US745326A - Alternating-current motor. - Google Patents

Description

No. 745,326. PATBNTED DEC. 1, 1903. A. J. OHUROHWARD.

ALTERNATING CURRENT MOTOR.

APPLIGATION FILED MAR. 29, 1897.

N0 MODEL.

WITNESSES: INVENTOR JZGzaraZar J (ZuM/bt wrd His ATTORNEY UNITED STATES Patented December 1, 1903.

PATENT OFFICE.

ALTERNATlNG-CURRENT MOTOR.

LPEOIFICATION forming part of Letters Patent No. 745,326, dated December 1, 1903. Application filed March 29,1897. erial No. 629,853. (No model.)

To all whom it may concern.-

Be it known that I, ALEXANDER J CHURCH- WARD, a citizen of the United States, and a resident of Brooklyn, in the county of Kings and State of New York, have invented a certain new and useful Alternating Current Motor, of which the following is a specification.

My invention relates to alternating-current motors of the type in which the armature has any usual direct or continuous current winding and commutator and is fed with singlephase alternating currents. Such machines, as is well known, will start and develop power, but are ordinarily inefficient and do not possess sufficient starting torque. \Nhen the motor is starting and running at low speeds, there are in the armature eddy-current losses, self-induction, and losses due to hysteresis, which all tend to reduce the useful voltage by increasing the self-induction in the motor-circuit. Consequently sufficient current may not pass to give a good starting torque. The usual method of overcoming this difficulty is to use a motor which is unnecessarily large for the service required of it when running at speed, or else to construct it so as to have an abnormally small self-induction, in order to allow sufficient current to pass at starting to give large torque, in which case it is inefficient when running at speed.

My present invention consists, essentially, in a novelway of starting this class of motors by adjusting the commutator devices during the starting operation to position where the machine will oppose a less self-induction to the alternating currents, thereby permitting a stronger current to pass, and after the armature has attained speed adjusting the said commutating devices back to their normal position.

My invention is especially useful in connection with alternating-current motors whose armature having a direct or continuous current winding and commutator therefor for starting purposes is operated in series with a field-coil, the alternating current being fed to the machine in such way that when the armature revolves at synchronous speed the currents flow as continuous currents in the armature, being rectified by the commutator used in starting as desired, while they flow in the field as an alternating current to rapidly reverse the polarity thereof and to produce, in effect, a rotary magnetic field.

In carrying out the invention the commutater adjustment may be made by hand or by means of devices responsive to differences in speed of the machineas, for instance, by any centrifugal governor connected to the commutator-brushes.

In the present case I claim the apparatus for accomplishing results herein specified. In a companion case, Serial No.15A,377, filed April 27, 1903, I claim the method.

In the accompanying drawings,l igurcsl and 2, the two positions of the brushes are illustrated diagrammatically in connection with a four-pole machine. Fig. 3 illustrates the application of a centrifugal governor to moving the brushes.

The armature A is wound with any desired system of coils, such as is employed on continuous or direct current dynamos or motors, but preferably with what is known as the closed-circuit winding, the commutatorcylinder for which is indicated at a and the commutator-brushes at Z). The latter are preferably mounted on any desired construction of rocker by which they may be adjusted circumferentially around the cylinder and are insulated from one another as usual in the art. The machine is supposed to have in this instance four field-magnets 0, whose coils are preferably in series circuit with the armature.

Alternating currents are fed to the machine from any desired source,as from a transformer diagrammatically indicated at D, which by preference is adapted to supply a constant current. These currents in the starting operation flow in the armature and field as alternating currents, but when the machine attains synchronous speed they flow as continuous currents in the armature, but still as alternating currents in the field.

In the starting operation the self -induction of the machine is high, and insufficient current will pass to give a high starting torque. To obviate this, I start the machine with the brushes set as in Fig. 1, in which they are shown slightly shifted from their normal positions as shown in Fig. 2. This shifting of the brushes from their normal po sitions has the effect of changing the relations of the poles of the field-magnets and armature, and thus decreasing the mutual magnetic reaction in the motor. This of course has the effect of reducing the self-induction of the motor. Other things being equal, of course the reduction of the magnetic reaction between the armature and the fields by shifting the brushes would have the eifect of reducing the motor torque-as, for instance, in a direct-current motor; but since the motor under consideration is an alternatingcurrent motor the reduction of the self-induction by the reduction of the magnetic reaction of the armature and fields is very great, so that the alternating current permitted to l'low by such reduction is so far in excess of that which would flow were the magnetic reaction between the poles and armature allowed to remain normal that the increase in the torque resulting from this larger current far exceeds the slight decrease that would result under other conditions. Consequently the torque of the motor is greatly increased at starting by the slight shifting of the brushes, as shown in Fig. 1. When the machine reaches the synchronous speed, the self-induction is greatly lessened, as the current then flows as a continuous current in the armai ure. l V hen the machine has reached the synchronous speed or as it runs up to such speed, the brushes are turned to their normal position for synchronous running, as indicated in Fig. 2. The adjustment may be made by hand or automatically. The latter mannerof adjustment is indicated in Fig. 3, where I show a centrifugal governor G connected to the rocker carrying the brushes. lVhen the machine is at rest,

the governor holds the brushes in the position shown in Fig. 1, but is adjusted to hold them in the position shown in Fig. 2 when turning at the synchronous speed.

It is obvious that the invention may be used, if desired, in connection with any desired means for keeping or maintaining the machine at synchronous speed.

The centrifugal govern or is connected with the armature in any desired way, so as to revolve at the same speed as the armature.

What I claim as my invention is 1. The combination with a self-starting alternating-current motor having a direct or continuous current armature-winding and commutator, of a field-coil in series therewith, means for feeding alternating currents to said armature, commutator and field in series both during non-synchronous or starting operation and during synchronous running, an adjustable commutator, and means responsive to changes of speed for adjusting the same, as and for the purpose described.

2. The combination with a self-starting alternating-current motor having a direct 01' continuous current armature-winding and commutator, of a field-coil in series therewith, means for feeding alternating current to said armature, commutator and field in series, both during non-synchronous or starting operation and during synchronous running, an adjustable commutator, and a centrifugal governor arranged on the armatureshaft and connected with said brushes for adjusting the same, as and for the purpose described.

Signed at New York, in the county of New York and State of New York, this 20th day of Februar A. D. 1897.

ALEXANDER J. CHURCIIWARD. lVitnesses:

WM. H. CAPEL, D. H. DECKER.

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