drop in otential across the starting resistor and, as t e motor is accelerated, there are corresponding successire reductions in the potential. across the starting resistor permitting a stepby-step operation of the accelerating relay. The relayissu cientlyisensitivetoensure that the movable contact members shall be automati cally reset step-by-step upon the reinsertion of corresponding portions of the starting resistor when the latter is usedjfor obtaining speed control. The relay is, therefore, al-

ways in operative condition for protecting the motor againstexcessive currents.

My invention will he described in connection with the accompanying" drawing in which, 2 I I Figure 1 is a diagrammatic view of circuits and apparatus embed ingmy invention, and Figs. 2 and 3 are e evational views of the accelerating relay'employed in the system of 'mounted upon the shaft 3 but are normally free to move independently thereof. Ad-

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m, 1 a. 7 arm madam.

just able springs 11 are provided for biasing contact members 8, 9 and 10, respectively, toward stationary contact members 12, 13 aildl l. y p

' 'When field-magnet winding 4 is energized armature 2 rotates in a clock-wise direction, causing staggered fingers 5, 6 and 7 to successively engage contact members-8, 9 and 10,'whereby the latter members are actuated I to the left, (open position) as viewedin Fig.

2, against theaction or the springs 11. When the winding 4 is fully energized, the armature 2 rotates in a clockwise direction until it engagesa stop member 15. It will be evident thatthe position of the armature 2 willdepend upon the degree of excitation. of the winding4 and, when the excitation of this winding is gradually reduced, the contact members 10, 9 and 8 are successively moved by springs 11 to engage stationary contact members 14, 13 and 12,.r'espectively. 7

Referring now to Fig: 1, a motor lt having an armature 17 and shunt, and series fieldmagnet windings 18 and 19, respectively, may be connected a source of supply comprising conductors 20-and 21 through a line switch 22. The motor is controlled in the usual manner by means of a starting and regulating resistor 2,3. The field-magnet winding or coil 4; of i the accelerating relay is connected across line conductors 20 and 21 through a resistor 24;. Aresistor 25 connects one terminal ofzthe coil 4 to a point between the armature 17 and starting resistor 23. It will be noted that ,a lVheat'stone-bridge connection is formed resistor 25 with respect to armature17, resistors 23 and 24 and coil 4. y

The relay contact members 8, 9, 10, 12, '13

andlt {are illustrated as controlling sections of the resistor 23. In some instances, it will be preferable to employ shunt contactorsfor controlling the resistor 23, these contactors being controlled by the relay 1. The operation of the system is the same, however, in either case and, for convenience, I have assumed the simplest diagram of connections.

When current is supplied to conductors 20 and 21, coil 4 is fully energized througl1 resistor 24 to cause relay 1 to assume its illustrated inoperatve position. The motor 16 is started by closing line switch 22, and the initial rush of starting current traversing resistor 23 produces a voltage drop across this resistor which is, of course, equal to" the line voltage minus the voltage drop in armature l7 and series winding 19. The coil 4, which is connected through resistor 25 to the terminals of resistor 2, is therefore, energized in accordance with the voltage drop across resistor 23. As motor 16 accelerates, the armature 17 generates a counter-electromotive force opposed to the impressed voltage, as is well understood, and, therefore, the voltage across resistor 23 and coil 4 is correspondingly decreased.

Resistor 25 is preferably of much lower ohmic value than resistor 2t, and, therefore, the coil l is subject primarily to the voltage of resistor 23. Resistors 24; and 25 are subject to the connter-electromotive force of the armature 1'7 and, since coil 4 is connected to a point between these resistors, it is also affected by the counter-electromotive force of the armature.

As the motor further accelerates, contact members 10, 9 and 8 successively close to shunt resistor 23, as previously explained. With resistor 23 removed from circuit, coil 4; is subject to the voltage across resistor 25. This resistor is chosen of such value as to maintain a certain ratio between the initial and the final voltage impressed on the coil 4, and it is thereby possible to approximately equalize the steps of voltage across this coil, corresponding to each step of control regulating the resistor 23.

In the operation of the relay 1, each of the movable contact members 8, 9 and 10 is balanced against the corresponding spring 11 at the instant that the movable contact member in question engages one of the stationary members 12, 13 and 14, so that only a relatively small increase in motor current is necessary to cause the relay to retrieve stepby-step. This sensitive feature of the relay is of particular value when employed with controllers for the purpose of effecting speed control, using resistor 23 as a regulating resistor. In such a system, it will be understood that a multipoint master switch (not shown) controls each step of acceleration and deceleration.

My invention, while utilizing the currentlimit principle of control, is of such character that, on account of employing a shunt winding in preference to a series winding, the same relay may be utilized without change for a large number of motors of different sizes and characteristics. The relay coil 4 need not be connected across the entire starting resistor but should be connected across such a portion as to provide proper operating characteristics in accordance with the size of the motor and the service required thereof.

In some prior forms of relays, difficulty has been experienced in causing the relay to retrieve properly when speed regulation is required. In other words, there was too great a difference between the closing and opening values of the respective relay contact members. In my system, the field strength of a relay may be nicely balanced against the operating springs controlling the contact members.

While I have illustrated my invention in connection with a direct-current system of control, it is also applicable to, and may be similarly connected for use in, alternatingcurrent circuits.

I claim as my invention:

1. An accelerating relay comprising a rotatable armature and a shaft therefor, a plurality of fingers mounted radially on the shaft in staggered relation to each other, movable contact members operated by the fingers, means for separately biasing each of said fingers 'to a closed circuit position, a fieldmagnet winding for biasing said armature to actuate said fingers to an open circuit position.

2. In a switch mechanism, the combination with means for creating a variable magnetic field, of a plurality of switch members, a rotatable armature adapted to be controlled by the force of said magnetic field and to retain said switch members in their inoperative positions, and individual means associated with each of said switch members for succes sively actuating said members to their respective operative positions in opposition to the variable force of said field.

In testimony whereof, I have hereunto subscribed my name this 4th day of November, 1922.

NIELS K. ANDERSEN.

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