US716445A - Means for regulating and protecting electric motors. - Google Patents

Description

Patented Dec. 23, I902.

2 Sheets-8heet I.

R. LUNDELL. MEANS FOR REGULATING AND PROTECTING ELECTRIC MOTORS.

(Application filed. Sept. 20, 1902.) (No Model.)

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Wdimeoaeo Patented Dec. 23, I902.

B. LUNOELL.

MEANS FOR REGULATING AND PROTECTING ELECTRIC MOTORS.

(Applicgtion filed Sept. 20. 1902.)

2 Sheets-Sheet 2.

(No Model.)

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UNITED STATES I PATENT OFFICE.

ROBERT LUNDELL, OF NEW YORK, N. Y.

MEANS FOR REGULATING AND PROTECTING ELECTRIC MOTORS.:

SPECIFICATION forming part of Letters Patent No. 716,445, dated December 1902- Applieation filetl-$eptemher 20, 1902. Serial No. 124,184. (No model.)

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Be it known that I, ROBERT LUNDELL, a citizen of the United States,residing at New York, borough of Manhattan, county and State of New York, have made a new and useful Invention in Means for Regulating and Protecting Electric Motors, of which the following is a specification.

My present invention relates to improvementsin the means for regulating and protecting electric motors like those described by me in a prior United States patent, No. 626,178, and to the general class of motors which at certain intervals are worked as generators.

The invention has for its objects, first, to devise means for automatically adjusting the field strength of the motor or motors at the time the armature-circuits are changed from series to parallel or from parallel to series and for preventing an undue rush of current at the time said changes are efi'ected; second, to provide means for automatically preventing the Voltage from rising above a predetermined or a safe limit when the motors work as generators, and particularly when the connection between the motors and the power-circuit is broken.

For a clear understanding of the invention reference is made to the accompanying drawings, in which Figure 1 is a diagrammatic view of the various principal parts of the apparatus and of the circuit connections between the said parts. Fig. 2 is a diagrammatic view of the motor connections at the various running notches as well as at the intermediate positions of the controller.

Referring now to the drawings in detail, and particularly to Fig. 1,the upper left-hand side of the figure illustrates the developed movable contacts of the main controller-cylinder, and the upper right-hand corner illustrates a similar development of the movable contacts of the reversing-cylinder. The row of contacts numbered 1, 2, 3 to 21, inclusive, represent the stationary contacts for the main controller-cylinder, and the other row of contacts, numbered 22, 23 to 33, inclusive, represent the stationary contacts for the reversing-cylinrler. A AA represent two similar armature circuits or windings on the same armature-core, and F Sh represent the respective series and shunt windings for the field-magnet in which the above-mentioned armature-core is supposed to be running. A

AA represent two other similar armature circuits or windings upon another armaturecore supposed to be running in another fieldmagnet, for which F and S771 represent the respective series and shunt windings. a I) represent diverting resistances used in connection with the series field-winding F, and a I) represent similar diverting resistances 'used in connection with the other series fieldwinding F 0, cl, and 6 represent high. resistances for regulating the amount of current flowing through the shunt-windings Sh and S71 R represents a starting resistance,

which is only used on the first notch of the NV in series with a suitable small but high Said relay 8o resistance to the ground-wire W has a stationary contact 34, against which the movable lever 1 is adapted to make contact when the magnetic pull of the relay overcomes the tension of the spring 3. Sw

represents an electromagnetic switch, which is normally closed by gravity and arranged to sever the connection between its stationary contacts 35 and 36 when a'current flows throiigh its solenoid.

Referring now to Fig. 2, which is a diagrammatic representation of the changes which take place in the circuit connections between the above-mentioned armature and field windings and the regulating resistances for the same, it will be noticed that the same 5 letters as in Fig. 1 are used to indicate similar parts. The upper part of the drawing shows the circuit or circuits as first made when the movable contacts strike the stationary contacts of the main controller-cylin- I4 0 der, and the lower part of the drawing shows the circuits as finally arranged for the last position of the controller or for the top speed of the motors. The intermediate circuit con- CB represents an au- '75 nections (shown in Fig. 2) are of course those which are successively established by the controller as the main cylinder is rotated from its first to its last position.

The principal features regarding the mode of regulation being substantially the same as those shown and described by me in the above-mentioned United States Patent No. 626,178, it is not deemed necessary to enter into a minute description of each and every circuit connection which would tend to turn attention away from the novel features of the present invention. It should, however, be pointed out that there are three distinct zones or groups of. regulation, the first being the one in which all four armaturecircuits are in series, the second the one in which two armature-circuits are in parallel and two in series, and the third in which all four armature-circuits are in parallel. (See Fig. 2 and the upper left-hand part of Fig. 1.)

The first zone of regulation includes the starting-notch or the first speed and the second, third, and fourth running-notches on the controller and is further characterized by the fact that the shunt-field is predominantthat is, the shunt excitation of the field-magnets of the two motors is of considerable magnitude as compared with the excitation from the series coils which have been cut down to a minimum on the second, third, and fourth notches by the diverting resistances a and a These resistances are so proportioned that they practically short-circuit the series field-coils. (See Fig. 2.) The figure illustrates clearly the difference between the above-mentioned running-notches. Itshows that the shunt excitation, which was extra strong at the second notch, has been successively reduced at the third and fourth notches by the resistances c and d, which have been connected in series with the shunt-windings.

The second zone of regulation includes the fifth, sixth, and seventh runningnotches. The shunt excitation is the same as for the second, third, and fourth notches; but the series excitation has been increased, owing to the fact that the main current has been nearly doubled, the armature-circuits being now in series parallel.

The third zone of regulation includes the eighth, ninth, and tenth running -notches. The shunt excitation is manipulated precisely as for the second, third, and fourth notches; but the series excitation is now considerable. At the eighth notch no diverting resistances are used at all for the series windings, and at the ninth and tenth notches the diverting resistances a and b and a and b are so proportioned that they do not materially weaken the strength of the series windings.

It will be understood that during the first zone of regulation the speed of the motors (except at the starting-notch) will be practically independent of the load, owing to the strong shunt characteristic given to the field excitation. In fact, the speed at a given notch will not be materially higher when the motors work as dynamos than when they work as motors. During the second zone of regu lation the series field excitation commences to become a factor in regard to the total field excitation, and during the third zone of regulation the series excitation is decidedly strongthat is to say, the field strength is now dependent upon the load.

Assuming now that the motors are used for propelling a tram-car and that the car is running at top speed, it follows that as the controller is gradually moved from the tenth to the second notch the motors will return current to the power-circuit while they at the same time are checking the speed of the car. In this respect the invention is similar to my prior invention described in the United States patent above referred to. As stated in the preamble of this specification, one of the objects of this invention is to provide means for automatically adjusting the field strength at the time the armature-circuits are changed from series to parallel, or vice versa. For a clear understanding of the means employed to accomplish said object reference is made to Fig. 2 and to the upper left-hand side of Fig. 1, which illustrates a development of the main controller-cylinder. It will be noticed upon inspection of the drawings that the armature-circuits are changed from series to series parallel between the fourth and the fifth running-notches and from series parallel to parallel between the seventh and the eighth running-notches.

It should be understood that the total field strength depends upon the combined action of the shunt and the series windings. The current in the shunt-windings will always flow in the same direction; but the current in the series windings will flow in either direction, dependent upon the counter electromotive force of the motors. The strength of the shunt-field is adjusted entirely by the controller; but the strength of the series field is self-adjusting at the time of the series-parallel changes, as will now be fully explained. The controller is arranged to short-circuit or to shunt the series windings at certain notches; but the strength and the direction of the current in the series windings (when not short-circuited) are solely dependent upon the difference between the electro motive force of the motors and the electromotive force of the power-circuit. The series windings are chiefly utilized during the transition steps, at which points the said windings are wholly in circuit. The effect or the action of the same is automatic-that is, it the electromotive force of the motors happens to be equal to the electromotive force of the power-circuit at the moment the armature-circuits are changed from series to parallel, or vice Versa, the eifect of the series windings will be m'Z. If, on the other hand, the electromotive force of the motors is lower than the electromotive force of the power-circuit, (as will be the case during acceleratiom) the effect of the series field-windings will be to automatically increase the total field strength, and if the electromotive force of the motors should be greater than the electromotive force of the power-circuit (as is the case during retardation) the effect of the series field-windings will be to automatically reduce the total field strength. In other words, the series fieldwindings will cause the field strength of the motor or motors to become self-regulating during the transition steps.

Supposing now that the tram-car has been started and that the speed is being gradually increased bya continued movement of the controller-cylinder, the first zone of regulation will of course soon be passed, and when the movable contacts on the controller-cylinder finally sever the main circuit connections (as they leave the stationary contacts) it will be noticed that the resistances a and c, which short-circuit the series field-windings F and F, are gradually cut out, and it will also be noticed that when the main circuit conections are reestablished (by a continued movement of the controller-cylinder) the said resistances a and a are again caused to gradually short-circuit the series fields. It will thus be seen that the motors during their transition steps, and particularly at the time of the break and make of the main motor-circuits, have become strongly compoundwound motors capable of increasing the field strength at the time the main current fiows through the armatures in the first series-parallel combination and likewise capable of decreasing the field strength if the controller were moved in the opposite direction from the fifth to the fourth notch. In other words, the series windings are caused to automatically assist the shunt field in building up a powerful field magnet during acceleration and to automatically decrease the strength of the field-magnet during retardation-that is, if a strong reverse-current should be generated by the motors and it should be desirable to reduce the counter electromotive force of the motors. The motors will thus automatically prevent an undue rush of current at the time the main circuit connections are reestablished, no matter which way the controller is moved.

