Improvements in the Method of and Means for Regulating the Phase Relation between Current and Electro-Motive Force in Alternating Current Systems of Electricity Distribution.
Year: 1897

page_text: Date of Application, 28th Dec., 1897-Accepted, 19th Feb., 1898
Improvements in the Method of and Means for Regulating the
Phase Relation between Current and Electro-Motive Force in
Alternating Current Systems of Electricity 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, and Edwin
W. Rice, Junior, both of Schenectady, in the County of Schenectady, State of New
York, United States of America) 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 a method of and apparatus for compensating for
the lag of current behind the electromotive force in alternating current systems of
distribution, or, more broadly stated, for controlling the phase relation between
It is now well known
current and electromotive force in such systems.
in the art, that it is frequently desirable to control the relation between
This regulation is
current and electromotive force in alternating currents circuits.
usually made necessary by the existence of self-induction in the distribution system,
which tends to lag the current behind the electromotive force, with the result of
decreasing the power-factor of the system in a serious and harmful degree.
It has been proposed to correct this disturbance in various ways, both by the use of
condensers and by the use of electro-dynamic phase controllers. This present invention
comprises an improvement in electro-dynamic phase controllers of the induction type,
rendering them more flexible and better suited for the purpose for which they
are designated.
Electro-dynamic phase controllers are superior to condensers in many respects,
since a condenser must be very delicately adjusted, with reference to the self-induction
of the circuit, and the frequency of the electromotive forces impressed thereon ;
moreover, a condenser tends frequently to respond to the harmonics of the fundamental
wave of electromotive force, and sometimes causes very serious and harmful resonant
rises of potential by reinforcing one of those harmonics. Neither can condensers be
used to advance or retard the phase as may be required, nor can they be readily
adjusted to suit any change in circuit conditions. For these and other reasons it
becomes necessary, in most cases, to resort to the use of electro-dynamic phase.
controllers.
Such phase controllers may be of the synchronous type or of the induction type.
The present invention relates particularly to phase controllers of the induction type,.
and has for its object to provide means by which their action may be improved, and
rendered more flexible and more susceptible to control.
In carrying the invention into practice our correspondents prefer to use a structure
like that of an induction motor, having inducing and induced windings such as are
ordinarily provided, but for the purpose of the invention it is essential that the wind-
ing ordinarily known as the induced winding should have a large self-induction,
and that the other element should have as little self-induction as possible, or at

