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Патент USA US3077786

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Feb. 19, 1963
R. E. ROOD
3,077,776
THERMAL INDl'CATOR FOR ELECTRICAL APPARATUS
me@ Feb. 1s. 1959
4Sheets-Sheet l
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WITNESSES
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INVENTOR
Robert E. Rood
M
fa ’ ATTORNEY
Feb. 19, 1963
R~ E ROOD
THERMAL INDICATOR FOR ELECTRICAL APPARATUS
Filed Feb. 15, 1959
4 Sheets-Sheet 2
Fig . 3 .
94
Fíg.4.
Feb. 19, 1963
R. E. ROOD
3,077,776
THERMAL INDICATOR FOR ELECTRICAL APPARATUS
Filed Feb. 15, 1959
Fig.6.
4 Sheets-Sheet 3
Feb. 19, 1963
R. E. ROOD
3,077,776
THERMAL INDICATOR FOR ELECTRICAL APPARATUS
Filed Feb. 13, 1959
4 Sheets-Sheet 4
United States Patent O
,.
ICC
Patented Feb. i9, i953
l
2
3,677,776
FlG. 2 is a top plan View, in section, of the indicator
shown in HG. l;
THERMAL ENDÍQÁTÜR iFÜl'l ELEC'ERECAL
AH’APATÍUS
Robert E. Rood, Sharon, Pa., assigner to Westinghouse
Electric Corporation, East Pittsburgh, Pa., a corpora
tion of Pennsylvania
Filed Feb. l5, 1959, Ser. No. 793,@26
ll’7 Claims. (Si. ’lâ-«356D
HG. 3 is a partial front sectional View, in elevation,
of the indicator shown in FlG. l;
FlG. 4 is a side elevational View, partially in section,
of the indicator shown in FlG. l;
yFl‘íl. 5 is a front view in elevation of a thermal indi
cator illustrating a second embodiment of the invention;
FlG. 6 is a top plan view, partially in section, of the
This invention relates to thermal indicators for elec 10 indicator shown in FlG. 5;
trical apparatus such as transformers.
FlG. 7 is a partial side elevational View, in section
In certain types of conventional electrical apparatus,
of the indicator shown in PEG. 5;
such as transformers, it has been the common practice in
FIG. 8 is a perspective view illustrating an alternative
building such appm‘atus to bury thermostats, thermo
form or" the magnetic member included in the indicators
couples and other thermally responsive devices in the
shown in FlGS. 2 and 6; and
windings or coils of such apparatus, the temperature or
FIG. 9 is a partial View in elevation illustrating the
thermal load condition of which it is desired to measure
manner in which the indicators shown in FIGS. l through
or indicate. If such thermal indicating equipment should
4 or in FIGS. 5 through 7, respectively, would be mount
require repair, it may be necessary to tear down the wind
ed on the associated electrical apparatus.
ings or other parts of such apparatus. The latter pro
Referring nonl to the drawings and FIGS. 1 through
cedure may also be necessary to add thermal indicating
4 and 9 in particular, there is shown in general a tem
equipment to existing electrical apparatus.
perature or thermal load indicator l@ illustrating a iirst
ln copending application Serial No. 793,027, tiled Feb
embodiment of the invention.
he indicator for elec
ruary 13, 1959, by Herbert W. Book and assigned to the
trical apparatus shown generally at lll is a modiiication
same assignee as the present yapp ication, there is disclosed
suitable for application to a distribution transformer.
an improved thermal or temperature indicator which does
riïhe casing or housing of the associated electrical ap
not require thermally responsive parts or devices to be
paratus, such as a transformer, is indicated at .'ä'tìtl‘k in FIG.
built into the windings or coils or” the associated electri
9. The electrical apparatus enclosed or disposed inside
cal apparatus and which is particularly adapted for in
the casing Soil: may be a transformer core and coil as
stallation external to, or on the outside of the casing or 30 sembly (not shown) to and from which electrical current
housing of electrical apparatus of the enclosed type.
is carried from outside of the casing fido by associated
While the thermal indicator disclosed in said copending
leads which may include one or more conductors, such
application is suitable for most applications, therc are cer
as the conductor 53d, having a covering of insulation
tain applications where it is required to provide an indi
thereon, as shown in FlG. 9. 'l`he conductor 53d may be
cator which shows that the associated electrical appara 35 connected to a suitable terminal connector 522 and the
tus is eing or has `been subjected to a thermal load in
electrical current carried by the conductor 53u may pass
excess of a predetermined value. It is, therefore, desir
through the casing or housing âtltl through a suitable
able to provide a thermal or temperature indicator for
bushing 52d Áas shown in FlG. 9.
electrical apparatus which has all of the advantages of
The ilovv or” electrical current to the associated electri
the indicator disclosed in said copending application and 40 cal apparatus through one or more of the conductor leads
which has several additional advantages in certain appli
55d causes the temperature or thermal load condition
cations.
f the electrical windings or coils of the associated ap
lt is an object of this invention to provide for indicat
paratus inside the casing Soil to change, the extent of such
ing the thermal load condition ot an electrical apparatus.
changes being ’measured and indicated by the thermal
lt is also an object of this invention to provide for 45 indicator
The thermal indicator lli, as illustrated, is
indicating the temperature of an electrical apparatus.
particularly adapted to indicate when the temperature or
Another object of this invention is to provide for meas
thermal load or the associated electrical apparatus eX
uring and indicating the temperature or thermal load con
yeeds a predetermined value. Since the thermal indicator
dition of an electrical winding or coil which is so dis
ltr is disposed adjacent to the leads of the assocated elec
posed in a casing or relative to other apparatus that it is 50 trical apparatus, it is preferable that, if the indicator lid
not readily accessible.
is employed with a transformer core and coil assembly,
A further object of this invention is to provide means
the indicator lll should be disposed adjacent to the sec
ondary or low voltage leads associated with said assembly
for indicating the thermal load condition of electrical
apparatus which responds to a magnetic field resulting
in order to reduce the insulation requirements in the con
struction of said indicator.
from the flow of electrical current which causes the
heating of said apparatus.
As best shown in FIG. 9, the thermal indicator lil is
mounted or secured on the outside of the casing Edil of
A still further object of the invention is to provide a
the associated electrical apparatus by any suitable means,
thermal indicator for electrical apparatus of the enclosed
such as the stud member Sli-.Z which is Welded or other
type which is particularly adapted for installation exter
nal to or on the outside of the casing of such apparatus. 60 wise secured to the casing Silo and a bracket member l‘îíì,
which in turn is secured to said stud member and the
A more speciilc object oi the invention is to provide
thermal indicator llt). Referring particularly to FlC-S. l,
for indicating when the thermal load condition of an en
closed electrical apparatus exceeds a predetermined value.
Other objects of the invention will in part be obvious
and will in part appear hereinafter.
For a fuller understanding of the nature and objects
of the invention, reference should be had to the followf
ing detailed description taken in connection with the
accompanying drawings, in which:
4 and 9, the thermal indicator ld comprises an indicating
case or housing 2G and a base member 3d which may be
both molded or cast from a suitable material, such as
a silicone rubber or elastomer, that will have adequate
strength and capacity to resist the Weather when mounted
outdoors. Since the indicator lil may be associated with
a transformer which is mounted on poles or in some
FlGURlE 1 is a iront View, in elevation, ot a thermal
location well above the ground level, the indicating case
2t“, the base member 3d and the bracket member l'îtl may
indicator illustrating a iirst embodiment of the invention;
be arranged so that the indicating case fît-d of tie indicator
3,077,776
f,
sa
itl will be inclined at an angle to the horizontal to facili
cylindrical projecting members lS’S which may be formed
sensing the temperature of the associated electrical ap
integrally with the cover member 32 to form the apertures'
122 through which one or more of the leads 53o may
pass. rl“he lower portion 34 of the base member 3@ is
paratus inside the casing Elli): rl'he sensing means com
prises a magnetic member lll@ which is mounted or dis
posed inside the base member or housing 3d as shown in
FlGS. 1, 2 and 3. Both the base member 3l? and the
M95 of the cover member 32 when the cover member 3?.
and said lower portion are assembled as shown in FlG. 3.
tate observation from the ground.
