US777198A - Alternate-current motor. - Google Patents

Description

No. 777,198. PATENTED DEC. 13, 1904.

V. A. PYNN.

ALTERNATE CURRENT MOTOR.

APPLICATION FILED SEPT. 17. 1903.

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PATENTED DEC. 13, 1904.

V. A. PYNN.

ALTERNATE CURRENT MOTOR.

APPLICATION FILED SEPT. 17. 1903.

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N0 MODEL.

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No. 777,198. PATENTED DEC. 13, 1904. V. A. PYNN.

ALTERNATE CURRENT MOTOR.

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UNITED STATES Patented December 13, 1904;.

PATENT OFFICE.

ALTERNATE-CURRENT MOTOR.

SPECIFICATION forming part of Letters Patent No. 777,198, dated December 13, 1904.

Application filed September 17, 1903. Serial Nix 173,635. (No model.)

To (LZZ whom it may concern.-

Be it known that I, VALERE ALFRED FYNN, electrical engineer, a subject of the King of Great Britain and Ireland, residing in Bradford, county of York, England, have invented certain new and useful Improvements in Alternate-Current Motors, of which the following is a specification.

The present invention consists in an improvement of the arrangement for self-excitation of single or poly phase motors. Such self-excitation is designed to serve for reducing as far as possible the difference of phase between current and electromotive force of the energy absorbed and of enabling a better regulation of the speed to be effected.

It further consists of an improvement in the rotor-Winding of single or poly phase motors, which improvement allows of obtaining to the full the advantages of the above excitation arrangement and which, even when employed alone, presents important advantages for such motors.

According to this invention the first-named object is attained by making the arrangement such that in any case the phase of the exciting electromotive force and also when possible the direction thereof corresponds with the phase and direction of the electromotive force induced in the rotor, (when this does not run synchronously.) I attain this object by displacing the exciting-winding upon the stator to a certain angle with respect to the main winding. Self-excitation has also, it is true, been proposed for induction-motors, but without taking into account either the phase or direction of the electromotive force induced in the rotor itself. This omission necessitated a larger expenditure of energy and regulation or adjustment generally secured by shifting the brushes and varying the voltage of the excitation in order to maintain the difference of phase between current and electromotive force approximately constant and near unity as soon as the speed differed materially from synchronism.

This new self-excitation arrangement can be applied to rotors which are provided in the known way with a direct-current winding and commutator. It can therefore be employed generally with all repulsion and similar motors. It can be used with special advantage with a rotor-winding, as shown diagrammatically in Fig. 3.

My improved exciting arrangement is shown diagrammatically in Figs. 1 and 2 in combination with two possible forms of the rotor-winding. It is here assumed that the motor is, for example, started as a repulsionmotor and runs on as an induction-motor.

For the introduction of the exciting-current into the rotor I preferably choose those points on the commutator at which in asynchronous running the greatest electromotive force of such direction is produced as would in case these points were connected together produce a current which would improve the power factor, (cos. This electromotive force alone, however, is not able to bring the power factor very near to unity, and therefore I introduce the exciting-winding N in such manner that the electromotive force thereof corresponds in phase and direction with the above-men tioned electromotive force, by which means I attain a large saving in energy. A further advantage of this disposition is that the best position of the brushes for starting as a repulsionanotor nearly coincides with those points on the commutator which exhibit the above-mentioned greatest useful electromotive force. In cases, therefore, where the motor is started as a repulsion-motor I prefer to use the starting-brushes for excitation also, thus simplifying and cheapening the machine. With this object I so dispose the exciting-winding N upon the stator that its electromotive force corresponds in phase and direction with the electromotive force which would exist in asynchronous run ning at the points of the rotor in which the repulsion-brushes stand. It is clear that by the same means I can obtain this correspondence notonly for these particular points, but for any others selected. It should be here remarked that absolute correspondence of phase can often only be obtained by slightly shifting the brushes when the motor is first adjusted, since the slot pitch of the stator is mostly too coarse. No subsequent regulation would in this case be necessary even with large variation of speed in order to maintain the difference of phase between current and electromotive-force-powcr factor in the stator in the neighborhood of unity. The motor can be started as a repulsion-motor with the aid of the slip-rings, and after reaching the full speed the repulsion-brushes A A themselves can be used for self-excitation by connecting them to the stator exciting-winding N, which has for this purpose been displaced with respect to the main winding S by the necessary angle X, Fig. 1. The regulation of the speed is effected by the insertion of more or less resistance between the sliprings, as indicated in Fig. 3 at R R or by variation of the exciting electromotive force by means of resistances, as shown at R in Fig. 1, or any other suitable way. Further, a combination of both methods may be used.

