IMPROVE- MENTS IN AUTOMATIC SAFETY DEVICES FOR USE WITH ELECTRIC CURRENTS
Year: 1885

page_text: COMPLETE SPECIFICATION.
I, ROBERT PERCY SELLON, Engineer, of 112, Belvedere Road, Lambeth, in the
County of Surrey do hereby declare the nature of my invention for "IMPROVE-
MENTS IN AUTOMATIC SAFETY DEVICES FOR USE WITH ELECTRIC CURRENTS and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
My Invention relates to Improvements in devices, for controlling the flow of
currents in electrical circuits and means for arresting the flow of current in a circuit,
of which it forms a part, when this becomes excessive, thus preventing injury being
done to the lamps by an undue passage of current or dangerous overheating of the
wires, conveying the electricity and which is capable of adjustment for use with
currents of varying strength.
It is well known that the safety devices commonly employed to guard against an
excess of current in an electric circuit, and which usually consist of a piece of wire
of lead, or an alloy of lead, tin, bismuth, antimony or other metals, fusible at a low
temperature are eminently unsatisfactory in their results, more especially when
such fusible safety devices are made to convey heavy currents. It has been found,
in these cases, extremely difficult to obtain fusible safety devices which, will both
break the circuit in which they are placed, when a slight excess of current sufficient
to destroy the lamps or overheat the wires carrying the currents takes place, and
also will continue to carry the normal current, without undue loss, heating or
disintegration, thereby suddenly and unexpectedly causing fracture of the circuit,
even when a current below the normal is passing in circuit.
These defects are overcome by the use of an efficient electro-magnetic safety
device, such as that hereinafter described and shewn in the accompanying
drawings.
The manner in which I carry out my Invention, will be readily understood on
reference being made to the Figures in the accompanying drawings.
Fig 1. is an end elevation of my improved apparatus.
Fig: 2 a side
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& Fig: 3 shews a plan of my apparatus.
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To carry out my Invention I mount upon a base of any convenient material a
bobbin "a" of suitable substance on which I wind a convenient quantity of
conducting wire, in this bobbin "a," I insert a soft iron core "b," capable of
longitudinal movement within the hollow bobbin "a," the movement of the core
being adjustable at will & the position of the core within the bobbin or electro-
magnet being registered on a dial "c" in any convenient way.
Preferably at right angles to the core "b" and at the opposite end to that at
which the indicating dial is placed, I place an armature "d" pivotted or suspended
above the bobbin "a" upon an arm "e" carried from the opposite end of the core

page_text: to which the armature itself is in proximity: this arm "e" I prefer to make of
soft iron, so that, when a current traverses the wire wound upon the bobbin, it
causes the core to develope a certain magnetic polarity, while the armature "d"
being magnetically connected to the core and 'arm to which it is pivotted, becomes
the opposite pole of the electromagnet and developes an opposite polarity to that
portion of the core to which it is in close contiguity. Thus, upon a current passing
through the coils of the electromagnet the armature is attracted towards the core,
this attraction being dependent on the current in circuit and upon the distance
apart of the core and armature, this distance being adjustable and indicated upon
the dial or scale provided for that purpose. To prevent the armature "d" coming
into contact with & sticking to the core "b," I employ a spring "f" shewn in
Fig 2; which allows the armature sufficient range of movement to disengage the
pins "g. g" hereinafter mentioned.
Supposing the dial "c" or scale to be graduated to the various strengths of
current and various distances through which the core will attract the armature
against it, it will be obvious that this electromagnet may be adjusted to operate
with any desired current, within the limits indicated on the dial "c
or scale
To the lower end of the armature "d," I attach a pin or stop "g," corresponding
to a second pin or stop "g" attached to a conducting strip of metal "h," the two
free ends of which dip into mercury cups "i" through which the current passes
into the circuits. One of these mercury cups corresponds to one terminal of the
electro magnetic safety device, the current passing thus from one terminal into
such mercury cup, then through the conducting strip "" before mentioned, into
the second mercury cup, and, finally through the coils of the electro magnet to the
opposite terminal of the device.
tr
This conducting strip "h" tends to be forced upward, so that its ends leave the
mercury cups, by means of a spring "j" suitably attached thereto; but it is
Dormally held down by the pin "g," attached to the armature "d" of the electro
magnet, impinging upon the pin "g" attached to the conducting strip "h," and
thus preventing the spring "," before mentioned, coming into action, until such
time as an excess of current, beyond the amount desired, passing through the coils
of the electromagnet, causes the core "6" to attract the suspended armature “d,"
when the pin "g" attached to the armature "d" will move off the pin "g" attached
to the conducting strip; thus allowing the latter to be impelled out of the mercury
cups by the action of the spring "j" and so breaking the circuit.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed, I declare that what
I claim is
(i). In an electromagnetic automatic "safety cut out" apparatus, the combination
with an electro-magnet, having a moveable core, whose position and range of
novement is indicated on a suitable device, of an armature, arranged to control the
movement of a conductor forming part of the circuit to be broken; substantially.
as herein before described and illustrated.
(ii). In an electromagnetic automatic "safety cut out" apparatus, the combination
with an electromagnet, with moveable core indicating device and armature, of a
conducting strip, arranged to break the circuit, of which it forms a part, when the
current exceeds a predetermined quantity, substantially as hereinbefore described
and illustrated.