US931302A - Induction-motor. - Google Patents

Description

E. E. HELLMUNDU INDUCTION MOTOR.

AFPLIOATIONI'ILED DEOA, 1907.

Patented Aug. 17, 1909.

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R. E 'HliLLMUND.

Patented Aug. 17, 1909.

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R. E. HBLLM -D.

INDUCTION MOTOR APPLICATION FILED DEG. 4,1907.

Patented Aug. 17, 1909.

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WI TNESSES INVENTOR I parts.

UNITED sTArEs rnrunr irm , RUDOL'F E. HELLMUND, or PITTsBURG, PENNSYLVANIA, Ass si 0a To nntiiiuun COLLBOHM ELECTRIC COMPANY, A OORPORATlON or nnwronu.

INDUCTIGN-MOTOR.

To all whom it may concern: Be it known that I, RUDOLE E. HELL4 MUND, residing at Pittsburg, in the county of Allegheny, and in the State of Pennsylvania, have invented certai new and'useful Improvements in Induction Motors, of which the following is a full, clear, and exact description.

My invention relates to induction motors, and more particularly to that kind of induction motors, which are known under the -name of squirrel cage ,induction motors.

' -The object of my invention is to insure a good starting torque=with such motors without drawing an excessive current from the line; and another object oi invention is, to obtain this result with a few and simple The squirrel cage induction motor being an ideal motor in almost every respect, has the disadvantage of drawing an exceedingly large starting currentfrom the line. Various kinds of special constructions have herebefore devised to improve the starting cond-ition, all of which have however the dis advantage, that they require a very large number of contact making and breaking parts int-he rotor, therefore they are expensive and unreliable in service.

A It is a Well known fact, that the current in the bars Ofe'fill induction motor secondary increases approximately in inverse proportion to any decrease of the number of bars in the secondary' From this fact it may be easily concluded that the secondary losses will increase, if the active number ofsccin groups so as to have in ondary bars is decreased, while the resistance of each bar is kept the same. It is also well known, that increased secondary losses will give increased starting torque and decreased starting current. It will follow therefore, that any reduction of the number of active secondary bars will tend to increase the starting torque and to decrease the starting current.

if with the number of active bars the number of active slots will be reduced, the leakage of the motor will be increased; this will also tend to decrease the starting current.

In order to reduce the number of active bars while starting, I arrange the conductors some of the groups only conductors, which are shifted about twicethe pole pitch against each other. The current flowing in such a group will he been It is also known that,

Specification of Letters Patent. Application filed December a, 1997.

' vices required for modifications of my rotor.

rotor.

' a d. u 17,1909, Serial N0.1.1.05,090. I

practically zero, while-"the group is disconnectedfrom the other groups, because the potential induced in all the conductors of the group will be of the same phase and amplitude; that means, that-all conductors of such a group are made inactive, while the group is disconnected from the other groups; By disconnecting several of such groups from the remaining conductors the starting conditionof the motor may beconsiderably improved; while the number of contact de-' accomplishing this result is very small. In order "to obtain good results in practice it is notnecessary, that all conductors, which belong to one of the disconnected groups aresuch that thep'otentials induced therein are exactly of the same phase. The action of the bar will always be reduced, if the potential induced .in the conductors in one group are shifted against each other in phase by any angle being smaller or larger than 180 electrical degrees; but the reduction of the action of the bars will be the larger the closer the phase difference of the potentials induced in bars of the same group is to Zero or toBbO oramultiple of 360 electrical degrees. The previous 'con siderations will be more readily understood upon inspection of the drawings.

