Improvements in or Relating to Apparatus for Indicating and Registering Variations of Insulation Resistance in Electric Networks and Circuits Generally.
Year: 1897

page_text: Date of Application, 17th Nov., 1897-Accepted, 12th Mar., 1898
CUMI DEI DI PULTIVATION.
Improvements in or Relating to Apparatus for Indicating and
Registering Variations of Insulation Resistance in Electric
Networks and Circuits Generally.
(A communication from MAURICE TRAVAILLEUR, of 80, Rue de Trêves, Brussels, in
the Kingdom of Belgium, Engineer.)
I, ALFRED JULIUS BOULT, of 111, Hatton Garden, in the County of Middlesex,
Chartered Patent Agent, 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 :-
This invention relates to an apparatus for indicating and registering variations of
insulation-resistance in an electric network and circuit generally.
=
,
The combined insulation-resistance of an electric live network may be expressed
Va-V¹ar
by the following formula: R:
in which Va represents the difference of
V¹a
the potential of one of the cables and earth and V'a the difference of the potential
of the same cable and earth when it is connected to earth through the resistance ».
These potentials Va and V¹a are measured by means of a voltmeter or a
galvanometer of a very strong resistance.
It is very useful to have the variations of the insulation resistance of an electric
network registered.
By means of the device hereinafter described any voltmeter may be converted
into an indicating and registering apparatus. This voltmeter must have a very
great resistance and be sensitive at any part of its scale. It may either be the
special voltmeter which my correspondent has devised for a complete apparatus, or
the new voltmeter made by Chauvin & Arnoux. The voltmeter which has been
constructed, indicated in the drawings by V, consists of a galvanometric frame G
mounted on pivots a and moving in a magnetic field formed by a permanent magnet
(Figs. 1 and 2).
The current is supplied to the frame by coils or spirals i. This frame is suitably
shunted and placed in tension with a resistance in order to obtain the desired
sensitiveness. The spindle of the frame is provided with a needle or a pen or a
style by means of which the registration is effected.
This voltmeter V with the registering device E being permanently connected to
one of the cables (+ terminal) and to earth (terminal T) registers Va. At variable
intervals and during a variable period the voltmeter is automatically shunted by a
suitable resistance S. At this moment the voltage of the conductor to which the
voltmeter is connected becomes V'a and the voltmeter registers this quantity during
the time that it remains shunted. In order to attain this result, the following
apparatus has been constructed.
A resistance S suitable for the network to be examined is placed in series with a
magnetic switch I. The two terminals of this circuit are connected to the terminals:

page_text: (+ terminal and T) of the registering voltmeter V which it is desired to use
(Fig. 4).
The winding of the magnets A of the magnetic switching device I-placed in
series with an additional resistance r, if desired-is connected to one of the poles of
a battery, or, still better, to one of the poles of the network (+ terminal). The
other extremity ends in a series of contacts c of variable size and number arranged
at variable distance apart (separated by an insulated part) on which contacts a
brush B' operated by a clock-work mechanism H moves.
The brush itself is con-
nected to the other pole of the battery or, still better, to the other pole of the
network (terminal). The clockwork may be that of the registering apparatus or
an independent mechanism.
It is clear that when the brush touches one of the contacts, the circuit con-
trolling the magnetic switching device will be closed, this switch is therefore closed
and closes the circuit of the resistance S which places the voltmeter in shunt.
The latter then indicates the quantity V'a as long as this circuit remains closed.
This operation may be repeated at shorter or longer intervals and for longer or
shorter time-periods. Each time that it happens, the data necessary for determining
the insulation resistance of the net-work are registered.
In the construction of the registering voltmeter according to the present invention
the inking device acting intermittently and normally held away from the paper is
a novel feature. Registering apparatus have sometimes (especially when they
measure the variations of the potential of a cable of a network) to register very
sudden variations taking place within short time-intervals from each other. In the
apparatus with a continuously acting inking device the diagram presents in these
places a black strip, the lines become blended together, and, moreover, at each
sudden change the style of the apparatus passes beyond the real position that it
ought to take and returns to said position only after a series of oscillations which
are marked on the paper. Finally the style remaining in contact with the paper
there is comparatively speaking, a considerable amount of friction. These draw-
backs are obviated by the device hereinafter described which reduces the friction 3
and registers by points or dots (Figs. 1 and 2).
On the spindle a of the movable part of the voltmeter V is secured the pen P, or
rather a needle, or rod, carrying at its end an ink-reservoir Z, which partly replaces
the pen. This reservoir is provided with a hole o and is arranged at a small distance
from the paper. Into the reservoir penetrates through the hole o a style s which 3
dips into the ink but does not touch the paper. This style is secured to the end of
an extremely light rod t oscillating or pivotted about a pin on the rod carrying
the reservoir. A balance-weight p normally holds the rod t and the style away
from the paper. These are the movable parts. To the fixed part of the voltmeter
is secured a segment g which can come in contact with the rod supporting the style 4
between the axis of oscillation of said rod and the style, whatever be the position
of the needle of the voltmeter. This segment, which can oscillate about a pin m
on the fixed portion of the voltmeter, normally does not touch the rod carrying the
style. But an electro-magnet E Á by acting on the extension n of said segment
attracts it and causes the segment to touch the rod supporting the style, thereby 4
causing the style to plunge into the ink and causes it to register a point on the
paper. The electro-magnet EA ceasing to act, the oscillating parts 9 and t rise
under the action of the balance weight p and n until the latter strikes against the
stops b limiting their movements. This electro-magnet is caused to act at greater
or smaller intervals. For this purpose its winding (Fig. 5) is connected by a 5
resistance as r, as has already been described for another electro-magnet, on one
side to one pole of the network (+ terminal) and on the other to a series of contacts C
with which engages
a brush B operated by clock-work and connected to the
other pole of the network (+ terminal). This clock-work may be independent of
those already described, but as a rule this is not the case, and the same clock-work 5
is used.

