Improvements in the Regulation of Alternating-current Electric Motors, applicable also to Distribution Systems.
Year: 1898

page_text: Date of Application, 18th Nov., 1898-Accepted, 11th Feb., 1899
Improvements in the Regulation of Alternating-current Electric
Motors, applicable also to Distribution Systems.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of
this invention (which has been communicated to us from abroad by Charles P.
Steinmetz, residing at Schenectady, County of Schenectady, State of New York,
United States of America, Electrical Engineer) and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement:-
This invention relates to alternating current motors, and distribution systems,
and comprises a method and apparatus adapted to improve the regulation of
such devices. In alternating current motors, whether of the single phase or
multiphase types, it is customary to use a multiphase secondary winding. This
winding is either two-phase or three-phase, usually, though, obviously, any
number of phases may be used. More commonly the winding is interlinked
or concatenated, and it is usually preferred to use what is known in the art as
a "Y" winding, though this is immaterial, as a delta winding as well as
winding formed of a number of independent circuits, is equally adapted to the
purposes of my invention. The interlinked windings are in general, preferable
to independent windings, for reasons well understood in the art, but my invention
is applicable to both types.
L
It has been customary hitherto, in controlling the current flowing in secondary
windings or in polyphase systems generally, to interpose a resistance or other
impedance in each winding of the set, and to vary the resistances or impedances.
simultaneously. For example, in induction motor secondaries it is usual to
interpose the maximum resistances at the time when the motor is starting, and
to gradually cut out the resistance as the speed rises. When it is desired to
slow up the motor, the resistances are simultaneously cut in. With such an
arrangement, it is necessary to provide a number of separate resistance contacts,
equal to the number of phases of the secondary winding multiplied by the
number of steps desired, and also to provide a correspondingly large number
of resistances or sections of resistances.
The invention comprises the method which consists in cutting resistances or
impedances into and out of the various secondary or other windings successively.
rather than simultaneously. In motors where fine control is not necessary, one
resistance is provided in each winding, and cut these resistances out by the.
action of a short circuiting bar or contact, which first cuts out one resistance,
then another resistance, and so on. Where finer speed control is desired, the
number of stops is increased and a portion of the resistance is cut out of one
winding, then a portion of the resistance of a second winding, and so on. finally,
cut out a second portion of the resistance of the first winding, a second portion.
of the resistance of the second winding, and so on.
In this way a much finer control is obtained with a given number of resistances
:

page_text: and resistance contacts, or to greatly reduce the number of resistances and
resistance contacts for a given fineness of regulation, as preferred.
Various embodiments of the invention are illustrated in the accompanying
drawings, in which Fig. 1 is an elevation, partly in section, of an alternating
current motor constructed in accordance with my invention; Fig. 2 is an end
view of the same; Fig. 3 is a diagram of the armature connections of such a
motor; Fig. 4 is a similar diagram showing a greater number of resistance
stops and Fig. 5 is a general view of a modification.
•
Referring more particularly to Figs. 1 and 2, A is the base plate of the
machine, which base plate supports the field magnet structure, or inducing
member B, and the shaft C, which in turn. carries the revolving induced member
or armature D. The inducing member B may be supposed to be wound with
three phase winding B', though the number of phases is immaterial. The
armature or induced member D is wound with an induced winding D¹, in which
is interposed the resistance above mentioned. A collar E, sliding on the shaft C,
carries the brushes E¹, E¹, which bear on resistance contacts F. This collar
is moved back and forth by the roller G, carried by the arm G', which is in
turn controlled by the handle G2 through the link G³. This arrangement makes
it possible to slide the brushes or contacts E¹ in and out while the armature
is rotating at full speed, and yet at the same time, allows them to rotate with
the armature.
The, electrical connections will be understood by reference to Fig. 3, in which
D2, D3, D are three coils of the armature, supposed to be displaced from each
other by one-third of the polar pitch, as is well understood. These coils are
connected together at one end to a common point D5, and at the other end are
connected together at D6 through three resistances R2, R3, R¹. A short circuiting
bar E, corresponding to the brushes in Figs. 1 and 2, slides over the contacts F³,
F, etc., which correspond to the resistance contacts F, in the first two figures.
The bar is shown in the position 1, in which position all the resistances R³, R³,
R³, are interposed in series with the windings D2, D3, D. This is the starting
position of the motor. As the speed gradually rises the short circuiting bar is
thrown to the right until it passes the line 2-2 and rests on the segment F4.
This cuts out the resistance R4, but does not actually short circuit the winding D,
since the current from D can only return through one of the windings D2, D3,
and thus through one of the resistances R2, R3. Nevertheless, the total resistance
of the induced winding is reduced, and the speed rises. Later, the bar E¹ is
thrown until it passes the line 3-3 and until it rests on the segment 15. In
this position the resistances R3, R are cut out. The result is that the coil D
still works through the resistance, but a portion of the current through each of
the coils D3, D4 returns through the other coil without meeting the resistance.
The total resistance of the induced member is thus still further reduced. When
the bar F has passed the line 4-4 and rests upon the segment F¹, it is obvious
that the armature is short circuited.
on,
SO
The arrangement shown in Fig. 4 differs only in multiplication of steps and
in their arrangement. The bar El first cuts out a portion, in this case one-third,
of the resistance R', then a portion of the resistance R³, then a portion of the
resistance R², then a second portion of the resistance R4, and
until all the resistance is cut out. It will be seen that this
particular arrangement gives ten steps with only three subdivisions of
each resistance, and that the resistance sections are cut out successively in the
different windings, and in regular order, which equalizes the current in the.
various portions of the induced member.
In Fig. 5 is shown a motor in which the resistance is external to the armature.
B is the inducing member as before, and D is the induced member, carrying
a winding of any preferred type, but in the case shown, preferably of the "Y"
type. The three free terminals of the induced member are connected to the
rings M1, M2, M, on which are brushes and the brushes are connected to the

page_text: rheostat N. This rheostat is of a type well known in the art, and contains three
sets of segments P1, P2, P³, connected and carried by a spider T actuated by
a handle T¹.
Right-handed rotation of the spider from the position shown, gradually cuts
the resistance in the secondary winding, but it will be noticed that the first
plate P is larger than the corresponding plate P³, and smaller than the corre-
sponding plate P2, so that the brush S¹ meets its second plate before the brush S
meets its second plate, and so on, so that the plates are really staggered with
relation to each other and the brushes, and the action is the same as in the forms
previously shown.
It will be evident that various changes in form and arrangement may be made
without departing from the spirit and scope of the invention. Nor is this inven-
tion limited to induction motor secondaries since it is in many of its aspects,
applicable generally to the regulation and control of multiphase systems, and
also of any interlinked system. It will be seen that, by the substitution of
reactances or condensances for resistances, or by the substitution of combined
resistances and reactances or of combined resistances and condensances, it is
enabled to regulate the flow as well, as the magnitude of the currents. All of
the above named quantities are included under the broad term impedances.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same
is to be performed, we declare that what we claim is:-
1-The method of regulating the magnitude or phase or both, of the current
in a multiphase system, which consists in inserting or withdrawing impedances
in the various branches or circuits successively rather than simultaneously.
2 The method of regulating an induction motor which consists in manipu-
lating the resistances in the induced windings successively rather than simul-
taneously.
3-The combination with a set of wires carrying multiphase currents, of means
for inserting impedances in various wires successively rather than simul-
taneously.
4-The combination with an interlinked system carrying electric currents, of
means for inserting impedances in the various wires successively rather than
simultaneously.
5-The combination of an induction motor, of a multiphase induced member,
a resistance therefor, and a means for cutting out the resistances in the different
branches successively rather than simultaneously.
6-The combination with an induction motor having a plurality of induced
windings, of resistances interposed in series with each of said windings, and
means for cutting out said resistances successively in the different windings.
7-The combination with an induced motor with a set of resistance contacts
for each phase, and a set of co-operating contacts moving relatively thereto, the
various contacts being so staggered with relation to each other that the
resistance is cut into or cut from the desired circuits successively, in a pre-
determined order.