The thermal indicator lt) also includes means for
also provided with two cylindrical projecting members
i9@ which iit over the outside of the cylindrical members
As shown in FIG. 3, the magnetic member' llt) may be
magnetic member lili include two openings or apertures
3.22 and 11.2, respectively, which permit one or more 10 supported between the cylindrical members 1194 of the
lower portion S-t» of the base member 39' and the shoulder
leads, such as the conductor lead 53d shown in FIG. 9,
or ledge portions 192 on the cylindrical members 195 of
to pass through said base member and said magnetic mem
the cover member 32.
ber. As best shown in FIG. 3, the magnetic member
ln order to control the heat transfer from the magnetic
llt? may be conveniently formed from two plates or
member litt, the base member 3€* is preferably formed
sheets 114, each of said plates including a curved portion
from a thermally insulating material which may also be
between the apertures llrZ to form a cavity or receptacle
an electrically insulating material to assist in insulating
as indicated at 125. , As explained in copending applica
the magnetic member lll from the conductor leads 53d.
tion Serial No. 649,116, tiled by Herbert W. Book and
The thermal insulation 15b may also be disposed around
assigned to the same assignee as the present application
for a magnetic member of the same general type, the 20 at least a portion of the magnetic member il@ to assist in
the control of heat transfer from said member. The
magnetic member lltl is preferably formed from a metal
lic magnetic material and may be molded from powdered
thermal insulation lStl may be provided in the form of
metals or cast in one piece from metallic material or
formed in other suitable ways that are well known in the
polyester glass, wool or matting or as a cast member
which assists in supporting the magnetic member llt?.
art and that will provide the features to be described here` 25 lt is to be understood that in certain applications, a por
tion of the base member 3% may be formed from ther
inafter. The size, shape and thickness of the magnetic
mally conducting .material to more closely create a ther
member llt) will depend to a large extent on the ap
paratus with which it is to be employed. The selection
mal image or reilection having similar thermal character
istics to the electrical apparatus inside the casing or
oí the magnetic material from which the magnetic mem
ber lli) is formed may also depend on the thermal insula 30 housing Still. ln other words, by proper selection and
design ot the base member 3@ and the thermal insulation
tion to be employed with said member and may be formed
l5@ as well as the magnetic member lill, the temperature
from any oí the well-known magneticmetals, alloys or
or thermal condition of the magnetic member lill may
metallic oxides which are available.
As explained in the copending application just men
_tioned, whenever electrical current flows through the
more closely correspond to the thermal operating char
acteristics ot the associated electrical apparatus.
ln order to supply electric power to indicating means
included in the thermal indicator lil', which will be de
jacent to or around the conductor leads 53u shown in
scribed hereinafter, a iirst terminal or external ground
FIG. 9. rl`he density of the magnetic iield set up around
strap 132 is secured to the base member lill by suitable
the conductor leads 530 will vary with the magnitude or 40 means such as the rivet 134, which is best shown in
amount of the current flowing in said leads. When a
FIG. 1. A suitable conductor or internal ground strap
136 having one end connected to the rivet 134 and hav
metallic magnetic member, such as the member llt), is
disposed in a magnetic field around one or more of the
ing the other end secured to the magnetic member lill
conductor leads 530, many of the lines of magnetic liuX
by suitable means, such as brazing or welding, connects
in the space around said member will be concentrated in
the tirst terminal 132 to the magnetic member 116. A
it to thereby heat up said member. The member lill
second terminal or line terminal 142 is secured to the
thus accumulates heat which varies with the density of
base member 3l? by the rivets 144, as shown in FIGS. 1,
the magnetic flux around oneY or more of the conductor
2 and 4. ln order to limit the voltage applied to the
leads 530, which in turn varies with the electrical current
associated indicating means when a source of electric
flowing in said leads and in the associated electrical ap
power is connected between the terminals 132; and 142, a
paratus inside the casing 509. Since the temperature or
suitable are shield or gap protector 160 is disposed ad
thermal load condition of the electrical apparatus, which
jacent to the second terminal 142. The gap protector i60
may include electrical windings or coils inside the casing
comprises a cylindrical member formed from a suitable
Stili, also varies with the current ilowing in the leads 530,
insulating material, such as porcelain, a lirst electrode
thel temperature or thermal condition of the magnetic
secured to the terminal lll?. and a second electrode i541.
member il@ will vary as a function of the temperature
The second electrode 15'4- of the protector löl?` is secured
or thermal condition of the apparatus inside the casing
to the base member 30 by the rivet 155 which in turn is
Slltl. In other words, the magnetic member liti may
connected to the magnetic member l‘ltl- by the conductor
be suitably designed to provide a thermal “image” of the
strap 152, which is secured to the magnetic member 110
electrical apparatus which is disposed inside the casing 60 by suitable means, such as brazing or welding. lt is to
Stltl.
be noted that the »base member Si? is secured to the bracket
The base member Sil comprises a cover member 32 and
member 170, as best shown in FIG. 2, by any suitable
conductor leads 536 to an associated electrical apparatus
inside the casting Still, a magnetic lield willbe set up ad
a lower portion 34.
The cover member 32 includes a
groove or narrow recess which extends around the pe
riphery on the underside of said cover member. The
lower portion 34 of the base member 36 includes a pro
jecting portion 184 which substantially lilis the groove
means such as the -bolts §64 and the associated nuts 368
and the lock washers 166. ln order to provide a seal
where the bolts ldd pass through the openings in the base
member 39, the gaskets or O-ring packing members 156
may be provided around said bolts.
186 of the cover member 32 when said cover member and
In order to sense the temperature or thermal condition
of the magnetic member lili), which is a function of the
said lower portion are assembled. The groove ‘13a may
be at least partially ñlled or coated with a suitable thermo 70 temperature of the associated electrical apparatus as previ
ously mentioned, a thermally responsive device or means,
setting resin, such as an epoxy resin, prior to the assembly
more specifically a helical bimetallic element 120, which
of the cover member 32 with the lower portion 3d» in
may be of any conventional type, is disposed in the re
order to secure said cover member to said lower portion
ceptacle 32S. In orderrto improve the response of the
and to seal the joint between said parts of the base mem
bimetal ‘rZtl to the temperature or thermal condition of
ber 36. T he cover member 32 is also provided with two
aoc/7,7715
5
6
the magnetic member llt?, the axes of the receptacle L25
and the bimetallic element F.2d lie in substantially the
In particular, a Contact arm Gti having a moving con
tact el mounted or disposed thereon is connected or at
same plane as the magnetic member il. l and said bimetal
tached to the rotatable shaft F.3d, as best shown in FIGS.
l and 2. The contact arm d@ is preferably formed from
an electrically conducting material for reasons which will
be explained hereinafter. The contact arm di?, as shown
in i‘llG. l, is arranged to rotate as the rotatable shaft
rotates in response to changes in the temperatures of the
magnetic member liti, as sensed by the helical bimetallic
element llZti, which actuates said rotatable shaft. A sta
tionary contact d2 is disposed in the path of the contact
is preferably surrounded by said magnetic member. ln
order to provide a smooth surface for the receptacle 125
in which the bimctal lill may rotate as it detorms in re~
spouse to or is actuated by the temperature of the mag
netic member illu, a sleeve or tube member lili is dis
posed insid-e the receptacle llZÈi as best shown in FÍGS.
