Improvements in Systems of Electrical Distribution.
Year: 1899

page_text: COMPLETE SPECIFICATION.
Improvements 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 1'. 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:-
The present invention relates to alternating current systems of distribution, and
especially to the arrangement of a frequency changer whereby from any given
circuit other circuits may be derived in which the frequency of the alternating
currents bears any desired relation to the frequency in the main supply circuit.
The invention also comprises certain novel arrangements for regulating the speed
of alternating motors, as hereinafter set forth.
In the accompanying drawing there is shown in diagram, a system of distribu-
tion illustrating typical forms of the various features comprised in this invention.
In the drawing, abc represent the mains of a three phase system of well known
character, which is selected for illustration, though the invention is equally
applicable to distribution systems in which the currents have any other desired
pase relation.
The mains a b c are supposed to be part of a circuit or distribu-
tion system connected to any suitable generator maintaining on the mains electro-
motive forces displaced 120 degrees in phase. The frequency changing apparatus
forming one feature of the invention, comprises an induction motor or rotating
transtormer, as it is sometimes otherwise called, having primary coils C con-
nected in delta or Y, in the usual manner. The drawing illustrates the delta
connection. The secondary S of the motor is constructed in any well known way,
the secondary winding being connected by collector rings and brushes with the
circuit abc. Mounted on the same shaft with the secondary of the motor or
geared thereto in any desired manner, as represented by the belt B, is an alter-
nating generator G. This is shown as a three-phase generator, whose armature
terminals lead to a circuit a,,, and whose field coils are supplied with current
by a direct current exciter E. The exciter is made regulable, so as to vary the
field excitation of the generator G. For this purpose many suitable arrangements
are well known. The drawing illustrates a shunt wound exciter having a variable
resistance or rheostat in the shunt circuit. Translating devices of any desired
nature may be operated from the circuits a, b, c, and a, b, and 2. There are
illustrated groups of lamps L fed from the circuit a, b, c, by transformers
T, T, T and from the circuit a, b, c, by transformers T, T, T. With the
arrangement thus far described it is evident that the motor will be driven after
tue manner of any ordinary induction motor, and the energy supplied thereto
will be divided partly into electrical energy induced in the secondary circuit of
the motor, in which the electro-motive forces will have the same phase relation

page_text: that exists on the primary side but a different frequency. The remaining portion
of the supplied energy is converted into mechanical energy which is consumed by
the motor in driving the generator G, and by the generator is again reconverted
into electrical energy fed to the circuit. By regulating the generator
in the manner explained already or in other well-known ways, the mechanical
ener consumed by the motor may be made greater or less, and the speed of the
motor controlled in this manner. The frequency of the currents in the cir-
cuits a, b, c, and a², b, c, will depend upon the speed of the motor and, in the
generator circuit, the frequency will also depend upon the number of poles given
the generator... Assume, for illustration, that the motor is loaded so as to run
at half speed, then the frequency in the circuit a', ', c', will be substantially one
half that upon the main supply circuit a, b, c. By giving the generator a proper
number of poles the frequency in a², 62, may be the same. If, now, the running
conditions be such that the mechanical load driven by the motor M be small, and
its speed consequently high, the frequency in circuit a, b, c¹ will be low, under
the conditions assumed, relatively to that in the circuit a², 62, c². If, now, the
mechanical load of the motor be increased, the speed will diminish, increasing the
frequency in circuit a, b, c, but decreasing the frequency in circuit a, b, c²
In this manner, the frequency in either of the circuits can be regulated, and for
this reason, we term the arrangement of apparatus a regulable frequency changer.
A second induction M', of any ordinary description, is shown coupled to
circuit a, b, c by a three arm switch 1), and the method of regulating this motor
forms another feature of the invention. The speed at which such a motor will
run, or, in fact, any alternating current motor whether of the synchronous or
induction type, is controlled, as is well known, by the frequency of the currents
supplied to it. In other words we mean to say, that it has been well known that
similar alternating current motors, will run faster under given conditions when
driven from a high frequency, alternator, and slower when driven from "a
low frequency alternator, and this knowledge .is availed of in the
present arrangement, where, in order to regulate the speed of the
motor corresponding regulation is made in the frequency of the
rents supplied to it. It has already been explained how the fre-
quency in circuit, may be regulated, and by using as we propose to do,
frequency in circuit a¹, may be regulated, and by using as we propose to do,
such a regulable frequency changer intermediate between the regulated motor
or motors and the main source of supply where the frequency is constant, corre-
sponding changes in speed are secured in the motors. To render the control of
the motor still more flexible, there are provided resistance coils R1, R2, R3, more
or less of which can be introduced in the secondary circuit of the motor, by any
suitable arrangement of switching mechanism. For this purpose we have shown
a three phase switch D'. the arms of which are connected to the secondary ter-
minals of the motor, and which are adapted to engage contacts r,,, etc.,
joined to successive points in the resistances. This arrangement is in itself
well known in the art, and will be understood without further description. The
switch is also arranged so as to transfer the motor from the circuit a', b', c' to'
the circuit a², 1, . When the switch is in the. position shown engaging con-
tacts e, e, e, the motor is connected with circuit a, b, c, but when thrown so as
to engage with contacts c', e', e', the motor will be connected with the second one'
of the circuits mentioned. This arrangement affords a practicable means for
regulating the speed of one or more motors within quite wide limits: Assume,
for example, that the frequency ou circuit a, b, c, is low relatively to that on
circuit ²². For the lowest speed of motor M it will be connected with the
former circuit and may be regulated within limits by the resistances R, R³, R³,
or by regulating the frequency changer so as to alter the frequency on the
primary side. For higher speeds the motor will be transferred to
the
circuit 2, 2, 3, and again regulated within limits in the ways previously men-
tioned.
..
cur-

