Improvements in Constructing or Winding Coils for Electrical Apparatus.
Year: 1889

page_text: Date of Application, 21st Aug., 1889
Complete Specification Left, 22nd May, 1890-Accepted, 9th Aug., 1890
PROVISIONAL SPECIFICATION.
Improvements in Constructing or Winding Coils for Electrical
Apparatus.
We, THOMAS MATHER of 5 Melrose Terrace Lillie Road Fulham S.W. Elec-
trician, and WILLIAM EDWARD SUMPNER of 24 Glebe Place Chelsea S.W.
Electrician, both of the County of London do hereby declare the nature of this
invention to be as follows:-
Our invention relates to the construction of coils or other arrangements of
electric conductors in such a manner that their effective resistance for alternating
currents of any ordinary frequency, and for intermittent currents of any ordinary
periodicity, is practically independent of that frequency or periodicity; and also
to the application of such coils or arrangements of conductors to electrical
apparatus.
We will refer to our arrangements of conductors as coils, but we would have
it understood that we do not confine ourselves to spirally wound coils, for the
conductors may be made in various forms without departing from the essential
nature of our invention.
It is well known that the effective resistance of a conductor for alternating or
intermittent currents is diminished by connecting its ends to the coatings of a
condenser, and is increased by forming it as a solenoid so as to have considerable
self induction. Now as resistance coils are ordinarily wound doubly, when a cur-
rent passes through them the contiguous parts of the going and return wires are
at different potentials, and so act as the coatings of a condenser (connected to the
wire), the capacity of which depends on the shape of the coil, the proximity of
the wires, on the shape of their cross section, and on the nature of the insulat-
ing media. In such coils the capacity effect and the self induction effect
seldom happen to be equal; and hence their effective resistance is not the same
when used for steady currents and for alternating or intermittent currents of
various frequencies, and if such coils be used as resistance standards in some of
the methods of measuring self induction, mutual induction, or capacity they will
give unreliable results.
To avoid such defects we make the condenser effect neutralize the self induc-
tion effect, or vice versa, and so obtain coils whose whose effective resistance <does
not depend on the frequency of alternation of intermittency.
Our coils may either be constructed so as to produce no external field, in which
case they are particularly suitable for standards of resistance, or they may be
constructed to produce an external magnetic field, in which case they are suit-
able for employment in electrical measuring instruments such as ammeters,
voltmeters, wattmeters, ohmmeters, coulombmeters, ergmeters, and in other elec-
trical apparatus requiring the production of a magnetic field.
The methods we adopt in carrying out our invention consist in varying the
proximity of the parts of the conductors, varying the material of the conductors,
varying the shape of the coil, varying the insulating medium, and varying the
size and shape of the cross section and the lengths of the conductors. We may
employ any of those methods, or a combination of two or more of them depending
somewhat on the resistance of the coil required, and on the purpose to which it
is to be applied.
As an example, one of the methods we adopt for comparitively low resistances,
in which, as ordinarily constructed, the self induction effect generally pre-
ponderates, is to construct them of sheet, strip, or ribbon, doubled on itself and
having thin insulating material of high specific inductive capacity between; by
these means we increase the capacity effect and diminish the self induction effect.
Another method consists in making coils of such a length or resistance that the

page_text: condenser effect balances the self induction effect, and then putting such coils in
multiple arc.
By using one of the last mentioned coils, or by arranging two or more in
aeries, moderate or large resistances are formed.
Another method is to wind one part of the coil doubly and the rest inductively
to neutralize the condenser effect of the first part, or the method may be reversed
when it is desired to neutralize the self induction effect of a coil constructed to
produce a magnetic field in instruments or apparatus such as are referred to above.
In some instruments, (such as wattmeters and ergmeters for alternating cur-
rents), whose working depend on the mutual action of magnetic fields, one of
the conditions necessary for accuracy is that the phase of the current in the
"volt circuit" should be coincident with that of the electromotive force impressed
on its terminals, and by suitably arranging coils constructed according to our
invention we are able to satisfy this condition.
