Improvements in or relating to Alternate Current Electric Distribution.
Year: 1889

page_text: Date of Application, 1st Oct., 1889
Complete Specification Left, 1st July, 1890-Accepted, 16th Aug., 1890
PROVISIONAL SPECIFICATION.
Improvements in or relating to Alternate Current Electric
Distribution.
A communication from abroad by GEORGE WESTINGHOUSE, Junior, of Pittsburg,
County of Alleghany, State of Pennsylvania, United States of America, Engineer.
I, WILLIAM PHILLIPS THOMPSON F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool, & 6, Bank Street, Manchester, both in
the County of Lancaster, and 323, High Holborn, in the County of Middlesex, Civil
Engineer, do hereby declare the nature of this invention to be as follows:-
The invention relates to the organisation of circuits and apparatus for distributing
electric currents.
The special object of the invention is to provide convenient and economical means
for operating isolated incandescent electric lamps or other translating devices requiring
electric currents of moderate potential, and, at the same time, to secure the advantages
pertaining to systems of electrical distribution and conversion known as alternate-
current or secondary systems.
In operating translating devices by these systems, it is customary to transmit
currents of very high tension to points within the immediate vicinity of the translating
devices, and, at such points, to reduce the potential of the currents as may be required,
by means of electric converters connected in multiple arc. When, however, only a
single translating device is required at any given point, as is the case with street-
lighting circuits, for instance, the employment of such a potential reducing converter
in connection with each translating device usually involves more expense than is
warranted, and therefore it becomes necessary either to employ secondary conductors
of sufficient length to include several more or less widely separated translating devices,.
or else to connect the converters in series. The use of long secondary conductors is
objectionable, because they are necessarily of much greater size than the primary
conductors; and therefore more expensive; and prior to this invention, the series plan
was considered impracticable, because no economical method had been discovered
whereby converters, suitable for supplying single incandescent lamps could be so
operated.
This invention consists in so proportioning the coils and core of each of a number
of converters which have their primary coils connected in series in an alternating
current electric circuit, and their secondary coils respectively including in their circuits
an incandescent lamp or other translating device, that, when the lamp is in circuit and
receiving its proper current, sufficient current will be allowed to traverse the primary
coil of each converter to supply all the remaining converters in circuit; and, when the
secondary circuit of any converter is interrupted, a consequent high magnetic
saturation of the core will cause the reactive effect of the primary coil to be so modified
as to oppose to the current an effective resistance approximately equivalent to that
which exists when the lainp is in circuit. The converters may be constructed to
develop a difference of potential at the terminals of the secondary coil equal to that
applied to the primary; that is to say, the lengths of the primary and secondary
coils may be equal. The total difference of potential applied to the series of converters
will then be equal to the sum of the difference of potential required for the individual
lamps.
In the circuit of a suitable source of alternating, intermittent, or pulsatory electric
currents, any convenient required number of electric converters is included in series.
These are designed to supply currents to the corresponding translating devices
respectively. The primary coils of the converters are included in the circuit, while.

page_text: the secondary coils are connected through the corresponding translating devices.
Electric energy is transferred from the primary coil to the secondary coil through the
instrumentality of the core of soft iron, the coils and the core being disposed in any
convenient manner. The core is preferably constructed of laminated soft iron, forming
closed magnetic circuits.
It will be evident that, if several devices of the character described, are connected
in series, currents of high potential, and consequently, wires of small cross-section
may be employed for supplying them.
When the secondary circuit of an electric converter as ordinarily constructed, is
open, a counter electromotive force is developed in the primary coil sufficient to greatly
reduce the current flowing through it. It has been found, however, that by properly
proportioning the coils and core, it is possible to develop, when the secondary is closed
and the normal difference of potential is applied to the primary, a counter electromotive
force, which, in one aspect, is the equivalent of a given definite resistance, and, when
the secondary circuit is open, to cause the core to attain such a point of high magnetic
saturation that a normal amount of current will still be allowed to pass, so that the
remaining lamps will not be affected by the cutting out of any one or more lamps; in
other words, the converter is so proportioned that the same amount of current will
flow through its primary coil under the influence of the normal difference of potential
upon the circuit, whether the secondary circuit be open or closed through the lamp.
Two factors must be considered in the determination of the effective resistance
offered by the counter electromotive force, first, its difference of potential and second,
the displacement of its phases with reference to those of the applied electromotive
force. If the counter electromotive force were equal to the applied electromotive
force and the phases of the two were synchronous, then the two forces would neutralise
each other, and no current would flow. But if the phases of the counter electromotive
force are subsequent to those of the applied electromotive force, then they do not
exactly neutralise each other; and a current flows, the phases of which are displaced
with reference to the phases of the applied electromotive force. The effective resistance
is therefore diminished. From this, if follows that an equivalent effective resistance
may be maintained, up to a certain limit, by increasing, by the proper amount, the
displacement of the phase, as the counter electromotive force is increased; or, in
other words, an increase in counter electromotive force may be compensated by a
corresponding displacement of phase, and the same effective resistance maintained.
When a high magnetic saturation of the core of a converter is attained, the counter
electromotive force is itself increased, but its phases are sufficiently displaced, with
reference to the phases of the applied electromotive force, to restore to the circuit an
amount of energy sufficient to compensate for such increase, and to thus maintain the
normal current value. The energy consumed is not equal to the product of the
electromotive force into the current; but these two factors must be multiplied by a
third factor depending upon the displacement of phase.
The point of saturation is approached as the ratio of current to the difference of
potential begins to increase; or, high magnetic saturation may be defined as the point at
which the rise in the effective counter electromotive force is very small in proportion
to that of the applied electromotive force, owing to the magnetic lag of the core.
With a properly proportioned converter, therefore, the current may be maintained
at practically the normal amount, whether the lamps or other translating devices are
in circuit or not, without either increasing or decreasing the electromotive force of
the circuit. In cases where the converters have been operated in series prior to this
invention, it has been necessary, in order to maintain a constant current, to vary the
difference of potential upon the circuit to compensate for every change in the resistance
of the secondary circuit of any converter, in practising this invention both the
difference of potential upon the circuit and the current are maintained constant, since
the effective resistance of the circuit is maintained practically constant. In practice,
the proportioning of the converters and general organisation will depend upon the
particular conditions of different systems, and it is evident that variations in the

