Improvements in Systems of Electrical Distribution.
Year: 1899

page_text: Date of Application, 22nd Nov., 1899-Accepted, 30th Dec.,
1899
COMPLETE SPECIFICATION.
Improvements in Systems of Electrical Distribution.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of our
said invention (which has been communicated to use from abroad by Elihu
Thomson, of Swampscott, in the County of Essex, State of Massachusetts,
United States of America, Electrical Engineer), and in what manner the same
is to be performed, to be particularly described and ascertained in and by the.
following statement:-
The present invention relates to safety devices for alternating current sys-
tems. Its particular object is to cut entirely out of action any transformer or
other translating device which proves defective and to prevent injury to apparatus
or the consumers in the branch line, from such an accident, for example, as
when primary current passes into the secondary system by puncture of the insu-
lation. This object we obtain by causing current to flow through a cut-out
device on a puncture of the insulation and thereby open the circuit. The cut-
grounded
out may be operated by leakage through what is known as the "
sheath," or the frame of the transformer or translating device, or the secondary
circuit, and serves to open a primary main connection of the transformer of the
supply circuit of a translating device of other character. In one of the best
embodiments of this invention, we provide a double-pole circuit-breaker in the
primary, with means for tripping it when current passes from the sheath of the
transformer to ground.
For a transformer under ordinary conditions of service, the grounded sheath
is the best way of applying the invention, we may however, attain the results
which we seek by other connections, some of which we indicate. For example,
we may operate the circuit opening means by a connection from one of the
secondary lines in a two wire system, or from the neutral in a three wire system;
or from the frame or casing of the transformor or translating device.
The accompanying drawings show in diagram arrangements within the in-
vention. Fig. 1 shows the circuit-opening means connected to the sheath of a
transformer; in Fig. 2 it is connected to one side of a two wire system; in
Fig. 3 the neutral of the three wire secondary system, and in Fig. 4 to the box
of the transformer.
In Fig. 1, H is a transformer which is supplied from the primary mains A, B,
its primary P being connected to these mains, and being protected against acci-
dental short-circuit by the fuses F, F¹, in the ordinary way. S is the secondary
supplying lamps L or other consuming device, of course any load whatever may
be put upon it. The sheath I is of copper or other conducting material, and is
interposed between the two windings in the usual way, a detailed description of
which is unnecessary.
Connected to the sheath is the coil C of an electro-
magnetic circuit-breaker N; a spark-gap K bridges the coils. The connection
from the sheath to ground may either be solid metal o: have the well known
film cut-out interposed. We have not deemed it necessary to illustrate this;
because its construction and application are well known.

page_text: The operation of the parts thus described is as follows; assume that current
flows from the primary to the sheath I, as a result of direct lightning stroke,
induced discharge, or defective insulation. In this case if there be a second
ground upon the primary. lines (which may nearly always be assumed in any
extensive system of distribution) or even if there be sufficient capacity in the
line, a rush of current will pass through the connection from the sheath or other
leakage point to earth at E; and in general; the potential will be so
high that
the discharge will pass the gap K, while more or less of the current which fol-
lows the discharge will pass through the coils C, opening the circuit-breaker
which bridges the gaps, in the primary lines.
In Fig. 2, the parts are illustrated as before, but in this case the coil C is
connected between the main a of the secondary distribution and ground, which
arrangement will protect the transformer not only in case of puncture of insu-
lation followed by discharge into the secondary, but also in case of other acci-
dents such as the grounding of opposite sides of the secondary distribution.
In Fig. 3 we show the application of the invention to the well known three
wire system, where the mains a, b, c are the positive, negative and neutral,
respectively. Here it is best to connect the circuit-breaker to the neutral, which
is in many installations, likely to be grounded at all times.
The action in this case is substantially like that in Fig. 2, except that both
sides of the three wire system are protected.
In Fig. 4, the box G of the transformer is used as a ground connection. This
is not so good an arrangement as that in the other figures, because it might
occur that the insulation between the primary and secondary coils would be
punctured without bringing the box into circuit; nevertheless, the invention
may be usefully applied in this way, and this is a good example of a mode of
protecting other types of devices than transformers.
In all of the figures we show as the preferred form for the purpose of this
case the electro magnetic circuit breaker opening the primary line, but not
directly dependent upon the current in the primary. Any usual or customary
protection against undue current in the primary, such as the fuses F, F¹, may
be employed in addition to the invention herein set out.
While the invention herein described is especially designed for use in connec-
tion with transformers and will have its principal field of use with them, it is
also applicable to any translating device fed with or carrying high tension cur-
rents and which it is desirable to cut out upon failure of the insulation.
Having now particularly described and ascertained the nature of our said in-
vention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is:-
1-In a system of electrical distribution, the combination of two circuits insu-
lated from one another, with means for opening one of them, brought into action
by puncture of the insulation.
2-In an alternating current system, means for opening a transformer circuit,
brought into action by the puncture of the insulation.
3 The combination of a transformer, with mechanical means for opening the
primary circuit, brought into action by the puncture of the transformer insu-
Iation.
4-The combination with a transformer, of an electro-magnetic circuit breaker
for opening the primary lines and a connection from the transformer to ground
including the coils of the circuit breaker.
5-The combination with a transformer, of an electro magnetic circuit-breaker,
the coil of which is included in a circuit between the transformer and ground
disconnected from the primary, and contacts operated by the circuit breaker for
opening the primary circuit.
6-The combination with the grounded sheath of a transformer, of a circuit

page_text: breaker for opening the primary leads, the coil of which is included in the
grounded connection.
7-The combination with the primary lines leading to a transformer, of a
common means for opening the circuit operated by either the puncture of the
transformer insulation or a ground in the secondary distribution.
8 The combination with a transformer or other translating device, of a cir-
cuit-breaker in the supply circuit, and a coil controlling said circuit-breaker in
a branch circuit, normally open at a point closely related to the winding of the
translating device, so as to be energized upon rupture of the insulation.
9-The combination with a transformer or other translating device, of a cir-
cuit-breaker in the supply circuit, and a coil controlling said circuit-breaker in
a ground branch normally open at a point closely related to the winding of the
translating device, so as to be energized upon rupture of the insulation.
Dated this 81st day of October 1899.
THE BRITISH THOMSON-HOUSTON CO. LTD.,
ALFRED CLEMENTS,
Assistant Secretary.
W. MARTINDALE, }
A. MONKS,
Directors.