Improved Method of and Means for Testing the Insulation of Electric Conductors.
Year: 1889

page_text: Date of Application, 22nd Jan., 1889
Complete Specification Left, 17th Oct., 1889-Accepted, 18th Jan., 1890
PRARIO
PROVISI AL SPECIFICATION.
Improved Method of and Means for Testing the Insulation of
Electric Conductors.
We, WILLIAM LOWRIE, Engineer, and CHARLES JAMES HALL, Electrician, both of
117 Bishopsgate Street Within, in the City of London, do hereby declare the nature
of this invention to be as follows:-
Our invention relates to the testing of the insulation of electric conductors while
used for conveying currents of electricity. The method adopted is that of indicating
the condition of the conductor by light, or by the absence of light. The means or
apparatus consists of a small box or receptacle containing a vacuum discharge tube,
usually known by the name of Geissler's tubes. Suitable terminals are placed in
the box to receive the vacuum tube, one of the electrodes of which is connected to
earth by its terminal, while the opposite electrode is connected, by its terminal, to
a pole of the conductor under test. The box is provided with a lid or door to give
access to the interior, an orifice through which the tube may be observed, one or
moro safety fuses to cut the apparatus out of circuit if the current is excessive;
and the interior of the box is blackened.
In testing a high potential conductor, one of the vacuum tube electrodes is
connected in the manner above stated to one pole of the conductor. If the
insulation of that portion of the conductor is bad, the characteristic glow of the
vacuum tube, when current is passing between the poles, is wanting; because earth
connection is made at the extremities of the testing circuit. On the other hand,
if the insulation is good, the glow of the tube is present, because current is dis-
charging through the vacuum tube to earth. The glow of the vacuum tubo (when
current is passing) is vivid or otherwise, in proportion to the quality of the insulation
and potential of the current, and may be compared with a standard vacuum tube
or other light giving means, and measured by a photometer. The comparison may
also be made by the chemical or thermal effect of the light produced; using an
actinic scale in the former case and a radiometer in the latter case; or other
equivalent devices.
Each pole of the insulated conductor should be tested in the manner indicated
above, as it is to be noted that if a fault exists upon another portion of the conductor
than that under test, (the latter being well insulated), the glow is present; but on
the connection being shifted to the opposite pole-on the faulty side of the cable-
the discharge through the tube is diminished or ceases, as the case may be, in the
manner before stated. The arrangement described applies to currents, usually of
high potentiality.
In the case of currents, of low potentiality, an induction coil, and a make and
break apparatus (if the current is continuous), is connected with one of the poles
of the cable to be tested, and put to earth; while the vacuum discharge tube is
placed in the secondary circuit. The rosult is that if there is a leak on the portion
of the conductor under test, no light is given upon the pole, because earth is made
at both extremities of the tube. But if light is given it follows that the insulation
of the opposite conductor is more or less bad, because the inducing current which
discharges (by induction) through the vacuum tube must pass through the imperfect
portion of the conductor to get to earth. Any section of a conducting cable may
be tested, and a fault localized, in the mannor described.
Dated this 21st ST 1000

