Note: Descriptions are shown in the official language in which they were submitted.
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AMORPHOU5 ~lETAL LAMP BALLAST HAVIN~ A CAPAOITOR
INTEGRAL ~JITH THE MAGNETIC CORE
Background of the Invention
This invention relates to magnetic lamp ballasts and especially
to improved ballasts having an amorphous metal core structure which
has a dual function as a capacitor.
Fluorescent and mercury vapor lamps require special circuitry
for their starting and running when excited from an alternating
current supply. These lamps have a negative resistance characteristic
which must be compensated by ballasting impedance, and the ballast
supplies a higher peaked voltage for starting and a regulated square
wave current for running. It is desirable that the current through the
lamp be flat-topped to increase the life of the lamp. A high reactance
transformer is needed to meet the requirements of a good ballast, and
a capacitor is added to the ballast circuit for starting and power
factor correction. A typical ballast for two fluorescent lamps (see
FIG. 2) has a relatively small starting capacitor and a large power
factor capacitor, both discrete components separate from the high
reactance transformer. Present magnetic ballasts are made from steel
lamination punchings and 1nclude magnetic shunts and cutaways to cause
core saturation. The present configurations substitute cores made from
amorphous metal ribbon for the lamination punchings.
Amorphous metal is also known as metallic glass and is made
from metallic alloys that can be quenched rapidly without crystalli2ation.
The material is fabricated on a rotating chill cylinder in the form
of a long ribbon with a thickness of 2 mils or iess; the thickness
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limitation is set by the rate of heat transfer through the
already-solidified material which must be rapid enough that
the last increment of material to solidify still avoids
crystallization. This is several times thinner than currently-
used lamination materials. Despite this possible limitation,
at power frequencies amorphous metal core material is
attractive because of the combination of potential low cost
and low magnetic losses; the core loss is about one-fourth
the loss found in silicon sheet steel.
It has been recognized that the thinness of amorphous
metal ribbon can be capitalized upon by utilizing the stator
or rotor core laminations as plates of a start/run capacitor
in a single phase electric motor. This integral construction
is made possible by the tremendously increased interlamination
area with the thinner material, and is described in Canadian
patent 1,125,344 issued June 8, 1982 to T.R. Haller and
titled "Amorphous Metal Electric Motor with Integral Capacitor".
Amorphous metal "0" core ballasts and reactors having magnetic
structures made of ribbon without interlaminar insulation
20 are disclosed in United States patent 4,288,773 issued
September 8, 1981 to R.P. Alley and R.E. Tompkins. Both
patents are assigned to the present assignee.
According to the present invention, magnetic lamp
ballasts use amorphous metal ribbon in several different ways and
include a capacitor as part of the core assembly to realize
potentially lower cost and higher power efficiency ballasts. The
laminated magnetic core of several ballast configurations with
an integral capacitor is comprised of bifilar or two-in-hand
wound magnetic amorphous metal strip and alternating insulation
layers which are electrically connected in circuit relationship
with a coil to be a power factor capacitor or, in some configura-
tions, a power factor capacitor and a starting capacitor.
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The magnetic alloy of this inherently thin (about 1.5-2 mils)
material preferred for this application has a sr/Bs ratio
exceeding 80 percent, i.e., it has a square hysteresis loop;
one such alloy is ~e82B15Si3.
The principal embodiment has a rectangular geometry and
has an inner core on which the primary and secondary coils
are assembled, end yokes made of cast compressed amorphous
metal flake, and an outer yoke which also serves as a case
and is comprised of multiple turns of a pair of edge-mounted
parallel amorphous metal strips separated by alternaking
insulation layers, the secondary coil being electrically
connected in series with the pair of strips separa-ted by
insulation which function as a power factor capacitor.
The inner core can be comprised of accordion-pleated folds
of a second pair of parallel amorphous metal strip and
alternated insulation which are electrically connected to be
a starting capacitor in series with the power factor capacitor.
Grooves are cut in the inner core to cause core saturation
and shape the lamp current waveform. A modification has a
round geometry; the outer yoke is helically wound and the
inner core is spirally wound two-in-hand.
Another embodiment of the ballast assembly has planar
end yokes and outer yokes in a four-walled structure, all
made of bifilar amorphous metal strips and dielectric that
are wound into accordion pleats and connected to be the
power factor capacitor. The accordion-pleated inner core
is the same as just described. A ballast with a combined
toroidal core and power factor capacitor is helically wound
and has cutaways under the secondary coil to secure the
proper flux nonlinearities. The dual use of magnetic core
components results in cost, weight, and space savings.
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Brief Description of the Drawings
FIG. 1 is a perspective view with portlons broken away to reveal
interior detail of the preferred emboidment of lamp ballast incorporating
power factor and starting capacitors in the magnetic structure;
FIG,. 2 is a circuit diagram of a typical ballast for two
fluorescent lamps;
FIGS. 3 and ~ are a partial expanded view and a fragmentary cross
section of the case in FIG. 1 to depict its configuration as a power
factor capacitor;
FIG. 5 is a sketch of one method for making the amorphous metal
case;
FIG. 6 is a perspective of the accordion-pleated inner core in
FIG,. 1 which also serves as a starting capacitor;
FIG. 7 is a modification of FIG. 1 having a round rather than ,
a rectangular geometry;
FIG. 8 is a partial expanded view of the two-in-hand helically
wound case in FIG,. 7;
FIG. 9 is a perspective of the inner core and integral capacitor
in FIG. 7;
FIG. 10 shows an embodiment of the ballast similar to FIG. 1
but with a rectangular outer yoke or case made of accordion-pleated
sections,
FIG. 11 is a perspective of another embodiment with a toroidal
core and integral capacitor and distributed primary and secondary
colls, and
FIG. 12 is a cross-section of the core in FIG.ll with a slot
to cause saturation.
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Description of the Preferred Embodiments
The lamp ballast assembly in FIG. i substitutes a wound amorphous
metal core for the stacks of steel laminations in conventional
ballasts. The added resistivity of the amorphous metal (about four
times that of silicon steel) increases the magnetic flux leakage of
the core assembly so that magnetic shunts are not necessary, thereby
saving material and assembly cost. Restrictions to reduce the core cross
section and cause core saturation are brought about by aluminum oxide grinding
cuts. The large power factor correction capacitor and smaller starting
capacitor are made up in the core of the ballast assembly.
The preferred embodiment of the invention in FIG. 1 has a rectangular
geometry and is comparable in overall size to present ballasts for
two 40-watt fluorescent lamps which require separate power factor
and starting capacitors. ~he magnetic core indicated generally at 10
provides a closed magnetic circuit and is comprised of an inner core
11 made of amorphous metal strip and which is specially constructed
to also be a dry starting capacitor, a pair of end yokes or end
members 12 and 13 made of cast amorphous magnetic material, and an outer
yoke 14 made of amorphous metal strip which doubles as the ballast
case and is further specially configured to also be a dry power factor
capacitor. Primary coil 15 and secondary coil 16 are assembled on
the innercore such that the former has a tight magnetic coupling and
the latter a loose magnetic coupling, and both are encased by the
outer yoke. Inner core 11 is made of bifilar or two-in-hand amorphous
strips that are wound in accordion pleats with at least one side of
every strip coated with a suitable material having a dielectric
constant compatible with the capacitance needed. End yokes 12 and 13
are compressed amorphous metal flake in a binder which is cast
directly on the ends of the inner core. Outer yoke 14 has multiple
turns of bifilar wound amorphous metal strip which are coated with
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appropriate dielectric material to realize the desired capacitance.
Although not shown~ the exterior of the case may be coveredwith
insulation for saFety purposes. Base plates 17 and 18 are glued to one
side of the case to facilitate installation.
FI~. 2 is a schematic circuit diagram of a typical ballast for
two 40-watt fluorescent lamps l9 and 20, and the equipment in FIG. l
includes all of the illustrated transformer components as well as power
factor capacitor 21 (about 4 microfarads) and starting capacitor 22
(about n.os microfarads). The various windin~s on common core 23 are
primary and secondary windings 24 and 25 and three filament windings
26 which are connected across lamp electrodes 27. The filament
wind1n~s 26 have only a few turns and may be included in either the
primary coil package or the secondary coil package. Power factor and
starting capacitors 21 and 22 are in series with one another and with
secondary winding 25, and starting capacitor 22 is placed across the
electrodes of one of the lamps such as lamp 19. A 120 volt ac voltage
is impressed across the primary coil and by autotransformer action
the voltage available for starting across the windings is 280 volts.
Initially, lamps l9 and 20 are off and appear as an open circuit,
and the reactance of starting capacitor 22 is small such that about
280 volts is impressed across lamp 20 and this is sufficient to turn it
on. The voltage drop across the turned on lamp decreases to about lOO -
volts and the remalning voltage is now impressed across lamp l9 and is
sufficient to turn it on.
eonstruction of the magnetic core to also be a dry capacitor permits
utilization of the core material which is required for the magnetic
circuit to serve also as the plate material of an integral capacitor,
resulting in cost, weight, and space savings. One of the previously
assumed disadvanta~es of using amorphous metal alloys in transformers
and motors has been the large number of lamlnations that have been
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reauired due to khe inherently thin nature of this material. In spite
of the thickness limitation, a number of ways are known for handling the
material and once assembled such a core has a significant interlaminar
area. The capacitance of a capacitor is directly proportional to the
area of the plates and to the dielectric constant of the insulator
between the plates, and is inversely proportional to the distance between
plates. The plate area ;s many times greater where the core laminations
are made of very thin amorphous metal strip rather than much thicker
punched steel stnip material.
FIG. 3 shows tc expanded scale a few turns of the bifilar,
edge-wound and formed amorphous ribbon outer yoke and case 14. This
laminated core section is made of a pair of parallel or superimposed
magnetic amorphous metal strips 28 and 29 of relatively long length
that alternate with insulatina layers 30 and 31 and are wound in the
nature of a squared-off helix. Viewed as a capacitor, the
structure can be called a dry parallel-plate capacitor and connections
are made to the ends of amorphous strips 28 and 29. When the core
is assembled and successive turns are contacting as in FIG. 4, èach
strip is capacitively coupled to the other strip on the other side
and the total capacitance is proportional to the total interlaminar area.
The ribbon core material in its dual function as power factor capacitor
21 is conductively or electrically connected in series circuit
relationship with secondary coil 16. Calculations prove that the
total capacitance of outer yoke 14 is sufficient to provide good power
factor in such a ballast.
The amorphous metal magnetic alloy needed for this application --
has a high ratio of remanent-to-saturation magnetization, i.e., Br/Bs is
80 percent or greater, where Br is the remanent induction and
Bs is the saturation or maximum induction. A core material of this
type has a relatively square hysteresis loop; one such alloy presently
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known is Fe82B15Si3, for which Br~s is about 30 percent. The dielectric may
be a coating of varnish with the proper dielectric constant, a film of p7astic
or other suitable material. The magnetic properties of the amorphous metal
alloy are improved by annealing the outer yoke after fabrication at
temperatures of 3no-3400c as taught generally in U.S. Patent 4,116,728
to Becker et al. Insulating materials compatible with this annealing
step are polyimide varnish (a DuPont product) and Kapton ~ plastic
tape. One way of fabricating the outer yoke and case is to coat one
surface of Fe82B15Si3 alloy ribbon with varnish, and then take two
such coated ribbons and wind them around a form two-in-hand.
Another method for fabricating amorphous metal case 14 is
diagramed in FIfi. 5. Molten alloy 32 is splatted onto the surface of
a rapidly rotating chill disk 33, is quenched at a high cooling rate
in the order of 105 - 108C/sec to prevent formation of crystal
structure, and is spun off in naturally curled ribbon form similar
to the Slinky`~R spring toy. This tight, edge-wound helix 34 is
profile formed such as over a progressive mandrel (not shown) by four
external rollers 35 to conform to the desired outer profile of a ballast
can. The helical core massaged into a more rectangular cross section
is cut off to size by abrasive wheel 36 and drops onto conveyor belt 37.
The resulting outer yoke component (two are needed with associated
dielectric) is shown at 38.
Referring to FIG. 6, inner core 11 which has a dual function
as starting capacitor 22 is bifilar wound into accordion pleats
from amorphous metal strip coated with an appropriate dielectric
material. The pair of parallel amorphous metal strips are indicated
at 39 and 40 and the alternated insulating layers at 41, 42, and 43.
External dielectric coatings on both sides of the strips are needed
to prevent metal-to-metal contact at the folds of the accordion-
pleated structure. Capacitor connections are illustrated and are made
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to the ends of amorphous strips 39 and 40. The dry parallel-plate
capacitor provided in this manner is connected in series circuit
relationship with the power factor capacitor embodied within
outer yoke 14, and with secondary coil 16. The core cross section
is reduced over a specified length by cutting a groove 44 with
a grinding wheel. This cutaway is located under the secondary
coil and causes core saturation to shape the lamp cllrrent wave-
form, as explained in greater detail in the previously-mentioned
United States patent 4,288,773. Additional grooves 45 may be
cut into the inner core to secure the proper magnetic flux
nonlinearities.
The lamp ballast assembly with integral capacitors of
FIG. 1 may be built with a round geometry as depicted in FIGS.
7-9. Inner core 44 is a long cylindrical rod made of spirally
wound bifilar strips coated with an insulator. Circular end
yokes 45 and 46 are cast onto the ends of the inner core and are
comprised of compressed amorphous metal flake in a binder. Outer
yoke 47 of the magnetic core is helically wound two-in-hand with
alternate insulating layers as illustrated to expanded scale in
20 FIG. 8. The parallel edge-mounted amorphous metal helices are
indicated at 50 and 51 and the dielectric coatings or layers at
52 and 53. The helical outer yoke as before serves as the ballast
case and is electrically connected in series with secondary coil
48 to be the power factor capacitor. This coil and primary coil
49 have a round shape.
The construction of spirally wound inner core 44
is given in greater detail in FIG . 9 . A first amorphous
metal ribbon 54 coated with dielectric 55 and a second ribbon
56 coated with dielectric 57 are bifilar wound like a spool
of tape, and the resulting capacitor structure has a cross
section similar to that in FIG . 4. Capacitor connections
are made to the exposed ends of ribbons 54 and 56. The starting
capacitor of the ballast assembly is relatively small (typically
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0.05 microfarads) and a resonable alternative is to use a discrete
capacitor which can be located in available space within the magnetic
structure. In this case, inner core ~4 (the same is true of inner
core ll) can also be fabricated of compressed amorphous flake or chips,
with or without a binder~ as ~aught in Canadian application Serial
No.339,994 dated Nov.16,19 79, tr) P.G. Frischmann, "Molded
Amorphous Metal Electrical Magnetic Components", assigned to the same
assignee as this invention. Another way of manufacturing the inner
core is to twist together long narrow ribbons of amorphous metal much
as cable is made.
Another embodiment of the invention in FIG, lO has a rectangular
geometry with planar end and outer yokes assembled together as a four-
walled structure to provide a closed magnetic circuit and return paths
for magnetic f1ux. The four-walled structure boxes in the ballast
assembly and is configured to be the power factor capacitor~ The
inner core can be identical to inner core ll in FIG. l, as are coils l5
and l6. Planar end yokes 58 and 59 and outer yokes 60 and 6l are all bifilar
wound or folded into accordion pleats as in FIG. 4. Considering that
each wall member is a capacitor, the four capacitor structures are
joined by welding together adjacent strip ends at three corners and
attaching electrical leads at one corner. Opposite ends of the inner
core are welded to the bared surfaces of end yokes 58 and 59 or are `
inserted into holes in the end yokes and welded in place.
A different configuration of the end and outer yokes is realized
by coating rectangular amorphous metal ribbon with dielectric materiai,
and stacking the coated ribbons to achieve the desired wall thickness.
One set of alternate ribbons are joined at one side of the yoke, and
the interleaved set of alternate ribbons are joined at the other
side of the yoke. This is also a dry parallel-plate capacitor, and
the four capacitors are connected ~n series or parallel to achieve the
desired capacitance.
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The lamp ballast with integral capacitor in FIG. 11 has a
toroidal core 62 on which are wound distributed primary and secondary
windings 63 and 64. The magnetic core is a two-in-hand wound helix
similar to outer yoke 47 shown in FIGS. 7 and 8. The helical core
is also a capacitor for power factor correction and starting and is
electrically connected in series circuit relationship with the secondary
coil. The core has one or more grooves 65 cut into its inner surface
under the secondary coil to secure core saturation and the proper
flux nonlinearities. Saturation of the core over a specified length
causes a pulse condition which initiates starting of the lamp, causes
a voltage regulation condition which filters out transistory voltage
waves in the line, and shapes the current waveform for optimum lamp
efficiency. A modification of this configuration or a previous embodi-
ment is that the ballast may have only one coil which is in series
with the lamp, and the integral capacitor is placed across the line.
Ballast or lighting reactors of this type are common in Europe for
220 volt circuits.
The ballast and capacitor may also be made up in modules which
are then assembled together, and the modular capacitors are connected
in series or parallel to obtain the desired capacitance. The forms of
the invention depicted in FIGS. 1, 7, and iO are all suitable for modular
fabrication, different loads are accommodated by adding more or less
modules. Toroidal modules are compatible with both core and capacitor
~ designs and are especially useful For Lucalox ~ lamp ballasts
25- Amorphous metal lamp ballasts have low core losses and are
efficient, and have the potential of being economical to manufa'cture ' ;
considering that there is no scrap (laminations punched from st'eel' ' ;,
strip generate considerable scrap~. Inclusion of the required
capacitor or capacitors in the core assembly is a significant step
in achieving lower cost magnetic lamp ballast with a higher power
efficiency.
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While the invention has been particularly shown and described with
reference to several preferred embodiments thereof, it will be understood
by those skilled in the art that the foregoing and other changes in form
and details may be made therein wjthout departing from the spirit and
scope of the invention.
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