Improved Method of and Apparatus for Making and Breaking or Varying High Potential Electric Currents.
Year: 1899

page_text: Date of Application, 9th Mar., 1899-Accepted, 3rd Feb., 1900
COMPLEIE SPECIFICATION.
Improved Method of and Apparatus for Making and Breaking or
Varying High Potential Electric Currents.
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 EDWARD M.
HEWLETT, 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:-
In the operation of circuits containing self induction and capacity, and more
especially in those in which high impressed alternating electro-motive forces
are employed, there is great danger of impairing or breaking down the insulation
of the lines when any sudden change take place in the flow of current therein.
Such danger is particularly apt to result disastrously in the case of cirenits opera-
ting underground cables. When the current passing through such cables is
suddenly interrupted or when the cable is connected suddenly with a source of
electro-motive force, violent electrical oscillations may and often do take place
such as to puncture the insulation of the cable and render the same useless.
Any sudden changes in the current flowing in a cable other than those caused
by making and breaking the circuit of the same are apt to give rise to the same
resonant increase in potential, but not in the same degree as that caused by
making and breaking the circuit. It has been discovered that the dangers
referred to may be prevented almost entirely by causing the making or breaking
to take place gradually, as for example, in the apparatus hereinafter described,
by gradually increasing the impedance of the circuit immediately before breaking
the same, or in making the circuit by first introducing a large impedance and
then gradually and progressively withdrawing it.
We consider ourselves to be the first to make and break high potential circuits
by gradually altering their impedance in such a manner as to prevent any relatively
large time changes of current therein and the consequent production of
dangerously high resonant or induced electro-motive forces.
Furthermore, we consider ourselves to be the first to carry out the operations
briefly outlined above by the use of automatically operated means.
These and other features of this invention will be more clearly understood by
reference to the following description taken in connection with the accompanying
drawings, while the scope of the invention, both in its broad as well as in its
more limited features will be clearly and particularly pointed out in the appended
claims.
Fig. 1 illustrates in diagram a type of manually operated apparatus for carrying

page_text: out the invention. Figs. 2 and 3 show different forms of apparatus for carrying
out the same general operation as that performed by the device shown in Fig. 1,
but differing trom the latter in being automatically actuated.
In Fig. the line circuit is indicated at 1, 2. The main switch for making
or breaking this line circuit is shown at 3. In order to make or break this circuit
gradually a reactance device is arranged to be introduced in circuit during such
operation. For this purpose we have shown a transformer T with its primary
arranged to be put in series with one of the mains as 2. This object is obtained
by the use of a switch 4 which, in its closed position, short-circuits the primary
of the transformer and which on being opened introduces the primary directly
in series with the circuit, as will readily be understood.
Some suitable means is provided for varying the resistance of the secondary,
and the drawings illustrate a suitable arrangement for this purpose. The
secondary terminals are illustrated at 5 and are shown as short circuited by the
bridging piece 6 formed of laminated metal so as to give good contact. Two
blocks of carbon 7, 7 are electrically connected with the terminals 5 and arranged
to slide longitudinally along the same so as to introduce a greater or less length
of carbon into the circuit formed by the transformer secondary and the spring
yoke piece 8 carrying the carbon blocks. The bridging contact may, if desired,
be arranged to operate independently of the resistance varying device, but in
practice it is found to be preferable to arranged them so as to be simultaneously
inovable.
Fig. 1 illustrates the condition of the circuit during normal operation. In case
it be desired to open-circuit the mains, the first operation to be performed is to
open the switch 4. This introduces in circuit the primary of the transformer T,
the secondary of which is short circuited by the bridging contact 6, thus causing
the self induction of the primary to be reduced to a minimum. After having
closed the switch 4, and thereby introduced into the circuit a small impedance,
the next step is to withdraw the bridging contact 6, and thus insert in the
secondary the small resistance due to the carbon blocks interposed between
the connecting yoke 8 and the contact blocks 5. By gradually sliding the blocks
along the contact blocks 5 the resistance of the transformer secondary is increased
in an obvious manner, thus increasing the impedance of the primary and so
gradually reducing the current in the mains. By properly proportioning the
parts in a manner such as will readily be understood by engineers, the value
of the current in the mains may be reduced sufficiently so that upon opening the
main switch 3 no dangerous increase in potential will result.
