US1849280A - Automatic starter for electric motors - Google Patents

Description

March 15, 1932. H. P. CHANDLER AUTOMATIC STARTER FOR ELECTRIC MOTORS Filed March 2. 1928 /2 INSULATION Inventor :1 luau/.4710

Atlorney HOME/P R CHANDLE Patented Mar; 15, 1932 UNITED STATES mum OFFICE- nomnn r. ciaANnLEn, or MANSFIELD, onro, assrenoa'ro arm: omo BRASS comm-1w,

or mnsmmn, onro, A conrona'rron or new mass! AUTOMATIC STARTER FOR FLECTRIC MOTORS Application filed unfit 2,

My invention relates to automatic starters for electric motors.

The main object of my invention is to provide a device having a resistanceelement which is inserted in the circuit between the electric motor and the source of power to protect the motor from a rush of excess current when current is first delivered to the motor while at rest, and which resistance will be automatically cut out when the motor has reached such speed as the current flowing through the motor and the load on the motor will permit, thereby connecting the motor directly to the source of-power.

Another object of my invention is to provide a device which will prevent connecting the motor directly to the source of power .for an appreciable time when first starting the motor except through a resistance.

Another object of myinvention is to pro-, vide a device which has initially inserted between the motor and the source of power a resistance of predetermined value and which it automatically cuts out after the starting current has flowed through the motor for a predetermined length of time.

Other objects of my invention will be disclosed herein and suggest themselves to those skilled in the art as I further describe my invention in detail'hereinafter.

My invention resides in the new and novel construction combination and relation ofv the various elements hereinafter described each other.

Fig. 2 is a plan view in detail of the thermally operated and magnetically held switch mechanism which forms apart of my invention and. shown as Tin Fig. 1.

Fig. 3 is a'side'view of Fig. 2. In starting an electric motor from rest tvery often happens that there is a load upon the motor considerably in excess of that nec-- 1928. Serial No. 258,528.

essary merely to rotate the armature of the.

motor and under such circumstances there is always aconsiderable delay in bringing the I motor up to a speed at which the back electromotive force is suflicient to check the initial excess flow of currentnecessary to start the motor under load, and if this starting current flows for a considerable time, it is very apt to injure or destroy'the motor.

For this reason it is common to insert in the circuit between the motor and the source of power some means whereby.,the initial flow of current through the motor' cannot exceed a predetermined amount but which means will be manually or automatically cut out of the circuit when the speed of the motor has and will accomplish other results hereinafter disclosed.

In the preferred embodiment of my invention I provide a self-contained device in which the various mechanisms, parts and elements are mounted upon insulated bases, which in turn are mounted within a frame and which frame is enclosed within a case.

The schematic arrangement of the various mechanisms and elements which I use in my invention and the relation to each other is shown in Fig. I, mounted within an enclosure and upon a suitable base 1 (see Fig. 2).. L and L represent the lines of the main source of power. The motor is shown at Mr My device comprises an automatic overload circuit breaker .C,a reslstor R and a thermally controlled electromagnetically operated and held switch T. l I a The circuit breakerC is shown of the single pole qi ick break automatic overload type having terminals 2.and 2 and a switch blade 3 with an operating handle 4. A coil 5 with a movable core 6 will automatically open the mechanism of the switch C. is connected to one side of the source of pow- 40 means of the conductor lead 21.

switch C when the current through the coil 5 exceeds a predetermined amount by sudden- 1y raising core 6 which impinges on the trip The terminal 2 er as, for instance L by the conductors 7 and 7' and is controlled, if desired, by the hand operated line switch 8.

