Improvements in or relating to Induction Motors.
Year: 1897

page_text: Date of Application, 8th June, 1897- Accepted, 27th Nov., 1897
COMPLETE SPECIFICATION.
Improvements in or relating to Induction Motors.
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, of Schenectady, County of Schenectady, State of New York, United
States of America) and in what manner the same is to be performed, to be par-
ticularly described and ascertained in and by the following statement:-
-
Our invention relates to motor meters, or more generally to motors which are
particularly adapted for meters of the alternating current type; and has for
its object to provide a simple induction motor meter arranged to efficiently
record the consumption of energy in a watt meter of current in an ammeter or of
potential in a voltmeter. The particular type which we have illustrated is
especially adapted to single phase circuits, but it may be employed in circuits
of other numbers of phases, by suitable modifications well known in the art but
which are hereinafter explained.
To adapt an induction motor to the registration of energy on single phase cir-.
cuits, it is necessary that a two phase effect should be obtained; this may be
done in a watt meter by combining a current coil and a potential coil with
inductance, capacity and resistance in various relations to obtain the displace-
ment required; but it is essential in order to obtain accurate registration
on inductive loads, that the displacement of phase between the current
and shunt coils shall be exactly ninety degrees. Several different arrangements
have been proposed for obtaining this, but the arrangement which we have devised
is different from any with which we are familiar.
In general the motor consists of a short-circuited armature, which in the case
of meters would be the usual drum or cylinder of metal of high electrical con-
ductivity, such as aluminium or copper, the drum being mounted for rotation
and having adjacent to it coils in which the alternating current flows. The
arrangement of the coils varies according to the object of the motor, which will
be described throughout in this application as one adapted to meters; but we do
not mean to limit ourselves to that, inasmuch as the devices shown and claimed
are useful for starting or running single-phase alternating current motors of
other types. In one arrangement of the motor, designed to measure current,
or a recording ampere-meter, we employ two current coils connected in multiple
with each other, but in series in one of the lines, together with a phase-displacing
means. In another form, designed for a recording voltmeter, we connect the two
coils in multiple across the lines and in series with the phase-displacing means.
In the watt meter form we employ a current coil and a shunt coil in the circuit
of which the phase-displacing means is connected. The latter, which is an impor-
tant feature of our invention, and one which we particularly claim as novel,
consists of a reactance of inductive character, having upon a single core coils
which are wound to have a certain difference of effect. The construction may
be a single coil wound in a given direction; the lead supplying current to the
coil taps it at an intermediate portion of its length, so that the current flows
in opposite ways through the two parts of the coil; or it may consist of two coils,
in which the current flows in the same direction, but still upon the same core,

page_text: so that they have a mutually inductive relation. In the lead to this regulating
inductance we may insert another inductive reactance serving to displace the phase
of current in the shunt coil to an approximation to ninety degrees, and the regu-
lating inductance is then only of such an amount as is necessary to get exact
quadrature; but we may dispense with the larger inductance and combine upon
the single core the windings necessary to produce exact quadrature. By suitably
proportioning the turns of the two coils in mutually inductive relation, we may
get any displacement of phase, from zero to opposition. Where the arrangement
is employed in a watt meter we prefer to employ also a small auxiliary starting
coil to compensate for friction. This would ordinarily be connected across the
mains, and its current would be in phase with the main line electro-motive force.
A non-inductive resistance is usually included in the circuit of the starting coil to
limit the amount of current consumed and to keep the current in phase with the
electro-motive force.
Our invention is illustrated in some of its forms in the accompanying drawings,
in which Figs. 1, 2 and 3 are diagrams of circuits, and Fig. 4 is a sectional plan
of a mechanical arrangement which may be employed. Fig. 5 is a diagram of
a three-phase circuit.
In Fig. 1, which represents the arrangement needed in a wattmeter A and B
are the mains; C is the current coil in series in one of the mains; D is a shunt
coil coupled across the mains, the current in which is to be adjusted to quadrature
with the main line current. I is a reactance in series with the shunt coil. I' is
the auxiliary regulating inductance, consisting of an iron core upon which is
wound a single coil. The lead from the inductance I is tapped into the coil
upon I at the point i, so that this latter winding forms in effect two coils having
different numbers of turns, part being in shunt around the shunt meter coil and
part being in series with it.
