Improvements in Safety Apparatus and Devices for Preventing Danger from High Tension Electric Currents and for Indicating Faults in Low Tension Circuits.
Year: 1890

page_text: Date of Application, 22nd Feb., 1890
Complete Specification Left, 19th Nov., 1890-Accepted, 31st Jan., 1891
PROVISIONAL SPECIFICATION.
Improvements in Safety Apparatus and Devices for Preventing
Danger from High Tension Electric Currents and for Indicating
Faults in Low Tension Circuits.
I, HENRY EDMOND WALTER, formerly of Schenectady in the State of New
York and United States of America, but at present residing at 19 Porchester
Gardens Bayswater in the County of Middlesex Electrical Engineer, do hereby
declare the nature of this invention to be as follows:-
:-
In the use of systems of electric lighting employing currents of low potential,
such for instance as the Edison three-wire system, when such systems are used in
connection with transformers and are thus exposed to contact with other circuits
which employ currents of much higher potential, danger may arise to persons
employed in connection with the system, for if the high volt circuit is accidentally
grounded as such circuits are very likely to be and also becomes accidentally
crossed with a conductor of the low volt circuit, then any person handling the low
volt circuit, which can ordinarily be done without danger, may, by grounding the
system through his body, receive the high volt current. The main object of my
invention is to avoid this danger and I primarily accomplish this in the three wire
system by making a permanent low resistance ground connection from the neutral
wire of the system at the central station whereby the high volt current when it
enters upon the low volt circuit finds a low resistance path through the earth at
this point whereby the difference of potential between the point where the cross
occurs and the ground is reduced practically to zero.
While a simple ground connection will accomplish this much, such a connection
has the disadvantage that if an accidental ground occurs on one of the other wires
of the low volt system, there is at once a low resistance cross through the ground
between such wire and the neutral wire which will of course result in a waste of
current and may cause injury to the system. To avoid this I place in the ground
connection from the neutral wire the armature of an electro dynamic motor, whose
field magnet may be in a shunt between the neutral and one of the other wires, or
is otherwise kept constantly charged, such armature being of low resistance and
proportioned in resistance with relation to the resistance of the generators employed
with any high volt system with which the three-wire system is liable to become
crossed, so that its resistance is a fraction of that of the high volt generator.
If a leak to ground occurs on either the positive or the negative wire of the three-
wire system, the current will flow through the motor armature and such motor will
start. This in the first place gives an indication of the fact that a ground has
accidentally occurred and according to the direction in which the motor starts it is
known whether the ground is on the positive or on the negative conductor; but,
further, the revolution of the motor produces a counter electro motive force which
is thrown into the ground connection and prevents the flow of excessive current
through such connection. The motor in fact takes the place of a translating device
connected across the two conductors parallel to the other translating devices of the
system, and it may if desired continue to run preventing a short circuit of the
system until the accidental ground is found and remedied.
When the three wire system is crossed with a high volt system on either of its
conductors, the danger to persons handling the system does not arise unless the
high volt system is grounded somewhere, but if it is grounded then, as above stated,

page_text: a circuit is established to the neutral wire through the ground connection containing
the motor. Such motor immediately begins to run and because of the high volt
current energizing it, it will be brought up to a very high speed much higher than
that to which it is run by the low volt current. This speed would be such as to
endanger the three-wire system by the high counter electro motive force developed
and also to endanger the motor itself. To avoid this I place on the shaft of the
motor a switch arranged to be operated by centrifugal force when the motor is brought
up to high speed, such switch being in a shunt around the motor armature.
switch when thrown out as stated shunts the motor and establishes a dead low
resistance ground from the neutral as before.
This
Where there is any danger of the three-wire system becoming crossed with a
high volt system employing an alternating current instead of a continuous one, I
place in the ground connection from the neutral an additional switch which is an
electro magnetic switch having a retarded movement and adapted to be operated
by an alternating current and to close a low resistance ground connection around
the motor armature.
I provide in the ground connection from the neutral wire an ampere meter for the
purpose of indicating the current in such ground connection at any time, such meter
or indicator being adapted to carry a heavy current and also to indicate a very
light current.
I provide also a switch by which either the positive or the negative wire may be
connected to ground through a resistance for the purpose of indicating grounds on
the neutral. Such a ground will not affect the motor, but by means of the switch
last referred to the positive or negative conductor may be connected to the ground
at any time through a resistance such as an incandescent electric lamp. Then if
there is no other ground on the neutral than the permanent one through the motor,
the motor will run at its normal speed; but if there is also some accidental ground
on the neutral this will be indicated by the failure of the motor to start or by its
starting very slowly. The ground on the neutral may then be found and remedied,
or it may be "burned out" by shunting the resistance lamps and so making a low
resistance cross through the earth.
This switch, with the resistance lamps and the connections for shunting the latter
are all conveniently placed on a switchboard secured to the yoke of the motor.
The switch, for protection from discontinuous or alternating high tension currents
is also placed on the motor yoke. This electro-magnetic switch has its movement
retarded by weights and is therefore not affected by the passage of a continuous
current, because before it can act, the counter electro motive force of the motor
has been thrown into the circuit thereby reducing the current to a very small
amount and preventing the magnet from acquiring energy enough to raise the
weights. When however a dangerous alternating or discontinuous current enters the
circuit the motor will not start but its armature may become heated to a dangerous
degree. At this time the retarded switch comes into use and closes a ground
circuit around the motor.
The centrifugal switch for protecting the motor consists of spring shoes on the
motor shaft thrown out by centrifugal force, and locked against a metal casing
so that the contact of said shoes with said casing closes a ground circuit around the
motor.
It will be seen that my invention is adapted for use wherever a low volt system
is in danger of becoming crossed with one employing a high potential current, as is
now often the case where a low volt incandescent system is run in proximity to arc
light systems, systems employing transformers, and high volt electric railway
systems. The invention was however as stated, specially designed with reference
to the use of continuous current transformer systems to prevent danger to the users
of the secondary circuits by reason of crosses between the primaries and secondaries
in the converters. It will be seen that such a cross would be precisely equivalent
to the connection between two separate systems.
It is further evident that my invention is applicable to a two-wire multiple