Dated this 21st day of August 1889.
T. MATHER.
W. E. SUMPNER.
COMPLETE SPECIFICATION.
Improvements in Constructing or Winding Coils for Electrical
Apparatus.
We, THOMAS MATHER of 5 Melrose Terrace, Lillie Road Fulham S.W. Elec-
trician, and WILLIAM EDWARD SUMPNER of 24 Glebe Place Chelsea S.W.
Electrician, both of the County of London, 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:―
(1.) Our invention relates to the construction of coils or other arrangements
of conductors in such a manner that their effective resistance for alternating
or intermittent currents of any ordinary frequency is practically independent
of the frequency of the changes, and to the application of such coils or arrange
ments of conductors to electrical apparatus.
(2.) We shall refer to our arrangements of conductors as the coils, but we
would have it understood that we do not confine ourselves to spirally wound coils,
for the conductors may be made of various forms without departing from the
essential nature of our invention.
(3.) It is well known that the effective resistance of a conductor for alternat-
ing or intermittent currents is diminished by connecting its ends to the coatings
of a condenser, and is increased by forming as a solenoid so as to have con-
siderable self-induction. Now as resistance coils are ordinarily wound doubly,
when a current passes through them the contiguous parts of the going and
return wires are at different potentials and so act as the coatings of a condenser
connected with the wire. The capacity of the condenser thus formed depends
on the shape of the coil, on the proximity of the wires, on the shape of their
cross section, on their length, and on the nature of the insulating medium. In
such coils the capacity and self-induction effects seldom happen to be equal and
hence their effective resistance is not the same when used for steady currents
and for alternating or intermittent currents of various frequencies. If such coils
are used in some of the methods of measuring self-induction, mutual induction,
or capacity, or in some other measurements in which varying currents are used,
the results obtained are unreliable unless troublesome precautions or correc-
tions are made. To avoid such defects we make the condenser effect neutralize
or balance the self-induction effect and so obtain coils whose effective resistance
does not depend on the frequency of alternation or intermittency.
(4.) Our coils may either be constructed to produce no external magnetic field,
(or only a slight one) in which case they are suitable for resistances and for
standards of resistance which may be used with secohmmeters, or other measuring
apparatus involving the use of varying currents; or they may be constructed

page_text: to produce an external magnetic field, in which case they are suitable for employ-
ment in electrical measuring instruments such as ammeters, voltmeters,
ohmmeters, coulombmeters, wattmeters, ergmeters, and in other electrical
apparatus requiring the production of a magnetic field or fields.
(5.) When a magnetic field is required, one or more part or parts of the coil
is or are wound inductively and as in this part or parts the self-induction effect
predominates it is evident that the capacity effect of the remaining part or
parts must preponderate in order that a balance may be effected. Such being
the case it will be readily understood that we may balance the self-induction of
a coil or coils by combining it or them with one or more coils in which the
capacity effect preponderates.
(6.) In what follows we shall speak of a coil balanced within itself and pro-
ducing little or no external magnetic field as a "compensated coil," and those
whose purpose is to balance the self-induction of another coil or coils we shall
call "compensating coils."
(7.) The methods we adopt in carrying out our invention consist in varying
the proximity of the parts of the conductor, varying the material of the con-
ductor, varying the shape of the coil, varying the insulating medium, and vary-
ing the shape and size of the cross section and the length of the conductor.
We may employ any of these methods, or a combination of two or more of them
depending somewhat on the resistance of the coil required and on the apparatus
to which it is to be applied.