The counter electro-motive forces and current induced in the local circuit, in-
cluding the regulating inductance and shunt coil D, by the current flowing through
the two branches of the coil I¹ combine with the Electro-motive force and current
impressed on the shunt circuit from the mains A, B, so as to create a difference
of phase between the currents in the two branches of the divided circuit. By
properly proportioning the windings of the regulating inductance, this difference
of phase may be made greater or less as desired. For example, assume that in
the watt meter of Fig. 1 the current in the series coil C is substantially in
phase with the electromotive force in the main circuit, and that the current
in the shunt circuit is lagged by the inductance I eightyfive degrees behind the
electromotive force. Thus to obtain the desired 90 degrees difference of phase
between the series and potential magnetisms, the windings of the phase-regulating
inductance I¹ would be so proportioned as to lag the current in the branch passing
through Da still further amount sufficient to make up the total of 90 degrees,
and of course in so doing the current in the second branch shunting coil D would
be advanced. Hence since by the phase-regulating inductance I¹ it is possible
to establish a desired difference of phase between the currents in, the two branch
circuits, it is possible in accordance with laws well understood by electricians.
to adjust such a device to produce desired results in various combinations when
the control of phase in a circuit or circuits is a desideratum.
E is the starting coil and R is a resistance in its circuit preserving the circuit
in phase or nearly in phase with the electromotive force, while M is the closed
circuited armature, consisting of a drum or cylinder of conducting metal, such
as aluminium, preferably non-magnetic in character, and of about the same size
as the well known Thomson recording watt meter. The coils acting on the arma-
ture are also about the same size as those in the Thomson recording watt meter,
or somewhat smaller where a large number are used, and may be arranged in the
same manner as in the Thomson recording watt meter, or mounted on polar pro-
jections of an iron magnetic circuit. The current coils consist of a few turns of
coarse wire, the potential or shunt coils of very many turns of fine wire of about

page_text: the same size as the shunt circuit, that is, the armature of the Thomson recording
watt meter. The resistances are about the same size also as in the Thomson
recording watt meter.
In Fig. 2 we show the disposition of the circuits adapted to the measurement
of current. Therein the parts are as before, except that there is no shunt coil,
and two current coils C, C are provided, the currents in which are to be in
quadrature, or displaced by any desired definite angle. These coils will be arranged
at different angles to the armature; as shown the axes of the coils are at right
angles to one another. This displacement of phase is effected by winding the
phase-regulating reactance I¹ with two coils 12, 13, upon the same core, but with
different numbers of turns; so as to afford different electromotive forces; the effect
being to displace the phase in the coil C¹ relative to that in coil C, as has been
already explained. The division of currents between coils C and C depends upon
the relative proportioning of the mutual inductive coils I2 and 13. thus for instance;
if the coils O, C¹ are equal and have each the reactance of 001 ohm, and effective
resistance of 003, such a number of turns as 12 are wound on an iron core as to
give to this coil a reactance of 1/400 or 0025 ohms, and twice as many turns
wound in the same direction on the same core as coil I³; thus making the reactance
of the latter coil 01 ohm. In this case, if 100 amperes pass over the mains B,
the current will be divided into a current of 90 amperes passing through coils 12
and C, and a current of 45 amperes passing through coils T and C, the voltage
at the terminals of coil C will be 28, and that at the terminals of C will be
14 volts, while the total voltage consumed by the meter is 59 volts.
As will be seen in this case, coil C has twice as many ampere turns as coil C¹,
and the currents in the two coils have exact phase displacement of 90° or one
quarter period.
In the above given figures, it is assumed that no loss of voltage takes place in
the coils 12 and 13. Since due to the internal reactance of these coils and the
hysteresis loss in the iron core, some energy is consumed in this phase displacing
device the number of turns has to be slightly modified to make up therefor.
Obviously, different proportions between the currents and the phase displace-
ment of C and C can be secured by different arrangement, that is, different
numbers of turns of the coils 12 and 13.
