Improvements in Electric Measuring and Regulating Apparatus for use with Alternate Currents.
Year: 1889

page_text: Date of Application, 1st Nov., 1889
Complete Specification Left, 28th July, 1830-Accepted, 6th Sept., 1890
Improvements in Electric Measuring and Regulating Apparatus for
use with Alternate Currents.
WALTER
THOMAS GOOLDEN and SYDNEY EVERSHED of Woodfield Works
Harrow Road London W., Electrical Engineers, do hereby declare the nature of this
invention to be as follows:-
The object of our invention is to render electro-magnetic measuring instruments,
regulating apparatus, and integrating meters, with or without iron or other kindred
material as the magnetic medium, suitable for the accurate measurement and
regulation of alternate currents.
It is well known that an electro-magnetic voltmeter, for example, does not indicate
correctly either the mean or effective electromotive force when used on an alternate
current circuit; in consequence chiefly of the impedance of the working coil, eddy
currents in the metal portions of the instrument, and effects of hysteresis when iron or
other magnetic substance is employed. The whole error arising from these causes is
nearly proportional to the period frequency of the current in the working coil, and
may be eliminated or neutralized according to our invention in several ways; of
which the following three methods are those we prefer to adopt, viz.:
First When a large resistance is used in series with the working coil the latter
may be shunted by an idle coil of large impedance, so that the portion of current
diverted from the working coil diminishes with the period frequency and the effective
current in the working coil may be made independent of the frequency by giving
suitable proportions to the impedances of the working and idle coils.
Second-An induction coil or transformer may be arranged with its primary circuit
in series with the working coil and its secondary circuit. wound in such a direction
round the working coil as to increase its effective magnetizing force, and so make the
indications of the instrument correct and independent of the period frequency. The
transformer must have a greater electromotive force than that produced in its
secondary circuit by the working coil and the latter force may be conveniently
reduced by winding the secondary circuit inside the working coil while still retaining
a sufficient number of turns to produce the desired effect; in this way the
secondary circuit has the maximum effect and occupies the minimum space on the
working coil.
Third A small induction coilor transformer may be arranged with one of itscircuits
in series with the working coil and the other circuit connected direct to the mains in
such a direction as will induce a positive effective electromotive-force in the working
coil circuit. By properly proportioning the coils of the transformer and working
circuit, the effective current in the latter may be raised to its proper value and will
be nearly independent of the period frequency of the main current; the working
circuit acting as though its impedance was equal to its ohmic resistance, the current
in it will be co-phasal with the electromotive force at its terminals.
These methods of carrying out our invention are applicable to all electromagnetic
voltmeters, and potential regulating apparatus, and the first and second methods are
also applicable to ammeters and current regulating apparatus. Our invention may
also be applied to wattmeters and integrating meters for measuring the power and
total work done in alternate current circuits, and for such instruments or meters the
third method alone is applicable; for in order to make them indicate the true power
or work done the current in their pressure coils must be co-phasal with the electro-
motive force at the terminals of that part of the main circuit in which the power or
work is being measured, and our third method secures this provided the impedance
of the pressure coils does not greatly exceed their ohmic resistance.

