Improvements relating to Inductance Coils.
Year: 1895

page_text: Date of Application, 22nd Oct., 1895
Complete Specification Left. 21st July, 1896-Accepted, 3rd Oct. 1896
Rochester, in the County of Beaver and State of Pennsylvania, one of the
United States of North America, Engineer.]
Improvements relating to Inductance Coils.
I, REGINALD BELFIELD, of 32, Victoria Street, Westminster, in the County
of London, Electrician, do bereby declare the nature of this invention to be as
follows:-
This invention relates to inductance coils and comprises the improvements
hereafter indicated.
The object of the present improvements 18 to construct & coil in such a manner
that the magnetic field due to the curiont circulating in such coil shall have a
desed phase relationship with the electromotive force producing the current.
(It is usually desuable that the magnetic field should be in quadrature with the
electiomotive force.)
It has hitherto been difficult to obtain exact results of this description and
moreover when such have been obtained the conditions of the circuit alter with
the temperature to such an extent that the requned difference of phase is not
maintained constant.
According to this invention a desned phase relationship, between the magnetic
field due to a current enculating in a coil and the electromotive force producing
such current is obtained by providing an auxiliary coil disposed in magnetic
relationship with the pincipal coil. By suitably proportioning this auxiliary coil
I can arrange that the total magnetic field due to the current flowing in the
principal coil and to the current induced in the auxiliary coil by the current
Howing in the principal coil, shall have the desired phase relationship with the
electromotive force at the terminals of the circuit. The auxiliary coil may be a
closed coil and may consist either of a single turn or of several tuins of conducting
material and may include within its cucuit a definite and adjustable resistance if
desned, or the auxiliary coil may be supplied with current by an electromotive
force of similar periodicity impressed on its terminal.
In order to correct for variations in temperature according to one method
I provide in Cнcuit with the principal coil an inductive resistance the magnetic
core of which is provided with one of more air gaps and I provide means by which
the dimensions of such an gap or air gaps will vary with the temperature This
valiation of the dimensions of the air gap or gaps is so arranged that when the
temperature rises the self-induction of the inductive resistance values as may ba
desired When the principal coil which is picducing the magnetic field is provided
with an iron core the devices for correcting for temperature as heroinabove
mentioned may be applied to such iron core.
In another method of correcting for temperature I anange that the resistance of
the auxilary coil shall be varied to a suitable extent by suitable means.
As an example of what may be accomplished by my invention I can arrange
that the magnetic field due to a coil which has very little self-induction shall be in

page_text: For
exact quadrature with the electromotive force at the terminals of the cucuit.
thus purpose
Include in the circuit an inductive resistance which causes the
curent to lag behind the electiomotive force and I apply to the coil an auxiliary
coil by means of which the magnetic held due to the coil is brought into exact
quadrature with the electromotive force at the terminals of the circuit.
that this relationship shall not alter with temperature the inductive resistance
included in the cucuit is provided with the device for altering the self-induction
when the temperature alters in the manner herembefore indicated.
Dated this 22nd day of October 1895.
In order
W. P. THOMPSON & Co.,
31, High Holborn, London, W.C, Patent Agents for the Applicant
Fonts folating to 10 QUIS.
I, REGINALD BELFIELD, of 32, Victoria Street, Westminster, in the County
of London, Electrician, do hereby declare the nature of this invent.on and in what
mauner the same is to be performed, to be particularly described and ascertained
in and by the following statement.-
This invention relates to inductance coils and comprises the improvements
hereinafter described.
The object of the present improvements is to construct a coil in such a manner
that the magnetic field due to the current circulating in such coil shall have a
desired phase relationship with the electromotive force producing the current
It has hitherto been difficult to obtain exact results of this description and
moreover when such have been obtained the conditions of the circunt altor with the
temperature to such an extent that the requied difference of phase is not
maintained constant My invention therefore further comprises means for ensuing
that the desued phase relationship above referred to shall be maintained irrespective
of variations in the temperature.
In order that my invention may be clearly understood I will now proceed to
describe the same with reference to the accompanying drawings, in which
Figure 1 is a diagram shewing one form of my improved device for collecting
the phase angle between the electromotive force and the magnetic field of one of
the coils of a measuring instrument of a well known type.
Figures 2 to 4 are elevations partly sectional shewing a modified form.
Figure 5 is a diagram shewing phase relations.
Figure 6 is a diagram of cucuits illustrating a further modification, and
Figue 7 is a diagram illustrating the phase relations of the circuits shown m
Figure 6.
Figme 8 is a central longitudinal section through the core of an inductance coil
constructed according to the present invention the coil being removed
Figure is a plan of the same shewing the coil in section.
Figure 10 is a side elevation shewing a modified form of core.
Figure 11 is a plan view shewing a further modification in which two coils are
employed and
Figure 12 is a section on line 12-12 Figure 11.
Referring now to Figure 1. A is a field coil connected in series with an
Inductance coil B wound about a laminated core band of suitable proportions to
obtain a high coefficient of self-induction. C 18 a second field coil, here shewu
located at right angles to coil A and connected in series with a resistance D having
a small self-induction. Such a resistance may consist of a circuit of lamps or other
translating devices. The circuit containing coil A is joined as a shunt to the