(8.) We will now refer in detail to the construction of compensated coils:-
One of the methods we adopt for comparatively low resistances, in which, as
ordinarily constructed, the self-induction effect usually preponderates is to con-
struct them of sheet, strip, or ribbon doubled on itself, the contiguous parts
being separated by a thin layer or layers of insulating material preferably of
high specific inductive capacity. The doubled strip thus formed is in some cases,
e.g. when an ordinary bridge coil is to be made, covered with insulating material
and formed into a coil or wound on a bobbin so as not to occupy a very large
space; this coiling increases the capacity effect considerably and enables us
to use shorter and narrower strips, sheet, or ribbon, than would otherwise be
required, or to use thicker insulating material or insulating material of smaller
specific inductive capacity. In other cases, as when a resistance is to be con-
structed to carry large currents without undue heating, we leave the outer sur-
faces of the strips (which may be covered or bare) exposed to the air to facilitate
cooling by radiation and convection. In both the above cases we preferably
take the strip, sheet, or ribbon of such length, breadth thickness, and material
so that it has about the resistance required and so that the capacity effect, when
the strip is doubled and made approximately to the required shape, may exceed
the self-induction effect, and after adjusting the resistance (if necessary) in
any ordinary manner we proceed to vary the proximity of the parts or the
character of the insulating material, or both, until by sufficiently reducing the
capacity effect or increasing the self-induction or both, compensation is effected.
To take a particular case we will suppose a compensated resistance of about a
quarter of an ohm to carry large currents, say 20 ampères, is required. A strip,
preferably of platinoid or German silver, about 20 feet long, 17 inches wide and
001 inch thick is taken, doubled on itself with two layers of varnished silk each
about 0.003 inch thick between the contiguous parts. The terminals are next
attached to the free ends of the strip and the resistance adjusted (if necessary) to
be of the correct value for steady currents in the ordinary way; it is then tested
with varying currents either by means of the secohmmeter or by the electrometer
and dynamometer, or by other well known means, and the relative position of
parts of the strip (preferably near the ends) varied by separating them or by
sliding one transversely over the other parallel to their own planes, or by both of
these or other equivalent methods, until the effective resistance is practically
independent of the frequency of the testing current. When the compensation
has been effected the parts of the conductor and the insulating material are

page_text: secured together in any convenient manner so that their relative positions are
maintained unaltered by the ordinary usage for which the resistance is intended.
We do not, however confine ourselves to the method or methods of compensating
just described, as the same may be carried out in any of the ways mentioned in
paragraph (7) without departing from the essential nature of our invention.
For example in the case above described we may effect the compensation by
replacing part of the insulating material by some other insulating substance of
smaller specific inductive capacity, or we may alter the shape of the cross section
of the strip at some part or parts by folding its edges back, or we may diminish
the width of the strip, preferably near the terminals where changes of capacity
are most effective, so as to diminish the capacity effect, and widen or thicken
them, or both, at another part or parts to make the resistance for steady currents
of the required value. In many cases, however, the exact value of the resistance
is unimportant and hence no trouble need then be taken to ensure that this is
unchanged by any variation of capacity or self-induction. It may happen that
a resistance when first tested with varying currents has preponderating self-
induction, and, in such cases, instead of compensating by decreasing the capacity
or increasing the self-induction, or both, converse methods would be employed.
Compensated coils such as the one described in detail above, are applicable for
the measurement of power by the electrometer methods. Larger compensated
resistances to carry the same current may be made by connecting two or more of
the above coils in series or we may commence de novo with strip of suitable
dimensions or specific resistance. Smaller compensated resistances may be made
with wider strip or thicker strip or both, or two or more larger compensated
resistances may be put in parallel, or other modifications of the above described
methods employed.
(9.) For resistance-box coils of moderate resistance where strips would be
inconveniently long and narrow, we prefer to wind them wholly or partly with
wire having insulating covering thin enough to keep the self-induction effect
only slightly predominant, and to the ends of this we may (if necessary) attach
pieces of strip, sheet, or ribbon of such shape, size or proximity as to give capacity
enough to compensate any predominant self-induction of the wire. Larger
resistances are made of wire alone and the compensation effected by varying the
proximity of the wires and the thickness or nature of their insulating covering.
Coils which have been compensated by any of the above described methods may
be combined in series or parallel to obtain compensated resistances which might
otherwise be difficult to make. For example it is difficult to wind a coil of very
large resistance say of 10000 ohms or more so as to be compensated without pro-
ducing an external magnetic field, whilst for very small resistances it is not
easy to make the capacity effect large enough to balance the self-induction effect.
