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Dec. 24, 1946.
M. c. HARROLD
2,412,981
moron PROTECTOR
'
\ FiledlAug. 27, 1942
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Patented Dec. 24, 1946
2,412,981 _
UNITED‘ STATES PATENT‘ orrica
2,412,981
MOTOR PROTECTOR
Marshall 0. Harroid, Dayton, Ohio, assignor to
General Motors Corporation, Dayton, Ohio, at
corporation of Delaware
Application August 27, 1942, Serial No. 456,324
25 ‘Claims. (Cl. 62—4)
This invention relates to motor protectors and
more particularly to motor protectors for motor
compressor units.
The proper protection of the windings of the
larger‘sealed motor-compressor units vof com
mercial size is a di?lcult problem. In the ?rst
place, the watts internal loss per square inch of '
radiating surface of the compressor becomes
greater as the motor ratings increase; second
ly, in sealed motor compressor units the wind
ing temperatures are greatly dependent upon the
superheat conditions of the refrigerant or vapor
These objects are attained by providing a mo
tor protector having an adjustment which is
automatically responsive to either the suction or
discharge pressure of the compressor, so that
the motor protector rating is raised in accord
ance with improved cooling conditions of the
motor. which are improved by the increase in
suction or discharge pressure. The control is
also provided with a thermally actuated reset
ting adjustment which is heated by an electric
heater coincidentally ‘with the energization of
the motor starting winding so that this adjust
ment is varied in substantially direct accordance
are also. dependent upon the particular refrig
erant or vapor being compressed; thirdly, the 15 with the number of successive attempts to start
the motor to increase the time between tripping
compressor may operate continuously at high
and
resetting so as to allow greater opportunity
back or suction pressures and tripping 01' the
for the motor to cool between attempts to start.
overload under such conditions, because of the
Further objects and advantages of the present
heavy loading, would be objectionable.
invention‘
will be apparent from the following de
It is an object of my invention to provide a 20
scription, reference being had to the accompany
motor protector which will allow the motor
ing drawing, wherein a preferred form of the
compressor unit to operate up to the highest safe
present
invention is clearly shown.
limit of motor winding temperature and yet ade
In the drawing:
being compressed and the winding temperatures
quately protect the motor windings by deener
gizing the motor when the highest safe tempera
ture is exceeded.
It is another object of my invention to provide
a motor protector whose rating or tripping set
Fig. 1 is a diagrammatic view of a motor pro
25 tector and refrigerating system embodying one
form of'my invention;
Fig. 2 is a diagrammatic view of a portion of
the motor protector and refrigerating system em
ting varies according to the cooling conditions
of the refrigerant passing through the sealed 30. bodying another form of my invention; and
Fig. 3 is a graph showing the increase in the
unit.
protector
rating with the increase in suction
It is another object of my invention to pro
vide a motor protector whose rating or tripping
setting varies according to the compressor load.
pressure.
Referring now to the drawing and more par
ticularly to Fig. 1, there is shown for the pur-.
It is another object of my invention to pro
vide a motor protector whose rating or tripping 35 pose of illustrating one speci?c application of my
invention, a refrigerating system including a
setting varies according to the suction or back
sealed unit 20 containing a compressor 22 and
pressure of the compressor.
an electric motor 24 having a running winding
It is still another ‘object of my invention to
26‘ and a starting winding 28. The sealed unit
provide a motor protector whose rating or trip
40 is of the so-called low side type in which the inte
ping setting varies according to the compressor
rior of the casing is connected to the suction
discharge or condenser pressure.
conduit 30 while the suction inlet 32 of the com
Where motor protectors are self-resetting it
is possible for the windings to be properly pro
pressor communicates directly with the interior
tected for one or several resettings, but where 45 of the sealed unit. The compressor 22 discharges
through a conduit 34 directly to the condenser 36
the stalling conditions continue for long periods
where
the compressed refrigerant is lique?ed and
of time, it is vpossible for the windings to be
supplied under the control of a suitable expan
come damaged by the successive rushes of current
sion valve 38 to an evaporator 40 where the lique
through the motor on each starting attempt.
