Improvements in Regulating Rotary Electric Converters.
Year: 1899

page_text: Date of Application, 22nd Nov., 1899-Accepted, 30th Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Regulating Rotary Electric Converters.
We, THE BRITISHI THOMSON-HOUSTON COMPANY LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of
our said invention (which has been communicated to us from abroad by
Ernst J. Berg, of 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:-
In modern rotary converter installations, the regulation of the direct current
voltage is ordinarily effected by varying the field excitation of the converter.
Such a variation of field excitation acts in a well understood manner to vary the
phase relations in the alternating current system connected to the converter, and
if the alternating current system contains reactance, the electro-motive force at
the alternating current terminals may be made to rise or fall as may be desired,
and thus cause the direct current voltage, which bears a definite relation to the
electro motive force across the alternating current terminals, to rise or fall
correspondingly. The means ordinarily employed for varying the field excitation
of the converter is a series field winding supplied with current from the direct
current system connected to the converter. An increase of load on the converter
thus acts to increase the field excitation, thus decreasing the amount of lagging
current in the alternating system if the current be lagging,
increasing the amount of leading current if the current be leading. If the
alternating current mains contain a sufficient amount of inductance, the electro-
inotive force at the alternating current terminals of the converter may be made to
rise an amount sufficient to maintain a constant electro-motive force at the direct
current terminals of the machine or, the rise in electro-motive force may be made
sufficient to secure an over-compounding effect on the direct current system, as
may be desired.
Rotary converters when thus provided with series field windings are open to
several objections. The cost of such a machine is considerably more than that of
a machine provided with a shunt field winding only, while at the same time the
machine with the series winding necessitates a more complicated and conse-
quently more expensive arrangement of switch board to be used in connection
therewith. Another disadvantage of the compound wound rotary converter is
the troublesome manipulation required where machines are run in multiple. In
addition to the connections necessary for the simple shunt wound rotary converter
under similar conditions, a compound wound machine requires equalizer con-
nections which must be closed at the proper time, and also in some cases it is
necessary to provide switches in the German silver adjusting resistances for the
series winding.
Because of these and other allied disadvantages we find it desirable, in some
instances to provide the rotary converter with a shunt winding only, and to
secure the necessary regulation of the direct current voltage by suitably varying

page_text: the reactance in the mains or conductors over which the alternating current is
supplied.
The particular method of varying the reactance in the alternating supply mains
depends upon the manner in which the field excitation of the converter is adjusted.
If, for, example, the field strength of the converter is such as to cause lagging
current to flow in the alternating supply mains, it is necessary to decrease the
amount of reactance in the alternating mains in order to increase the electro-
motive force at the rotary converter terminals and so maintain the direct current
voltage, either constant or variable with respect to the load as may be desired.
If, on the other hand, the current in the alternating supply mains is made
leading by means of over excitation of the field of the converter, or from other
causes, it is necessary to increase the inductance in the alternating supply mains
with increase of load in order to secure the desired regulation of the direct
current system supplied by the converter.
In accordance with the mode of operation thus briefly outlined, our invention
generally speaking, consists in regulating a rotary converter by automatically
varying the reactance in the alternating current system in a manner dependent
upon the load on the rotary converter.
Our invention will be more readily understood by reference to the following
description taken in connection with the accompanying drawings, while its scope
will be more clearly and particularly pointed out in the appended claims.
Fig. 1 illustrates the application of our invention to a rotary converter system
in which the alternating currents are supposed to be lagging. Fig. 2, shows
the inductance varying device which is to be used in cases where the alternating
currents are caused to be leading.
Fig. 3 shows a different form of inductance varying device. Referring to Fig. 1,
C indicates a rotary converter having the usual collector rings K, and commu-
tator brushes L. The field of the machine is excited by the shant winding S con-
nected across the direct current mains a b. The translating devices of any suitable
nature, such as motors or lights, are arranged to be fed from these direct current
mains.
The alternating current mains over which energy is supplied to the converter
are indicated at c, d, e, and in this case are shown as of the three phase type,
although it will be readily understood that any other phase relation whether
single phase or multiphase, may be employed. In order to vary the reactance
in the alternating current mains, we provide a device having relatively movable
members and similar to an induction motor. Upon one of the members, indicated
in the drawings at A, a number of coils or sets of coils are wound equal in number
to the number of alternating current mains, and one of these coils is included
in each main. In the structure shown, the member A consists of a ring core hav-
ing wound thereon three coils, cd, e, displaced from each other by equal angles,
and included respectively in series with the alternating current mains c, d, e. The
relatively movable member E consists of a toothed core of magnetic material similar
to the core of the rotor of an induction motor. This core is provided with short-
circuited coils, displaced from each other by the same angles as the coils of the
member A. The shaft I), carrying the member B has mounted thereon a lever
arm E provided with an adjustable weight F, the action of which produces a
turning moment which tends to move the short circuited coils away from the
corresponding exciting coils on the relatively rotatable member A. The function
of the weight F, is chiefly as a counter balance for the weight of the core U and
its connected parts, and for the additional purpose of returning the movable
member B to a fixed neutral position when no current is flowing in the system.
In the position of the parts indicated in the drawings, the lever E or some con-
nected part, is supposed to be resting against a stop which is not here shown, this
position corresponding to the position in which no current is flowing in the system.
In order to secure the desired relative motion between the two members of the
inductance varying device, we provide in this instance a solenoid T, which is con-