2 and 3. The tube member lî?l is preferably formed
from a material having a high degree of thermal con
ductivity and preferably one of a non-corrosive type,
such as copper or brass. ln order to adjust the response
of the bimetallic element l2@ to the temperature or ther
mal condition of the magnetic member il@ or to corn
pensate for different environmental ambient temperatures,
a bimetal adjusting knob ldd is secured to one end oi the
bimetallic element l2@ by any `suitable means, such as
bonding with an epoxy resin. In order to prevent axial
movement or” the birnetal adjusting knob ist@ while still
arm titl as it rotates in a clockwise direction, the stationary
contact 62 being preferably formed from a material which
has permanent magnetic properties. The stationary con~
tact 62 is secured to a bracket member 5?. by suitable
means, such as the rivet '64. The bracket member 52 is
secured in turn to the indicating case Ztl by the rivets 54
which also assist in securing the indicating case 2d to the
base member 3d', as best shown in FlGS. 2 and 4.
disposed a retaining ring 172 at the point Where said
The indicating lamp titl which is preferably of the neon
glow type, is supported by a bracket member 5S which is
secured to the indicating case 2d by the rivet 56 and by
the supporting member de which may be formed integrally
knob passes into the inside of the base member 39. A
with the indicating case Ztl as a projecting part on the in
permitting said knob to be rotated, said knob is pro
vided with a circular groove or recess lai in which is
spring type lock washer le@ is disposed around the ad 25 side ot’ said indicating case, as best shown in FlGS. l
justing knob lid-tl to assist in preventing axial movement
and 4. ln order to increase the visibility oi’ the indicating
of said knob and is disposed where said knob passes
lamp dil when energized and viewed from the ground or
throngl the bracket member
in order to provide a
any distant location, a reilecting member 85 which may
seal Where the adiustiug knob
passes through the base
be of the polished metal type, is disposed between the
member 3ft, a suita le gasket or G-ring packing member 30 lamp dll and the supporting member Sd, said supporting
läd is provided or disposed around said knob at the point
member having a suitable curved recess in which said re
where the adjusting knob le@ leaves the outside of the
fleeting member may be attached or otherwise secured.
base member Fill. ln order `to complete an electrical cir
cuit which will be described hereinafter, a leaf spring
type contact may be electrically connected to the helical
bimetallic element l2@ at the point where said bimetal
is secured to the adjusting knob idf-5 and arranged to ro
tate with said knob in contact with the inside surface of
the tube member 124i. The latter arrangement is based
on providing an adjusting knob l/iil» formed from elec
trically insulating material. lAlternatively, the adjusting
knob liâitì may be formed `lrom an electri ily conduct~
ing material in electrical contact with the bnnetallic ele~
ment lit@ and the leal spring Contact llfzfl omitted.
ln order to indicate tie temperature or thermal condi
tion ci the magnetic member llt?, a rotatable shaft 13%
is secured or attached to tre helical bimetal i2@ by suit~
able means, such as soldering or brazing. As the electrical
current which flows in the lead conductors 5Std changes,
the magnetic linx around said leads changes and the tem
perature of the magnetic member il@ changes.
helical bimetallic element l2@ responds to, or
rîhe
actuated
by changes in the temperature ot the magnetic member
to cause the rotatable shaft i3d to turn in one direc
tion or the other depending upon the change in the te ir
erature of the magnetic member lili.
in order to provide a visual indication of the tempera
ture or thermal condition of the magnetic member il@
when the temperature or thermal condition of the mag
netic member liti and the increasing temperature or
thermal load condition of the associated electrical ap
paratus inside the casing ddd exceeds a predetermined
value, contact means are coupled or disposed to be re
sponsive to the temperature or thermal condition of the
magnetic member Zilli as sensed by the helical bi .ietaliic
element 12th in general, when the temperature of the
magnetic member il@ and the corresponding temperature
it should be noted also that the rivet 56 which secures the
bracket member dil to the indicating case Ztl and assists
in securing said indicating case to the base member 3@ is
electrically connected to the second terminal M2 by the
conductor left, as best shown in FiG. 4.
ln order to complete the electric circuit which energizes the lamp dit, one terminal of the lamp 8i? is con
ne<l ted to a current limiting resistor ed through a con-
doctor 'l2 and the other terminal of the lamp d@ is con
nected through a conductor 82 to the bracket member 5S
which is preferably formed from electrically conducting
material. The other side of the current limiting resistor
de is connected through the conductor dit to the bracket
member 52 which is also preferably formed from elec
trically conducting material. The current limiting resistor
tid may be supported inside the indicating case Ztl by any
suitable means such as the supporting member 7d, which
in turn is secured to the indicating case 2d. In order
to clamp the conductors 82 and ed to the bracket mem
bers S3 and 52 respectively and to insure a good electrical
connection between said conductors and said bracket mem
bers, a generally tJ-shaped clamping member 65, which
is preferably formed from an electrically insulating mate
rial, is disposed to hold the conductors 82 and 63 in posi
tion. The clamping member dS is secured in turn by
suitable means such as the screw or rivet '76 which en
gages a projecting supporting member 67 which is prefer
ably formed integrally with the indicating case Ztl. It is
to be noted that the material from which the indicating
case 2@ is termed must be electrically insulating as well
as weatherproof for a purpose which will be discussed
hereinafter.
ln order to protect the parts of the indicator lill, which
are disposed inside the indicating case 2t?, a suitable
window made from a transparent material, such as glass
or thermal load condition of the associated electrical ap
or a suitable plastic material, is secured to the front end of
paratus exceeds a predetermined value, the contact means,
which is disposed in the indicating case or housing Ztl 70 the indicating case Ztl by a metallic bezel ring 94 which
clamps the window @2; to the flanged portion 96 of the
and which cooperates or is actuated by the helical bimetal
lic element Mtl, is arranged to energize or change the
indicating case Ztl. ln order to seal the indicating case
energization of an indicating device or means, more spe
2d, a gasket 9S is disposed between the window 92 and
cifically, the signalling lamp or light Sil which is also dis
the ílanged portion @d of the indicating case 2d. In order
posed inside the indicating case Ztl.
to seal the joint between the base member Si) and the
amarre
¿i
7
ciated electrical apparatus has exceeded a predetermined
value, is maintained by the stationary contact d2 which
indicating case 2d, which are secured to each other by the
rivets
and d6, a suitable gasket or O-ring packing
member l'ïd is disposed in a suitable recess in said base
member at the point where the indicating case Zh* and the
base member
are in contact with each other.
lit is to be noted that the stationary contact
which
is preferably formed as a permanent magnet operates to
latch or hold the moving contact
which is disposed on
and rotates with the contact arm di? in the closed posi
tion, after the temperature of the magnetic member il@
and the corresponding temperature of the associated ele -
trical apparatus has exceeded a predetermined value. In
order to provide means for resetting the contact arm d@
after it has reached the position shown in PEG. l and is
being held in the position shown in FlG. _l by the perma
nent magnet from which the stationary contact
is
formed, a resetting member
is disposed adjacent to the
contact arm
when it is in the closed position. rThe re
setting member ¿l2 includes a projecting part d3 which
passes through and extends below the indicating case
2d, as shown
FlG. l.
setting member
in order to maintain the re
in the position shown in FIG. l, a
biasing spring '73 is disposed between said resetting menber and the bracket member 52. The biasing spring 78
may be positioned by the projecting part @d on the bracket
member 52 and the projecting part ‘t6 on the resetting
functions as a latching or holding means to keep the
5
contacts di and
in the closed position, as shown in
FÍG. l and as previously discussed.
lt is to be understood that the terminals E132 and 142
of the thermal indicator lo may be conveniently connected
to the associated electrical apparatus to provide a source
of electrical current or power to energize the lamp 86.