?ed
refrigerant evaporates substantially at the
It is still another object of my invention to
provide a motor protector having a resetting con 50 suction pressure of the compressor 22. The re
frigerant is withdrawn from the evaporator 40
trol which is varied according to the number or
and
through the suction conduit 30 in a vapor
successive attempts to start so that the time
form.
between tripping and resetting is increased as
When the system operates under light loads,
the successive attempts to start increase.
65 the suction or back pressure is low and the con
2,412,981
3
denser pressure is low. The evaporated refrig
erant enters the sealed unit at a low temperature
and receives heat from the electric motor there
conditions.
1
'
In order to overcome this dimculty and to make
by raising its temperature, increasing its volume
and reducing its density while it is cooling the
electric motor 24 and its windings 26 and 28.
Although the possible rise in temperature of the
refrigerant drawn into the sealed unit is quite
large, its cooling capacity is limted because of
10
its low density. In fact as the load increases,
. the suction or evaporator pressure and tempera
d
and-lack of adequate cooling during light load
it possible for the motor to operate at its maxi
mum load under all conditions without tripping
the protector and yet to adequately protect the
windings under all conditions, I propose to in
crease the protector rating in accordance with
the increase in suction pressure. The graph dis
closed in Fig. 3 shows that at zero pounds back
pressure the protector rating is about 4.8 am
peres, while at 35 lbs. suction pressures the pro
ture increases so that the possibletemperature
tector rating is about '7 amperes.
rise of the refrigerant in the sealed unit is re
To accomplish this change in protector rating, ‘
duced. But in spite of this, the cooling effect
I provide a bellows 88 which is connected by tub
15
of the refrigerant is greater because the density
ing 82 to suction conduit 38.‘ This bellows 80
of the refrigerant entering the sealed unit in
supports the movable end of the adjusting bar 12
creases at a much faster rate than the decrease
and is opposed by a, compression type coil spring
in the maximum possible rise in temperature.
Heretofore it has been customary to use a sim
ple thermal overload for protecting such a mo
tor-compressor unit. Such a thermal overload
may include, for example, an operating bimetal
42 heated by radiant heat from an electric heater
44 which is connected in series with one of the
' supply conductors 46. The operating bimetal 42
is connected to one end of each of a pair of ten
sion toggle springs 48 of a toggle mechanism
which includes a rigid toggle arm 50 provided
with a pair of ears which receive the other ends
of the toggle springs 48. The other end of the
arm 50 is riveted by amovable switch contact 52
to a ?exible strip 54 having its opposite end an
chored to a post 56. The electric heater 44 is
connected to a stationary switch contact 58 and
when the protector is closed the current ?ows
to the movable contact 52 and through the strip
54 to the post 56 which is connected by a con
ductor 60 to the supply conductor 46. The heater
44 is connected by a conductor 45 to the starting
relay 62 connected to the common terminal of
the running winding 26 and the starting wind
84 which has its tension adjusted by an adjust
With this arrangement, when the
suction pressure is lowered, the bellows 8|) par
20 ing screw 88.
tially collapses thereby lowering the right end of
the adjusting bar 12 to reduce the protector rat
ing. Likewise as the suction pressure increases,
25 the bellows 88 will expand and raise the adjust
ing bar 12 against the tension of the spring 84
to raise the protector rating. The adjusting
screw 86 may be turned to vary the tension of
the spring 84 so as to adjust the protector for
30 di?erent refrigerants and for di?erent sizes and
types of systems. The set screws 88 and 90 are
provided to keep the expansion of the bellows 88
within safe limits and also to provide an upper
and a lower limit upon this adjustment of the
85
protector rating.