page_text: nected in series with one of the direct, current mains a, b as indicated. Within
the influence of this solenoid is a core U of any suitable form, connected by the
link V with a lever arm carried by the shaft D and shown in dotted lines at W.
In the operation of the system, thus described, the shunt field winding S is sup-
posed to have been adjusted, either by hand or otherwise, so as to insure that the
currents flowing in the alternating current system are lagging. If, under these
conditions, the load on the direct current system were to increase, its electro-
motive force would have a tendency to drop. This tendency is however counter-
acted by means of the inductance varying device A, controlled by the solenoid T.
The increase in current though the solenoid T, due to increase of load, increases
the attraction upon the core U and causes a partial rotation of the member B,
against the combined resisting turning moment due to the reaction between the
currents in the relatively movable members of the device A and to the downward
pull produced by the weight F. When the short-circuited coils on the niember B
are thus brought into closer mutual inductive relation to the coils on the other
member of the inductance varying device, the immediate effect is an increase in
the amount of current flowing in these short-circuited coils and a consequent re-
action of the same upon the primary inducing windings to set up lines of force in
opposition to those produced by current in the primary windings, thus cutting
down the self induction of the latter windings. It will thus be seen that the
inductance, varying device acts, upon an increase in load on the system, to cut
down the inductive drop in the alternating current lines and by consequence to
increase the electro-motive force at the receiving end of the alternating current
system. By suitably proportioning of parts, the rise in electro-motive force at the
alternating current terminals of the rotary converter may be made just sufficient
to maintain a constant electro-motive force at any selected point of the direct
current system. Ordinarily little attention need be paid to the field excitation
of the converter, since the inductance in series with the alternating current
mains, due to the action of the inductance device A, is generally sufficient to pro-
duce the needed amount of lagging current required for the purpose of regulation.
When the currents flowing in an alternating current system are caused to be
leading, as would be the case if the field of the rotary converter were over-excited,
a reactance varying device of somwhat different nature is required. Where lead-
ing currents flow in a system containing inductance, the electro-motive force at
the receiving end of the line may be caused to vary with variation of either or
both of these factors. Heretofore, in the regulation of alternating current
systems by means of varying the field excitation of the rotary converter, the
action has been one in which the induction of the line is maintained constant,
while the amount of leading current is varied. According to our present inven-
tion, the field excitation of the rotary converter is normally not altered in
response to variation of load, the regulation of the system by phase control being
effected by suitably varying the reactance in the alternating current system. In
the present case, where leading currents are supposed to flow in the alternating
current system, increase in electro-motive force at the receiving end of the line is
secured by increasing the inductance of the transmission lines. In Fig. 3, we
Unlike
have shown an automatically actuated device for effecting this purpose.
the arrangement shown in Fig. 1, this device requires no connection with the
direct current system, but on the contrary is actuated solely by the alternating
currents flowing therein. In structure this device is similar in nature to a cou-
stant current transformer of the type having relatively movable members. The
only essential difference between this device and such a transformer is that the
secondary coils are short-circuited upon themselves. The mode of action of this
inductance regulating device is the same as that of the constant current trans-
former of the kind mentioned, and a detailed explanation of the action of the same
is therefore unnecessary. It will suffice to say that one primary coil is placed
in each of the alternating supply mains, and that, as the current in these mains
increases, the short circuited secondary coils move away from their corresponding

