Improvements in Indicating Apparatus for High Tension Circuits.
Year: 1892

page_text: Date of Application, 15th June, 1892
Complete Specification Left, 11th Apr., 1893-Accepted, 15th June, 1893
PROVISIONAL SPECIFICATION.
Improvements in Indicating Apparatus for High Tension Circuits.
We, BERNARD MERVYN DRAKE and JOHN MARSHALL GORHAM, Electrical
Engineers, both of 66 Victoria Street in the City of Westminster, S.W. do
hereby declare the nature of this invention to be as follows:-
Our invention relates to further improvements in indicating apparatus for high
tension circuits described in our Patent 4053 of 1890. The previous instruments
formed a ready means of showing whether the insulation of one of the leads was
greater or less than that of the other as compared with the earth but did not deter-
mine the actual resistance to earth in ohms. In order to enable the absolute insulation
resistance to be determined we provide a high resistance of known value which we
connect permanently to earth and we connect to this a 2 way switch by which
means we can put first one and afterwards the other of the leads to earth through
the known resistance. It is obvious that by an observation of the alteration of the
We find a
divergence made on closing the switch the insulation can be computed.
graphite resistance to be well suited for this purpose.
Dated this 15th day of June 1892
BERNARD MERVYN DRAKE.
JOHN MARSHALL GORHAM.
COMPLETE SPECIFICATION.
Improvements in Indicating Apparatus for High Tension Circuits.
We BERNARD MERVYN DRAKE and JOHN MARSHALL GORHAM, Electrical
Engineers, both of 66 Victoria Street in the City of Westminster, S.W. 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 further improvements in indicating apparatus for high
tension circuits described in our Patent 4053 of 1890. The previous instruments
formed a ready means of showing whether the insulation of one of the leads was
greater or less than that of the other as compared with the earth but did not
determine the actual resistance to earth in ohms. In order to enable the absolute
insulation resistance to be determined we provide a high resistance of known value
which we connect permanently to earth and we connect to this a 2 way switch by
which means we can put first one and afterwards the other of the leads to earth
through the known resistance. It is obvious that by an observation of the
alteration of the divergence made on closing the switch the insulation can be
computed.
-
Let R₁ & R, be the insulation resistances on the two sides of your circuit and
put the artificial leak L on side of R₁. Let V₁ & V, be the potentials from earth
before L is put on V, & V, corresponding when L is on.
Then R₂ = (✓✓.
-
V₁
1
2
✓✓) L. R₁ = ✓✓ R2. Now if we suppose the whole pressure V
2
1 2
to remain constant the locus of all values of the components V₁ V, etc. is given by
a straight line X+Y=C. Therefore it should be sufficient to read V, & V₂, or
the deflections on the side on which you put the artificial leak and a table can
V
be given of figures which are the values of ratios ✓ say from 10 to 1. Thus
B

page_text: when V=2000 volts the deflection given by 182 volts would be marked 10,
200 volts 9, 222 volts 8, 250 7, 286 6, 333 5, 400 4, 500 3, 667 2, 1000 1,
1143 75, 1333 5, 1600 25, 1818 1. Thu ssuppose you have a leak on side B
and put artificial leak on side A, reading deflections on side A. Let deflections
before putting on artificial leak on side A be that due to 1333 volts marked *5.
When artificial leak is on let it be 1000 volts, marked 1, then resistance of leak on
We find a graphite
L
side B = (1-5) L= or if L be 10,000 === 5,000 ohms.
resistance to be well suited for this purpose.
-
In the drawings accompanying it will be seen that A & B are the two plates with
foils attached, these being connected to the + and of the circuit under test.
They are also connected to the switch S by means of which they can be in turn
connected to earth through the resistance Ŕ of known value.
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 use of a resistance of known amount connected at one end to earth, and
at the other end to each pole of a leakage indicator in turn so as to determine the
insulation in absolute terms.
(2) The use of graphite resistance for this purpose.
(3) The apparatus substantially as described.
Dated this 11th dove of Annil 1902
BERNARD MERVYN DRAKE.
JOHN MARSHALL GORHAM.