page_text: Where iron or other magnetic material is employed in the working parts of the
instrument or apparatus we prefer to use an equivalent quantity of magnetic material
in the transformers and shunt coils described so that they may be in the same
magnetic condition as the working, coils of the apparatus.
In ammeters and, the coils of regulating apparatus which are used to measure or
regulate large alternate currents, eddy currents are set up in the wire, strip, or bars
used to form the coils, reducing their effective magnetizing force and unduly heating
the coils. According to our invention the coils of such apparatus may be, formed
from a number of strips or wires connected in parallel but wound so that the magnetic
induction enclosed by each strip is as nearly as possible equal to that enclosed by the
central or average strip; thus, we wind the central strip of the set concentric with
the axis of the coil; about half the length of the next strip is wound outside and the
remainder inside the central strip, and so on until the requisite number of strips has
been wound. By winding a coil in this way the electromotive forces, due to changing
magnetic induction, in the strips are made very nearly equal and no serious eddy
currents can occur.
FITT
1000
WALTER T. GOOLDEN.
SYDNEY EVERSHED.
COMPLETE SPECIFICATION.
Improvements in Electric Measuring and Regulating Apparatus for
use with Alternate Currents.
We WALTER THOMAS GOOLDEN and SYDNEY EVERSHED of Woodfield Works
Harrow Road London W., Electrical Engineers, 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:-
The object of our invention is to render electromagnetic measuring instruments,
regulating apparatus and integrating meters, with or without iron or other kindred
material as the magnetic medium, suitable for the accurate measurement and regulation
of alternate currents.
It is well known that an electromagnetic voltimeter, for example, calibrated so that
it reads correctly on a direct current circuit, does not indicate correctly either the
mean, or the effective potential difference or pressure when used on an alternato
current circuit the error when so employed is due chiefly to the impedance of the
working coil, eddy currents in the metal portions of the instrument, and effects of
hysteresis when iron or other magnetic substance is employed.
In an ammeter the error is due to eddy currents, hysteresis etc., but the
impedance of the working coil does not usually affect the indications of the
instrument.
Regulating apparatus, wattmeters and integrating meters are affected by similar
errors and in addition there is usually an error in wattmeters and integrating meters
due to the current in the pressure coil not being co-phasal with the potential
difference at its terminals; and occasionally, to the current in the current coil not
being co-phasal with the main current.
These errors may be almost entirely eliminated, according to our invention, in
several ways of which the following methods are those we prefer to adopt.
First. The working coil of an instrument may be shunted by an idle coil of large
impedance so that the portion of current diverted from the working coil diminishes
as the period frequency of the current increases, and when a suitable value is given
to the impedance of the shunt coil the indications of the instrument will be very
nearly the same for alternate as for direct currents and consequently nearly
independent of the frequency. Fig. 1. of the diagrams attached to this specification
illustrates this method: M M is the main carrying the current to be measured, W is
the working coil and S the inductive shunt coil, which is so arranged as to have no

page_text: direct magnetic effect on the working coil or on the mechanism of the instrument..
The proper proportions between the resistances number of turns and coefficients of
induction of S and W are most easily determined by experiment thus:-First
determine the difference between the indications of the instrument for direct and
alternate currents of average commercial frequency. Suppose the instrument is found
to read three per cent. lower on alternate than on direct currents; then S must he
made of such resistance that with direct currents it shunts about six per cent. of the
whole current in MM; having wound a shunt coil of this resistance into as many
turns as possible and connected it as a shunt to W, the instrument is placed in au
alternate current circuit once more and the current through S is diminished by
placing a properly laminated core of iron in it, and by changing the position of the.
core or varying the quantity of iron used in it, the current in S may be adjusted until
the instrument reads correctly. This method is applicable to ammeters, current.
regulators, the current coils of wattmeters etc., and can also be applied to a
voltmeter or a pressure regulator, provided there is an idle and inductionless
resistance in series with the working coil, the latter alone being shunted by S.
to
Second. We arrange an induction coil or transformer with its primary winding
in series with the working coil and its secondary winding connected to a circuit
wound in such a direction round the working coil as will increase its effective
magnetizing force. This is illustrated in Fig. 2 where P and S are the primary and
secondary windings of the transformer T; and A is the additional magnetizing coil
wound concentrically with the working coil W. It is clear that W will cause a
negative electromotive force in A and the primary winding of T must therefore give
a sufficiently large positive electromotive force to overcome it and produce the
current required in A to bring the total magnetizing force of the working coils up.
its proper value. When the mechanism to be magnetized is wholly within the.
working coil it is best to wind A entirely within W, so that while it has the greatest
direct magnetic effect it is cut by the least possible induction and so has the least
possible negative electromotive force. A modification of this method must be made
when, as is sometimes the case, an instrument reads higher with an alternate than
with a direct current. For instance the instrument described in the Specification of
our Patent No. 1628, 1887, if wound as an ammeter to measure about two ampères or
less, reads higher with an alternate than with a direct current.
In such a case it
is clear that the effective magnetizing force with alternate currents must be diminished
and the additional circuit A must be wound in reverse direction round W or its
connections to S reversed; but we prefer to dispense with the transformer for as we
have already said there is a negative electromotive force in A due to the changing
induction in W and we allow this force to produce the required de-magnetizing
current by simply closing A. on itself.'
The necessary adjustment in any case is obtained by varying the resistance and
number of turns in A or A and S, the proper values being determined by
experiments similar to those described in connection with our first method... Our
second method is usually applicable to all electromagnetic instruments except
wattmeters and the like.
Third. In applying our invention to voltmeters pressure regulators and the pressure
coils of wattmeters and integrating meters we prefer to arrange a small
transformer T, Fig. 3, with its secondary 'winding S in series with the working
coil W of the instrument or apparatus, and its primary winding P connected through
a resistance directly to the positive and negative mains M M, or to the terminals of
the instrument: this connection is made in the direction which shall produce a
positive electromotive force in S so that the effect of the negative electromotive force
of W may be eliminated. The working circuit as a whole then acts as though its
ecefficient of self induction were nearly zero and the current in it will not only obey
Ohm's law but will be very nearly co-phasal with the potential difference of the
mains, and this method is therefore particularly useful when applied to wattmeters
and other apparatus in which a current coil acts on a pressure coil, as it is essential