page_text: primary coils, thus increasing the leakage flux between the two sets of coils and
so increasing the inductance of the primary coils.
At 1, 1, 1, in Fig. 3, we have indicated the primary windings of a device of the
character described. The short circuited, relatively movable, secondary windings
are shown at 2, 2, 2. The latter windings are carried by one end of a lever 3,
to the other end of which is suspended a weight W. The weight W is attached to
a cord 4 or other flexible connection which passes over an adjustable, eccentric
winding surface attached to the end of the lever 3 and acts to partially counter-
balance the weight of the windings 2, 2, 2, and co-operating parts. The winding
surface is formed by suitably shaping a cam-like device 5 which device is pivoted
at 6 to the end of the lever 3, and may be secured in position by means of a bolt
passing through the slot 7 in the device.
By varying the adjustment of this device, the turning moment exerted by the
weight W, about the axis of oscillation of the lever 3 may be caused to vary
as the angular position of the lever varies, thus causing the inductance of the
primary windings 1, 1, 1, of the inductance varying device to vary, within limits,
according to any desired law.
In place of the device just described, we may, if desired, produce a change in
the inductance in the alternating current system by means of solenoids placed
in series with the respective lines, and acting respectively upon relatively mov-
able cores of magnetic material, arranged to be normally urged out of, or away
from the solenoids by the action of a spring, gravity or some other similar means
Such a device is indicated diagrammatically in Fig. 2 and consists of three
coils S, 8, 8, one of which is included in each of the three mains leading to the
rotary converter, and within the influence of each of which, is located a normally
retracted, subdivided iron core. As shown in the drawings, in Fig. 2, the
cores 9, 9, 9, are carried respectively by arms 10, 10, 10, fixed to the shaft 1. A
spring 12 or other suitable means acts to withdraw the cores 9, 9, 9, from their
respective coils or solenoids when no current is flowing therein, and to oppose
the attraction due to current in the solenoids when current does flow.
It will readily be understood that, with increase of current in the solenoids
the cores are more strongly attracted and thus are drawn further into the solenoid
and so increase the inductance of the alternating current lines into which the
solenoids are connected.
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 a rotary converter, which consists in over-excit-
ing its field and automatically increasing the inductance in the alternating
current system in response to increase of load on the rotary converter.
2-The method of regulating a rotary converter, which consists in automatically
varying the inductance in the alternating current system in a manner dependent
on the load on the rotary converter.
3-The method which consists in varying the reactance on the alternating
current side of a rotary converter as a load on the direct current side changes, in
such a manner as to maintain the direct current electro-motive force at the ter-
minals of the rotary converter or at some other selected points on the direct cur-
rent system substantially constant.
4 The method of regulating a rotary converter, which consists in maintaining
its field excitation at a substantially constant value and varying the phase angle
between current and electro-motive force in the alternating current lines con-
nected to the rotary converter.
5-The method of regulating a rotary converter which consists in maintaining
its field excitation proportional to the electro-motive force between its direct
current terminals, and varying the phase angle between current and electro-

page_text: motive force in the alternating current system in response to variation of lead
on the rotary converter.
6-he method of regulating the electro motive force on the direct current
system supplied by a rotary converter which consists in maintaining the field
excitation of the rotary converter constant and automatically decreasing the
phase angle between current and electro-motive force on the alternating current
mains as the load on the rotary converter increases.
The method of regulating a rotary converter which consists in maintaining
the field excitation of the rotary converter at a substantially constant value, and
automatically changing the reactance in the alternating current lines connected
to the rotary converter.
8 The method of regulating a rotary converter which consists in maintaining
the field excitation of the rotary converter at a substantially constant value, and
automatically changing the inductance in the alternating current lines connected
to the rotary converter.
9 The method of regulating a rotary converter which consists in over-exciting
its field and automatically changing the reactance in the alternating current
lines connected to the rotary converter.
10 The method of regulating a rotary converter which consists in over-
exciting its field and varying the amount of inductance in the alternating current
lines connected to the rotary converter.
11 In a system of electrical distribution, the combination of alternating cur-
rent mains, a self exciting rotary converter connected thereto, an inductance
device in series with the alternating current mains and means for automatically
varying the inductance in the alternating current mains with variation of load
on the rotary converter.
12 The combination if a self-exciting rotary converter an alternating current
supply system connected thereto, and automatically actuated means for varying
the reactance of said supply system, in response to variations of load on the
rotary converter.
13 The combination of a self-exciting rotary converter, an alternating current
system connected thereto, and automatically actuated means dependent upon the
load on the rotary converter for varying the inductance of said system.
14 The combination of a self-exciting rotary converter, conductors connected
thereto, and carrying alternating currents, and means external to said rotary
converter for varying the impedance in the circuit traversed by said alternating
currents, the said means acting responsively to variation of load on the rotary
converter.
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