page_text: arc-system as well as to the three-wire system shown, the motor and other devices
being connected between either of the two conductors and the earth.
Dated this 22nd day of February 1890.
HENRY EDMOND WALTER.
By Harris & Mills,
23, Southampton Buildings, London, Agents.
COMPLETE
SPECIFICATION.
Improvements in Safety Apparatus and Devices for Preventing
Danger from High Tension Electric Currents and for Indicating
Faults in Low Tension Circuits.
I, HENRY EDMOND WALTER, formerly of Schenectady in the State of New
York and United States of America but at present residing at 19 Porchester
Terrace, Bayswater in the County of Middlesex, Electrical Engineer, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed to be particularly described and ascertained in and by the following
statement :-
In the use of systems of electric lighting employing currents of low potential,
such for instance as the Edison three-wire system, when such systems are used
in connection with transformers and are thus exposed to contact with other
circuits which employ currents of much higher potential, danger may arise to
persons employed in connection with the system, for if the high volt circuit is
accidentally grounded as such circuits are very likely to be and also becomes
accidentally crossed with a conductor of the low volt circuit, then any person
handling the low volt circuit, which can ordinarily be done without danger, may
by grounding the system through his body, receive the high volt current. The
main object of my invention is to avoid this danger and I primarily accomplish
this, in the three-wire system, by making a permanent low resistance ground
connection from the neutral wire of the system at the central station whereby
the high volt current when it enters upon the low volt circuit finds a low resistance
path through the earth at this point whereby the difference of potential between
the point where the cross occurs and the ground is reduced practically to zero.
While a simple ground connection will accomplish this much, such a connection
has the disadvantage that if an accidental ground occurs on one of the other
wires of the low volt system, there is at once a low resistance cross through the
ground between such wire and the neutral wire which will of course result in a
waste of current and may cause injury to the system. To avoid this I place in
the ground connection from the neutral wire the armature of an electro dynamic
motor, whose field magnet may be in a shunt between the neutral and one of
the other wires, or is otherwise kept constantly charged, such armature being
of low resistance and proportioned in resistance with relation to the resistance of
the generators employed with any high volt system with which the three-wire
system is liable to become crossed, so that its resistance is a fraction of that of
the high volt generator.
If a leak to ground occurs on either the positive or the negative wire of the three
wire system, the current will flow through the motor armature and such motor
will start.
This in the first place gives an indication of the fact that a ground has
accidentally occurred and according to the direction in which the motor starts it is
known whether the ground is on the positive or on the negative conductor; but,
urther, the revolution of the motor produces a counter electro motive force which
s thrown into the ground connection and prevents the flow of excessive current
hrough such connection. The motor in fact takes the place of a translating device
onnected across the two conductors parallel to the other translating devices of the