In making the circuit, precisely the reverse is gone through with. The
switches 3 and 4 being open and the total resistance being inserted in the
secondary of the transformer T, the first step is to close the main switch 3, thus
making the circuit and including therein a large impedance due to the transformer
having its primary in series with the line. The resistance of the secondary is
then slowly decreased until finally the terminals 5 are short circuited by the
bridging contacts ü, thus reducing the impedance of the primary winding to a
minimum. The switch 4 is then closed, thus wholly completing the circuit and
eliminating the last trace of impedance.
Fig. illustrates diagrammatically an automatically-actuated circuit-breaker,
operative upon an overload, and provided with automatically operated means for
breaking the circuit gradually. As before, the main circuit is indicated at 1, 2.
The circuit-breaker actuating coil is indicated at 9, and operating in conjunction
therewith is the armature 10 which serves to trip the bridging contact piece
of the circuit-breaker in any well-known manner. As shown, one end of the
armature 10 serves to retain in place the knuckle of a toggle lever 11 which
operates a bridging contact piece 12 for connecting together the contact blocks 13
inserted in the line 2. Shunted about the switch formed by the terminals 13
and bridging piece 12 is the primary P" of the transformer T. In series with
the primary P is the primary P² of another transformer T.

page_text: The secondary S' of the transformer T is connected to a resistance changing
device, such, for example, as a water rheostat 14. This rheostat consists pre-
ferably of a metallic retaining vessel containing acidulated water and in contact
electrically with one terminal of the secondary S. The other terminal of the
secondary is connected to a metallic plate 15 which may be inserted at different
depths in the liquid contained by the rheostat and which in one of its extreme.
positions is embraced by two metallic spring fingers 16 secured to the bottom.
of the retaining vessel 14. The plate 15 is pivotally connected through an
insulating rod 17 with one end of a lever 18 fulcrumed, for example, at 19.
weight is suspended from the opposite end of the lever and is of such a value
as to overbalance the plate 15, but the apparatus is normally retained in the
position shown by a catch 20 which engages the lever 18 in any suitable manner.
The catch 20 is suitably pivoted and carries an armature 21 within the influence
of an actuating coil 22 excited by current derived from the secondary Sof
the transformer T already referred to, the primary 12 of which, as has been.
noted, is in series with the primary P" of the transformer T'.
A
The lever 18 carries a bridging contact 23 which operates in conjunction with
the terminals 24 to close a local circuit. This circuit has in series therewith some.
suitable source of electro-motive force, as, for example, the battery B, and a
circuit breaker coil 25 which operates a circuit-breaker C of any suitable form,
thus serving to open the main line 2 at the contacts 26.
In the operation of an apparatus such as just described, let it be supposed that
the current in the mains 1 and 2 has increased beyond the limit allowed by the
circuit-breaker included therein. The current in the circuit-breaker coil 9 then
acts to draw down the armature 10 thus releasing the toggle 11 and opening
the circuit at the contacts 13. This operation does not actually break the main
circuit, but diverts the current, through the primaries P1, P2 of the trans-.
formers T, T. The resistances of the respective secondaries are comparatively
small so that only a moderate amount of impedance is by this operation introduced
into the main line. Current then flows through the actuating coil 22 and releases.
the catch 20, thus allowing the weight W to fall and so raise the contact. plate 15
away from the bottom of the retaining vessel of the water rheostat 14. The
resistance of the secondary S' is thus gradually increased in an obvious manner.
and so gradually increases the impedance of the main circuit and thus reduces
the current flowing therein. The downward motion of the weight W forces.
the bridging contact 23 into connection with the contacts 24 and so closes the
local circuit through the battery B or other source of electro-motive force, and
the circuit-breaking coil 25, this operates the circuit-breaker C and so opening
the main circuit, the current in which has been reduced to a safe amount by the
operation of the transformer T and the water rheostat operated in conjunction.
therewith.