The resistor R which has one end connected to the terminal post 9 has the other end norminal 2'. Mounted upon the U-shaped element 10 is an adjustable slider 12 by means of which the operation of the thermal ele- .ment 10 can be controlled as hereinafter ex plained. Secured to the free end of the ole-- ment 10 is an armature 18 under control of the electromagnet 14, operated by coil 15 which has one end connected to the terminal 9 by the conductor 16 and the other end connected by the conductor 16 to a fixed terminal 17, fixedly secured to the base or panel and spaced from the element 10. The spaced ends 18 and 19 of the element 10 are fixedly secured to the base and the opposite end is movable with the armature 13 thereon toward and away from the magnet 14, as the temperature of the element 10 changes. Fixedly secured to the element 10 by a spring element 20 projecting from the lower end of the element 10 (see Fig. 3) and movable therewith but insulated therefrom is a contact 20 adapted to engage with the contact 17 when the free end of the element 10 moves toward the magnet 14. The movable terminal 20 is connected to the terminal 19 by When the switch 8 is open and no current is flowing through the device, the lower end of the element 10 with the armature 13 secured thereto is at its remote distance from the magnet 14 and the terminal 20 is out of engagenientwith the terminal 17 with the elements 17 and 20 closer together than the elements 13 and 14. (See Fig. 3.)

The terminal 9 is connected by means of the conductor 22 to one of the armature poles and the other armature pole is connected to the main line L by the conductor 23 and the switch 8. One end of the motor field is connected to the conductor 23 by means of the conductor 24 and the other end of the field is connected to the terminal 19 by means of the conductor 25.

From the above description it will be seen that when the switch 8 is open and all other 0 elements are in their normal position that the circuit breaker C will be open and the connection between the fixed contact 17 and the movable contact 20 will also be open, but the resistor will be connected to the blade 5 of the circuitbreaker C through the elements 10, 11 and 5 and if the switch 8 is closed and the circuit breaker C is closed, then the current will flow from the source of power through the circuit breaker G, conductor 11, thermal element 10 and slider 12, resistor It and conductor 22 to the motor M and from there throughthe conductor 23 and switch 8 back to the main circuit. This will form a complete circuit through the various mechanisms and elements of the motor and the motor will start and gain speed, and the thermal element 10 will immediately begin to heat up andits temperature increase through a sustained current flow to the motor as the speed of the motor increases, and the armature 13 will gradually approach the magnet 14 and likewise the movable terminal 20 will approach the fixed terminal 17 until finally the sustained current flowing through the elements 10 and 12 will have caused the element 10 to distort sufiiciently to contact the terminals 17 and 20. Vhen this takes place the resistor R will be shunted as current will then flow from the terminal 19, through the conductor 21, terminals 20 and 17, conductor 16, coil 15, conductors 16 and 22, to the motor, thus by passing the resistor R and connecting the motor across the main lines L and L by a low resistance path.

Instantly upon the terminals 17 and 20 contacting, the coil 15 is energized and the magnet 14 magnetized and will act upon the armature 13, thereby quickly drawing the lower end of the element 10 to its final position, and with it the positive closing of the circuit through the terminals 17 and 20, and so long as current flows through the motor under normal operating conditions, the coil 15 is energized and the circuit through the terminals 17 and 20 positively held closed. If the current for any reason through the partsshould suddenly increase beyond a predetermined amount, then the coil 5 will be excessively energized and the plunger 6 will be suddenly raised and impinge upon the latch of the circuit breaker C, thereby releasing the blade 3 and automatically opening the circuit at the contact 2 and de-energizing the coil 15. o

The switch 8 may be eliminated if desired and the circuit breaker C depended upon for manually and automatically opening the circuit, depending upon its construction.

I employ the switch '1 shown in isometric view in Fig. 1 and in detail in Figs. 2 and 3 to control the shunting of the resistor R upon completing the circuit to the motor and to control the closing of said switch T and in order to bring about a delayed action thereof I employ a U-shapcd binietal thermal element 10.

In Figs. 2 and 3 I show a base 1, preferably oi insulated material, and upon which is mounted an insulated block 27. Upon the block 27 are mounted two metal standards the contact'terminal 20.