Under stalling conditions with this type of sys
tem, the protector will continuously trip and re
set, allowing current to flow through the motor
. during each starting attempt between the reset
40 ting and the tripping time. I have found that
with the thermal type of overload protection, the
temperature of the motor windings rises accord
ing to the number of successive starting attempts.
ing 28.
Under such conditions,~the windings may be prop
The other end of the running winding 26 is con
erly protected for several resettings, but with
nected to the supply conductor 64. The other
many successive resettings, the windings will
end of the starting winding 28 is connected to
gradually rise in temperature until they exceed
the starting winding contacts 86 which in turn
a safe limit. In order to overcome this, I pro
are connected through the conductor 68 and an
pose to increase the time between tripping and
electric heater ‘ill to the supply conductor 64.
The motor protector is provided with an'adjust 50 resetting according to the number of starting at_
tempts.
ing bar 12 upon which is anchored one end of
To do this, I mount the usual adjustable reset
the operating bimetal 42. The adjusting bar 12
ting screw 92, which serves as a stop to limit
is pivoted at its left end to a post 14 extending
the opening movement of the movable contact 52,
up from the frame 16.
upon the free end of a. bimetal strip 94. The
_ A simple motor protector in series with the
resetting time of the thermal overload is deter
supply conductor will not take into account the
mined by the position of the resetting screw 92.
varying cooling conditions and the varying suc
If the resetting screw 92 is moved away from the
tion and discharge pressures of the compressor
stationary contact 58 to allow a wider opening
and its sealed unit. _ With the simple motor pro
tector, the motor is deenergized when the current 60 of the contacts, the temperature is lowered at
which the bimetal 42 resets the toggle mechanism
?ow increases to the rating for which it is set.
and closes the contacts. In order to use this
Obviously, such a protector has no means to take
property of the toggle mechanism to increase the
into account the difference in motor winding tem
tripping time in accordance with the number of
peratures which occurwith varying loads. Inas
starting attempts, I position the bimetal 42 with
much as the motor windings are the danger
its material of lesser expansion adjacent the
points, the motor will not be allowed to operate at
heater 44 so that when the starting relay 62 is
its full load under conditions of heavy load and
closed
during each starting attempt, the heater
high back and suction pressure if the protector
10 will heat the bimetal 94 to cause it to curl up
is set low enough to properly protect the wind
a very short distance and raise the reset
ings under low load conditions and low back pres 70 wardly
adjusting screw 92. The heating effect upon the
sures. Also, if the protector is set to allow the
bimetal 94 will be cumulative for successive start
maximum current passage through the motor
ing attempts so that the temperature of thebi
under heavy load conditions when it is most need
metal 94 and the resetting time of the relay will
ed, then the'motor windings are subject to dam
increase according to successive starting at
age because of excessive winding temperatures 75
2,412,981
tempts. This adjustment of the resetting time
will allow increased loading of the electric motor
without damage to the windings and will give
more rapid resetting when conditions permit so
as to reduce the amount of idle time because of CI
motor failure under most circumstances, and yet
the windings are properly protected at all times.
In Fig. 2 I have shown a modi?ed form of the
invention illustrating .some of the variations
which can be made in the control and its applica-. 10
tion to another type of system.‘ In this system,
the sealed unit I20 is placed upon the high side
of the system and the compressor H22 withdraws
refrigerant directly from the evaporator I 40
through the suction conduit I30. The com 15
pressor I22 discharges directly into the interior
of the sealed unit I20 so that the compressed
refrigerant may contact and cool the electric
motor I24, its running winding I26 and its start
ing winding I 20. The interior of the sealed unit 20
is connected to the condenser I36 from which
lique?ed refrigerant flows to the evaporator un
der the control of a suitable expansion valve I30.
6
orator may be used as the equivalents of the direct
pressure connections, if desired. Thus by these
expedients the permissible power output of the
motor is increased without reducing its protec
tion.