page_text: least a self-induction far below that of the induced element. If this structure were
connected in an alternating current circuit and if the losses of friction, hysteresis,
ohmic losses and so forth, could be avoided it would run up to a speed of absolute
synchronism with the alternations of the main current and would have no influence
upon the circuit, but if it is run below synchronism it will act as a self-inductance in
the circuit retarding the current relatively to the electro-motive force, and if run
above synchronism it will have the reverse effect, serving as a negative inductance, so
to speak, and may be used in substitution for a condenser connected in shunt across
the mains. An induction motor or phase controller modified as above mentioned, that
is, having the larger self-induction in the induced member, will supply a corrective
or modifying current, as it may be regarded, of advanced phase with relation to the
main current, when driven mechanically at any considerable speed above that which
it would have when energized to run as an induction motor upon the alternating
circuit, or in general; above synchronism, and when driven below such normal speed,
or below synchronism, the corrective current it generates is retarded relatively to the
main current.
The advancing or retarding action upon the current relatively to the electromotive
force thus secured can further be modified so as to correspond with the nature and
amount of the load in the circuit by increasing or decreasing the self-induction of the
secondary member of the phase controller. This can be readily done by putting in'
circuit therewith an adjustable reactive coil.
In the drawings attached to this specification, Fig. 1 is a general view of a system
of distribution of the single-phase type, provided with an induction phase controller
embodying the improved adjusting device, and Fig. 2 is a view of a similar three-
phase system.
G, G¹ are sources of alternating currents of single-phase and three-phase character
respectively, which currents are fed by the lines L L to transformers T T' and from
the secondaries thereof, at reduced potential, to local circuits of corresponding
character in which are circuit controlling switches S S¹ and also translating devices,
such as induction motors M M¹ adapted to the current thereon. K K¹ are mechanisms,
machines, or electro-magnetic structures operating by electro-dynamic induction
serving as phase controllers, and having two magnetic elements movable with respect
to each other, the one preferably having a high and the other a low self-induction.
The member A is shown as the induced and movable element and it is wound with
coils on closed circuit upon a core so as to have a high self-induction, which is found
to add to the regulating effect. This may be accomplished by carrying the wind-
ing a through holes in the core of laminated iron as is shown, and by properly
proportioning and designing the winding, or if desired by putting a self-induction
coil in the circuit of this winding, while the induction motors M and M¹ would be
made with as little self-induction as possible in their armatures to prevent a lagging
of the induced current behind its electromotive force. The primary or induced
member has its coils B connected in series in a shunt across the mains of the
secondary circuit. It will be seen, then, that the structure which our corres-
pondents have found best adapted to generate the corrective impulses to com-
pensate for the lagging currents of the system differs from that of an induction
motor as ordinarily constructed in that the character of the induced element, as
regards self-induction, bas been changed. A convenient way of running this
phase controller K at a speed which will give the advanced or retarded wave of
phase required is to belt it to another motor fed from the line, using such a
size of pulley as will give it a speed greater or less than synchronism. In the
drawings the pulleys PP are shown proportioned so
as to increase the
speed of the controller, as the natural tendency of the current to lag
in. an alternating circuit more often demands in practice an advance of
the current relatively to the electromotive force by the controller.
Any other
power able to drive the controller K at the necessary speed will, of course,
suffice. Again, the controller K may have a greater number of poles than the machine'
M, and be driven at the same speed, when the result will be manifestly the same.

page_text: In the case of the three-phase machines M¹, or other plural phase machines, it is of
course only necessary to wind the controller machine correspondingly, as indicated
at K¹ and to adjust its speed or the number of poles used as in the case of the
machine M and the controller K. When coupled in shunt to the circuit as shown
the controller will generate current waves which are behind or ahead of the main
current waves and are added thereto to establish the desired resultant relation.
its broadest aspects, however, the invention includes an induction controller of the
character described when coupled in series, as the modifying electro-motive force
waves which would then be set up may accomplish the same result of controlling the
phase of the current and electromotive force waves relatively to one another.
In
In order to regulate the advancing or retarding action of the controller as the
nature or the amount of the load in the circuit is changed and the lagging or lead of
the main current increases or diminishes in amount, the self-induction of the secondary
member of the controller should be changed correspondingly. For this purpose there
are shown, both in Fig. 1 and Fig. 2, reactive coils R R R² included respectively in
the three branches of the three-phase winding, and corresponding movable
cores QQ1 Q2 are provided for varying the reactive effects of the coils as needed.
Having now particularly described and ascertained the nature of the 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 controlling the phase relation between current and electro-
motive force in an alternating current circuit, which consists in revolving a closed
secondary conductor relatively to its primary conductor at a rate above or below
synchronism according as an advance or retardation of the current relatively to the
electromotive force is desired, and varying the self-induction of such secondary
member to modify the advancing or retarding influence thereby secured upon the
phase relation of the main current.
2. The combination in an alternating current circuit of an electro-dynamic phase
controller having inducing and induced members, means for increasing the self-
induction of the induced member, and a source of power driving said controller
above its normal speed.
3. The combination in an alternating current circuit of a phase controller composed
of an inducing member connected to the circuit, and an induced member capable of
relative rotation, and means for varying the self-induction of the induced member to
vary the phase control.
Dated the 28th day of December 1897.
For the Applicants.
J. C. CHAPMAN,
Chartered Patent Agent, 70, Chancery Lane, W.C.