The object of using a local circuit for actuating the main circuit breaker C
is to produce a positively actuated device and obviate the disadvantages involved
in the use of a device dependent for its operation upon the current in the circuit
to be broken. Instead of a local electric circuit we might employ some mechani-
cally actuated device operated, for example, by a weight or spring. This latter
arrangement is not, however, in all respects as desirable as a local circuit, since
it will not, like the latter, allow the circuit-breaker to be located in one place
and a tripping device in another at a distance therefrom.
While we have shown an arrangement which operates automatically to open-
circuit the mains upon the occurrence of an overload, cases may and often do
arise in which we desire to be able to open the main circuit at will. To provide
for such cases we supply the overload circuit-breaker 11, 12 with an additional
coil K which is connected by a normally open circuit with the battery B or other
suitable source of electro-motive force. When it is desired to open the main
circuit the switch M is closed, thus operating in an obvious manner to trip the

page_text: circuit breaker 11, 12, and so produce the sequence of operation already described,
the final result of which is to trip the circuit breaker C and open the main
circuit.
In Fig. 3 there is shown an arrangement similar in many respects to that shown
in Fig. 2 but differing therefrom in that the impedance which is introduced into
the main circuit is varied by varying the magnetic reluctance of the core of the
reactance coil which furnishes the impedance. A further difference consists in
operating the main circuit-breaker by energy derived from the main circuit.
The circuit-breaker D), included in one of the mains 1, 2, is of any preferred form.
Shunted about the contacts 27 is a reactance coil L having an adjustable core N
adapted to vary the reluctance of the magnetic circuit. The pivoted catch 28
in the form of a bell-crank lever serves to retain the bridging contact 29 in
connection with the contacts 30 inserted in one of the mains 1, 2. One end
of the catch 28 is engaged by a projection carried by the core N and is so arranged
as, to release the bridging contact 29 when it has reached its limit of motion into
the coil of the reactance device. A spring 31 serves to withdraw the contact 29
when released by the catch 28. The contacts 30 are electrically connected to an
actuating coil 32 of a circuit-breaker E in the main line 2.
In the operation of this device let it be supposed that the current in the
lines 1,2 increases abnormally, in which case the circuit-breaker Doperates
and thus inserts in the main line 2 the reactance coil L the core of which is as
shown in a position corresponding to minimum impedance. The core N is
then drawn into the coil by the attraction due to the current flowing therein.
Just before it has reached its limit of motion the projection 33, carried thereby
engages the catch 28, thus releasing the bridging contact 29 which is drawn
back out of contact with the terminals 30 by its spring 31 and thus introduces
the coil 32 of the circuit-breaker E into the main circuit. The circuit-breaker E
then operates and opens the main circuit the current of which has already been
reduced to a shaft amount by the insertion of the impedance due to the reactance
coil L.
In some cases we may dispense with the circuit-breaker E and open the circuit
directly at the switch 29, 30. The arrangement shown however possesses the
advantage that the circuit-breaker D and the parts co-operating immediately
therewith may be located at one point, while the main circuit-breaker E may be
located at any other point on the line, whether distant or otherwise.
Although we have shown by way of illustration certain arrangements which we
have found desirable for carrying out the invention, we do not desire to be limited
thereto, for it is evident that many changes and rearrangements may be produced
for accomplishing the objects of the invention without departing from the spirit
thereof.
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 breaking an electric circuit which consists in first introducing
into the circuit a coil of low impedance, increasing the impedance of the coil,
and then breaking the circuit.