page_text: When the speed of the motor M' is to be regulated by the regulation of the
frequency changer, that is to say by varying the speed of the phase changer, and
therefore the frequency of the currents supplied to the motor, it will be con-
venient to place the rheostat It, or other means for regulating the frequency
changer, at or near the motor to be regulated. It will be noticed that when the
motor M is to be retarded, in order to vary the frequency of the current on the
circuit a, b, c, the energy consumed by the retardation is not wasted, but is
utilized and converted into electric current in the circuit of the generator G.
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 changing the frequency of alternating current circuits; or
systems, which consists in supplying currents of given frequency to the primary
of an induction or transformer motor maintained in rotation at a speed different
from that corresponding to the frequency of the supplied currents; feeding one
cireuit with currents induced in the secondary of the motor, and a second circuit
with currents, generated in a generator mechanically coupled with the motor, and
representing the mechanical energy consumed by the motor, as set forth.
2. The method of changing the frequency of alternating current circuits or
systems, which consists in supplying alternating currents of given frequency to
the primary of an induction motor, which divides the initial energy, first, into
alternating.currents of different frequency induced in the secondary member of
the motor, and second, into mechanical energy; reconverting the whole or portion
of the mechanical energy into alternating currents, and feeding separate circuits
with the currents induced in the motor, and those reconverted from mechanical
into electrical energy..
3. The method of supplying a translating device with currents of any desired
frequency, which consists in generating alternating currents, supplying then 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.
4. The method of operating an alternating current motor at different speeds,
which consists in generating alternating currents, supplying them to a frequency
changer, supplying current from the frequency changer at a plurality of different
frequencies on a plurality of different secondary circuits, varying the frequency
of the currents on said secondary circuits, and shifting the motor from one to
another of said circuits.
5. The method of changing the frequency of alternating current circuits, or
systems, which consists in converting electrical energy, in the form of alternating
currents of given frequency, by a frequency changer, into currents of different
frequency in two or more electric circuits, and regulating the frequency changer
so as to vary the relative frequencies in the last named circuits.
6.--The method of operating variable speed alternating current motors, which
consists in deriving from a given distribution system by a frequency changer,
two or more circuits of different frequencies, and transferring the motor or motors
to be regulated from one to the other of such circuits in accordance with the speed
desired, as set forth.
7. The combination of an induction motor connected to an alternating current
circuit, a generator geared thereto, separate circuits for operating translating
devices connected respectively with the generator and the secondary of the motor,
and means for regulating the amount of mechanical energy consumed by the
motor in driving the generator.
8. The herein described means for changing the frequency of alternating
current circuits, consisting of an induction motor having its primary connected
with a source of alternating currents of given frequency, an alternating generator

page_text: geared to the motor, and separate circuits connected respectively to the secondary
of the motor and with the generator driven thereby.
9. The combination of an induction motor, an alternating generator geared
thereto, with separate circuits leading from the secondary of the motor and from
the generator terminals, an alternating current motor, and a switch for trans-
ferring the motor from one to another of said circuits, as set forth.
10. The combination of a source of alternating currents, a frequency changer,
a plurality of secondary circuits from the frequency changer carrying currents of
different frequencies, a translating device, and means for transferring the trans-
lafing device from one to another of said secondary circuits.
11. The combination of an alternating current supply system, a frequency
changer, a plurality of secondary circuits leading from different points on said
frequency changer, such that currents of more than one frequency may exist at
the same time on the secondary circuits, and means for varying the frequency
of said currents.
12. The combination of a plurality of dynamo electric machines, each adapted
to develop a polyphase current of different frequency, a single source of electri-
cal energy for driving said machines, an energy-consuming circuit, and means
for shifting the connections of the circuit from one machine to another.
Dated 14th day of March 1899.
THE BRITISH THOMSON-HOUSTON CO. LTD.
ALFRED CLEMENTS,
Applicants,
Assistant Secretary.
W. MARTINDALE,
A. R. MoxкS,
Directors.