page_text: that the currents in these coils should be co-phasal with the main current and pressure
respectively. To obtain the correct proportions between the coils W, S & P, the
average electromotive force of W must be calculated or determined by experiment.
For a voltmeter it is usually sufficient to take the difference in volts indicated by the
instrument with direct and alternate pressures as being the average electromotive
force of W. The transformer is then designed so as to give an equal positive
electromotive force in S, and any outstanding error is eliminated by varying the
resistance until the instrument reads correctly. In ordinary commercial
instruments where extreme accuracy is not required we use a transformer of usual
design, taking care to employ a low induction density in the iron of the magnetic
circuit, which may be closed or open according to convenience. In special cases we
design the transformer to suit the particular apparatus with which it is to be used,
and when the space occupied and power spent by the transformer are not limited we
prefer to dispense with iron, using air as the magnetic medium.
In our Provisional Specification we describe a method of constructing the coils of
instruments, intended to carry largealternate currents,so that no serious eddy currents
shall occur.
At the time of applying for this Patent we believed the method to be
novel but we now know that a more or less similar construction for effecting
substantially the same purpose had been previously used and we do not therefore
make any claim for the particular method we described although we find it
to be of great service in making ammeters to measure large alternate currents.
In this Specification the phrase "reading correctly" signifies that the instrument
or apparatus gives the same indications with a direct current as it does with an
alternate current of usual frequency of the same effective value as the direct current,
and it has been assumed that the instruments to which our invention is to applied
are to be made to indicate the effective current or pressure, and the true power or
work; but ammeters and voltmeters can be made to read the mean value of the
current and pressure by adopting one of the methods we have described and
determining the proportions the various coils resistances etc. by experiment.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is
1. In any electromagnetic apparatus used for the measurement or regulation of
alternating electric pressure or current:-the employment of an inductive shunt on
the working coils, substantially as, and for the purposes set forth.
2. In any electromagnetic apparatus used for the measurement or regulation of
alternating electric pressure or current: the employment of a transformer or
induction coil having its primary winding in series with the working coils and its
secondary winding connected to a coil wound within around or adjacent to the
working coils so as to increase or diminish their effective magnetizing force,
substantially as and for the purposes set forth.
3. In any electromagnetic apparatus used for the measurement or regulation of
alternating currents: the employment of a closed coil wound within around or
adjacent to the working coils so as to diminish their effective magnetizing force,
substantially as and for the purposes set forth.
4. In any electromagnetic apparatus used for the measurement or regulation of
alternating electric pressure: the employment of a transformer or induction coil
having its secondary winding in series with the working coils and its primary
winding connected directly to the mains as illustrated in Fig. 3, and substantially as,
and for the purposes, set forth.
5. In any electromagnetic apparatus used for the measurement or regulation of
electric power or work in alternate current circuits:-the employment of an inductive
shunt on the current coils, substantially as, and for the purposes set forth.
6. In any electromagnetic apparatus used for the measurement or regulation of
electric power or work in alternate current circuits:-the employment of a

page_text: transformer or induction coil having its secondary winding in series with the pressure
coils of the apparatus and its primary winding connected directly to the mains
as illustrated in Fig. 3 and substantially as, and for the purposes set forth.
Dated this 28th day of July. 1990
WALTER T. GOOLDEN.
SYDNEY EVERSHED.