Figure 1 shows a side view of a squirrel cage rotor of my improved type to be used in connection with an eight pole motor. Fig. 2 shows the three rings A, B and C and he bars of the same rotor; Figs. 3 and 4: are improved squirrel cage Fig. 5 is a front-view of an induction motor, to which my improved rotor construction is applied, the front bearing of the motor being removed; and Fig. (3 is a section through the szimc' motor along the-line mu. v

Referring first to Fig. 1 in particular, R represents the laminated iron core' of the Embedded in the same'in the customary way are conductors a a .b b c c, which are at one end of the rotor connected to a ring D of conducting material. In 2 the bars are represented by the small circles a a" Z L c. The crosses and points inside of the small circles indicate in'the conventional manner'the direction of the potentials being induced in therotor bars at a certain point of time based on the assumption of aneight pole primary. It is obvious, that in all the conductors c a potential of equal ditil? duced in the conductors a. If therefore the conductors c and ,0 are connected to a common ring C, the current flowing in these bars will be very small and the bars will be practieall inactive. The same is true in regard to t e conductors b and b, which are connected tothe ring 13', because all the conductors bare again shifted 360 electrical derees against each other, because all the con-v doctors b are also shifted 360 electrical degrees .against each other and because the shift between any of the adjacent conductors 0 and a is very small. Conditions are essentially. diiferent however for the conductors connected to the ring A. This group of conductors contains conductors, which are approximately 180 electrical degrees apart from other conductorsforming part of the same group. Therefore the potentials induced in the conductors a and a are different in direction and the currents flowing in these bars will be similar to those flowing in anysquirrel cage rotor. The ohmic losses in these bars and therefore the starting torque of the motor will'be larger however than it would be if all the bars 0 c b and 6 would be active; moreover the starting current in the primary will be reduced.

Fig. 4 shows the bars and rings of another eight pole rotor being different from the rotor in Figs. 1 and 2 only in so far as more bars are applied and some irregularity in the grouping of the bars is devised in order to avoid dead points for starting.

Fig. 3 shows a modification of my invention. The rotor has only one end ring on each side; one of the end rings is divided into sections in such a manner, that there are sent ions E E, designed to connect only conduetors, in which potentials of a small phase inference are induced and which consequently are only little active. Contact brushes H H are'mounted to pivots 79 77 and kept in a position as shown inFig. 3 by springs S S, while the motor is in stationary condition. After themotor has come up to speed the centrifugal force of the contact bru hes will overcome the tension of the springs and the brushes will move outwardly thereby establishing electrical connections between the ring segments E E and F F, Whereafter the rotor will operate like any regular rotor.

Referring now to Figs. 5 and 6, the latter represent a motor provided with a rotor similar to the one shown in Figs. 1 and 2. K is a cast iron frame, in which the stator laminations are held in a well known manner by end plates M M and keys N N. Coils O O are placed into the slots of the stator core L. Two bearing brackets P P support a shaft Q. Mounted to the shaft Q is the rotor iron core R; the same is held by two end plates T T and a key U. Embedded in the rotor body are the conductors a aetc. and at the ends of the bars the rings A, B, C and D are arranged as described before. Contact brushes Z Z are mounted to a casting Y, which is arranged to be shifted along the portion of the shaft between the rotor 1t and the bearings I P. The shifting accomplished by a pin X, which is fastened to a rod V. The latter extends through a hole in the shaft to the outside of the motor, where a circular handle W is fastened to the rod V. A small slot 8 is provided in the shaft to allow the movement of the pin X. In Fig. 6 the contact brushes Z are shown in a position, in whibh they connect the three rings A, B and C, that is the figure shows the motor in the running condition. By pulling at the handle W the brushes Z Z and their support Y may be moved toward the bearing and may be thereby brought into a position, in which they do not establish a connection between the rings. The contact will be moved to this position, while the motor is started or desired to run at a reduced speed. An intermediate speed may be obtained by placing the contact so as to connect two of three rings only.

It is evident to any one skilled in the art, that my invention may be reduced to practice by a great number of modifications different from those described above and I do not want to limit myself to the latter.

I claim as my invention:

In the squirrel cage winding of an alternating current motor conductor and members, each of which connects a number of said conductors i. multiple, and at least one of said members being arranged so as to connect only conductors, which are apart from each other by a distance, which is different from the pole pitch, and means designed to establish amlintcrrupt electrical connections between said members.

In witness whereof I have hereunto set my hand in the presence of two witnesses.

RUDOLF E. HELLMUND.

Witnesses:

A. WV. Bonus. W. F. SANVILLE.

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