page_text: different conditions may require variations in the proportioning of the various parts,
but from the instructions herein before given those skilled in the art will be able to
practice the invention.
Dated this 30th day of September 1889
WM. P. THOMPSON & Co.,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in or relating to Alternate Current Electric
Distribution.
A communication from abroad by GEORGE WESTINGHOUSE, Junior, of Pittsburg,
County of Alleghany, State of Pennsylvania, United States of America, Engineer.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool and 6, Bank Street, Manchester, both
in the County of Lancaster, and 323, High Holborn, in the County of Middlesex,
Civil Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and by the
following statement :-
The invention relates to the organisation of circuits and apparatus for distributing
electric currents.
The special object of the invention is to provide convenient and economical means
for operating isolated incandescent electric lamps or other translating devices requiring
electric currents of moderate potential, and at the same time, to secure the advantages
pertaining to systems of electrical distribution and conversion known as alternate-
current or secondary systems.
In operating translating devices by these systems, it is customary to transmit
currents of very high tension to points within the immediate vicinity of the translating
devices, and, at such points, to reduce the potential of the currents as may be required,
by means of electrical converters connected in multiple are. When, however, only a
single translating device is required at any given point, as is the case with street-
lighting circuits, for instance, the employment of such a potential reducing converter
in connection with each translating device usually involves more expense than is
warranted, and therefore it becomes necessary either to employ secondary conductors
of sufficient length to include several more or less widely separated translating
devices, or else to connect the converters in series. The use of long secondary con-
ductors is objectionable, because they are necessarily of much greater size than the
primary conductors, and therefore more expensive; and prior to this invention, the
series plan was considered impracticable, because no economical method had been dis-
covered whereby converters, suitable for supplying single incandescent lamps, could be
so operated.
This invention consists in so proportioning the coils and core of each of a number
of converters, which have their primary coils connected in series, or in alternating
current electric circuit, and their secondary coils respectively including in their circuits
an incandescent lamp or other translating device, that, when the lamp is in circuit and
receiving its proper current, sufficient current will be allowed to traverse the primary
coil of each converter to supply all the remaining converters in circuit; and, when the
secondary circuit of any converter is interrupted, a consequent high magnetic satura-
tion of the core will cause the reactive effect of the primary coil to be so modified as
to oppose to the current an effective resistance approximately equivalent to that which
exists when the lamp is in circuit. The converters may be constructed to develop a
difference of potentials at the terminals of the secondary coil equal to that applied to
the primary that is to say, the lengths of the primary and secondary coils may be
equal. The total difference of potential applied to the series of converters will
then be equal to the sum of the difference of potential required for the individual
lamps.