page_text: In the construction of these brushes it is necessary to obtain good contact
(without causing them to work too stiffly) and a sudden interruption of the contact.
For this purpose the constructions shown in Figs. 6 and 7 are convenient. On the
end of the rod b' which is secured to the pin h (Fig. 6) is secured the brush which
may consist of a metallic spiral B secured at its centre to the rod b¹; the other free
end of which is bent somewhat vertically in order to engage with the projecting
contacts. Each time that the spiral passes over a contact, it is stressed, and
forming a spring suddenly interrupts the current, when as the clock-work continues
to rotate the rod b', the end of the spiral springs off the contact, which is preferably
slightly curved.
This form of brush is not absolutely necessary, and any other suitable device may
be used.
Another form (Fig. 7) has also been used, where the brush B is formed of a
metal blade secured to the rod b¹ at an angle with the vertical. This very thin
blade is split several times ou a portion of its length so as to form a kind of elastic
comb, which also acts as a spring in order to obtain sudden interruption of
contact.
The direction of rotation of the spindles b' carrying the brushes is indicated by
an arrow.
The drawings illustrate devices which can be applied to any form of voltmeter.
The plan and the side and front elevation show a complete apparatus with a
proportional. voltmeter V, provided with a pen P registering on the surface E. The
terminals S' serve to connect the resistance S for shunting the voltmeter. The
signs and T are the positive, negative or neutral (according to circumstances)
terminals, of the network, and the terminals connected to earth. I is the magnetic
switching device. The clock-work H controls the two brushes B₁ and B. The
first brush touches the contacts c which serves to shunt the voltmeter by the
resistance S, and the second touches the contacts C which serve for operating
the electro-magnet E A of the pen. In the apparatus shown in this drawing, the
clockwork is arranged to make one revolution an hour, the contacts c lasts ten
minutes and the contacts C are closed every five minutes.
Having now particularly described and ascertained the nature of the said
invention as communicated to me by my foreign correspondent and in what manner
the same is to be performed, I declare that what I claim is :-
:-
1. In apparatus for indicating and registering variations of insulation resistance
in electric networks and circuits generally, an intermittently acting inking device
with a marker normally held out of contact with the paper and brought in contact
with the latter at regular or irregular intervals by the pressure of a movable
segment attracted by an electro-magnet which is switched in and becomes operative
each time that a brush driven by a clock-work closes one of a series of contacts,
substantially as described.
2. Apparatus used in connection with any voltmeter (of great resistance and
sensitive at any parts of its scale) by means of which the voltmeter may be used for
registering the variations of the insulation resistance of a live electric network or
circuit generally, the voltmeter being for said purpose, connected to one of the
poles of the network and to earth, while the apparatus automatically shunts it by
means of a suitable resistance at intervals and during time periods of desired
length, said shunting being effected by means of an electro-magnet which when
excited forms a magnetic switching device arranged in series with the shunt
resistance. The exciting of the electro-magnet being obtained at intervals and for
time-periods of any desired length by closing the circuit containing the winding of
said electro-magnet by means of a contact-piece driven by a clock-work and
engaging successively with a series of contacts substantially as described.
3. The combination and arrangement of parts constituting the complete
apparatus for indicating and registering variations of insulation resistance in

page_text: electric networks and circuits generally substantially as described and illustrated in
the accompanying drawings.
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