For esa- ple, it the associated electrical apparatus inside
the casing or tank Süd, shown in FIG. 9, is a transformer,
the terminal i3?. could be conveniently connected to a
ground terminal on the casing 56d and the terminal 142
could be conveniently connected to the terminal connec
tor 522 on the low voltage or secondary bushing 52d, as
shown in FIG. 9. Since certain types of electrical appa
ratus are subject to surge voltages, the gap protector or
arc shield Teti, shown in FÍGS. l and 2, would operate to
limit the voltage applied to the thermal indicator ld to a
safe value in order to prevent damage to said indicator.
in other words, the electrodes §54 and 148 of the gap
protector le@ are arranged to break down at substantially
a predetermined value and limit the voltage applied to
the thermal indicator it! Whenever a predetermined surge
voltage is present between the terminals l32 and M2.
Referring now to FlGS. 5 through 7, there is illus
The resetting member 4Z also includes a
trated a thermal load indicator 2% which is similar to
projecting arm 44» which moves up to lift the Contact arm
the thermal indicator lil, except that the thermal indicator
’26S also includes means for indicating ’che thermal load
condition of the associated electrical apparatus at any
given time, as well as indicating when said apparatus is
member 42.
6i) oit the stationary Contact 62 when the projecting part
d3 of the resetting member d2 is pushed upward against
the biasing spring 7d. When pressure is removed from
the projecting part ¿i3 of the resetting member 42, said
resetting member is returned to the position shown in
FIG. 1 by the biasing spring 78. In order to seal the
opening in the indicating case 2d where the resetting
member 42 passes through said indicating case, a suitable
being or has been subjected to a thermal load in excess of
a predetermined value. ‘ln addition, the thermal indicator
Ziltl, as illustrated, includes means for indicating the maxi
mum thermal load of the associated electrical apparatus
between successive readings of said indicator.
is disposed adjacent
In particular, the thermal indicator 200 comprises a
to the inside of said indicating case where the resetting
member d?. passes through said indicating case.
base member 3G’ which is identical to the base member 30
gasket or O-ring packing member
The over-all operation of the thermal indicator lil will
now be considered. Referring to FlGS. l, 3 and 9, when
current flows in one or more or" the conductor leads 53€?
to and from the electrical apparatus inside the casing
509 to thereby cause said apparatus to heat up, the tem
perature of the magnetic member il@ will vary with the
temperature or thermal load condition of the associated
electrical apparatus inside the casing Stili. The helical
bimetallic element lid is then actuated by the change in
the temperature ot the magnetic member ll@ to thereby
cause the rotatable shaft i3d which in turn causes a
corresponding rotation of the contact arm ed, as shown
in FlG. l. As the temperature oí the magnetic member
il@ and the corresponding temperature of the associ
ated electrical apparatus increases, the contact arm 6@
will rotate in a clockwise direction until the moving con
tact el disposed thereon comes into Contact with or into
a closed position with the stationary contact 62. Assum
ing that the terminals 132 and Irl-@12 are connected to a
source of electrical power or current, the lamp d@ will
be energized when the contacts 6l and 63 are in a closed
position, as shown in FIG. l. The electrical circuit which
energizes the lamp {it} may be traced starting from termi
nal .1132, then through the rivet 134
the internal con
ductor strap i3d to the magnetic member lid, the to
the tube member
through the leaf spring contact lili
to the helical bimetallic element lfàiì, then through the
rotatable shaft i3@ to the contact arm ab, through the
moving contact di to tue stationary contact 62, then
of the thermal indicator 1d, except with respect to several
minor details which will be discussed hereinafter, and an
indicating case 22% which is similar to the indicating case
2d of the thermal indicator lli?, except for the type of indi
cating means which is disposed inside the indicating case
22d. The parts of the base member 30’ which are identi
cal to the equivalent parts of the base member 3h bear
the same reference numerals.
The indicating case E20 is secured to the base member
3d’ by the rivets 273 and 277 and is preferably formed
from the same type of material as previously described
for the indicating case Ztl of the thermal indicator It).
For reasons which will be discussed hereinafter, the rivet
2273 is electrically connected to the magnetic member
il@ by the conductor 275 and the rivet 277 is electrical
ly connected to the second terminal 142 through one of
the rivets ldd» and the conductor 279. The base member
3d', except as just noted, is otherwise identical to the
`base member Si? previously described for the thermal in
dicator ld. Similarly to the indicating case 2t), the i11
dicating case 22d includes a window 292 which is secured
to the hanged portion 29d of the indicating case 220 by
the bezel ring 294 and is sealed by the gasket 298.
ln order to provide a visual indication of the tempera
ture of tl e magnetic member lit), an indicating hand
pointer 2,96 is attached to the rotatable shaft 13d and dis
posed in front or" a dial member 24th, shown in FIGS. 5
and 6. The dial member Zdti is disposed inside the in
dicating case '22@ and may be supported by any suitable
means such as the supporting members 225 which may
be formed integrally with the indicating case 220 and
through the bracket member 52, through the conductor titi,
the current lim ing resistor 6d and the conductor 72 to 70 the screws 2M which pass through the dial member 246
and engage the supporting members 225'.
one terminal of the lamp Sil. The other terminal of the
Since the temperature of the magnetic member 1li?
lamp titl is connected to the terminal W” through the
varies with the temperature or thermal load condition
conductor 82, the bracket member 53, the rivet
and
of the associated electrical apparatus inside the casing
the conductor §82, as best shown in FiG. 4. The encr
bdd, .he dial member 25rd may be calibrated in terms of
gization of the lamp ist), after the thermal load of t' e asso
3,077,776
the ther-mal load of the associated apparatus, which may
include windings or coils. In particular, the dial mem
ber 2d@ may be calibrated to indicate the percentage of
the rated thermal load of the associated electrical ap
paratus. The deñection or location of the indicating Ol
may be of the spring type or brush type contact, engages
>the stationary contact 253, the lamp 280 is energized
'from the source of electric current which is connected be
tween the terminals 132 and M2 of the base member 30’.
The electrical circuit which energizes the lamp 2S@ may be
hand pointer 29d provides a visual indication of the
thermal load condition or temperature of the associated
traced from the terminal B2, through the .rivet 134, the
conductor strap 136, the magnetic member 11d, the tube
electrical apparatus. In order to indicate the maximum
member T24, the leaf spring contact 121, the bimetallic
thermal load of the associated electrical apparatus be
element 12d, the shaft 130, the indicating hand pointer
tween isuccessive readings, a maximum indicating hand 10 2M, the moving contact 278, the stationary Contact 253,
through the conductor 233 to the terminal 243v and
pointer is movably disposed about the axis of the rotata
supporting member 254 may lbe attached to the indicat
ing case 22d at the point where the shaft 130 passes
through said indicating case and the maximum indicating
hand pointer 27d` rotatably mounted or disposed on the
supporting member 254. The `supporting member 254
may also assist in supporting the shaft 13d as said shaft
through the conductor 245 to one terminal of the lamp
2&1?. The other terminal of the lamp 230 is connected
to the terminal 142 through the conductor 239, the cur~
rent limiting resistor 266, the conductor 26S, the rivet
277, the conductor 279 and through the rivet 144 to the
terminal 142. The indicating lamp 23d and the current
limiting resistor 266 may be suitably supported inside the
Vpasses into the indicating case 220 as indicated at 259.
indicating casing 22d by the supporting members 28d and
Since the maximum indicating hand pointer 279 is dis
posed between the indicating hand pointer 290 and the
dial member 24d, the maximum ‘hand pointer 276 may be
257, respectively, which are in turn secured to said in
dicating case. It is important to note that the electrical
circuit just described for energizing the lamp 23d is com~
ble shaft 13G in any suitable manner.
As illustrated, a
pleted .by the moving cont-act 278 yon the indicating hand
pointer 29@ only when the indicating hand pointer in
arranged to lbe driven or rotated by the indicating hand
pointer 29d to the highest or maximum point of travel 25 dicates a thermal load in excess of a predetermined value.
