Preventing Disruptive Discharges therefrom.
Year: 1888

page_text: Preventing Disruptive Discharges therefrom.
A communication from abroad by EDWARD G. ACHESON, of Pittsburgh, in the
County of Allegheny, and State of Pennsylvania, United States of America,
Electrician.
I, PHILIP MIDDLETON JUSTICE of 55 and 56 Chancery Lane in the County of
Middlesex Fellow of the Institute of Patent Agents 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 object of this invention is to provide means for protecting the insulation of
electrical conductors, particularly those carrying heavy currents such for instance as
electric light cables, from the evil effects of disruptive discharges causing "grounds"
or short circuits.
It is well known that most of the "grounds" or short circuits that occur in cables
are at the terminals. Many attempts have been made to discover the cause and to
remedy the evils of such troubles, and this has been done generally by taking especial
pains to properly insulate the terminals and prevent the access of moisture to the
conductors. My correspondent has discovered that the principal, if not the sole cause
of this disturbance is due to the static charge which is received by the cable and which
after a time increases to such a strength that a disruptive discharge takes place through
the insulating or dielectric material surrounding the conductors.
It is well known that when an electric body receives a static charge the electricity
is distributed throughout the body but tends to accumulate at any points, angles, or
projections which may be associated with or form part of the body. Applying this
principle to conductors, as lead covered conductors or cables carrying a. plurality of
conductors, which as is well known becomes highly charged with what is termed
static electricity, when currents of electricity are passed through the conductors we
find they act as condensers, the couductor forming one pole and the lead covering the
other pole and each receiving a static charge of opposite polarity. This static charge

page_text: evenly applied it may occur at other points.
In order to prevent these evils the present invention consists in providing means
whereby this discharge may be caused to take place at such a point as to prevent the
destruction of the insulation and before its potential is sufficiently great to pass
through the dielectric surrounding the conductor, or to cause a dangerous strain
upon it.
The invention may be carried out practically by a variety of devices, there
being illustrated in the accompanying drawings some that have been found to be
efficient.
In said drawings
Fig. 1 is a perspective view of a simple arrangement for this purpose applied to an
ordinary lead covered conductor.
Fig. 2 is a sectional view of another arrangement on a similar conductor.
Fig. 3 is a side view, illustrating the invention applied to two conductors of a
cable.
Figs. 4 and 5 are side views illustrating other means, all of which operate upon
substantially the same principles.
Fig. 6 shows a signal and indicator applied to the conductor to designate the position
and time of discharge.
In Fig. 1. A is the lead or other metallic casing or covering, the conductor, and I
the dielectric or insulating material surrounding the conductor, P is a wire or arm of
some conducting material connected to the covering A, and extending into proximity
to the conductor C but not in contact therewith. It is shown as being pointed at its
free end which is preferable though not absoluicly necessary. The disruptive
discharge has been usually founed to take place at the end of the tube as at E causing
a carbonization of the insulator I and destroying the utility of the conductor. By
arranging the arm P so that the distance between its point and the conductor is the
same or less than the shortest distance between the covering A and the insulated con-
ductor, the discharge will take place at K, and this will happen before the potential of
the charge reaches a degree sufficient to pass through the insulation.
In Fig. 2, the case A and conductor are insulated from each other by 1. Suitable
means, as a tape T, are provided to cover the points of juncture of the conductor,
insulator, and covering to protect them from moisture. B is a metal clamp secured
to the conductor by screw s² and P is an arm clamped to the covering A by suitable
means as the rings a secured by screws s. R, R, are rods or points of platinum,
carbon, or other suitable material adjustably held in the arm and clamped by
Screws &³.
The distance between the adjacent ends of the rods may be adjusted as desired and
this distance will determine the potential of the static charge attained before the
discharge will occur, and should be less than that necessary to produce the disruptive
discharge through the insulation. By making the ends of these rods pointed and
properly adjusting them, the static charge may be caused to flow from point to point
without a visible discharge and the charge may thus be prevented from reaching a
dangerous potential.
If the distance between the ends of the rods is comparatively small, my correspondent
has found that a cable of considerable length may be properly protected by a single
set, but in practice, especially when heavy currents are used, it is preferred to supply
each section of cable or each terminal with the protective device. It has been found
convenient to arrange the protectors at the translating devices for instance,, so that
they can be readily inspected although of course they may be otherwise arranged as
desired
•
In Fig. 3, C, C, are two conductors of the cable A with the rods R, R¹, mounted

page_text: on them, V being a block of insulating material to hold the conductors at a
constant distance apart. Each conductor is shown as provided with a number of
rods R, so that if one set should be burned away and the distance between them
increased as by an are forming, another set would remain for use.
In Fig. 4, one rod R is held by a clamping ring P to the covering A and the
other by a ring B to the conductor C, and between the rod and ring is a fusible
connector F. The free ends of the rods R are enclosed in an insulating tube G, as
of glass.
In Fig. 5, the clamping rings are connected by a fusible connector F and a
dielectric D, of such a resisting strength as to permit the discharge to pass through
it before it will pass through the insulation of the conductor, is interposed between the
ring and the conductor.
In Fig. 6, there are shown means for giving a signal and indicating to a greater or
less extent the location of the discharge. A line is connected to the generator X at
the neutral point of the armature and the other end is connected to a condenser M,
and a polarized relay N is interposed in the line and this is shown in position to close
a local circuit and operate a signal O therein. By knowing the direction of the main
current flowing through the conductors C, C, the half of the circuit in which the
discharge took place may be determined by observing the position of the armature of
the polarized relay.
From the above it will be seen that the invention may be carried out in a variety of
ways, which will be understood by those skilled in the art, and is therefore not limited
to the particular arrangements shown, the essential feature being that the discharge
points are arranged at a less electrical distance from each other than the electrical
resistance or distance of the insulation surrounding the conductor, so that the static
charge of the conductor or cable will be discharged through the points before it
reaches a potential sufficiently high to cause a disruptive discharge through the
insulation.
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. As a incans of preventing the disruptive discharge of a conductor through its
surrounding insulator, an arm arranged to receive the discharge at a potential below
that necessary for striking through the insulator, substantially as described.
2. An insulated conductor or cable having static discharge points arranged at a less
electrical distance than the electrical distance of the insulation surrounding the
conductor, substantially as described.
3. The combination with an insulated conductor and its enclosing casing, of static
discharge rods arranged on the conductor and case, substantially as described.
4. The combination with an insulated conductor and an enclosing case of adjustable
rods connected to the conductor and case, substantially as described.
5. The combination with an insulated conductor and enclosing case, of clamps
mounted on said conductor and case, and adjustable rods supported in said clamps,
substantially as described.
6. The combination with a cable having an insulated conductor, of static discharge
points connected therewith, and a signal apparatus connected with the cable to indicate
the discharge, substantially as described.
7. The combination with an insulated conductor and enclosing case, of static
discharge rods connected with the conductor and case and a fusible connection between
the rods and conductor, substantially as described.