Improvements in Electric Maximum Demand Indicators.
Year: 1899

page_text: Date of Application, 2nd May, 1899-Accepted, 2nd May, 1900
COMPLETE SPECIFICATION.
Improvements in Electric Maximum Demand Indicators.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon
Street, in the City of London, Electrical Engineers, do hereby declare the nature
of this invention (which has been communicated to us from abroad by Frank
P. Cox, residing at Lynn, 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:
-
It has been proposed heretofore to provide each electrical installation with a
suitable indicator to indicate the maximum consumption of energy at a given
time, and this in addition to the regular metering devices, the indications thus
obtained being employed as the basis from which the cost of energy for that par-
ticular installation is calculated. It has also been proposed to use this arrange-
ment in connection with a three-wire system and place a maximum demand indi-
cator in each of the outside mains and to add the sum of the indications of the
instruments to give the total. This arrangement is defective since it does not
indicate the maximum demand on the system but only the maximum demand on
the separate sides of the system. This will readily be understood when it is con-
sidered that all the lights might be burning at one time on one side of the system
and only one or two lights on the other side of the system, and further that at
times the positions might be reversed and the load be thrown upon what was the
lightly loaded side. On the other hand, suppose the consumer throws all, or
substantially all, of his load on both sides of the system at the same time, or
substantially the same time, in other words uses about twice as much current
as before, it is evident that the sum of the two indications of the maximum
demand instruments will--(provided the load is the same as in the first instance)
be the same as before, but on further consideration it will be seen that the
consumer has taxed the output of the central station just twice as much as in the
first place.. The present invention has for its object to overcome the objection
above pointed out, and to provide a maximum demand indicator which will
accurately register or indicate the maximum amount of energy delivered at a
given instant or period so that the proper charge may be made therefor.
In the accompanying drawing, which illustrates an embodiment of the inven-
tion, Fig. 1 is a diagrammatic view of a three-wire system having a maximum
demand indicator in circuit; and Fig. 2 is also a diagrammatic view of a three-
wire system, but with a modified form of an indicator.
In so far as the operation of this invention is concerned it matters not what kind
of maximum indicator is used so long as it is affected by the current flowing in
both sides of the three-wire system, neither does it matter whether it is applied
o alternating or direct current systems.
In the drawing there is shown two types of instruments, but it is evident that
other forms may be employed.
Referring to Fig. 1 A and B indicate the two outside wires and C the neutral
wire of a three-wire system. Extending from these wires are auxiliary or house
mains A, B, C, which supply energy to the lamps or other translating devices D.
•