28 spaced and insulated from each other, and to which are secured the spaced ends 18-19 of the U-shaped thermal element 10 by'means of the nuts 29 and 30. To the free end of the bimetal element 10 is the soft iron armature 13 and also to the lower end ofthe member 10 is the spring conducting member 20', preferably hard copper or phosphor bronze, and the members 13 and 1 20' are insulated from the member b1};

means of the insulating members 31 and a .are held in relative position b the screws or rivets 32. On the free end 0 the member 20' is, a contact-block- 20 movable with the member 10. Mounted upon the block 27 is the contact terminal 17 which is engaged by By means of the adjustable slider 12, the movement of the member 10 is controlled and 20 also the elapsed time at which the resistor R is shunted; By moving the slider 12 away from the fixed terminals 18-19 there is a greater length of thermal element which is affected by the curtent flow therethrough and consequently the deflection for a given current becomes greater asthe slider'12 is moved farther from the fixed terminals.

The electroma'gnet 14 is provided with a core 33 and end pole members 34. The core 3 and 'poles are energized by means of the coil 15, one end of which is attached to the contact 17, the other end attached to the terminal 9. The terminal 20 is electrically connected to the terminal 29 ofthe thermal element by means of the flexible cable 21.

The spacing of- elements 17 and 20 is less than that of elements 13 and 34 and therefore 17 and 20 contact while 13 and 34 are still apart. As. soon .as 17 and 20 engage,

40 full operating current or greater flows between'elements l7 and 20 and sparking is liable to occur as element 17 engages element 20 under the very slow movement of the thermal element 10, but immediately upon a contact between elements 17 and 20 the coil 15 is energized and the elements 17 and 20 brought into strong engagement simultaneously with a sliding or wiping movement of the element 20 upon the element 17.

' o In the relay switch just described current flowing through; they thermal element 10 c'ausesthe same to heat up, moving the free end thereof toward the pole pieces 34 and the 'contact 20 toward .the, contact 17. As

soon as the contacts 17 and 20 engage, the jresistorR is short circuited and the coil 15 r is in series with the motor and, therefore,

becomes energized attracting the armature v13 toward the poles 3 1 and maintaining such' relation as long as the coil 15 is energized and'the motor operating under normal conditions, with the resistor cut out.

The pressure of the contact 20 against the 7 contact 17 due to the spring in the element 20 will tend to preventsticking of the conresistor R, will permit or approximate tacts 17 and 20 when the armature 13 is rerent will flow from the line L through the conductors 7 'and 7 and switch 8, if employed, to the contact 2, thence throu h the circuitbreaker, conductor 11.to terminal 19 of 'the thermal element 10. Then throu h thethermal element 10 and out through t e terminal 18 to and through the resistorR, then to the terminal 9. The current then passes through conductor 22 to the armature of the motor M and through the conductor 23, switch 8 and conductor 23' to the other power line L. Field connections for the motor are shown by the conductors 24 and 25.

T The resistance ofthe resistor R is such that it will prevent a rush of current throu h the motor M but will allow the speed of t e motor to become suflicient so that when the resistor R is shunted, the motor will not be subjected to a current flow which is liable to dama o it or operate the circuit breaker C; The t ermal element 10 is of such capacity and so adjusted that it is not aflected by the current flowing therethrough for some appreciabletime and which time is suflicient topermit the motor M to assume the maximum.

speed which the current, controlled b the y so. Thermal element 10 is of bimetal which is well known in'the art and the current passing through the legs of the thermal elementtend to heat the same in accordance with Ohms' law; I

-'It will be evident to those skilled in the art that the adjustment of the thermal element and the spacing of the movable contact from thefixed contact may be such that a given current could flow through the thermal element for an indefinite time without the contacts 17 and 20 engaging as the deflection of the thermal element would not be suflicient, i

but with other values of current, the contacts would engage after an appreciable time and.

the lapse of time would depend upon the 1 current value, therefore, the use-of the bimetal element permits of a very simple and reliable means of controlling the shunting out of theresistor R with respectito predetermined current and time values.

Fromthe foregoing description it will be seen that I have provided a'self-contained motor starter which can be used with a switch 8 if desired, but is not necessaryas the automatic switch C, can be used for closing the" circuit through the device and to, the motor.

and may also be used for disconnecting the device from the source of power, and it will also automatically open should the current at.

will take place until the motor has reached a predetermined speed or approximately the same, and then the thermal relay switch will automatically connect a low resistance bypass across the resistor 1", thereby, in effect, throwing the motor directlyacrossthe line. The thermal relay switch will remain in its closed position, thus shunting the resistor R, as long as the motor is running normally and as long as the circuit breaker C remains closed.