page_text: Systemy
10
may
system until the accidental ground is found and remedied.
When the three-wire system is crossed with a high volt system on either of its
conductors, the danger to persons handling the system does not arise unless the high
volt system is grounded somewhere, but if it is grounded then, as above stated, a
circuit is established to the neutral wire through the ground connection containing
the motor. Such motor immediately begins to run and because of the high volt
current energizing it, it will be brought up to a very high speed, much higher than
that to which it is run by the low volt current. This speed would be such as to
endanger the three wire system by the high counter electro motive force developed
and also to endanger the motor itself. To avoid this I place on the shaft of the
motor a switch arranged to be operated by centrifugal force when the motor is
brought up to high speed, such switch being in a shunt around the motor armature.
This switch when thrown out as stated shunts the motor and establishes a dead low
resistance ground from the neutral as before.
Where there is any danger of the three-wire system becoming crossed with a
high volt system employing an alternating current instead of a continuous one,
I place in the ground connection from the neutral an additional switch which is an
electro magnetic switch having a retarded movement and adapted to be operated
by an alternating current and to close a low resistance ground connection around
the motor armature.
I provide in the ground connection from the neutral wire an Ampere meter for the
purpose of indicating the current in such ground connection at any time, such meter
or indicator being adapted to carry a heavy current and also to indicate a very
light current.
I provide also a switch by which either the positive or the negative wire may be
connected to ground through a resistance for the purpose of indicating grounds on
the neutral as will be more fully explained.
In the accompanying drawings,
Figure 1 is a diagram illustrating the arrangement of apparatus embodying my
invention with special reference to the electrical connections and circuits, and
showing also conditions under which the apparatus is brought into use;
Figure 2, a top view of the motor and apparatus used therewith ;
Figure 3, a rear elevation of the same with the alternating switch magnet in
vertical section ;
Figure 4, a front elevation of the motor with the said alternating current switch
omitted for the purpose of clearness, and
Figure 5, a diagram showing my invention as used with a two wire continuous
current transformer system.
Referring mainly to the diagram, Figure 1, A A. represent the generators
supplying the three-wire system, of which p, n and c are the main conductors,
I being incandescent lamps or other translating devices supplied by the system.
B is the armature of the switching electric motor placed at the central station.
One pole of said armature is connected by a heavy conductor 1 with the neutral
wire c and the other pole by a heavy conductor 2 with the earth.
C
The coils of the field magnet Care connected by wires 3, 4, from one terminal
to the negative main conductor n, the other field terminal being joined to the
wire 1 so that the field is connected between the negative and neutral wires
and is constantly charged. D represents the ampere meter in the ground con-
nection 2, above referred to, and E is the magnet controlling the alternating
current switch which is adapted to close the circuit 5-5. The centrifugal
switch of the motor armature is arranged to close the circuit 6-7 around such
armature. F is a pivotted switch lever connected by wire 8 with the grounded
terminal of the motor armature and arranged to be placed in contact with one
or the other of the plates d and e which are normally connected through incan-
descent electric lamps for other suitable resistance, the plate e being connected
with the wire 4 extending to the negative main, and the plate d to the wire 9

page_text: extending to the positive main. The plates d and e are furthermore arranged
to be connected with wires 9 and 4 through fusible safety catches which may
be inserted at g g.
G represents the generator supplying a high volt continuous
current system whose main conductors are represented by P. N.
The apparatus above described is preferably arranged as illustrated in
Figures 2, 3, and 4. The motor is provided with an insulating switch board on
each side of its yoke or keeper and at one side thereof are placed the plates d. e.
and the corresponding safety catch terminals and also the pivotted switch F.
The resistance lamps are set on top of the motor where is also placed a
standard for supporting the alternating current switch. The magnet or
solenoid E of this switch consists of a U-shaped core of iron wires i carrying a
spool kon which are wound the coils m and sliding in which spool is another
similar U-shaped core o.
The core o carries a pivotted arm H having weights I at its ends and provided
with a finger adapted to strike a locking catch when the arm H is raised and
disengage the said catch from a switch lever K which is then quickly drawn down
by the spring L and closes the circuit 5-5 between the plates
3.
For the purpose of making connections the copper rod M extends around one end
of the keeper from the pivot of the switch F to the end of the plate s. This rod or
frame forms part of the ground connection 2 from the armature terminal and the
wire 7 from the locking switch is also connected to it.
The locking switch on the armature shaft consists of a metal ring or casing O and
a ring fixed to the shaft from which two stems t extend on which slide curved
shoes u held inwardly by springs on the stems. Spring catches are provided for
locking the shoes u against the casing O when they are thrown out against the
springs by centrifugal force.
Upon the motor shaft is a collar wo on which rests a brush or spring by means of
which the connection 7 is made to the shoes u. A connection 6 is made directly
to the ring or casing O so that the circuit 6, 7 is closed by the contact of the shoes
with the casing.
The operation of these devices is as follows: Suppose a ground connection to
occur on the negative wire n as indicated at .r. It is evident that a ground circuit
will thereby be formed by means of wires 1 and 2 through the armature B and the
motor will begin to run. If the ground connection was on the positive side the
motor would begin to run in the opposite direction. It will thus be seen that a
ground exists, and on which side it exists, and such ground cannot result in injury
to the system since the motor forms a translating device preventing an excessive
flow of current through the earth. The motor may therefore be allowed to run
until the fault is located and remedied. The action of the switch E being retarded
by the weights I, such switch is not released by the passage of current because
before it can act the counter electro motive force of the motor has been thrown into
the circuit and prevents the magnet from acquiring sufficient energy to lift the
weights.
If the accidental ground occurs on the neutral wire such ground will not affect
the motor.
In order however to test the system at any time for grounds on the neutral, the
switch F may be employed, by means of which either the positive or the negative
conductor may be connected to ground through the resistance lamps f. Then if
there is no ground on the neutral besides the permanent one through the motor B,
such motor will run at its normal speed; but if there is also some accidental ground
on the neutral, this will be indicated by the failure of the motor to start or by its
starting very slowly. The ground on the neutral may then be found and remedied
or it may be "burned out" by shunting the lamps fby a fusible strip at g and thus
making a dead cross through the earth.
If, as indicated at a', the negative wire comes in contact with a wire of a high
volt system and such high volt system has an accidental ground as at ³, it will be
seen that if a ground is formed from any part of the low volt system through the