page_text: In the accompanying drawings, there are shown in diagram two slightly different
organisations of apparatus illustrating the invention.
Referring ptincipally to Figure 1 :-
A represents a suitable source of alternating intermittent, or pulsatory electric
currents, and L. its circuit. In the circuit, any convenient required number of electric
converters, C, C, are included in series. These are designed to supply currents to the
corresponding translating devices d d, respectively. The primary coils p of the con-
verters are inclined in the circuit L, while the secondary coils are connected through
the corresponding translating devices. Electric energy is transferred from the primary
coil to the secondary coil through the instrumentality of the core e of soft iron, the
coils and the core being disposed in any convenient manner. The core c is preferably
constructed of laminated soft iron, forming closed magnetic circuits.
It will be evident that if several devices of the character described are connected
in series, currents of high potential, and, consequently, wires of small cross section,
may be employed for supplying them.
When the secondary circuit of an electric converter, as ordinarily constructed, is
open, a counter electromotive force is developed in the primary coil sufficient to
greatly reduce the current flowing through it. It has been found, however, that by
properly proportioning the coils and core, it is possible to develop, when the secondary
is closed and the normal difference of potential is applied to the primary, a counter
electromotive force, which, in one aspect, is the equivalent of a given definite resis-
tance, and, when the secondary circuit is open, to cause the core to attain such a point
of high magnetic saturation that a normal amount of current will still be allowed to
pass, so that the remaining lamps will not be affected by the cutting out of any one
or more lamps, in other words, the converter is so proportioned that the same amount
of current will flow through its primary coil under the influence of the normal
difference of potential upon the circuit, whether the secondary circuit be open or
closed through the lamp.
Two factors must be considered in the determination of the effective resistance
offered by the counter electromotive force; first, its difference of potential, and
second, the displacement of its phases with reference to those of the applied electro-
motive force. If the counter electromotive force were equal to the applied electro-
motive force and the phases of the two were synchronous, then the two forces would
neutralise each other, and no current would flow. But if the phases of the counter
electromotive force are subsequent to those of the applied electromotive force, then they
do not exactly neutralise each other, and a current flows, the phases of which are dis-
placed with reference to the phases of the applied electromotive force. The effective
resistance is therefore diminished. From this, it follows that an equivalent effective
resistance may be maintained up to a certain limit, by increasing, by the proper
amount, the displacement of the phase, as the counter electromotive force in increased;
or, in other words, an increase in counter electromotive force may be compensated
by a corresponding displacement of phase, and the same effective resistance
maintained.
When a high magnetic saturation of the core of a converter is attained, the counter
electromotive force is itself increased, but its phases are sufficiently displaced, with
reference to the phases of the applied electromotive force, to restore to the circuit an
amount of energy sufficient to compensate for such increase, and to thus maintain the
normal current value. The energy consumed is not equal to the product of the
electromotive force into the current; but these two factors must be multiplied by a
third factor depending upon the displacement of phase.
The point of saturation is approached as the ratio of current to the difference of
potential begins to increase; or high magnetic saturation may be defined as the point
at which the rise in the effective counter electromotive force is very small in
proportion to that of the applied electromotive force, owing to the magnetic lag of the
core.
With a properly proportioned converter, therefore, the current inay be maintained at
practically the normal amount, whether the lamps or other translating devices are in

page_text: circuit or not, without either increasing or decreasing the electromotive force of the
circuit. In cases where the converters have been operated in series, prior to this
invention, it has been necessary, in order to maintain a constant current, to vary the
difference of potential upon the circuit to compensate for every change in the resis-
tance of the secondary circuit of any converter; in practising this invention,
both the difference of potential upon the circuit and the current are maintained
constant, since the effective resistance of the circuit is maintained practically
constant.
In practice, the proportioning of the converters and general organisation will depend
upon the particular conditions of different systems, but very good results can be
obtained by the following organisation. Nineteen converters connected in series in a
circuit supplied by a current of 1000 volts having 16000 alternations per minute and
each converter constructed with like primary and secondary coils and as follows:
Length of each coil, 140 feet.
Length of so-called active wire in each coil, about 75 feet.
Number of turns in each coil, 102,
Size of wire, No. 15 B. and S. gauge, that is 1651 square millimetres sectional
area.
Resistance of each coil, 403 ohms,
Core 41-4 inches in length, composed of 320 thin plates of soft iron insulated by
paper and of the general character described in the Patent No. 9728 of 1887 the size
of the plates being 3 3-4 inches by 2 1-4 inches and the weight of iron being four
pounds. Each converter normally having connected in its secondary circuit an
incandescent electric lamp designed to receive a current of 1.45 ampères at a pressure
of approximately 50 volts.
It is evident that variations in the different conditions may require variations in
the proportioning of the various parts, but from the instructions hereinbefore given
those skilled in the art will be able to practise the invention.
Having now particularly described and ascertained the nature of the said invention
and in what manner the same is to be performed, as communicated to me by my
foreign correspondent, I declare that what I claim is :-
1. The combination with a circuit supplied by alternating electric currents, of two
or more electric converters having their primary coils connected in series in said
circuit, and an incandescent electric lamp or other translating device connected in the
secondary circuit of each converter, the coils of the converters being so proportioned
to the mass of iron in the corresponding cores that, upon the interruption of the
circuit through any lamp, a normal current is allowed to pass through the other
converters by reason of the high magnetic saturation of the core of the corresponding
converter.
2. In a series system of secondary distribution, a converter so proportioned that the
self-induction of its primary with open secondary is the equivalent of the resistance
of the translating devices normally on the secondary circuit.
3. In a series system of electrical secondary distribution, converters having their
primary coils so proportioned that the inductive opposition to the current is approxi-
mately the same when the secondary is open as when the secondary is closed through
its norinal circuit.
20th day of Luna 1800
WM. P. THOMPSON & Co.,
Agents for the Applicant.