The above remarks apply without important modification to the transition steps be tween the seventh and eighth or rather the seventh and ninth notches, and a glance at the drawings willsuffice to explain the mode of operation.

Attentionis now called to the second object of this invention, and particular reference is made to the lower part of Fig. 1, which illustrates the means employed for preventing the voltage from rising above a safe limit when the motors work as generators. It will be noticed that the electromotive force of the power-circuit is between the conductors W and W The circuit connections between the power-circuit, the motors, the relay X, and the electromagnet-switch Sw will be fully understood by tracing the circuits in one position of the controller-for instance, at notch No. 10. The current would normally flow as follows: from the trolley through the automatic circuit-breaker OB to wire W, where it divides itself, one small part (about onetenth of an ampere) going directly through the coils of the relay X and its auxiliary resistance to the ground or the return-conductor W and the other or the main portion of the current flowing by Wire W to the stationary contact 10 of the controller. At this point the current again divides itself into several circuits. One circuit leads from contact 10 to 9 through resistances d and c to contacts 26 and 27 of the reversing-switch, through the shunt-winding Sh of one motor to contacts 36 and 35 of the electromagnetic switch, then through shunt-winding Sh of the other motor to contacts 28 and 29 of the reversing-switch, and finally to the ground or the return-conductor W Another circuit leads from contact 10 to contacts 6 and 5 through the armature-windings A and AA in parallel to contacts 4, 3, 2-, 22, and 23, through resistances 1) plus ct in parallel with series field-wind ing F to contacts 24, 25, 17, and 21 to the ground or the return-conductor V A third circuit leads from contact 10 to contacts 11 and 12 through the armature-windings AA and A in parallel to contacts 13, 14, 16, 30, and 31 through the resistances a and b in parallel with the series field-winding F to contacts 19, 32, 33, 20, and 21 to the ground or the return-conductor W It will thus be understood that the relay X is connected in parallel with the motors. Supposing now that the tram-car is running at top speed with the controller at the tenth notch and that the trolley-wheel Tr jumps off the line, or that the circuit-breaker OB flies open owing to some cause or other. The motorman will impulsively turn the controller toward the OE position, with the result that the electromotive force of the motors will rapidly increase, owing to the fact that they are keeping their shunt fields energized by their own armatures. In fact, the electromotive force would become four times as great as the normal electromotive force of the power-circuit when the first Zone of regulation was reached. In order to overcome the evil effects of such an abnormal voltage, the automatic device, consisting of the relay X and the electromagnetic switch Stl), has been provided.

The operation is as follows: When the voltage of the motors rises to about twentyfive per cent. more than the normal or maximum voltage of the power-circuit, the little switch will immediately open the circuit &

through the shunt-windings of the motors, or it may be arranged to draw an are at contacts 35 and 36 long enough to out down the ampere-turns in the shunt-windings to a safe amount. The relay and the switch, both being comparatively small, will naturally do their work quickly and will thus prevent any abnormal voltage in the apparatus.

Having thus described my invention, what I claim, and desire to secure by Letters Patent of the United States, is

1. The combination of an electric-circuit controller; one or more electric motors the speed of whichis chiefly governed by coupling the armature-circuits in series or in parallel; means for preventing an undue rush of current at the time the armature-circuits are changed from series to parallel, and from parallel to series with additional means for keeping the field strength practically independent of the armature-current after the circuits are reestablished, so that the motor or motors may be driven by the load as a generator, and the changes in the armature-circuits may be effected Without shock to the apparatus.

2. An electric motor or motors the speed of which is chiefly governed by changes of the electromotive force applied to the individual armature windings; in combination with means for causing the field strength of the motor to become self-regulating at the time the said changes are effected and additional means for afterward adjusting said field strength so that it may become practically independent of the armature-current for the purpose set forth.

3. The combination of an electric-circuit controller; one or more electric motors the speed of which is chiefly governed by changes of the electromotive force applied to the individualarmature-windings; means for automatically preventing an undue rush of current at the time the electromotive force applied to the individual armature-windings is either increased or decreased; with additional means for keeping the field strength practically independent of the armature-current after the said changes of electromotive force are effected.

4. The combination of one or more motors of the regenerative type, with an automatic device for reducing the elect-romotive force of the motor or motors when it becomes abnormal, owing to an accidental rupture of the power-circuit.

5. The combination of one or more motors capable of returning current to a power-circuit when driven as a generator or generators, with electromagnetic means for reducing the electromotive force of the motor or motors when it exceeds the electromotive force of the power-circuit, owing to a break in the said circuit.

6. An automatic safety device for electricrailway motors or similar apparatus, consisting of a relay arranged to close a circuit through an electromagnetic switch or apparatus which reduces the counter electrometive force of the motors when it exceeds the amount for which the relay has been adjusted.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ROBERT LUNDELL.

Witnesses:

O. J. KINTNER, M. F. KEATING.

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