I claim 1. A control apparatus comprising a resistor to be connected in a circuit, a by-pass circuit, a fixed contact and a movable contact to connect the said by-pass circuit across the resistor, thermally operated mechanism having a free end to which themovable contact is secured and is insulated therefrom and moved by said mechanism to preliminarily close said contacts and electro-magnetically operated mechanism arranged to be energized when the contacts engage to'act' upon the thermal mechanism to finally close and hold the contacts closed after the initial closing by the thermal element.

2. A control apparatus comprising a resistor to be connected in a circuit, a circuit to shunt the resistor, a contact mechanism having fixed and movable contacts to connect the shunt circuit around the resistor, thermally operate-d'means in series with the'resistor and heated by the current through the resistor to preliminarily close said contact mechanism,

the movable contact being secured to the thermal mechanism in insulating relation thereto and movable with said thermal means to engage the fixed contact and electro-magnetic mechanism operated by the current in said shunting circuit acting to finally close and hold the contact mechanism closed and the thermally operated means in its contact closing position.

3. A control device comprising a resistor and means to automatically shunt the resistor after current has flowed therethrough for a predetermined length of time, the said means comprising a-U-s'hapedthermal element, having its closed end free, connected in series with the resistor and adapted to be heated directly by the current flowing in said element, a movable contact secured to the free end of the thermal element in insulated relation thereto and to be moved by said thermal element to engage a fixed contact, and a coil arranged to be energized when the contacts engage and hold the contacts in engagement,

the U-shaped thermal element being shunted when the contacts are in engagement.

4:. A control device comprising a deformable thermal element having a limited movement inone direction and a resistor in series, the thermal element being controlled in its movement by current flowing therethrough andthrough the resistor, contact means controlled by the thermal element toconnect a by-pass about the thermal element and the resistor prior to the limit of movement of the thermal element in one direction, and means controlled by the contact means to complete the movement of the thermal element in said direction and maintain the thermal element and resistor by-passed after current has fiowed through the thermal element for a predetermined time.

5. In an electric circuit, a resistor, a bypass circuit therefor, a movable member arranged to complete the by-pass around the resistor, a thermostatic element operated initially by the current flowing through the resistor and arranged to actuate the movable member and close the by-pass and a coil energized by current through the by-pass to operate the thermostatic element to its final position and to hold said movable member in its by-passing position.

6. A control device comprising a resistor, a by-passing circuit and switch normally open when the device is inoperative and having an initial and a final closing position, a thermally controlled element arranged to move the switch to its initially closed position and an electro-responsive mechanism controlled by movement of the thermal element to act upon the thermal element to move the switch to its finally closed position and hold the switch closed and the resistor and thermally controlled element by-passed.

7. An electric control device comprisin a resistor to be shunted out, a thermostatic e ement heated by the current through the resistor, a switch and circuit controlled thereby and actuated by the thermostatic element to shunt the thermostatic element and electromagnetic means acting upon the thermostatic element and controlled by thermostatic element to maintain switch and thermostatic element in their shunting position.

8. A control device adapted to connect a translating device to a source of electric energy comprising, a resistor, a thermal element having a cold position and a hot position connected in series with the resistor and controlled directly by the current through the resistor, a circuit to by-pass the resistor and the thermal element and a switch operated by the thermal element when hot'to connect the by-pass around the resistor and thermal element and electro-magnetic means to hold the switch closed and the thermal element in its hot position.

9. A control device adapted to connect a translating device to a source of electric energy comprising, a resistor, a thermal element having a cold position and a hot position connected in series with the resistor and 6 controlled directly by the current through the resistor, a circuit to by-pass the resistor and the thermal element and a switch operated by the thermal element when hot to connect the by-pass around the resistor and m thermal element and electro-magnetic means to prevent the return of the thermal element to its cold position while the device is functioning. In testimony whereof I afiix my signature. HOMER P. CHANDLER.

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