Improvements in Systems of Electrical Distribution and in Cutouts therefor.
Year: 1899

page_text: Date of Application, 22nd Nov., 1899-Accepted, 27th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Systems of Electrical Distribution and in Cutouts
therefor.
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 us from abroad by Elihu
Thomson, of Swampscott, 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
We
This invention relates to safety devices for alternating current systems, the
object being to protect translating or consumption devices upon a breaking
down of their insulation. The invention is particularly directed to the pro-
tection of transformers and the interruption of the supply circuit upon failure
of the transformer insulation or extraordinary leakage in the secondary circuit.
In carrying out this invention we provide in the supply circuit of the trans-
former or consumption device a thermal or other cut-out, and cause a heavy
eurrent, sufficient to fuse or operate the same, to flow when a leakage or ground
branch of the consumption device is energized by a failure of insulation.
provide between the cut-out and the transformer a short circuit normally open at
a spark-gap through which the line current may flow when an arc is sprung,
and provide means for breaking down the gap when the transformer insulation
gives way or when for any reason there is an extraordinary increase of energy in
the secondary system. The leakage current by which the cut-out is controlled
" or conductor between the
may be, for example, from a "grounded sheath
primary and secondary transformer windings, or from a ground to the trans-
former casing, or from the secondary mains the result being in any case that
upon the breaking down of the insulation, sufficient current will leak to ground
to close the short circuit through the spark-gap and actuate the thermal cut-out
and interrupt the circuit.
This invention therefore, in one of its aspects, comprises a distribution circuit
for alternating currents, including a consumption device fed through a thermal
cut-out, and means for operating said cut-out upon the energization of a ground
branch controlled by a rupture of insulation of the consumption device.
The invention further comprises a distribution circuit including a transformer
and a cut-out in the main or primary circuit thereof, depending for its operation
upon the energization of a ground branch controlled by the condition of the
insulation of the transformer or by the potential of its secondary circuit and
controlling in turn a short circuit of the primary mains through the cut-out.
The invention also comprises other and more specific features which will be
hereinafter more fully described and will be definitely indicated in the claims.
In the drawings, Fig. 1 is a diagram showng a cut-out operated by the

page_text: "
"grounded sheath" of the transformer; Fig. 2 shows a system in which the
controlling ground connection is taken from one side of the secondary; in Fig. 3,
the ground connection is taken from the neutral wire of a three-wire system;
in Fig. 4 the ground connection is made with the transformer frame or casing.
Referring to the drawings, 1, 2 represent the primary leads of a transformer,
or the supply leads of a consumption device of other character. 3 represents the
primary winding of the transformer, the secondary of which feeds a lamp or
other consumption circuit, 4. 5 represents what is known in the art as
grounded-sheath," being a copper separating medium between the two trans-
former windings, provided with an earth connection. In this connection we
interpose the primary of a small auxiliary transformer, 6, the secondary of which
controls the operation of a thermal cut-out 7, 7", shown specificially as fuse-
wires. To prevent the reaction of the secondary winding of the transformer 6
upon the line, we differentially connect the windings so that like terminals--
that is to say, those which are in the same inductive relation to the transformer
core-connect with opposite mains of the supply circuit. In order to prevent
the secondary circuits of this auxiliary transformer from normally short-
circuiting the main supply circuit of the consumption device or main transformer,
we interpose between the main circuit leads 1, 2 and the said secondary circuit,
spark-gaps 8, 8", consisting of metallic terminals separated by an air space or
by a thin film or stratum of insulating material adapted to break down upon
a definite increase of potential. The sparking devices are connected through a
condenser 9. The parts may with advantage be arranged as shown in the
diagram, the connections from the main circuit leading to a point between
the spark-gaps and the condenser terminals, and the middle point of the
differential winding on the secondary of the auxiliary transformer 6 being con-
nected with an intermediate part of the condenser.
The condenser is of comparatively small capacity. Its leaves are provided-with
three terminals, two connecting with the mains and the third with the junction
of the differential transformer coils. The auxiliary transformer should pre-
ferably be step-up in character, the number of turns being such to admit of
small reactance.
As thus organized, it will be seen that upon the breaking down of the insula-
tion of the transformer, part of the primary current will leak through the
grounded sheath 5 and react inductively upon the auxiliary transformer, thereby
breaking down the insulating film in the spark-gaps and exciting the con-
denser rhythmically with the line rate. The bridging of the spark-gaps per-
mits a heavy current to be drawn through the fusible cut-outs 7, 7", causing
their fusion and the opening of the circuit.
In Fig. 2 an organization somewhat similar to that which has just been
described is depicted, except that herein the auxiliary transformer 6 is provided
with independent magnetic circuits for the two secondary sections, which are
differentially connected and discharge into the line terminals through the
common connection 10. This arrangement is not so satisfactory, as the separate
magnetic circuits produce a larger reactance than a superposed winding. In
this diagram we show the secondary circuit as connected with the ground or
leakage branch. It follows in this case also that if the insulation of the trans-
former break down, the secondary circuit will be charged with extraordinary
potential, and will cause the primary fuse or thermal cut-outs to act in the same
manner as described in connection with Fig. 1.
In Fig. 3 the relationship of the parts is the same as in Fig. 1, except that the
secondary is shown as a three-wire system, the middle wire being connected
in the ground branch which controls the automatic cut-out.
In Fig. 4 the organization differs from that shown in Fig. 1, in that the trans-
former frame or casing is connected in the ground or leakage branch instead of
the grounded sheath between the two windings.
It will be evident that this invention may be applied to various types of