page_text: The maximum demand indicator consists of a U-shaped transparent tube E
having an enlargement or bulb K at one end around which the heating coils are
placed, and an enlargement or bulb L into which the fluid flows when it is
desired to empty the middle tube G. The bulb K is preferably formed integral
with the tube and surrounding it are two heating coils H and I, the former is
connected in series with the main A' and the latter is in series with the main B'.
The coils and tube are so proportioned and arranged that the momentary impulses
of current will not cause the fluid to overflow into the tube G, and if after a
brief interval the current flow still persists, the température of the air or gas in
the bulb K will rise to a point which causes the fluid F, in the tube E, to flow
into the-tube G The expansion of the air or gas in bulb Kisproportional to
the amount of current flowing in the heating coils H and I, and the flow of fluid F
into the tube G, 'is in accordance with this expansion: On the sides of the last
mentioned tube are suitable indication's by means of which readings may be made.
Owing to the difficulty of making current coils develop the same amount of heat
for a given flow of current a resistance Jis provided by means of which more or
less of the current may be shunted past one of the coils until its heating effect,
for a given-load, corresponds to the other coil We have shown the resistance
shunting the coil J, but it is evident that we may employ a second resistance for
shunting the coil I, as indicated in dotted lines. The resistance Jin addition to
adjusting the coils performs another useful function, since it is useful.for chang-
ing the rate of a given consumer; for example, suppose that an indicator has been
installed at. a given place where one rate of charge is established and it is
desired to change the indicator to a place where a different rate is charged. To
accomplish this it is only necessary to change the amount of resistance shunting
the heating coils H and I, and the indicator will operate as desired."
Assuming that sufficient load is included between the mains A, B, C to cause
the heating coils H and I to raise the temperature of the air or gas in bulb K to
a point above normal, the fluid F will then flow into the tube G, and by its amount
indicate the maximum demand on the central station. It will, be noted that the
same effect is obtained whether the load is all on one side or on the other or
equally distributed between them.
•
Referring to Fig. 2, A, B, and C indicate respectively the outside mains and
the neutral of a three-wire system and D indicates incandescent lamps or other
translating device. In circuit with the main A' is a coil H, and in circuit with
the main B is a coil I, and mounted for movement between these coils is an
iron armature M. Thus far the arrangement of the coils and needle is the same
as in an ordinary ammeter, except that two coils are employed instead of one.
Mounted on the shaft of the instrument is a contact arm N which engages with
a pin O carried by the pointer O. The pointer O is mounted on a shaft O2, which
is driven by a clock of any suitable construction, the one shown being driven by
the spring P in the ordinary manner. For convenience of illustration, the spring
and the gears of the clock are shown in dotted lines. Mounted on the shaft
which carries the escapement is an arm Q which engages with a magnetically
actuated lever Q¹. Situated in operative relation to this lever is an electro-
magnet R and the winding thereon is connected between the outside main B. and
the contact arm N. Extending from the neutral wire C to the pointer. O is a
connection S.
r
The operation will now be described: As the lamps or other translating devices
are included in circuit with either or both sides of the system the armature Mis
"deflected and if this deflection is sufficient the contact arm N is moved into
engagement with the pin 0. As soon as this is done the circuit is complete from
the main B' through the contact arm N, pointer 0 and wire S to the neutral
wire C. The magnet R then attracts the armature of lever Q and releases the
escapement.lever Q and the clock begins to run. This operation continues unti
the pin O on the pointer moves out of engagement with the contact arm N.
soon as this is done the circuit of the energizing coil or magnet R is interrupted

page_text: the lever Q assumes the position shown in the drawing due to gravity, and further
movement of the escapement is prevented. The construction and arrangement of
the parts is such that the pointer O can be moved forward by the clock mechanism
over the scale T shown in dotted lines, but it remains in its last position until
manually returned by the inspector to its initial position.
Having now particularly described and ascertained the nature of our said inven-
tion (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 maximum demand instrument for three-wire systems, the combination
of an indicating means which is moved by the action of the current flowing in
the system and is incapable of automatically returning to its initial position, and
means controlled by the current flowing in both sides of the system for actuating
the indicator.
2-In a maximum demand instrument for use on systemis of distribution other
than two-wire, the combination of an indicator, which, as an indicator of the
consumption of energy is capable of being moved in one direction only from its
initial position, and means controlled by the load on more than one of the mains
for moving the indicator.
3-In a maximum demand instrument for use on systems of distribution other
than two-wire, the combination of an indicator which is capable of being moved in
one direction only by the current flowing in the system, and always remains in
the position of maximum even after the How of current decreases, and coils which
receive energy from at least two of the mains for actuating the indicator.
4-In a maximum demand instrument for use on three-wire systems, the com-
bination of an indicator which is moved from its initial position by the energy
consumed by the translating device in the circuit and is returned thereto manu-
ally, with coils, one in each of the outside mains of the system, for moving the
indicator.
5-In a maximum demand instrument, the combination of an indicator which
has no self returning tendency but is moved away from its initial position by the
action of the current in the system, and as the flow of current increases assumes
a new position in accordance therewith, a plurality of coils for moving the indi-
cator and means for adjusting the power of the coils.
In a maximum demand instrument for three-wire systems, the combination
of a tube, a body of fluid located therein which acts as an indicator, a coil included
in circuit with each of the outside mains for moving the fluid, the two coils
acting simultaneously and with an effect corresponding to the energy flowing in
the mains in which they are located:
7-In a maximum demand instrument for three-wire systems the combination
of an indicator which is progressively moved by increases in current strength, and
by its position indicates the maximum demand on the central station, the indi-
cator always standing at the point of maximum demand irrespective of the amount
of current being consumed at that time, heating coils for moving the indicator
each coil being included in one of the outside mains of the system, and shunts
for adjusting the effect of the coils.