-
While the form of embodiment of the invention
as herein disclosed, constitutes a preferred form.
it is to be understood that other forms might be
adopted, all coming within the scope of the
claims.
.
What is claimed is as follows:
1. In combination, a compressor having a suc
tion entrance and a discharge outlet for com
pressed ?uid, an electric motor for driving the
compressor, said electric motor being cooled by
the circulation of said ?uid, an'overload protec
tor responsive to the electric motor current for
deenergizing said electric motor, and pressure re
sponsive means for adjusting in accordance with
the load upon the compressor the setting of the
current value ‘of which said protector deener
gizes said electric motor.
2. In combination, a compressor having a suc_
A bimetal type thermal overload protector has its
contacts I52 and its main operating heater H4 25 ticn entrance and a discharge outlet for com~
pressed fluid, an electric motor for driving the
connected in series with the supply conductor Hit
compressor, said electric motor being cooled by
which connects to the starting relay E32.
the circulation of said fluid, an overload protec
As the load on the refrigerating system in
tor responsive to the electric motor current for
creases, the evaporator or suction pressure rises,
thus increasing the volume of compressed refrig 30 deenergizing said electric motor, and means for
adjusting in accordance with the suction pres
erant discharged into the sealed unit iZd. The
sure of the compressor the setting of the current
increase in volume of refrigerant discharged in
value at which said protector deenergizes said
creases the condenser pressure and temperature.
electric motor.
_
This causes an increased density of the refriger
3. In combination, a compressor having a suc~
ant circulating within the sealed unit so that 35
tion entrance and a discharge outlet for com
pressed ?uid, an electric motor for driving the
compressor, said electric motor being cooled by
with the higher condenser pressure and tempera
the circulation of said ?uid, an overload protec
ture. To'allow a greater load upon the motor in
tor responsive to the electric motor current for
accordance with the increased cooling, I provide
the amount of cooling of the motor H4 and its
windings E28 and I28 is increased in accordance
'
40 deenergizing said electric motor, and means for
a bellows I00 which is connected by tubing I82to
adjusting in accordance with the discharge pres
the discharge conduit I83 extending from the
sure of the compressor the setting of the current
sealed unit I20 to the condenser I36. As the dis
value at which said protector deenergizes said
charge pressure and the condenser temperature
rises, the bellows I80 expands to raise the adjust 45 electric motor.
4.. Refrigerating apparatus including an evap
ing bar I72 to increase the temperature at which
orator, a condenser, a sealed unit containing a
the operating bimetal I42 trips and resets. This
compressor and an electric motor for driving the
arrangement increases the maximum current
compressor for withdrawing refrigerant from the
?ow permitted by the relay before tripping,
evaporator and forwarding it to the condenser
- As before, set screws I88 and I90, are provided
and for circulating the refrigerant in contact
for limiting the adjustment of the adjusting bar
with the motor, an overload protector responsive
_ 5712 provided by the bellows i 80. The expansion
to the electric motor current for deenergizing the
of the bellows I180 may be controlled by a spring
motor, and means for adjusting in accordance
I84 and adjusted by an adjusting screw I00. To
with evaporator pressure the setting of the cur
increase the resetting time of the relay in accord
rent value at which said protector deenergizes
ance with the number of successive attempts to
saidelectric motor.
start, there is provided a bimetal I06 which raises
5. Refrigerating apparatus including an evap
the adjusting screw in increasing amounts when
orator, a condenser, a sealed, unit containing a
heated by successive energizations oi‘ the auxil
iary heater I‘I0.v This auxiliary heater I70 is 60 compressor and an electric motor for driving the
compressor for withdrawing refrigerant from the
connected in a separate shunt circuit controlled
evaporator and forwarding it to the condenser
by the second set of relay contacts I01 which are
and for circulating the refrigerant in contact with
controlled simultaneously with the first relay
the motor, an overload ‘protector responsive to
contacts I66 which control the starting winding
the electric motor current for deenergizing the
circuit.