page_text: electrical devices for transferring, translating or consuming electric energy,
and we refer to such generically in the claims by the comprehensive term
lating device."
trans-
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same
is to be performed, we declare that what we claim is:-
In a system of alternating-current distribution the combination of two
circuits insulated from one another, one including a source of current and the
other consumption devices, a thermal cut-out in the supply circuit, and a mag-
netic operating device therefor actuated upon failure of the insulation.
2-In a system of alternating-current distribution, the combination of a trans-
former the primary circuit of which includes a thermal cut-out and the secondary
translating devices, a leakage branch and magnetic means controlled thereby to
admit an operating current through the cut-out.
In a system of alternating-current distribution, the combination of a trans-
former, the primary of which includes the thermal cut-out, and the secondary
translating devices, a leakage branch, and magnetic means controlled thereby
to admit an operating current through the cut-out upon extraordinary rise of
potential in the secondary system.
4-In a system of alternating-current distribution, the combination of a
transformer, the primary of which includes a thermal cut-out, a leakage branch
from the transformer fed with current upon a failure of insulation, an auxiliary
transformer having its primary in said branch and its secondary controlling the
cut-out.
5-In a system of alternating-current distribution, the combination of a trans-
former, the primary of which includes a thermal cut-out, a leakage branch from
the transformer rendered active upon a failure of insulation, an auxiliary trans-
former having its primary in said branch and its secondary adapted to short circuit
the primary mains of the cut-out.
6 The combination with a translating device of a ground branch normally
completed from a metallic part of said device but insulated from the supply
circuit adapted to be energized upon a failure of insulation in said device, and a
current interrupter controlled by said branch.
7-The combination with a translating device, of a leakage branch for current
operating upon the failure of insulation in the said device, a transformer fed
by such leakage currents, the secondary winding of which is connected with
the supply circuit through a spark-gap and controlling a thermal cut-out in
the supply circuit.
S-The combination with a translating device, of a ground branch protecting
the same, energized upon a breaking down of the insulation, a transformer
having its primary in said branch, and a split secondary differentially connected
with the supply circuit to neutralize the effect of the several sections upon said
circuit, a spark-gap between the transformer secondary and the supply circuit,
and a thermal cut-out in the supply circuit controlled by said secondary.
9 The combination with a translating device, of a ground branch energized
upon a failure of insulation in said device, a circuit-breaker in the supply circuit,
and a spark-gap in the branch of a supply circuit controlled by said ground
branch.
10. The combination with a translating device, of a ground branch protecting
the same and adapted to be energized upon a failure of the insulation in the
device, a transformer controlled by said ground branch, and a circuit-interrupter
actuated by said transformer.
11 The combination with a translating device, of a branch connection open
at a point closely related to its winding so as to complete a leak upon rupture
of the insulation and a circuit interrupter for the supply circuit operated by
said branch.

page_text: 12 The combination with a trauslating device, of a branch connection open at
a point closely related to its winding so as to complete a leak upon rupture of the
insulation a thermal cut-out in the supply circuit, and means controlled by the
branch when energized to direct an operating current through the cut-out.
13 The combination with a translating device, of a branch connection open at
a point closely related to its winding so as to complete a leak upon rupture of the
insulation, a fuse in the supply circuit, and means for directing current through
the fuse sufficient to blow it when the branch is energized.
14 The combination with a translating device, of a branch connection open
at a point closely related to its winding so as to complete a leak upon rupture
of the insulation a circuit interrupter in the supply circuit operating upon
determined increased current flow, a short-circuit including said interrupter
and a spark-gap, an electromotive device controlled by a leak branch for bridging
the spark-gap, and a condenser around the spark gap.
T
1.
fataban 1900
THE BRITISH THOMSON-HOUSTON Co., LTD.,
W. MARTINDALE,
A. R. MONKS,
ALFRED CLEMENTS,
}
Directors.
Assistant Secretary.