Instead of starting the. motor as above described I may while leaving the brushes in approximately the best position for starting as a repulsion-motor, which would, as is known, in the case of a two-pole machine be that in which their axis is at about forty-five degrees to the axis of the stator-field, connect them directly to the exciting-winding. the regulation of the motor being effected in the same way as above described. (See Fig. 1.)

A further modification of the invention is shown in Fig. 2. Here the repulsion-brushes A A always remain short-circuited, or, as generally known, connected over resistances or the like. The exciting-winding N is displaced with respect to the main stator-winding by such an angle X that the brushes E E, serving for excitation, touch the rotor-winding of the commutator at such places (for the purpose of obtaining the most favorable distribution of the exciting-current) that as equal as possible a number of windings must be traversed in any direction through the winding H, connected to the commutator, in passing from the exciting-brushes E E to the repulsion-brushes A A. The starting and the variation of the speed can be carried out, as already explained, and the self-excitation can be employed at any desired time.

K in the figures indicates the assumed direction of the alternating field of the bipolar motor shown.

a '22 represents the symmetry line of the exciting-winding N, and .s' .s the symmetry line of the main stator-winding S.

Instead of employing monophase current for the self-excitation polyphase current may be employed.

The field is preferably made of the asynchronous stator type.

It has already been proposed in the case of motors which are started as repulsion-motors and then run as induction-motors to employ rotor-windings of the direct-current type, connected on the one hand to a commutator and on the other hand to slip-rings. (See Fig.

2.) The drawbacks of such a construction are to be found in the reduction of the starting torque when running up to and varying the speed,this reduction being due to periodical interference with the fixed short circuit formed by the repulsion-hrushes of the rotary short circuits formed by the slip-rings bridged over with relatively low resistances; further, in the fact that a lower voltage is available for the slip-rings where no sparking is to be feared than for the commutator where sparking is greatly to be feared. Self-excitation cannot be employed with advantage in such a rotor, because far too great a portion of the current flows uselessly through the short circuits formed over the slip-rings. On the other hand, two separate windings have also been proposed, (cf. Fig. 1;) but this arrangement also possesses very considerable drawbacks, since it does not allow of fully utilizing the winding-space of the rotor. On this account the loadlimit of the motor is greatly reduced. The reason for this is that in approximately synchronous running no appreciable current flows through the short-circuited repulsionbrushes, and consequently through the appertaining winding. Therefore this whole winding contributes nothing to the torque of the motor when it should be furnishing its maxi mum work, (as an induction -.motor.) It is known that the degree of efliciency of such motors and their limit of load depends principally on the useful copper section in the rotor. Accordingly a machine made as shown in Fig. 1 would come out considerably larger than a machine of equal power made as shown in Fig. 3.

All the above mentioned drawbacks are avoided according to the present invention by employing upon the rotor a winding all parts of which (H and Z) are always operative so far as the slip-rings are concerned, whereas only a portion thereof (H) is operative so far as the commutator is concerned. The latter portion is connected to the slip-rings, not directly but through the remaining portion Z of the whole winding. These partsc'. 0., main part II and supplementary part Z lie in the same slots and are disposed relatively to each other in such manner that the electromotive force in Z corresponds in phase and direction with the electromotive force resulting at the points of connection between H and Z. A rotor-winding fulfilling these conditions is shown diagrammatically in Fig. 8, the supplementary part Z being shown as an open three-phase winding having its ends connected on the one hand to three symmetrically-situated points of the main directcurrent winding H and on the other hand to three slip-rings. Algebraically expressed and applied, for example, to a three-phase supplementary winding, as shown in Fig. 3, the connections should be so made that if the electromotive force per phase of the main winding equal a, and the electro- IIS motive force per phase of the star-connected supplementary winding equal 6, the resulting electrom otive force between slip-rings equal a Z) J3. By observing this rule I am in a position to fully utilize the copper of the rotor.