In Fig. 1, where a lag of 90° is desired in D, the reactance I consisting of an
iron core wound with about the same size wire as D), will produce approximately
this lag, and the phase-displacing device I' is very small and is used only to
produce a small phase displacement for the purpose of getting D in exact quad-
rature.
In Fig. 3 the connections for a volt meter are shown. They are identical with
the connections shown in Fig. 2; except that the whole arrangement embracing
the two shunt coils D D' and the reactance I is coupled across the mains.
In Fig. 4 we show a mechanical arrangement which may be adopted. Therein
the coils C and D) of Fig. 1 are arranged at right angles upon the inside of the
drum M, and the starting coil E is arranged parallel to the current coil, so that
there will always be a slight starting effect sufficient to overcome friction at small
loads.
Fig. 5 shows the application of an induction meter of the type described in this
specification to a polyphase system which, in the illustrated case, is the well-
known three-phase system, with the phases differing from each other by 120º.
To record the energy in such a system, it is necessary to integrate the current
and potential values upon the two sides; that is to say, the watt energy would
be the product of current in one side by volts in that side, measured between the
in which the current flows and the third line of the system, plus the watts in the
other side of the system, that is, the current flowing in the second line, into the
volts between that line and the third line of the system.
To conveniently effect this registration, in a three-phase system, in a meter
operating on the inductive principle, two of the devices which have previously

page_text: illustrated may be employed, connected as shown in this figure, and the sum of
the readings of the two meters will give the watt energy in the three-phase mains.
In this figure, the parts are lettered as before, but it will be observed that the
current coils C, C of the two meters, of which M, M are the revolving armatures,
are respectively in the lines B, E of the three-phase system, while the potential
coils D, D are connected respectively in conjunction with the phase-displacing
devices, which are similar to those already described, between the lines B, A,
(in case of the coil D), and E, A, in case of the coil D¹.
By the combination of apparatus pointed out, we are enabled to measure with
accuracy the watt energy of a three-phase system, regardless of the balance of
load upon the lines, and also independent of changes of lead and lag between
current and electro-motive force.
It is of course designed that the usual co-operating parts of the meter shall he
employed, counting apparatus of any desired type, gearing for transmitting the
movement of the drum, and the usual brake, frictional or magnetic; but none
of these parts is illustrated, as they do not constitute any part of our invention,
and may be indefinitely varied.
Having now particularly described and ascertained the nature of our said in-
vention (as communicated from abroad) and in what manner the same is to be
performed, we declare that what wo claim is :-
1. An inductive device for obtaining a definite phase displacement between a
circuit and a branch thereof, consisting of two windings having different numbers
of turus inductively related upon a common core, said windings being included
respectively in branches of the circuit.
2. An inductive device for obtaining a definite phase displacement between two
branches of a circuit or two circuits, consisting of two windings having different
numbers of turns upon a common core, and inserted respectively in the circuits or
branches between which the phase displacement is to be produced.
3. An induction motor device comprising two inducing circuits or coils in which
currents in exact quadrature are to be maintained, an induced member in the
field of the inducing coils and means for producing currents in quadrature in the
two inducing circuits; such means consisting of a core provided with two coils
of different numbers of turns included in branches of a circuit magnetizing the
motor.
4. An induction motor meter comprising a drum of good conducting metal,
and inducing coils co-operating to induce current in the drum and thereby pro-
duce its rotation, the coils energized by current from a single-phase circuit, and
one of the coils having in circuit with it an inductive device for displacing the
phase of current in the energizing coils by ninety degrees, the device consisting
of coils of different numbers of turns inductively related upon a common core
and included in branches of one of the energizing circuits.
5. An induction motor meter comprising a drum of good conducting metal,
inducing coils co-operating to induce current in the drum and thereby produce
its rotation, the coils energized by single-phase current and one of the coils having
in circuit with it an inductive device for displacing the phase of current therein
to exactly ninety degrees, the device consisting of coils of different numbers of
turns upon a common core, and an auxiliary starting coil compensating for friction
in the meter.
Dated this 8th day of Tuna 1907