(10.) For coils of very high resistance in which as ordinarily wound, the
capacity effect greatly preponderates; we may, in cases where a slight external
magnetic field is not important, separate the parts of the doubled conductor and
wind them on different portions of the bobbin or in any other convenient way
so as to diminish the capacity and increase the self-induction effect.
(11.) We will now refer to "compensating coils" and their applications:-
In measuring instruments such as ammeters, voltmeters, ohmmeters, watt-
meters, ergmeters, and coulombmeters and in other electrical apparatus, it is
sometimes desirable to neutralize the self-induction of a coil constructed to pro-
duce a magnetic field. In such cases we make a compensating coil to be used 5
with or to form part of the instrument so that its predominant capacity effect
may neutralize the self-induction of the field-producing coil of the instrument
and thus cause the instrument or apparatus to indicate or register correctly in
or on circuits in which variations in the current alternations may otherwise cause
errors.
In some instruments such as wattmeters ergmeters and ohmmeters for alter-
nating or intermittent currents whose working depends on the mutual action of
magnetic fields, one of the conditions necessary for accuracy is that the phase
5

page_text: of the currents in the volt circuit should be identical with or bear some definite
relation independent of the frequency-to the phase of the electromotive force
impressed on its terminals and by suitably arranging compensating coils con-
structed in accordance with our invention we are enabled to practically satisfy
this condition. To give an example we will describe the volt circuit of a watt-
meter to be used on say a 50 volt circuit. The swinging coil which is in this
case in the volt circuit is made of approximately rectangular shape of dimen-
sions 4.5 inches by 21 inches and has about 50 turns of wire on it.
induction of the coil is about 00035 secohms and this is neutralized by the
capacity effect of a doubly wound coil of the following approximate dimensions :-
Length of bobbin
Outside diameter of bobbin
5.5 inches.
2.2 inches.
The self-
1
Length of wire
Diameter of wire, bare,
"
"
Material of wire
covered
Insulating material
450 yards.
021 inch.
*034 inch.
German silver.
Silk.
When this coil is placed in series with the swinging coil above referred to the
effective resistance of the combination is constant for small currents of all
ordinary frequencies and the current in the swinging coil is of the proper strength
and phase required to give correct readings when used to measure the power
spent in circuits having self-induction such as transformers. The capacity and
self-induction effects of compensating coils can be increased or diminished so as
to effect compensation by any of the methods described in § (7) (8) (9) and (10)
as applicable to compensated coils, the particular method or arrangement
employed depending on the instrument or purpose to which the compensating
coil is to be applied. The testing for compensation is carried out in a way
similar to those referred to in § (8).
(12.) The compensating of voltmeters and volt coils of ergmeters and ohm-
meters may be effected in a manner similar to those described and referred to
in §(11) and they will then indicate or register correctly whatever the rate or
character of the alternations or fluctuations in the circuit or circuits to which
they are applied.
(13.) We compensate ammeters and coulombmeters, particularly those intended
for working with small currents and which may have considerable resistance and
self-induction 1st in order that the volts between the terminals of the instru-
ment may not be larger than necessary, and 2nd so that there may be no unneces
sary lag between the current and the impressed electromotive force, or diminu-
tion of the power which a given electromotive force can develope in the circuit.
(14.) In the foregoing text we have referred to compensation being effected
for alternating or intermittent currents, but as the effects of self-induction and
capacity depend on the changes of the current and not on their absolute direc-
tion, it will be understood that the coils such as we have described are com-
pensated for currents varying or fluctuating in any ordinary manner.
Having now described and ascertained our invention and means by which the
same may be carried into effect we would have it understood that what we claim to
be novel and original and desire to have secured to us by Letters Patent are:-
1. The construction of resistances and resistance standards compensated as
and for the purpose described in § (7) (8) (9) and (10).
2. The construction of coils the whole or part of which produces an external
magnetic field compensated as and for the purpose described in § (11) (12)
and (13).
3 The construction of compensating coils as and for the purpose described.