When the indicating hand pointer 2% rotates to a lower
or deiiection of the hand pointer 294) during the opera
thermal load position below said predetermined value,
tion of the indicator 20d. Suitable means may also be
the above circuit is interrupted since the moving contact
provided for retaining the maximum indicating hand
278 no longer engages the stationary contact 253 and
pointer in the highest point or position to which it is
the above circuit is interrupted to deenergize the indicat
driven by the hand pointer, such as the spring 213 which
provided with a projection or cam member 272 which is
still permits the maximum indicating hand pointer 27@
to be driven or rotated by the hand pointer 2%. Since
the indicating hand pointer 2%- is arranged to drive the
maximum indicating hand pointer 270 only in the up
ward or clockwise direction, the maximum indicating
hand pointer 27d remains at the maximum point of travel
or dei'iection of the indicating hand pointer 2% when
ing lamp 2de. in other words, when the conductor 24S
connects one terminal of the lamp 28d` to the terminal
243 the indicating lamp is operated in essentially an “on
oíî” manner.
Alternatively, the indicator 2% may «be connected to
have the indicating lamp 23@ controlled by the operation
of the maximum hand pointer 27d. This may be accom
ever the bimetallic element i2@ cools and causes the in
plished yby connecting one terminal of the indicating lamp
dica'ting hand pointer 29d to rotate in a counterciockwise
direction to a lower thermal load reading.
In order to provide a visual indication when the
thermal load of the associated electrical apparatus is
presently exceeding or has exceeded a predetermined
23d by the conductor 2-/i7 to the terminal 241, which
in turn is connected to the stationary contact 252.
The
iight or «lamp 22d which i-s preferably of the neon glow
type. Ey suitable selection of the connections of the in
dica-usar 2id?, the indicating lamp 2S@ lmay be energized
wherever the thermal load ot the associate-d electrical
apparatus is presently in excess of a predetermined value
by the operation of contacts associated with the indicat
stationary contact 252 is similar to the stationary contact
253 and is mounted on the back of the hanged portion 255
of the supporting member 254:, as shown in FIGS. 6 and
7. A moving contact 26S is disposed or mounted on the
maximum hand pointer 270 and rotates with said maxi
mum hand pointer. The moving Contact 26S may also be
formed integraily with the maximum hand pointer 270
and ‘may be of the spring type or brush type to Slidably
engage the stationary contact 252 whenever the position of
the maximum hand pointer 27dy is above a predetermined
thermal load reading on the dial member 246. The posi
tion at which the moving contact 26S slidably engages
ing hand pointer
the stationary contact 252 may be the same or at a diiier
value, Contact means are provided in the indicating case
for energizing or changing the energization of an in
dicating device or means, more speciíically an indicating
Alternatively, the indicating lamp
ent position as for the indicating hand pointer 29d.
Whenever the indicating hand pointer 2%" drives the
maximum hand pointer 27€) above a predetermined posi
tion or when the corresponding thermal load of the
associated electrical apparatus exceeds a predetermined
since the resetting of the maximum hand pointer 27d
value, the contacts associated with the maximum hand
virile the associated electrical apparatus has been in
operation.
`
60 pointer 27d slidably engage to close an electrical circuit
which cnergizes the indicating lamp from the source or"
in particular, a moving contact 27S is disposed or
electrical current connected between the terminals 132
mounted on the indicating hand pointer 29d and rotates
and M2. The electrical circuit which energizes the
with said indicating hand pointer. A stationary contact
indicating lamp 23@ in the latter case may be traced
255, which is generally C-shaped as shown in HG. 5, is
mounted on the hanged portion 255 of the supporting « from the terminal 232, through the rivet i3d, the con
ductor strap 136, the magnetic member 110, the conduc
member
The moving contact 278 on the indicating
tor 275, the rivet 273, the conductor 262 which elec
hand pointer 2% is arranged to slidably engage the sta
trically connectsthe rivet 273 and the spring 2id, the
tionary contact 253 when the thermal load of the associ~
spring 218, the maximum indicating hand pointer 270,
ated electrical apparatus exceeds a predetermined value
the moving contact 26S, the stationary Contact 252, the
such as the thermal load indicated by the numeral 2 on
conductor 23ì, the terminal 241 and the conductor 247
the dial member 24d which may correspond to or indi
to one terminal of the lamp 280. The other terminal of
‘ cate 209% of the rated thermal load of the associated
may be energized and maintained in an energized
condition to indicate that the thermal load of associated
electrical apparatus 'has exceeded a predetermined value
‘between successive readings or during a particular period
the lamp 28th is completed through the electrical circuit,
ypreviously described, to the terminal 142 to thereby
’ integrally from the indicating hand pointer 2% and which 75 energize the lamp 284).> The' contacts 268 and 252
electrical apparatus.
` When the moving contact 278, which may be formed
3,077,776
ll
which are closed by the movement or rotation of lthe
The changes in the electrical current through the conduc
maximum indicating hand pointer 270, therefore, en
ergize the indicating lamp 28@ when the thermal load
tor leads 536) also causes a corresponding change in the
«temperature of the magnetic member 1l() which is a
function of and varies with the temperature of the asso
of the associated electrical apparatus exceeds a predeter
mined value and said maximum hand pointer is driven by
the indicating hand pointer 29@ to ya position which closes
said contacts. Since the contacts 268 and 252 associated
with the indicating hand pointer then remain closed inde
pendently of the position of the indicating hand pointer
ciated electrical apparatus inside the casing 500.
A
change in the temperature or thermal condition of the
magnetic member 1l@ causes the helical bimetallic ele
ment l2@ to be actuated in response to said changes in
temperature which in turn causes a turning movement
when the associated electrical apparatus cools down and 10 of the rotating shaft 130. The rotation of the shaft 130
causes a change in the deflection of the indicating hand
the indicating hand pointer 290 rotates in a counter
pointer 290 which causes -a change in the thermal load
clockwise direction, said contacts provide a holding cir
reading on the calibrated dial member 240 of the indica
cuit yfor maintaining the energization of the indication
tor 260. The maximum travel or dellection of the indi
lamp 280, similarly lto the stationary contact 62 of the
cating hand pointer 299 between successive readings is
thermal indicator 10 which was preferably formed as
indicated visually by the position of the maximum
a permanent magnet. It is thereby noted that for
indicating hand pointer 279, as previously discussed. It
proper operation of the electrical circuits just described
is to be understood that the dial member 24u may also
for energizing the lamp 280, the supporting member 254
be calibrated in terms of various other conductors asso
on which the stationary contacts 252 and 253» are
mounted and the dial member 240 must be formed from 20 ciated with an electrical apparatus which varies with
the electrical current ñowing to and from said apparatus.
an electrically insulating material.
In summary, the mode of operation of the indicator
200 with respect to the energization of the lamp 280 is
determined by connecting one terminal of the lamp 280
lFinally, as previously discussed, the indicating lamp 289
provides an indication of Whether the thermal load of
an associated electrical apparatus is presently exceeding
to either the terminal 241 or to the terminal 243 by 25 a predetermined value or alternatively has exceeded said
predetermined Value since the maximum hand pointer 290
either the conductor 247 or the conductor 245, respec
was previously reset to a position which corresponds to
tively. The selection of the latter connection determines
a value below said predetermined value. It is to be
whether the energization of the indicating lamp 280 is
understood that in a particular application, only one of
control-led by the contacts associated with the indicating
hand pointer 290 or by the contacts associated with the 30 the latter modes of operation may Ibe provided in a
thermal indicator similar to the thermal indicator 200.
maximum hand pointer 270, «as just discussed. When the
tis to be understood that the magnetic member lill may
energization of the lamp 280 is controlled by the move
be provided in different sizes and shapes in different appli
ment of the indicating hand pointer 290, said indicating
cations, but Vit is essential that the magnetic member 110
lamp is only energized when the indicating hand pointer
be disposed in the magnetic field of the leads in which
290 is at a position which indicates that the thermal load
electrical current ñows to and from associated electrical
of the `associated electrical apparatus is presently in
apparatus whose thermal condition depends on the
excess of a predetermined value. When the associated
apparatus cools and the thermal load decreases below
amount of electrical current ñow in said apparatus.