_
7
motor, and means for adjusting in accordance
Thus, as in the first modi?cation, the protector
with condenser pressure the setting ofthe cur
is adjusted to provide an increased rating in ac
rent value at which said protector deenergizes
cordance with increasing discharge or condenser
said electric motor.
pressure and to provide an increased resetting
6. Refrigerating apparatus including an evap
time in accordance with the number of successive 70
orator, a condenser, a compressor for withdraw
attempts to start. Inasmuch as the condenser
ing evaporated refrigerant from the evaporator
pressure is proportional to the condenser tem
and for forwarding it to the condenser, an elec
perature and the evaporator temperature is pro
tric motor for driving the compressor, an over
portional to the evaporator pressure, thermostat
load protector responsive to the electric motor
bulbs applied to either the condenser or the evap
current for deenergizing the motor, and means
?
for adlusting in accordance with evaporator pres
sure the setting of the current value at which
said protector deenergizes said electric motor.
7. Refrigerating apparatus including an evap
orator, a condenser, a compressor for withdraw
tor, said overload protector including a toggle
mechanism having a stop for determining‘ its
reclosing setting, and thermal means heated dur
ing each starting period of said motor for chang
ing the,position of said stop.
16. In combination, an electric motor, an over
load protector for deenergizing, the electric mo
and for forwarding it to the condenser, an elec-v
tor, said overload protector including a toggle
tric motor for driving the compressor, an over
mechanism having a stop for determining its re
load protector responsive to the electric motor
closing'setting, a thermal means operatively con
current for deenergizing the motor, and means 10 nected to said stop, and means for changing the
for adjusting in accordance with condenser pres
temperature of said thermal means during each
sure the setting of the current value at which
starting period of said motor.
,
ing evaporated refrigerant from the evaporator
said protector deenergizes said electric motor.
8. In combination, a compressor having a suc
tion entrance and a discharge outlet, an electric
motor for driving the compressor, an overload
, protector responsive to the electric motor cur
1'7. In combination, an electric motor, a start
ing control for controlling the electric motor dur
ing the starting period, a self-resetting overload
protector for deenergizing said electric motor,
said overload protector‘ including a stop for de
rent for deenergizing said electric motor, and
termining its reclosing setting, and means re
pressure responsive means for adjusting in ac
sponsive to said starting control for moving said
20
cordance with the load upon the compressor the
stop.
setting of the current value at which said pro
18. In combination, an electric motor, a start
tector deenergizes said electric motor.
ing control for controlling the electric motor dur
9. In combination, a compressor having a suc
ing the starting period, a self-resetting overload
tion entrance and a discharge outlet, an electric
protector having a movable means for deenergiz
motor for driving the compressor, an overload 25 ing said electric motor, and a second movable
protector responsive to the electric motor current
for deenergizing said electric motor, and means
means controlled directly by said starting con
trol and responsive to successive starting e?orts
for adjusting in accordance with the suction pres
of the electric motor for controlling the resetting
sure of the compressor the setting of the current
of said overload protector, said second movable
30
value at which said protector deenergizes said
means operating independently of the ?rst men
electric motor.
,
I
tioned movable means to protect the motor against
10. In combination, a compressor having a suc
excessive temperatures.
tion entrance and a discharge outlet, an electric
19. Refrigerating apparatus including an evap
motor for driving the compressor, an overload
protector responsive to the electric motor cur
rent for deenergizing said electric motor, and
orator, a condenser, a sealed unit containing a
compressor and an electric motor for driving the
compressor for withdrawing refrigerant from the
means for adjusting in accordance with the dis
evaporator and forwarding it to the condenser
charge pressure of the compressor the setting of,
and for circulating the refrigerant in contact with
the current value at which said protector de
the motor, an overload protector responsive to
40
energizes said electric motor.
current flow through. the motor for deenergizing
11. In combination, a compressor having a suc
tion entrance and a discharge outlet, an electric
motor for driving the compressor, an overload
the motor upon an overload, and means for ad
protector for deenergizing said electric motor,
said protector including a toggle mechanism hav
unit the setting of the current value at which
ing a stop for determining its reclosing setting,
and means cumulatively responsive to successive
starting efforts for moving said stop.
