Improvements in Devices for Changing the Frequency of Alternating Currents and in Systems of Electrical Distribution.
Year: 1899

page_text: Date of Application, 14th Mar., 1899-Accepted, 20th Jan., 1900
1
COMPLETE SPECIFICATION.
Improvements in Devices for Changing the Frequency of Alternating
Currents and in Systems of Electrical Distribution.
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, in the 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;-
4. St ...
The present invention relates to certain novel arrangements for changing the
frequency of alternating currents either of one or a plurality of phases, the object
being to take currents from any distribution system in which the currents have
a given frequency, and to convert these currents into other currents having a
frequency different from that of the current supplied.
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In the accompanying drawing, Fig. 1 shows in diagram a system of distribu-
tion embodying a simple form of the invention, and Fig. 2 is a similar diagram
showing the invention in a more extended form, and comprising some improve-
ments not present in Fig. 1.
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In the drawing, a, b, c, represent the mains of a three phase system which is
selected to illustrate the invention, though other polyphase systems, or 'even
single phase systems, may be treated in a similar manner. An induction motor, M,
has its primary coils connected to the respective mains, and its secondary mein-
ber is coupled in circuit with the primary coils of a second similar motor M¹.
The secondary of motor M is closed through variable resistance R, R, R², more
or less of which may be cut into or out of circuit by any suitable switching
mechanism, as, for example, the three-arm switch B, which connects with con-
tacts joined to various points in the resistances, as shown. To secure steadiness
of action, the motors are geared mechanically so as to run in unison. In prac-
tice this may be accomplished by mounting the rotating members on a common
shaft or by any desired form of gearing. A belt C is shown for this purpose in
the drawing which is supposed to pass around pulleys of like diameter on the
shafts of the rotating members of the motors. With such an arrangement the
inotors will be maintained in rotation at equal speeds each running at substan-
tially half the speed which either one alone would attain under similar conditions
if connected to the circuit b, c. The frequency in the circuit connecting the
secondary motor M to the primary of motor Al is equal to the difference between
the line frequency and the speed of the secondary member of motor M. From
these connecting leads we bring out a working circuit a, b, c, in which the
frequency will have a value different from that in the circuit a, b, c, by an
amount depending upon the conditions under which the motors are operated.
Translating devices of any desired character may be operated on this last circuit.
There is shown a synchronous motor M² whose field coils are excited in the
ordinary manner by a direct current generator E.

page_text: In the system shown in Fig. 2 there are three induction motors M, M³, M³,
geared together by belts C or in any other manner, and coupled in tandem,
as already explained. The primary of motor M receives current from the
mains a, b, c, and resistances are provided in the second circuit of the last motor M².
Circuits a¹; b¹, and a², b², c², are brought out from the leads connecting
respectively the motors M, M and M', M. From these last circuits, translating
devices are operated as required. Lamps L are shown coupled with the cir
cuit a, b, c, through transformers T, T" and in a similar manner lamps are
operated from circuit a², 62, c, by transformers T², T³, T.
With this arrangement, the motors M, M³, M², will run at one third the speed
corresponding to the line frequency, which means, that the frequency in cir-
cuit a, b, c, will be substantially two-thirds of the line frequency, while the
frequency in circuit a, b, c, will be one-third of the line frequency, In this
manner the line frequency is divided up into two or more circuits having rela-
tively different frequencies. By adding more motors the subdivision can be
carried to any extent desired, and a group of working circuits secured of gradu-
ated frequencies. An induction motor M³ is shown as having its primary con-
nected to the circuit a¹, bc, by a three-arm switch S, while its secondary is
closed through adjustable resistances. K, R1, R2, more or less of which may be
brought into circuit by the switch B, or any other preferred form of switching
mechanism. Contacts are brought out from the circuit a³, 62, c² so that the motor
may be thrown from one circuit to another by the switch S, as will be understood
from the drawings. The speed of the motor may then be regulated partly by
the resistances in the secondary circuit, or by throwing the primary from one
to another of the circuits a, b, c and a, b, c, which are maintained as explained,
at different frequencies, or without shifting the motor from the circuit a, b, c,
the running conditions of the inductions motors M, M, M may be regulated in
a variety of ways, so as to change the frequency in the circuit a¹, ¿¹, c¹. For
example, if one of the motors, M2, be cut out of the circuit by the switch S' and
the secondary of the motor M be closed so as to leave only two motors in tandem
series, the speed of the motors will rise to one-half of the line frequency, and
the frequency in circuit a, b, c, will fall from two-thirds to one-half of the line
frequency. Other methods of regulating the irequency in the secondary circuit
of one or more of the motors by adjusting the running conditions, will be under-
stood by engineers.
20.
.11.1
Though the secondary machines of each series are constructed like ordinary
induction motors, and though we have spoken of them as such, it is evident
that, in the actual operation of the machines, they may act as generators," driven
mechanically by one or more of the motors in series, and supplying currents
to the secondary systems in multiple with the secondary member of the next
preceeding motor. In Fig. 1 for example, the machine M¹ acts as a mechanical
brake on the machine M, and the energy thus absorbed is transferred along the
belt C to drive ¹ as a generator, in multiple with the secondary of M. At cer-
tain speeds of mechanical rotation, and at certain corresponding frequencies on
the secondary circuit the machine M', which is only excited by its own currents
will not tend to act as a generator, as is well understood in the art. But under
these conditions, there will be not mechanical load on the machine M, which
will speed up slightly. This will increase the speed of M, and at the same
time reduce the frequency of the currents in the intermediate circuits. When
this speeding up has reached a certain amount, the speed of M will become
greater than the speed corresponding to the frequency of the currents in the
intermediate circuits, and M¹ will be in the condition of an induction machine
driven above synchronism, and will exert a drag on the machine M, through
the belt C, which will prevent any further increase of speed. The machine M',
acting as a generator then delivers current to the intermediate circuits, of the
same frequency as that of the current already flowing therein, and the energy
which drives M is transferred along the belt C from the machine M.