In further explanation of the above described method of connection it may be added that even if the supplementary Winding be not connected to the main Winding exactly in accordance With the above rule an advantage will still be obtained over previous constructions, but, as will be understood, not to so great an extent.

hat I claim as my invention, and desire to secure by Letters Patent, is-

1. In a single or poly phase motor, the combination of a stator, a rotor, a commutator, brushes and slip-rings, a main Winding on the stator, an exciting-winding on the stator, said exciting-winding being displaced with respect to said main Winding by an angle adapted to give an exciting electromotive force corresponding in phase With the electromotive force produced at any selected points of the rotorcommutator in asynchronous running, a winding on the rotor and connected to the commutator and to the slip-rings, the whole of said rotor-Winding being operative so far as the slip-rings are concerned, but only a portion thereof being operative so far as the commutator is concerned, said latter portion being connected to the slip-rings through the medium of other portions of the said rotorwinding.

2. In a single or poly phase motor, the combination of a stator, a rotor, a commutator, brushes and slip-rings, a main winding on the stator, an exciting-winding on the stator, said exciting-winding being displaced with respect to said main winding by an angle adapted to give an exciting electromotive force corresponding in phase and direction with the electromotive force produced at any selected points of the rotor-commutator in asynchronous running, a Winding on the rotor and connected to the commutator and to the slip-rings, the Whole of said rotor-Winding being operative so far as the slip-rings are concerned, but only a portion thereof being operative so far as the commutator is concerned, said latter portion being connected to the slip-rings through the medium of other portions of the said rotor-winding.

3. In a single or poly phase motor, the combination of a stator, a rotor, a commutator and brushes, a main Winding on the stator, and an exciting-winding on the stator, said excitingwinding being displaced with respect to said main winding by an angle adapted to give an exciting electromotive force corresponding in phase with the electromotive force produced at any selected points of the rotor-connnutator in asynchronous running.

4. In a single or poly phase motor, the combination of a stator, a rotor, a commutator and brushes, a main winding on the stator, and an exciting-winding on the stator, said excitingwinding being displaced with respect to said main winding by an angle adapted to give an exciting electromotive force corresponding in phase and direction with the electromotive force produced at any selected points of the rotor-commutator in asynchronous running.

5. In a single or poly phase motor, the combination of a stator, a rotor, acommutator and brushes, and slip-rings, and a winding on the rotor, said winding connected to the commutator and to the slip-rings, the whole of said rotor-winding being operative so far as the slip-rings are concerned, but only a portion thereof being operative so far as the commutator is concerned, said latter portion being connected to the slip-rings through the medium of other portions of the said rotor-winding.

6. In a single or poly phase motor, the combination of a stator, a rotor, a commutato and brushes, a main winding on the stator and an exciting-winding on the stator, said excitingwinding being displaced to such an extent with respect to the main winding as to necessitate a position of said brushes for exciting which corresponds with the position which repulsion starting brushes would assume, whereby one and the same set of brushes can be used both for starting and self-excitation.

7. In a single or poly phase motor, the combination of astator, arotor, acommutator, exciting-brushes and repulsion starting-brushes, a main winding on the stator and an excitingwinding on the stator, said exciting-winding being displaced to such an extent with respect to the main winding as to necessitate a position of the exciting-brushes so far situated from the repulsion-brushes serving for starting, that as equal as possible a number of windings must be traversed in any direction through the Winding connected to the commutator in passing from the exciting-brushes to the starting-brushes.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

VALERE ALFRED FYNN.

\Vitnesses:

ALFRED B. CAMPBELL, H. 1). JAMEsoN.

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