page_text: circuit containing coil C, and it will therefore appear that the current in and
magnetic field produced by coil C will be in phase with the electromotive force at
the terminals of the cucuit in which coil A and resistance B are connected. By
suitably proportioning the circuits which include the coils A and C, a difference of
phase of nearly 90° may be obtained between the magnetic fields of the coils. In
order to cause the fields produced by the coil A to approach more nearly to exact
quadrature with the field of the coil C, I introduce an auxiliary coil or conductor E
closed upon itself and within the inductive influence of the coil A, so that secondary
alternating currents are induced in it, upon the passage of an alternating current
through coil A.
This closed secondary circuit may consist either of a single turn of conducting
material, or of a coil of several turns, and may include within its circuit a definite
and adjustable resistance, as will be described in connection with Figure 2. The
secondary current induced in the coil E differs in phase from the current in the
coil C by an amount depending upon the construction, but necessarily within
the limits of 90° and 180º.
These phase relations are illustrated in Figure 5 m which phase angles are
indicated in the customary way by means of the angular position of lines. The
line e represents at a given instant the electiomotive force impressed upon a given
circuit, and corresponds in angular position with the phase of the curent through
coil when the circuit including said coil possesses no self-induction or capacity.
The line a represents the phase-angle and magnitude of the magnetic field produced
by the coil A and lagging, as shown, less than 90° behind the impressed electro-
motive force c. The line e represents by its magnitude and direction the strength
and phase angle of the field produced by the induced cuments in coil E. The
line obtained by completing the parallelogram represents in like manner the
strength and phase-angle of the resultant magnetic field which is exactly in
quadrature with the impressed electromotive force represented by hne c. It 19
evident that by suitably proportioning the strength and phase angle of the field
represented by the line e the phase-angle of the resultant magnetic field represented
by the line & may be modified at will and may be caused to take a position either
more or less than 90° from the impressed locomotive force, if desired, or may be
adjusted to quadrature as accurately as may be found necessary. This adjustment
Is effected by suitably proportioning the self-induction and resistance of the coil E.
I have found in practice that the position of the resultant field may be varied
though a considerable angle on either side of 90º.
In Figure 2 the coil A. 18 provided with a magnetic core A' and the closed
coil Eis wound on the core, moreover an adjustable resistance G is shewn in
series with the coil E which may be used when desired to correct the indications
of the instrument with which the coil is used. The resistance may be of any
convenient form and is shewn for example as a rod which is adjustable as to
length.
Figure 3 shows another modification in which two closed secondaries E and E
are mounted on the core A' in such a position that the lines of force passing
through the coil A pass also though said coils E' and E. Although these coils
are disposed substantially at right angles to the coil A, yet the thice coils bear
substantially the same magnetic relation to each other that they would if con-
centrically an anged, since their effective magnetic fields are substantially coincident
in position owing to the presence of the non cole.
Where the secondary is in the form of simple closed bands of conducting
material, as indicated in this figure the dimensions and specific resistance thereof
must be so chosen as to produce the phase angle required. This may be
determined by trial for the particular form of instrument in connection with which
the coils are used, and these may be so constructed as to have an adjustable
resistance as described in Figure 2.
In Figure 4 the coil surrounds the core A' being supported from the frame-

page_text: work H. The coil E can therefore be readily lowered or raised by turning the
screw H. This adjustment of the coil answers the same purpose as the adjustable
resistance shewn in Figure 2.
Figure 6 is a diagram of a measuring instrument A being a coil shunting the
work circuit Wand C, C coils in series with the work cucuit fed by wires 1 and 2.
The coils A and C, C the magnetic fields of which are approximately in quadrature
act upon a rotatable armature G in a manner well understood. The coil A 18 n
series with an inductance coil B which causes the current in coil A to be very
nearly quadrature with the electromotive force between the wues 1, 2. The
current in coil E which is m series with a non-inductive resistance E³ and is joined
as a shunt to the work cucuit is substantially in phase with the electiomotive
force at its terminals since coil E has a very little self-iduction. Under these
circumstances the magnetic field in the core A can be brought into exact
quadrature with clectiomotive force between the wires 1, 2, or the current in
coils CC when there is no self-induction in the work circuit by which it is ensured
that the indications of the instrument will also be correct where the main encuit
bas self-induction or capacity or both included. The phase relations will be
readily understood by reference to the phase diagiam Figme 7 in which the line e
represents the electromotive force impressed upon the circuit 1, 2, and corresponds
in augula position with the phase of current through the coils C, C when there is
no self-induction in the work cucunt The ne a represents the phase angle and
magnitude of the magnetic field poduced by the coil A and lagging, as shown,
less than 90° Lebind the impressed electromotive force e¹ The line e represents
by its magnitude and duection the strength and phase angle of the field produced
by the current in the coil E, the phase angle hetween this field and the field
epresented by line being 180° which is secured by winding the coil Em the
proper direction relatively to the coil C. The line like manner represents
the strength and phase angle of the resultant magnetic field which is in quadrature
with the impressed electromotive force c'. The conditions of quadrature between
the magnetic helds of two coils of a measuring instrument may also be obtained by
means such as those described hereinabove with reference to Figures 1 to 5 of the
drawings.
In order that the quadrature or other phase relationship between the electro-
motive force at the terminals of the ciremit and the resultant magnetic field due to
coils A and E may be maintamed nespective of vauations of temperature I provide
means whereby the self induction of the circuit shall automatically vary with the
temperature. This may be done by means of resistance coils of special design,
which I will now describe.
In Figues 8 and 9 I is the core and J is the coil of an inductive resistance, said
core having a central part I separated from the sides by an gaps it.
2 The sides I
of the core are secured to bars or strips K, K and the bars are connected
by stups L, L of a metal having a high coefficient of expansion when heated.,
The bais K, K may be of iron for example while L, Lare of zinc. Under the
circumstances when the core 18 heated the bars L, L expand more than the
bais K, K and consequently the air gaps t, i, widen and vice versa When
the core cools the width of the air gaps decreases hence the self induction of the
coil will decrease as the tempeinture ses and increase as the temperature falls.
Hence the current through the shunt coil of the instrument is varied to compensate
for variations in temperature.
In Figure 10 the core is of a different form having a part 12 of a wedge shape
interposed between the ends of the other part I of the core. This part I 18
supported by a stup or strips L of zinc or other suitable highly expansive metal
which are secured at the ends to supports K, K bolted to the part I of the core.
When the core is heated the strip or strips L expanding more than their supports
will bend and withdraw the wedge shaped piece 12 from the core thus increasing
the width of the air gaps and acting in a similar manner to the arrangement shown

page_text: in Figures 8 and 9. The piece 1³ is adjusted by means of the screw k' so that tho
width of the air gaps may be adjusted.
The strip L shewn in the drawing has its curvature exaggerated to shew the
operation of the parts more clearly.
In Figures 11 and 12 the core is composed of two L-shaped sections 13, 14
between which are the gaps, . The two parts of the core are connected to the
onter ends of the expansion bais L, L through the strips K, K as shewn. The
operation of the device is similar to what has already been described with reference
to the other figures of the drawing and need not be further repeated. Two
coils J, J are preferably used with this form of core as shewn but obviously it may
be arranged to be used with one coil only if desired.
Instead of using the inductance coil 1 to correct the temperature variation I may
provide for this purpose a simpler device whereby the resistance G in the circuit
of the auxiliary coil E (see Figure 2) shall vary with the temperature and thereby
maintain the resultant magnetic field of the coils A and E in its proper phase.
Such devices are well known in connection with other electrical encuits and need
not here be described.
I furthermore desire it to be understood that my invention may be utilised for
obtaining any desired phase relationship between the magnetic field due to a coil
and the impressed electromotive force, although the attainment of exact quidrature
is the in mediate object which I have in view as this condition is important in.
connection with certain well known mensuing instruments.
It is evident also that many modifications of form may be adopted, but I have
shewn such forms as are necessary to illustrate my invention and render its method
of operation sufficiently clear to enable those skilled in the art to embody the
invention in any required form of apparatus. It is evident also that the same
method may be applied to the modification of any magnetic field irrespective of
the manner in which the primary angular position of that field may be obtained,
such, for instance, as by the use of condensers of transformers in any well
known way.
Having now particularly descube and ascertained the nature of my said inven-
tion and what manner the same is to be performed, I declare that what I
claim is
1 The means for ensuing that the magnetic field due to the cutient flowing in
a coil shall have any desired phase angle with the electromotive force producing
Buch current, substantially as described.
2. The combination with a coil, of a closed secondary coil having a magnetic
field substantially co-axial with that of the first coil for the purpose -pecified
3. The various arrangements of coils described with reference to either of
Figures 1, 2, 3, or 4 of the accompanying drawings, operating as and for the
purpose specified.
4. In a measuring Instrument having a rotatable armature, a pan of coils acting
on said aimature one of said coils being in series with the main circuit and having
its magnetic field in phase with the main current, and the other of said cuils
shunting the main en cuit and having its magnetic field brought into quadrature
with the field of the first-named coil by means of an auxiliary coil which may o
may not be electrically connected to the circuit, substantially as described.
5. The means for maintaining, respective of temperature the requned phase
relationship between the magnetic field produced by a coil and the electiomotive
force at the terminals of said coil, substantially as described.
6. An inductance coil having a core provided with air gaps and means for
automatically varying the dimensions of such gaps in accordance with changes in
the temperature, for the purpose specified.
7. An inductance coil having air gaps in its core and having expansion bars for
varying the dimensions of the air gaps in the manner herein before set forth.

page_text: 8. An inductance coil constructed substantially as described with reference to
Figures 8 and 9 or to Figure 10 or to Figures 11 and 12 of the accompanying
drawings and operating as specified
Dated this 21st day of July 1896.
W. P. THOMPSON & Co..
322, High Holborn, London, W.C., Patent Agents for the Applicant.