page_text: Having now particularly described and ascertained the nature of our said in-
vention (as communicated to use from abroad) and in what manner the same is
to be performed, we declare that what we claim is:-
1 The combination of two or more induction motors connected in tandem,
with the secondary of the first motor in circuit with the primary of a succeeding
motor, and the primary of the first motor connected with an alternating distri-
bution system, with means for maintaining said motors in rotation at a speed
different from that corresponding to the line frequency, and a circuit for operat-
ing translating devices connected in multiple with the secondary of one motor
and the primary of the succeeding one.
2-The combination as a frequency changer, of two or more mechanically con-
nected induction motors coupled in tandem, and absorbing power from a supply
circuit, with a working circuit of different frequency from the supply circuit
connected in multiple with the secondary of one such motor and the primary of
the succeeding motor in series.
3-The combination of two induction motors connected in tandem, one of
which is coupled to an alternating supply circuit, with a working circuit con-
nected between the motors in multiple with the secondary of one and the primary
of another, and means for regulating the speed of the motors and thereby the
frequency of the last mentioned circuit.
4 The combination of a series of mechanically connected induction motors
coupled in tandem, with the secondary of one motor connected to the primary
member of a succeeding motor, and circuits of different frequencies leading- off
from between the different pairs of motors, as set forth.
5 The combination of a series of induction motors geared together and coupled
in tandem, with circuits of different frequencies joined to the leads coupling
the different pairs of motors, one or more alternating current motors, and switches
for transferring the motors from one to another of the last mentioned circuits,
as set forth.
6-The combination of two induction motors, with the secondary of one con-
nected to the primary of the other, means in addition of said connections for
causing a transfer of energy from one motor to the other, and a circuit extend-
ing from the leads connecting the said primary with the said secondary to a
translating device, whereby the two motors act as a converter of frequency.
7-The combination of two induction motors connected in tandem one of which
is coupled to an alternating supply circuit, with a working circuit connected
between the two motors in multiple with the secondary of one and the primary
of the other, and means for fixing the speed of the second motor, to fix the fre-
quency of the currents in the working circuit.
S-A frequency changer composed of two dynamo electric machines of the
rotary field type, connections from one of the machines to a supply system, con-
nections from the frequency changer to a secondary system, and means whereby
the speed of one of the machines is so modified by the action of the other that
the currents induced in its secondary member, and fed therefrom to the secondary
system, are of a definite frequency different from the frequency of the currents
in the supply system.
9-A frequency changer composed of two dynamo electric machines of the
rotary field type, connection from one of the machines to a supply system, con-
nections from the frequency changer to a secondary system, and means whereby
the speed of one of the machines is so modified by the action of the other that
the currents induced in its secondary member, and fed therefrom to the secondary
system, are of a frequency different from the frequency of the currents which
would normally be induced therein.
10 The methods of distributing electrical energy which consists in generat-
ing alternating-current of a given frequency and supplying it to a distribution
system, and at one or more points on said system, producing by said current a