12. In combination, a compressor having a suc
tion entrance and a discharge outlet, an electric -
motor for driving the compressor, an overload
protector for deenergizing said electric motor,
said protector including a toggle mechanism hav
ing a stop for determining its reclosing setting,
and thermal means heated during each starting
‘period for changing the position of said stop.
‘ 13. In combination, a-compressor having a suc
tion entrance and a discharge outlet, an electric
motor for driving the compressor, an overload
justing substantially in accordance with the re
frigerant pressure conditions within the “sealed
said protector- deenengizes said electric motor.
20. Refrigerating apparatus including an evap
orator, a condenser, a sealed unit containing a
compressor and an electric motor for driving the
compressor for withdrawing refrigerant from the
evaporator and forwarding it to the condenser
and for circulatingthe refrigerant in contact with
the motor, an overload protector responsive to
current flow through the motor for deenergizing
the motor upon an overload, and means for ad
justing substantially in accordance with the heat
dissipating effect of the refrigerant in the sealed
unit upon the motor the setting of the current
value at which said protector deenergizes said
motor.
,
protector for deenergizing said electric motor, 60 electric
21. Refrigerating apparatus including an evap
said protector including a toggle mechanism hav
orator, a condenser, a sealed unit containing a
ing a stop for determining its reclosing setting,
compressor and an electric motor for driving the
a thermal means operatively connectedto said
compressor for withdrawing refrigerant from the
stop, and means for changing the temperature
evaporator and forwarding it to the condenser
' of said thermal means during each starting pe 65
and for circulating the refrigerant in contact with
riod.
the motor, an overload protector responsive to
14. In combination, an electric motor, an over
current flow through the motor for deenergizing
load protector for deenergizing the electric mo
the motor upon an overload, and means for ad
tor, said overload protector including a toggle
mechanism having a stop for determining its 70 vjusting substantially in accordance with the re
rrigerant temperature conditions within the sealed
reclosing setting, and means cumulatively respon
unit the setting of the current value at which
sive only to successive starting efforts of the elec
said protector deenergizes said electric motor.
tric motor for moving said stop.
'
22. Refrigerating apparatus including an evap
15. In combination, an electric motor, an over
load protector for deenergizing the electric mo 75 orator,va condenser, a‘compressor for withdraw-v
2,419,981
ing evaporated refrigerant from the evaporator
, and for forwarding it to the condenser, an elec
tric motor for driving the compressor, an over
load protector responsive to the electric motor
current for deenergizing the motor, and means
for adjusting in accordance with evaporator tem
perature the setting of the current value at which
said protector deenergizes said electric motor.
23. Refrigerating apparatus including an evap
orator, a condenser, a compressor for withdraw 10
ing evaporated refrigerant from the evaporator
10
24. In combination, a compressor having a suc
tion entrance and a discharge outlet, an elec
tric motor for driving the compressor, an over
load protector responsive to the electric motor
current for deenergizing said electric motor, and
temperature responsive means for adjusting in
accordance with the load upon the compressor the
setting or the current value at which said protec_
tor deenergizes said electric motor.
,
25. In combination, an electric motor, an over
load protector for deenergizing the electric mo
tor, said overload protector including a toggle
mechanism having a stop for determining its re
load protector responsive to the electric motor
closing setting, and thermal means heated by
current for deenergizing the motor, and means 15 current during the starting or said motor for
for adjusting in accordance with condenser tem
changing the position of said stop.
'
perature the setting of the current value at which
said protector deenergizes said electric motor.
MARSHALL C. H‘ARROLD.
and for forwarding it to the condenser, an elec
tric motor for driving the compressor, an over
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