Improvements relating to Meters for the Measurement of Alternating Currents of Electricity.
Year: 1888

page_text: Date of Application, 20th Sept., 1888
Complete Specification Left. 19th June, 1889-Accepted, 20th Sept., 1889
PROVISIONAL SPECIFICATION.
Improvements relating to Meters for the Measurement of Alternating
Currents of Electricity.
[, SEBASTIAN ZIANI DE FERRANTI of 120 Fellows Road, Hampstead, in the County
of Middlesex, Electrician, do hereby declare the nature of this invention to be as
follows:-
This Invention has for its object Improvements relating to meters for the measure-
ment of alternating currents of electricity..
When an uncompensated meter adjusted for a certain average current is applied
upon an electric main its record will be found to be below the truth when the current
is small and above the truth when the current is large.
To avoid these errors I do not pass through the meter the actual current which I
desire to measure but another current which the former is caused to generate by the
aid of a converter. This converter is so contrived as to supply to the meter such
current as is necessary to propel it at a speed always proportional to the current
passing in the main.
I obtain another advantage by avoiding the actual passage of the current to be
measured through the meter namely this, that whatever the proportions of the meter
I can adjust the current passing through it so that it may always be suitable.
The converter which I employ has two primary coils and a secondary coil.
:-
In one of the primary coils the current to be measured passes; for example in a
lamp circuit this coil will form part of one of the main leads from the dynamo to
the lamps, the other primary coil is connected across the mains in parallel with the
lamps or between points where the difference of potential is constant or nearly so the
secondary coil of the converter is in circuit with the meter. The action is then as
follows the current passing in the primary coil or coils of the converter generates
a current in the secondary which passing through the meter propel its counting
wheels or mechanism. When the current in the first primary is small that in the
secondary primary aids in magnetizing the core of the converter, and in generating
current in the meter circuit to propel the meter, when otherwise its movement would
be too slow. On the other hand when the current in the first primary is large its
inductive influence on the second primary is such that current is induced or generated
in the second primary and this current passes from the converter into the mains and
less current is generated in the secondary circuit than there would be if the second
primary coil were removed from the converter. In this way the ineter is prevented
from running too fast when large currents are passing.
Another way in which I can apply an uncompensated meter to obtain an approxi-
mately accurate record is the following:
Where a lamp circuit is fed by a converter I insert into the primary circuit of this
converter another small converter and this I make to feed the meter. When the lamp
circuit is open, all the lamps being out, a small current will still pass in the primary
and this will induce a current to pass through the meter sufficient to balance the
friction of the parts.
Dated this 20th day of September 1888
CADDMART
ADDMA TAL
Agents.

page_text: COMPLETE SPECIFICATION.
Improvements relating to Meters for the Measurement of Alternating
Currents of Electricity.
1, SEBASTIAN ZLANI DE FERRANTI of 120 Fellows Road, Hampstead, in the County
of Middlesex, Electrician, 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 :-
This invention has for its object improvements relating to meters for the measure-
ment of alternating currents of electricity.
When an uncompensated meter adjusted for a certain average current is applied
upon an electric main its record will be found to be below the truth when the current
is small and above the truth when the current is large.
To avoid these errors I do not pass through the meter the actual current which I
desire to measure but another current which the former is caused to generate by the aid
of a converter. This converter is so contrived as to supply to the meter such current
as is necessary to propel it at a speed always proportional to the current passing in
the main.
I obtain another advantage by avoiding the actual passage of the current to be
measured through the meter namely this, that whatever the proportions of the
meter can adjust the current passing through it so that it may always be
suitable.
The converter which I employ has two primary coils and a secondary coil.
In one of the primary coils the current to be measured passes for example in a
lamp circuit this coil will form part of one of the main leads from the dynamo
to the lamps, the other primary coil is connected across the mains in parallel
with the lamps or between points where the difference of potential is constant or
nearly so.
The secondary coil of the converter is in circuit with the meter. The action is then
as follows the current passing in the primary coil or coils of the converter generates
a current in the secondary which passing through the meter propels its counting
wheels or mechanism. When the current in the first primary is small that in the
second primary aids in magnetising the core of the converter and in generating
current in the meter circuit to propel the meter, when otherwise its movement would
be too slow. On the other hand when the current in the first primary is large its
inductive influence on the second primary is such that current is induced or generated
in the second primary and this current passes from the converter into the mains and
less current is generated in the secondary circuit than there would be if the second
primary coil were removed from the converter. In this way the meter is prevented
from running too fast when large currents are passing.
The annexed diagram illustrates the invention by the aid of the usual conventional
symbols + indicate the terminals of a dynamo generating alternating currents A
and B are the main leads passing from the dynamo to the place or places where the
current is to be utilised. C is the soft iron core of the converter, it is drawn in
the form of a ring as is usual when representing a converter by diagram and in
practice it may be of the ring form but other efficient forms are well known.
It will be understood that as in other converters there should be a sufficiency of
iron in the core and that this iron should be divided into numerous parts in each of
which the magnetic circuit should be complete. D is the first primary coil upon the
converter core, through it the current flowing through the lead A passes.
This coil D is proportioned in accordance with known rules to generate in the
secondary circuit of the converter such an amount of energy as it is desired to expend
in the meter.
E is the secondary coil upon the converter core, it is proportioned by known rules
to the coil D, and so that the potential between the terminals of the secondary coil
may be suited to the meter in use. F is the meter through which the current

page_text: generated in the secondary coil is passed. This meter may be any efficient uncom-.
pensated continuously recording meter, that is to say, a small electro motor driving
a train of counting wheels or recording mechanism. G is the second primary coil
also wound upon the core of the converter it is of fine wire and proportioned by
trial to suit the meter, the number of turns being increased or diminished until its
influence on the current supplied to the meter is such that the meter registers
accurately. The wire might be of a high resistance material such as Platinoid or a
resistance R may be inserted as indicated.
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 employment of a compound wound converter for feeding electrical meters
used for measuring alternating currents substantially as described.
2. The combination with an alternating current recording meter of a converter
having primary and secondary coils viz. :-one primary so connected that the current
to be measured passes through it; another primary connected with points maintained
at an approximately uniform difference of potential and a secondary in the circuit of
which a meter is included so that the meter receives the induced current resulting
from the influence of the two primary coils upon the converter.
3. The combination with the leads A and B of an alternate current dynamo of
the converter core C primary coil D forming part of the lead A secondary coil E and
recording meter F in the secondary circuit and the coil G cross connected between
the leads A and B.
thin 10th don
T1000