page_text: i
rotary field in the primary member of one of a pair of dynamo-electric machines,
receiving energy from the said system, generating in the secondary of said, ma-
chine an alternating current by the relative rotation between the said field and
the secondary, and so modifying the speed of the said rotation by the action of
the other machine, that the frequency of the current induced in the secondary is
different from that which would be normally induced therein, and also different
from the frequency of the original. alternating currents, and supplying-the-cur-
rent thus induced to a secondary system.
1.
11 The combination of two dynamo-electric machines of the rotary field type,
mechanically coupled together and adapted to exert torque in opposition-to each
other, and means whereby current of one frequency, delivered to the machines
is. delivered: by the machines at a different, frequency.
12-The combination of two dynamo-electric machines, the rotors of which
have a fixed ratio of rotation,, means. for applying electrical energy directly to
one only of said..machines, and means whereby both machines co-operate to
change the frequency of the current supplied:
13 The combination of two dynamo-electric machines each having two mem-
bers capable of relative rotation when electrical energy is supplied directly to
but one member only of one of the machines, a single source from which energy
is derived, electrical connections, between said source and one of said machines,
means whereby the machines co-operate to produce electric currents of a fre-
quency different from that of the current supplied and means for supplying the
currents so produced to a translating device.
..14 The combination with a system of electrical distribution, of a frequency
changer consisting of a pair of dynamo-electric machines, so connected as to
transfer energy from one to the other, a single set of connections from the sys-
tem for supplying energy to the frequency changer, a winding on one of said
dynamo electric machines in which currents are developed of a frequency hav-
ing a definite ratio to that of the currents of the supply system, and a secondary
system supplied with current generated in and derived from said winding..
15 The combination of two alternating-current dynamo-electric machines
mechanically coupled together, one of said machines having a secondary member
in which current of a definite frequency is induced, means whereby the reaction
of the other machine definitely determines the frequency of the current so induced,
a circuit containing one or more translating devices, and means for supplying
said circuit with current induced and derived from said secondary member.
16 The combination of two dynamo electric machines of the rotary-field type,
means for supplying to one member of each machine an electric current, an
energy consuming circuit containing one or more translating devices, and means
for supplying said current with energy derived from the induced member of one
of said dynamo-electric machines.
17 The combination of a plurality of dynamo-electric machines, the rotors of
which are mechanically geared together, means for producing in each machine
a.rotary magnetic field, electrical connections between one of the members 'of
one machine and a line circuit, a work circuit adapted to feed one or more trans-
lating devices, and means for supplying said work circuit with current derived
from the secondary member of one of said machines.
:
18 The combination of a plurality of dynamo-electric machines of the rotary-
field type, means for maintaining a definite ratio between the respective rates
of rotation of the rotors of said dynamo-electric machines, means for supplying
an electric current to one member of each machine, a work circuit adapted to
feed one or more translating devices, and means for supplying said work circuit
with current derived from the secondary member of the machines.
19 The combination with a system of electrical distribution, of a frequency
changer consisting of a pair of dynamo electric machines, one of which is
adapted to act as an induction generator and the other as a motor, means for

page_text: maintaining a predetermined ratio of rotation between the two machines, con-
nections for supplying current from the system of distribution to the frequency
changer, and means for deriving from the induction generator current of a
frequency different from that supplied to the frequency changer.
20 The method of changing the frequency of alternating currents which con-
sists in supplying the initial currents to the primary of an induction or trans-
former motor, braking the secondary of the motor by gearing it to a mechanical
load, reconverting the energy so expended into alternating currents, and feeding
a circuit with currents representing the mechanical energy when thus recon-
verted and with the currents induced in the secondary of the transformer.
21-The method of changing the frequency of alternating currents, which con-
sists in supplying alternating currents of given frequency to the primary of an
induction or transformer motor. maintaining the speed of the motor at a rate
different from that corresponding to the frequency of the supplied currents, and
thereby inducing currents of different frequency in the secondary of the motor,
converting the energy expended in maintaining the motor at the desired speed
into electrical energy in the form of alternating currents of the same frequency
as those induced in the secondary of the motor, and feeding the last named cur-
rents into a circuit connected with the secondary of the motor.
22 The combination of a transformer or induction motor having its primary
supplied with alternating currents of given frequency, and maintained in rota-
tion at a speed different from that corresponding to the frequency of the sup-
plied currents, a second dynamo-electric machine receiving power from the motor
and a circuit containing translating devices connected with the secondary of the
motor, as set forth.
23-The method of changing the frequency of an alternating electric current
which consists in supplying it to a frequency changer comprising two alternating-
current dynamo-electric machines connected in tandem, driving one of said
machines as a motor and one as a generator, transferring energy from one to the
other, taking off current from said frequency changer of a frequency different
from that of the current supplied, and feeding said current to translating
devices, substantially as described.
24 The method of utilizing electric current which consists in supplying it
to the primary of an induction motor, producing thereby a current in the second-
ary of said motor and a torque upon its shaft, supplying the secondary current
thus produced to a translating device, utilizing the said torque to drive a genera-
tor, and feeding the current from said generator to the translating device upon
the same mains with the said secondary current, substantially as described.
25-The method of supplying a translating device with currents of any desired
frequency, which consists in generating alternating currents, supplying them to
the primary of an induction motor, supplying currents from the secondary of
the induction motor to the translating device, retarding the induction motor so
as to vary its slip according to the frequency desired upon the secondary circuit,
and generating by the energy consumed by such retardation an electric current.
Dated 14th day of March, 1899.