said predetermined value, the indicating lamp 280 is
then deenergized by the counterclockwise rotation of the
form of the magnetic member 110 which is particularly
Referring to FIG. 8, there is illustrated an alternative
indicating hand pointer 290. On the other hand, if the
adapted for installation around the leads of an associated
energization of the indicating lamp 280 is controlled by
electrical apparatus without disturbing said leads since
the rotation of the maximum hand pointer 270 which is
said leads are not required to pass through holes in the
magnetic member 410, shown in FIG. 8. In particular,
the magnetic member 410 is similar to the magnetic
member 110 since it is formed from two plates 41.4
each having a curved portion near the middle of the said
.plates to form a cavity 425 in which a thermally re
sponsive device such as a helical bimetallic element may
be disposed. Each of the plates 414 which comprises the
magnetic member 410 includes a generally U-shaped
recess, as indicated at 422, which permits the mounting
of the magnetic member 410 around the leads of an
associated electrical apparatus such as the leads 530,
driven bythe hand pointer 290, the indicating lamp 280
is energized when the maximum hand pointer 270 is
driven by the hand pointer 290 to a position which in
dicates that the thermal load of the associated electrical
apparatus has exceeded a predetermined value and the
llamp then remains energized independently of the position
of the indicating hand pointer 290 until the maximum
hand pointer 29() is reset by suitable means (not shown),
such as an external magnetic device.
It is to be under
stood that the alternative connections of the indicating
lamp 280 to the contacts associated with either the indi
cating hand pointer 290 or the maximum hand pointer 270
may be accomplished by a suitable selector switch rather
than by the changes in -the connections of one of the
shown in FlG. 9, without disturbing said leads.
It is
to ybe _understood that in an indicator which includes the
magnetic member 41% rather than the magnetic member
lit) that the base member surrounding the magnetic
Vterminals of said lamp to one of the terminals 241 or 243.
member 410 would have to Ibe suitably modified to also
it is to -be noted that the contacts associated with the
hand pointers 290 and 270 are each equivalent to a 60 include recesses which would correspond to the recesses
rotary switch whose position is controlled by the move
ment or' said hand pointers, and it is to be understood
that conventional rotary switches could be substituted for
the contact means associated with either of the indicator
hands 270 and 290. It is to be noted that the mounting
of the indicator 200 on the associated electrical appara
tus could be provided similarly to that of the indicator
1t), as shown in FlG. 9, with the indicator 200 substituted
for the indicator 10.
Considering the over-all operation of the thermal load
or temperature indicator Zitti, the temperatur-e or thermal
load condition of the associated electrical apparatus in
side the casing dit@ changes whenever the electrical cur
422 >included in the magnetic member 410.
Although it is preferred to have the magnetic member,
such as the magnetic member 110, included in an indica
tor of the type disclosed, substantially surrounded by
thermally insulating materials as described for the indi
cators llt) and Zitti, it may be desirable in certain appli
cations to provide thermally conductive material ad
jacent to a portion of said magnetic member to function
as a heat sink in order to have the magnetic member more
closely simulate the thermal operating characteristics or
qualities of an associated electrical apparatus. lt is also
desirable that the magnetic member 110 and the ther
mally insulating material employed to control the heat
transfer from said member .be designed so that the ther
rent flowing through the conductor ,leads 530 changes. 75 mal time constant of said member more closely ap
3,077,776
13
proaches the thermal time constant of the associated
electrical apparatus.
It is also to be understood that other types of signalling
devices, such as audible alarms may be substituted for
the signal lamps S0 and 236 in the indicators 16 and
Zitti, respectively.
The apparatus embodying the teachings of this inven
tion has several advantages. For example, the thermal
load indicator or temperature indicator, as disclosed, may
be readily mounted or installed on existing electrical
apparatus of the enclosed type without the necessity for
opening the casing of said apparatus. In addition, the
thermal image of an electrical apparatus made availble
outside the casing of said apparatus is eiîectively em
ployed in a thermal indicator which either may indicate
whether the associated apparatus is presently exceeding
3. A thermal load indicato-r for a transformer having
an electrical coil in >a casing which heats up when carry
ing electric current and leads connected to said coil for
supplying electric current thereto, the current ilow through
said leads setting up a magnetic field around said leads,
comprising a magnetic member disposed outside said
casing in said iield to heat up when current iiows in
said leads, said magnetic member comprising two as
sembled plates shaped to provide a receptacle therebe
tween and provided with one or more openings through
which one or more leads may pass, the temperature
of said member varying with that of said coil, a helical
bimetallic element disposed in the receptacle of said
mem-ber for detorming in response to the temperature
of said member, a rotatable shaft connected to said bi
metallic element Contact means coupled through said shaft
or has exceeded a predetermined value of thermal load
to said bimetallic element to be actuated when the thermal
and may also indicate the present thermal load of the
associated apparatus in terms of a percentage of the rated
load of said transformer exceeds a predetermined value,
and a signal light responsive to the actuation of said
thermal load of said apparatus.
Since numerous changes maybe made in the above
described apparatus and different embodiments of the in
vention may be made without departing from the spirit
magnetic member, said bimetallic element and said shaft
connected in series circuit relation for indicating when
and scope thereof, it is intended that all the matter
contained in the foregoing description or shown in the
accompanying drawing, shall be interpreted as illustrative
and not in a limiting sense.k
i
contact means through a circuit which includes said
the thermal load of said transformer exceeds said pre
determined value.
4. A thermal load indicator for a transformer having
an electrical winding in a casing which heats up when
carrying electric current and leads connected to said wind
ing for carrying current to and from said Winding, the
iiow of current causing a magnetic -held around said leads,
including an electrical winding inside a casing which is 30 comprising a magnetic member disposed outside said
casing in the tield oí at least one of said leads, the tem
subject to heating when conducting electrical current and
à erature of said member varying with that of said wind
leads connected to said winding for conducting current
ing, a bimetallic element disposed adjacent to said mem
to and from said winding, the current flow through said
ber for deforming in response to the temperature of said
leads setting up a magnetic field around said leads, com
prising a magnetic member disposed in said ñeld outside 35 member, a rotatable shaft connected to said bimetallic
element, a contact arm having a moving contact dis
said casing which causes said member to heat up when
posed thereon, said arm being disposed on said shaft,
current flows in said leads, said magnetic member includ
a stationary contact disposed in the path of said contact
ing one or more conductor passages through which said
I claim as my invention:
l. A thermal load indicator for electrical apparatus
leads may pass, a bimetallic element disposed adjacent to
arm, said contacts being arranged to close when the
said member for deforming in response to the tempera 40 thermal load of said transformer exceeds a predetermined
value, and signalling means connected in series c"cuit
ture of said member, a base member for enclosing said
relation with said bimetallic element, said shaft, said con
magnetic member, said base member being formed from
tacts and said magnetic member to be energized there
a thermally insulating material and including a cover
through when said thermal load exceeds said predeter
tending portions around each of said openings which pass 45 mined value.
member having one or more openings and having ex
through the conductor passages of said magnetic mem
ber, and indicating means associated with said bimetallic
element -for indicating when the thermal load of said
apparatus exceeds a predetermined value as said bimetal
deforma.