page_text: COMPLETE SPECIFICATION.
Improved Method of and Means for Testing the Insulation of
Electric Conductors.
We, WILLIAM LOWRIE, Engineer, and CHARLES JAMES HALL, Electrician, both of
117 Bishopsgate Street Within, in the City of London, 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:-
Our invention relates to the testing of the insulation of electric conductors used for
conveying currents of electricity. The method adopted is that of indicating the
condition of the conductor by light, or by the absence of light. The means or
apparatus consists of a small box or receptacle containing a vacuum discharge tube,
usually known by the name Geissler's tubes. Suitable terminals are placed in the box
to receive the vacuum tube, one of the electrodes of which is connected to earth by its
terminal, while the opposite electrode is connected, by its terminal, to a pole of the
conductor under test. The box is provided with a lid or door to give access to the
interior, an orifice through which the tube may be observed, one or more safety fuses
to cut the apparatus out of circuit if the current is excessive; and the interior of the
box is blackened.
In testing a high potential conductor, one of the vacuum tube electrodes is connected
in the manner above stated to one pole of the conductor. If the insulation of that
portion of the conductor is bad, the characteristic glow of the vacuum tube, when
current is passing between the poles, is wanting; because earth connection is made at
the extremities of the testing circuit. On the other hand, if the insulation is good, the
glow of the tube is present; because current is discharging through the vacuum tube
to earth. The glow of the vacuum tube (when current is passing) is vivid or other-
wise, in proportion to the quality of the insulation and potential of the current, and
may be compared with a standard vacuum tube or other light giving means, and
measured by a photometer. The comparison may also be made by the chemical or
thermal effect of the light produced; using an actinic scale in the former case and a
radiometer in the latter case; or other equivalent devices.
Each pole of the insulated conductor should be tested in the manner indicated
above, as it is to be noted that if a fault exists upon another portion of the conductor
than that under test, (the latter being well insulated), the glow is present; but on the
connection being shifted to the opposite pole-on the faulty side of the cable-the
discharge through the tube is diminished or censes as the case may be, in the manner
before stated. The arrangement described applies to currents, usually of high
potentiality.
In the case of currents, of low potentiality, an induction coil, and a make and break
apparatus (if the current is continuous), is connected to one of the poles of the cable
to be tested, and put to earth; while the vacuum discharge tube is placed in the
secondary circuit. The result is that if there is leak on the portion of the conductor
under test, no light is given when connection is made upon that pole of the conductor
because earth is made and there is no difference of potential. But if light is given it
follows that the insulation of the opposite conductor is more or less bad, because the
inducing current which discharges (by induction) through the vacuum tube must pass
through the imperfect portion of the conductor to get to earth.
In the accompanying drawings Figs. 1, 2, and 3 are diagrams, indicating the
method of using the apparatus shown by Figs. 4, 5, and 6. In Fig. 1 the circuit of
insulated conductor, a, and a is shown with the vacuum discharge tube b connected
to the pole of a. As the insulation is supposed to be good in this instance, the
characteristic glow of the vacuum tube is present, because current is discharging
through the tube to earth c and in doing so produces light in the tube b. In Fig. 2 a
defective insulation is indicated at d and light is absent in consequence, as there are
earth connections made at both c and d. The above are examples of testing high
potential conductors, but Fig. 3 indicates a method of testing the insulation of low

page_text: potential currents of electricity. For this purpose, an induction coil e is connected to
the pole a of the cable under test, and put to earth at c, but if the conductor is used
for continuous currents, (instead of alternating as in the former instances) a make and
break apparatus f, is also inserted, while the vacuum tube is placed in the secondary
circuit g. If there is no leak, there is no light given, but if there is a leak d in the
circuit, no light is given while connection is made upon that side of the conductor, but
if light is given, it follows that the insulation of the opposite side of the conductor is
more or less bad, because the inducing current which discharges (by induction)
through the vacuum tube must pass through the imperfect portion of the conductor to
get to earth.
Fig. 4 is a sectional elevation through the testing apparatus, in which the vacuum
discharge tube is suspended by its electrodes and 6 to terminals secured to the
darkened hox A. The upper terminal h is used for the cable connection, and the
lower one h¹, for the earth connection. Safety fuses i, i, are mounted upon the door A¹
of the box A, spring contacts being made at their lower terminals 1, 1, and an eye
piece or orifice A2 provides for the observation of the vacuum tube. Fig. 5 is a
sectional elevation through the box A at right angles to Fig. 4; and Fig. 6 is a
sectional plan of the same.
Having now particularly described and ascertained the nature of our said Inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is:
1. The method of testing the insulation of a conductor conveying high potential
currents of electricity which comprises the introduction of a vacuum discharge tube
between a pole of the conductor under test, and an earth connection; substantially
as described.
2. The method of testing the insulation of a conductor conveying low tension
alternating currents of electricity which comprises the introduction of an induction
coil between a pole of the conductor under test and an earth connection, with a
vacuum discharge tube inserted in the secondary circuit of the said induction coil;
substantially as described.
3. The method of testing the insulation of a conductor conveying low tension
continuous currents of electricity which comprises the introduction of an induction
coil and a make and break apparatus between a pole of the conductor under test
and an earth connection, with a vacuum discharge tube inserted in the secondary
circuit of the said induction coil; substantially as described.
4. The method of testing the relative insulation of an electric conductor by means
of the glow or discharge in a vacuum tube and comparing the said glow with a
standard of light or indicating its actinic or thermal effect; substantially as and
for the purpose described.
.5. An apparatus for testing the insulation of electric conductors consisting of a
box or receptacle having a sight orifice and containing a vacuum discharge tube,
terminals attached to the said box and arranged to make electrical contact with the
electrodes of the said vacuum tube, a connection from one of the electrodes through
its terminal to a pole of the conductor to be tested and an earth connection from
the other electrode through its corresponding terminal; substantially as described.
6. An apparatus for testing the insulation of electric conductors by means of
light comprising a box or receptacle blackened inside and having a sight orifice
or opening, one or more vacuum discharge tubes with suitable terminal supports
therefor, and a safety fuse or fuses; substantially as described.
7. The combination of a photometer, or an actinic scale, or a radiometer with a
Geissler tube, for the purpose of indicating the relative insulation of an electric
conductor; substantially as described.
Dated this 16th dow of Oninho 1800
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicants.