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Патент USA US3037186

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May 29, 1962
D. F. CHAPMAN
3,037,176
ELECTRICAL INDUCTORS
Filed Dec. 30, 1959
/A/l/E/VTO>Q
DOA/A LD F CHAPMAN
BY
3,037,176
Unite States atent
Patented May'29, 1962
2
1
core. This shell comprises two elongated, U-shaped, lam
inated yokes 14, 15 so ?tted into one another as to form
3,037,176
ELECTRICAL INDUCTORS
Donald Frederick Chapman, London, England, assignor
to Thorn Electrical Industries Limited, London, Eng
a closed, elongated, box-shaped structure 16 (see FIG.
2). The limbs of the elongated U-shaped yokes 14, 15
constitute the four adjacent side faces respectively of the
outer shell and their transverse portions constitute the
two end faces. This ‘box-like construction is achieved by
5 Claims. (Cl. 336—83)
?tting the U-shaped yokes together in the manner shown
in FIG. 2, that is the limbs of each yoke bridge the gaps
The present invention relates to electrical inductors.
One use of an electrical inductor is as a choke in cir 10 between the side edges of the limbs of the other yoke
and the transverse portion of each yoke bridges the gap
cuit with a gaseous discharge device, such as, for example,
between the ends of the limbs of the other yoke.
a ?uorescent lamp, supplied by alternating current.
land, a company of Great Britain
Filed Dec. 30, 1959, Ser. No. 862,978
It is often required to mount such an inductor in a
Thus the outer shell serves to screen magnetically the
gap in the inner core and to reduce ?ux leakage from the
shallow channel which forms parts of a ?uorescent light
ing ?tting. It is also required that the inductor be sub 15gap.
Although the U-shaped yokes 14, 15 need not neces
stantially silent and that stray magnetic ?eld which could
sarily be elongated, the form of construction described is
cause vibration of adjacent steel or iron parts of the light
particularly suitable for an inductor which is long and
ing ?tting is not excessive.
slim and is therefore of a convenient shape for mounting
It is well known that an inductor or choke having a
magnetic core must be provided with an air-gap in the 20 in assemblies such as fluorescent lighting ?ttings.
In order to reduce still further the ?ux leakage which
magnetic circuit in order to prevent flux saturation of the
would occur in the case where one central gap is provided
in the inner core, two further gaps 17, 18‘ may be pro
vided between the ends of the inner core and the end
sary to shield the inductor so as to prevent this ?ux leak
age and thereby prevent the stray alternating magnetic 25 faces of the outer shell. These gaps may also be ?lled
with a non-magnetic cement. It has been found that pro
?eld from causing noise and vibration in adjacent steel
vision in this Way of three relatively small ‘gaps considera
or iron parts which may be located near the inductor.
bly reduces ?ux leakage as compared with that occurring
The stray ?eld will pulsate at 50 cycles per second on
magnetic circuit. Considerable leakage flux is present in
the vicinity of the air-gap and precautions may be neces
in an inductor assembly having one relatively large gap.
ordinary A.C. mains and may cause ‘appreciable hum
and noise to be generated by the lighting ?tting. Such 30 All three gaps are, of course, completely screened by the
outer shell.
noise is undesirable.
Measurements obtained on an 80 watt ?uorescent lamp
In one known form of inductor construction the in
choke constructed as described and placed inside a sheet
ductor is shielded with thick iron castings in the form of
steel channel showed that there was no detectable in
plates which are clamped around the inductor. These
castings effectively form a magnetic screen for the in 35 crease of vibration or noise due to stray magnetic ?eld
eifects.
ductor but add considerably to the cost and weight of the
This 80 watt choke, suitable for a 230/2/l0 volts 50,
inductor.
cycles A.C. supply, was constructed as follows:
It is ‘an object of the present invention to provide an
The two yokes 14, 15 forming the outer shell were each
improved inductor suitable for use as a choke in a ?uores
cent lighting ?tting and having, in operation, stray mag 430 made from six strips of 19" x 1%” x .02" dynamo iron
netic ?elds of such small value as not to cause appreciable
noise to be produced in neighbouring parts of the ?tting.
According to the present invention there is provided
bent at the centre to give a width of 1%” between the
limbs of the U~shaped member thereby produced. The
centre core was made from two 13/16" deep stacks 11, 12
of strips of 4” x 13/16” x .02" dynamo iron. The coil 10
of laminated ferro-magnetic material, the magnetic cir 45 comprised 1900 turns of 25 S.W.G. enamelled copper wire
layer wound in 6 layers round the core. The gap 13 be
cuit 'being in the form of an inner core around which the
tween the two halves of the inner core and the gaps 17,
winding is disposed and an outer shell co-operating with
18 between the ends of the inner core and the end faces
the inner core and comprising two laminated U-shaped
of the outer yokes were each 0.05 inch wide.
yokes ?tted one into the other, the limbs of each yoke
bridging the gaps between the side edges of the limbs 50 I claim:
1. An electrical inductor comprising an inner core of
of the other and the transverse portion of each yoke bridg
laminated ferromagnetic material having a series gap
ing the gap between the ends of the limbs of the other
therein ?lled with a non-magnetic material, a winding
yoke, the magnetic circuit including a series gap in the
disposed around said inner core, and ‘an outer shell of
inner core or between the inner core and the outer shell
55 laminated ferromagnetic material, said outer shell com
or both.
‘an inductor comprising a winding and a magnetic circuit
An inductor embodying the invention will be described,
by way of example, with reference to the accompanying
drawings in which:
FIG. 1 is a somewhat diagrammatic exploded perspec
tive view of the inductor, and
FIG. 2 is a side elevation of the assembled inductor.
The inductor includes a winding 10‘ of enamelled cop
per wire on an inner magnetic core.
This inner core
prising two laminated, U-shaped yokes ?tted together to
form a hollow enclosed shell surrounding said winding
‘and said inner core.
2. An electrical inductor according to claim 1 wherein
gaps ?lled with a non-magnetic material are provided be
tween the extremities of said inner core and the adjacent
end-faces of said outer shell.
3. An electrical inductor comprising an inner core of
laminated ferromagnetic material, a winding disposed
comprises two stacks 11, 12 of strip-shaped laminations
of silicon-iron, the two stacks being separated by a gap 65 around said inner core, and :an outer shell of laminated
ferromagnetic material surrounding said winding and said
13 ?lled with a non-magnetic cement. A suitable cement
inner core, said outer shell comprising two laminated, U
shaped yokes ?tted together to form a hollow enclosed
shell, gaps ?lled with a non-magnetic material ‘being pro
material, such as, for example, varnish, in order to reduce
70 vided between the extremities of said inner core and the
eddy-current losses.
is one of the well known epoxy resin compounds. The
laminations are coated in the usual way with an insulating
The magnetic circuit of the inductor is completed by an
outer shell completely surrounding the winding and inner
‘adjacent end~faces of said outer shell.
4. An electrical inductor comprising an elongated inner
3,037,176
3
A
core of laminated ferromagnetic material having a cen
5. An electrical inductor according to claim 4 wherein
Wally-disposed series gap therein ?lled with a non-mag
said centrally-disposed series gap in said inner core and
netic material, a Winding disposed around said inner core,
said gaps between the extremities of said inner core and
‘and an elongated outer shell surrounding said winding and
said transverse portions of said yokes are equal in width.
said inner core, said outer shell comprising two laminated, 5
elongated U-shaped yokes of laminated ferromagnetic m a
References Cited in the ?le of this patent
terial ?tted one into the other, the limbs of each yoke
UNITED STATES PATENTS
bridging the gaps between the side edges of the limbs of
the other yoke and the transverse portion of each yoke
2,948,871
Craige ________________ __ Aug. 9, 1960
bridging the gap between the ends of the limbs of the 10
other yoke, gaps ?lled with a non-magnetic material be
FOREIGN PATENTS
ing provided between the extremities of said inner core
‘and said transverse portions of said yokes.
647,995
Great Britain _________ __ Dec. 28, 1950
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