2. A thermal load indicator for a transformer having
an electrical coil disposed in a casing which heats up
when carrying electric current and leads connected to
saidcoil for supplying electric current thereto, the cur
rent flow through said leads setting up a magnetic iield
around said leads, comprising a magnetic member dis
posed outside said casing in said ñeld to heat up when
current flows in said'leads, said magnetic member com
5. A thermal load indicator for a transformer having
an electrical winding in a casing which heats up when
carrying electric current and leads connected to said wind
ing for carrying current to and from said winding, the
iiow of current causing a magnetic iield around said
leads, comprising a magnetic member disposed outside
said casing in the field of at least one of said leads,
the temperature of said member varying with that of
said winding, a bimetallic element disposed adjacent to
said member for deforming in response to the tempera
ture or" said member, a rotatable shaft connected to said
bimetallic element, a contact arm having a moving con
tact disposed thereon, said arm being disposed on said
shaft', a stationary contact disposed in the path of said
assembled in substantial registry to form a receptacle 60 contact arm, said contacts being arranged to close when
the thermal load of said transformer exceeds a predeter
therebetween, the temperature of said member varying
mined value, signalling means connected in circuit re
with that of said coil, a helical bimetallic element dis
lation with said contacts to be energized when said
posed in the receptacle of said member for deforming
thermal load exceeds said predetermined value, the ener
in response to the temperature of said member, contact
gizing circuit of said signalling means including said mag
means coupled to said bimetallic element to be actuated
netic member, said bimetaliic element and said shaft
when the thermal load of said transformer exceeds a
connected in series circuit relation and holding means for
predetermined value, a base member for enclosing said
maintaining said contacts in the closed position after said
magnetic member, said base member being formed from
prising two plates each having tirst and second apertures
thermal load exceeds said predetermined value independ
a thermally insulating material and including a cover
member having one or more openings and having ex 70 ently of the position of said contact arm,
tending portions around each of said openings which
pass through the apertures of said magnetic member, and
indicating means responsive to the actuation of said con
tact means for indicating when the thermal load of said
transformer exceeds said predetermined value.
6. A thermal load indicator for mounting outside the
casing of a transformer having an electrical winding
which heats up when carrying electric current and leads
connected to said winding for carrying current to and
from said winding, the flow of current causing a magnetic
3,077,776
id
field around said leads, comprising a magnetic member
disposed outside said casing in the field of at least one
of> said leads, said magnetic member comprising two assembled plates having one or more apertures through
which one or more leads may pass, the temperature of
said member varying with that or" said winding, a helical
relation and for maintaining the energization of said sig
nalling means after said thermal load exceeds said prede
termined value, independently of the subsequent thermal
load of said transformer, said holding means comprising
a permanent magnet disposed adjacent to said stationary
Contact.
bimetallic element disposed adjacent to said member for
deforrning in response to the temperature of said member,
9. A thermal load indicator for a transformer having
an electrical winding in a casing subject to heating when
a casing of thermally insulating material for enclosing
carrying electric current and leads for carrying current
to and from said winding, the iiow of current through
said leads creating a magnetic field around said leads,
said member and said bimetallic element to control the
heat transfer from said member, the latter casing includ
ing a cover member having one or more openings and
extending portions around said openings which pass
through each of said apertures of said magnetic member,
a rotatable shaft connected to said bimetal, a contact
arm having a moving Contact disposed thereon, said arm
4being disposed on said shaft, a stationary Contact dis
posed in the path of said contact arm, said contacts being
arranged to close when the thermal load of said trans~
comprising a magnetic member disposed outside said cas~
ing in the field of said leads to heat up when current
fiows in at least one of said leads, the temperature of
said member varying with that of said winding, a helical
bimetallic element disposed adjacent to said member to
deform in response to the temperature of said member,
a rotatable shaft connected to said bimetailic element in
dicating means actuated by said bimetallic element through
former exceeds a predetermined value, and signalling 20 said shaft for indicating the thermal load of said trans
former, and a signalling means Venergized by said indi
means connected in circuit relation with said contacts to
cating means through a circuit which includes said- mag
be energized when said thermal load exceeds said pre
netic member, said bimetallic element and said shaft
determined value independently of the position of said
electrically connected in series circuit relation when the
Contact arm.
7. A thermal load indicator for a transformer having
an electrical winding in a casing which heats up when
carrying electric current and leads connected to said wind
thermal load of said transformer exceeds a predetermined
value.
l0. A thermal load indicator for mounting outside the
casing of a transformer having an electrical winding sub
ing for carrying current to and from said winding, the
ject to heating when carrying electric current and leads
liow of current causing a magnetic field around said
leads, comprising a magnetic member disposed outside 30 for carrying current to and from said winding, the fiow
of current through said leads creating a magnetic field
said casing in the field of at least one of said leads,
around said leads, comprising a magnetic member dis
said magnetic> member comprising two plates assembled
posed outside said casing in the field of said leads to heat
to provide a receptacle therebetween, the temperature
up when current flows in at least one of said leads, said
of said member varying with that of said winding, a heli
magnetic members including one or more conductor
cal bimetallic element disposed in the receptacle of said
passages through which said leads pass the temperature
member for deforming in response to the temperature of
of said member varying with that of said winding, a heli~
said member, a rotatable shaft connected to said
cal bimetallic element disposed adjacent to said mem
ber to deform in response to the temperature of said mem
tact disposed thereon, said contact arm being disposed
on said shaft, a stationary contact disposed in the path 40 ber, indicating means for indicating the temperature of
said member, said indicating means comprising a rotatable
of said contact arm, said contacts being arranged to close
shaft connected to said bimetallic element, an indicating
when the thermal load of said transformer exceeds a
hand pointer attached to said shaft, and a dial member
predetermined value, signalling means connected in cir~
disposed back of said hand pointer, a base member for
cuit relation with said contacts to be energized when said
enclosing said magnetic member, said base member being
thermal load exceeds said predetermined value, the ener
formed from a thermally insulating material and includ~
gizing circuit of said signalling means including said mag
ing a cover member having one or more openings and
netic member, said bimetallic element and said shaft con
having extending portions around each of said openings
nected in series circuit relation and holding means for
which pass through the conductor passages of said mag
maintaining said contacts in closed relation and for main
taining the energization of said signalling means after said . netic member, and signalling means actuated by said in
dicating means when the thermal load of said transformer
thermal load exceeds said predetermined value independ
exceeds a predetermined value.
ently of the position of said contact arm.
11. A thermal load indicator for a transformer having
8. A thermal load indicator for mounting outside the
an electrical winding in a casing subject to heating when
casing of a transformer having an electrical winding
carrying electric current and leads for carrying current
which heats up when carrying electric current and leads
to and from said winding, the flow of vcurrent through
connected to said winding for carrying current to and
said leads creatinga magnetic field around said leads,
from said winding, the flow of current causing a magnetic
comprising a magnetic member disposed outside said cas
field around said leads, comprising a magnetic member
ing in the field of said leads to heat up when Current flows
disposed outside said casing in the field of at least one
in at least one of said leads, the temperature of said
of said leads, the temperature of said member varying
member varying with that of said winding, a helical bi'
with that of said winding, a helical bimetallic element
metsllic element disposed adjacent tov said member to de
disposed adjacent to said member for deforming in re
form in response to the temperature of said member, in
sponse to the temperature of said member, a rotatable
dicating means for indicating the temperature of said
shaft connected to said bimetallic element, a contact arm
member, said indicating means comprising a rotatable
having a moving contact disposed thereon, said arm being
shaft connected to said bimettallic element, an indicating
disposed on said shaft, a stationary contact disposed
hand pointer attached to said shaft, and a dial member
in the path of said contact arm, said contacts being ar
disposed back of said hand pointer, and signalling means
ranged to close when the thermal load of said trans
actuated by said indicating means when the thermal load
former exceeds a predetermined value, signalling means
connected in circuit relation with said contacts to be 70 of said transformer exceeds a predetermined value, said
signalling means comprising a moving contact disposed
energized when said thermal load exceeds said predeter
on said indicating hand pointer and a stationary contact
mined value, the energizing circuit of said signalling
disposed adjacent to said indicating hand to be slidabiy
means including said magnetic member, said bimetallic
engaged by said moving Contact when the thermal load
element and said shaft connected in series circuit relation
of said transformer exceeds a predetermined value, and
and holding means for maintaining said contacts in closed
bimetallic element, a contact arm having a moving con
3,077,776
17-‘
a signal light connected in series circuit relation with said
bimetallic element, said shaft, said contacts and said mag
netic member to be energized when said thermal load
exceeds said predetermined value.