2-The method of varying the value of current flowing in a circuit, from one
extreme to another, which consists in passing said current through the primary
of a transformer and then varying the resistance of its secondary until the required
change has been produced in the value of the current passing through the primary.
3-The method of preventing disruptive discharges in making or breaking of
high potential circuits, which consists in varying the current in the circuit, from
its original value before being operated upon to approximately its final value,
by inserting in series with the circuit the primary of a transformer and then
gradually, varying the resistance of the secondary so as to vary the reactance in
series with the high potential circuit including the primary.

page_text: 4-The method of preventing the production of dangerously high electro-motive
forces in making and breaking high potential circuits, which consists in gradually
increasing the impedance of the circuit before breaking it and gradually decreasing
the impedance of the circuit after making it, and causing the increase or decrease
in impedance of the circuit to be effected by including in the circuit a coil the
flux through which may be varied by externally controlled means.
5 The method of breaking an electric circuit which consists in first intro-
ducing into the circuit a coil having impedance, increasing the impedance of the
coil, and then breaking the circuit.
6-The method of breaking an electric circuit which consists in first introducing
into the circuit a coil having impedance, varying the flux passing through the
coil without varying the number of turns of the coil, and then breaking the
circuit.
7 The method of breaking an electric circuit which consists in first intro-
ducing into the circuit a coil inductively related to a closed circuit, varying the
resistance in said closed circuit, and then breaking the first mentioned circuit.
8-The method of breaking an electric circuit which consists in first intro-
ducing into the circuit the primary of a transformer the secondary of which is
closed-circuited, increasing the resistance in the secondary circuit, and then break-
ing the first mentioned circuit.
9-The method of interrupting the current in a main circuit which consists in
diverting the current through a coil having a predetermined self induction,
gradually increasing said self-induction and then breaking the main circuit.
10 The method of controlling an electric circuit which consists in cutting a
coil into the circuit when the current in the circuit equals or exceeds a pre-
determined value, increasing the impedance of said coil, and then breaking said
circuit.
11 The method of controlling an electric circuit which consists in cutting a
coil into the circuit when the current in the circuit equals or exceeds a pre-
determined value, increasing the impedance of said coil, and then opening a
switch in the circuit by the application of energy derived from a local circuit.
12 An electric circuit having a switch included therein. a transformer primary
arranged to be cut into circuit by the opening of said switch and a liquid
rheostat in series with the transformer secondary.
13 An electric circuit having a switch included therein, a transformer primary
arranged to be cut into circuit by the opening of said switch, a variable resistance
in the transformer secondary and a second switch in said circuit arranged to be
operated when said resistance is increased.
14 An electric circuit having in series therewith two switches, a transformer
primary shunted about one of said switches and means for varying the resistance
of the transformer secondary.
15 An electric circuit having in series therewith two switches, a coil shunted
about one of said switches, and means for varying the impedance of said coil.
16 An electric circuit having in series therewith two switches, a coil adapted
to be shunted about one of said switches and means for varying the impedance of
said coil without altering its number of turns.
17 An electric circuit having a circuit-breaker included therein, a coil arranged
to be cut into circuit by the opening of the circuit breaker, means for varying the
impedance of the coil, and means for completely opening said circuit after varying
the impedance of said coil.
18 An electric circuit having an overload circuit-breaker included therein, a
coil arranged to be included in the circuit when the circuit-breaker is opened.
means for automatically increasing the impedance of the coil after it is included
in circuit and means for subsequently breaking said circuit.
19 An electric circuit having a circuit-breaker included therein, a coil
arranged to be included in the circuit when the circuit-breaker is opened, means

page_text: for automatically varying the impedance of said coil and means for automatically
opening said circuit after the impedance of said coil has been varied.
Dated 9th day of March 1899.
THE BRITISH THOMSON-HOUSTON Co. LTD.
A. R. MONKS,
Managing Director,
Applicants,
ALFRED CLEMENTS,
Assistant Secretary.