page_text: person of any one handling the system, he will ordinarily receive the full high volt
current, but where my invention is used there is already provided a low resistance
path to ground for the high volt current so that the difference of potential is
lowered to zero, and this therefore does not occur. When a high volt connection
occurs the motor B begins to run and attains a high speed, so high as to throw out
the shoes u of the switch O and close the ground connection 6, 7, so that the motor
stops running. The switch O is so constructed that it will not be affected by any
speed, which can be attained under the normal current of the low volt system but
only by the high speed given it by the high volt current. The system is thus
protected from the high counter electro motive force of the motor and the motor
itself is protected from excessive speed while at the same time the permanent low
resistance ground connection is maintained.
If the system supplied by the generator G is an alternating or discontinuous
current system then the current given by such system to the three-wire system does
not start the motor running but it will heat the armature of the motor to a
dangerous extent. At this time however the retarded switch E comes into use
and lifting the weighted arm H trips the catch r and allows the switch K to close
the circuit 5-5º.
It will be seen that my invention is adapted for use wherever a low volt system
is in danger of becoming crossed with one employing a high potential current, as is
now often the case where a low volt incandescent system is run in proximity to arc
light systems, systems employing transformers, and high volt electric railway
⚫systems.
The invention was however as stated, specially designed with reference to the
use of continuous current transformer systems to prevent danger to the users of the
secondary circuits by reason of crosses between the primaries and secondaries in
the converters. It will be seen that such a cross would be precisely equivalent to
the connection between two separate systems illustrated in the diagram.
It is further evident that my invention is applicable to a two-wire multiple arc
system as well as to the three-wire system shown, the motor and other devices
being connected between either of the two conductors and the earth.
Figure 5 shows the connections for a two-wire system and also illustrates the use
of my invention with continuous current transformers as above referred to.
From the high volt generator G a circuit extends to the high volt commutator
of the continuous current transformer W and from the low volt commutator of the
transformer, extends the low volt translation circuit with which the protective
devices are connected as already explained, the motor armature B being connected
with either side of the two wire low tension circuit, and its field magnet in a shunt
as before.
The alternating current switch E K and the centrifugally operated switch O are
also arranged and connected as before explained and the operation will be readily
understood from what has been already stated. The dotted line at z indicates an
accidental cross between the two windings of the transformer. At x², as before, is
indicated an accidental ground on the high volt circuit.
I have illustrated my invention in connection with a three-wire direct current
system and with a two-wire transformer system. Its application to a two wire
direct system or to a three wire transformer system will be apparent without
further explanation.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The use in systems of electrical distribution of the character described, for
the purpose set forth, of a low resistance electric motor in a permanent ground
connection between a conductor of the system and the earth, substantially as herein-
before described.
2. The combination with such motor, of the switch operated by the motor for

page_text: closing the grounded shunt around the motor, substantially as hereinbefore
described.
3. The combination with such motor, of the electro magnet in the circuit of the
notor and the retarded switch in a shunt around the motor and controlled by said
magnet substantially as hereinbefore described.
4. In a three wire system of electrical distribution, the combination with the
motor in a permanent ground connection from the neutral wire, of a switch for
connecting either the positive or the negative wire to ground, and an indicator of
electric current in the earth circuit thus formed, substantially as hereinbefore
described.
5. The devices and apparatus for preventing danger from high tension currents
in systems of electrical distribution substantially as hereinbefore described.
Dated this 19th day of November 1890.
HENRY EDMOND WALTER.
By Harris & Mills,
23, Southampton Buildings, London, Agents.
HENRY EDMOND WALTER.
By Harris & Mills,
23, Southampton Buildings, London, Agents.