l2. A thermal load indicator for mounting outside the
casing of a transformer having an electrical winding sub
temperature of said member varying with that of said
Winding, a helical bimetallic element disposed adjacent to
said member to deform in response to the temperature
of said member, indicating means for indicating the tem
ject to heating when carrying electric current and leads
perature of said member, said indicating means compris
posed outside said casing in the field of said leads to heat
up when current liows in at least one of said leads, the
for carrying current to and from said winding, the flow
ing a rotatable shaft connected to said bimetallic element,
of current through said leads creating a magnetic field
an indicating hand pointer attached to said shaft, and
around said leads, comprising a magnetic member dis 10 a dial member disposed back of Said hand pointer, and
posed outside said casing in the field of said leads to heat
a follower hand pointer disposed about said shaft to be
up when current ñows in at least one of said leads, said
driven by said indicating hand pointer to indicate the
magnetic member having two plates each having first
maximum indication of said indicating hand pointer, and
and second conducto-r passages through which said leads
signalling means actuated by said indicating means when
may pass, said plates being shaped and assembled in 15 the thermal load of said transformer exceeds a predeter
mined value, said signalling means comprising contact
substantial registry to form a receptacle therebetween,
the temperature of said member varying with that of said
means actuated by said follower hand pointer when said
winding, a helical bimetallic element disposed in the re
thermal load exceeds said predetermined value and a sig
ceptacle of said member to deform in response to the
nal lamp connected in series circuit relation with said
temperature of said member, indicating means for indi 20 magnetic member, said follower hand pointer and said
cating the temperature of said member, said indicating
contact means to be energized independently of the posi
means comprising a rotatable shaft connected to said
tion of said indicating hand pointer after said contact
bimetallic element, an indicating hand pointer attached to
means are actuated.
said shaft, and a dial member disposed back of said hand
l5. A thermal load indicator for a transformer hav
pointer, and a follower hand pointer disposed about said 25 ing an electrical winding in a casing subject to heating
shaft to be driven by said indicating hand pointer to in
when carrying electric current and leads for carrying
dicate the maximum indication of said indicating hand
current to and from said winding, the flow of current
pointer, a base member for enclosing said magnetic mem
through said leads creating a magnetic field around said
ber, said base member being formed from a thermally
leads, comprising a magnetic member disposed outside
insulating material and including a cover member having 30 said casing in the field of said leads to heat up when
one or more openings and having extending portions
current flows in at least one of said leads, said magnetic
around each of said openings which pass through the
member comprising two assembled plates having one
conductor passages of said magnetic member, and sig
or more openings through which one or more leads may
nalling means actuated by said indicating means when
pass, the temperature of said member varying with that
the thermal load of said transformer exceeds a predeter 35 of said winding, a helical bimetallic element dispose
mined value.
adjacent to said member to deform in response to the
13. A thermal load indicator for a transformer having
temperature of said member, a casing of thermally in
an electrical winding in a casing subject to heating when
sulating material for enclosing said member and said
carrying electric current and leads for carrying current
bimetal to control the heat transfer from said member
to and from said winding, the ñow of current through said 40 and match the thermal characteristics of said member
leads creating a magnetic field around said leads, Com
with those of said transformer, said latter casing including
prising a magnetic member disposed outside said casing
a cover member having one or more apertures and ex
in the field of said leads to heat up when current flows
tending portions around each of said apertures which
pass through said openings indicating means for indicat
in at least one of said leads, the temperature of Said
member varying with that of said winding, a helical bi
.ing the temperature of said member, said indicating means
metallic element disposed adjacent to said member to
comprising a rotatable shaft connected to said bimetallic
deform in response to the temperature of said member,
element, an indicating hand pointer attached to said
indicating means for indicating the temperature of said
shaft, and a dial member disposed back of said hand
member, said indicating means comprising a rotatable
pointer, and a follower hand pointer disposed about said
shaft connected to said bimetallic element, an indicating
shaft to be driven by said indicating hand pointer to in
hand pointer attached to said shaft, and a dial member
dicate the maximum indication of said indicating hand
disposed back of said hand pointer, and a follower hand
pointer, and signalling means actuated by said indicating
pointer disposed about said shaft to be driven by said
means when the thermal load of said transformer exceeds
indicating hand pointer to indicate the maximum indica
a predetermined value, said signalling means comprising
tion of said indicating hand pointer, and signalling means
contact means actuated by said follower hand pointer
actuated by said indicating means when the thermal load
when said thermal load exceeds said predetermined value
of said transformer exceeds a predetermined value, said
and a signal lamp connected in series circuit relation with
signalling means comprising a rotary switch having a mov
said follower hand pointer, said magnetic member and
ing contact disposed on said follower hand pointer and a
said contact means to be controlled independently of the
stationary contact disposed adjacent to said follower hand 60 position of said indicating hand pointer after said con
pointer to be slidably engaged by said moving contact
tact means are actuated.
when the thermal load o-f said transformer exceeds a pre
16. A thermal load indicator for a transformer having
determined value, and a signalling lamp connected in
an electrical winding subject to heating when carrying
series circuit relation with said follower hand pointer,
electric current and leads for carrying current to and
said magnetic members and said contacts to be energized
from said winding, the flow of current through said leads
when said contacts are engaged by the movement of said
creating a magnetic field around said leads, comprising
follower hand pointer, said lamp being then energized
a magnetic member disposed in the field of said leads
independently of the position of said indicating hand
pointer.
to heat up when current flows in at least one of said leads,
said magnetic member comprising two plates shaped and
14. A thermal load indicator for mounting outside the 70 assembled to form a receptacle therebetween, the tem
casing of a transformer having an electrical winding sub
perature of said member varying with that of said wind
ject to heating when carrying electric current and leads
ing, a helical bimetallic element disposed in the receptacle
for carrying current to and from said winding, the flow
of said member to deform in response to the temperature
of current through said leads creating a magnetic field
of said member, indicating means for indicating the tem
around said leads, comprising a magnetic member dis 75 perature of said member, said indicating means compris
3,077,776
1.9
20
ing a rotatable shaft connected to said bimetallic element,
an indicating hand pointer attached to said shaft, and a
nected to said bimetallic element thermal insulation dis
posed around said member and said bimetallic element to
control the heat transfer from said member so that the
thermal time constant of said member approaches that of
said transformer, indicating means actuated by said bi
metallic element through said shaft for indicating the ther~
dial member disposed back of said hand pointer, and
signalling means actuated by said indicating means when
the thermal load of said transformer exceeds a prede~
termined value, said signalling means comprising a rotary
switch actuated by the movement of said indicating hand,
mal load of said transformer, and a signalling means en
ergized by said indicating means through a series circuit
said switch hand having a moving contact `disposed on
said indicating hand pointer and a stationary contact dis
which includes said bimetallic element, said magnetic
posed adjacent to said indicating hand to be slidably en 10 member and said shaft when the thermal load of said
transformer exceeds a predetermined value.
gaged by said moving contact when the thermal load of
said transformer exceeds a predetermined value, and a
signal light connected in series circuit relation with said
contacts to be energized through said magnetic member,
said bimetallic element and said shaft When said ther- 15
mal load exceeds said predetermined value.
17. A thermal load indicator for mounting outside the
casing of a transformer having an electrical winding sub~
ject to heating when carrying electric current and leads
for carrying current to and from said winding, the ñow 20
of current through said leads creating a magnetic field
around said leads, comprising a magnetic member dis
posed outside said casing in the ñeld of said leads to heat
up when current ñows in at least rone of said leads, said
magnetic member comprising two assembled plates hav 25
ing one or more openings through which one or more
leads may pass, the temperature of said member varying
with that of said winding, a helical bimetallic element
disposed adjacent to said member to deform in respo-nse
to the temperature of said member, a rotatable shaft con
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Bristol ______________ __ Dec. 15,
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Baker ________________ __ July 31,
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