US2972708A

US2972708A - Protective means for submersible pump-motors

Info

Publication number: US2972708A
Application number: US614205A
Authority: US
Inventors: Edward J Schaefer
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-10-05
Filing date: 1956-10-05
Publication date: 1961-02-21
Anticipated expiration: 1978-02-21

Description

Feb. 21, 1961 J SCHAEFER 2,972,708

PROTECTIVE MEANS FOR SUBMERSIBLE PUMP-MOTORS Filed Oct. 5, 1956 n :25 INVENTO 60 1mm JSc/zafw;

6Q 77 BY I United States Patent Edward J. 'Schaefer, Fort Wayne, Ind. Franklin Electric Co., Inc., 400 E. Spring St., Blutfton, Ind.)

"Filed (let. 5, 1956, Ser. No. 614,205

21 Claims. c1. 317-13 This invention relates to improvements in the protection of submersible pump-motor units.

In pumping liquids from a subterranean level it is frequently desirable to employ a combination unit in which both the pump and the motor are located below ground so as to avoid the necessity for a long drive shaft extending from the pump located below ground to a motor at or near the ground level. Such combina tion units are commonly referred to as submersible pumprnotors and are widely used, e.g. in water wells or the like and in pumping gasoline from an underground storage tank to a dispenser at the ground level.

Since such units are located below ground and are, therefore, relatively inaccessible, it is obviously desirable to provide adequate protection both electrically and mechanically. However, the protective schemes heretofore in use have been inadequate in several important respects. For example, it is common practice to provide an electric motor with a thermal protector which will prevent overload current through the motor windings and, particularly in the case of a gasoline pumpmotor, may also include a protector element arranged to open the motor circuit in response to an unusually high ambient temperature at the motor. However, the overload protector is most often located in a control box at the ground level so that it can readily be tampered with and as a result there have been numerous instances of deliberate misoperation of and serious damage to submersible pump-motor units.

Even more important, however, is the fact that submersible pump-motor units should be protected aganst operation without an adequate supply of Working fluid. For example, in the case of water wells it has been found that low water levels are becoming particularly critical in certain regions of the country and are responsible for an increasing number of pump failures. In order to preserve the life of both the motors and the pumps it is essential to prevent operation of the pump-motor unit after the supply of fluid being pumped has been exhausted, eg when the water level in a well becomes low or when a gasoline storage tank is empty.

Accordingly, it is a primary object of the present invention to provide novel and improved protective means for submersible pump-motor units.

A further object of the invention is to provide a novel protective arrangement for submersible pump-motor units which affords combined protection against both overload operation and loss of fluid being pumped.

Another object of 'the invention is to provide a pro tective arrangement of the foregoing character which utilizes a conventional and readily available overload protector.

Still another object of the invention is to provide a novel protective arrangement for submersible pumpmotor units including an overload protector in a relativelyinaccessible location so as to discourage improper operation of the equipment.

Other objects and advantages of the invention will become apparent from the subsequent detailed description taken in conjunction with the accompanying drawing, wherein:

Fig. 1 is a fragmentary vertical sectional view of the upper end of the motor section of a submersible pumpmotor unit embodying a preferred form of the protective means of the present invention;

Fig. 2 is a plan view looking into the interior of an overload protector unit comprising a part of the protective arrangement illustrated in Fig. 1;

Fig. 3 is a plan view looking into the interior of another portion of the protective means shown in Fig. 1;

Fig. 4 is a fragmentary sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 is a schematic circuit diagram of the protective arrangement shown in Figs. 1 to 4;

Fig. 6 is a fragmentary sectional view similar to Fig. 1 but showing a modified form of the invention; and

Fig. 7 is a fragmentary schematic circuit diagram showing a modification of the circuit arrangement illustrated in Fig. 5.

Referring first to Fig. l, the invention is illustrated in connection with a submersible pump-motor unit 10 of a type used for pumping gasoline. The electric motor portion of the unit comprises a frame portion including a laminated stator core 11 and a rotor 12 carried on a rotor shaft 13. Usually, the electric motor is of the single phase alternating current type in which case the stator core 11 will be provided with the usual starting and running windings. However, it is to be understood that the invention is applicable to any type of electric motor. The lower end of the rotor shaft 13 of the motor has a driving connection with the shaft of a pump (not shown) connected in unitary end-to-end relation with the motor so as to form a single compact unit therewith in the manner well known in the pump-motor art. A tubular element 14 mounted in the upper end of the stator bore provides support for a bearing member 16 in which the upper end portion 17 of the rotor shaft is journaled. An end bell structure, designated generally at 18, is secured to the upper end of the stator 11 by means of a plurality of elongated screws 19 extending through suitable apertures in the end bell into threaded openings 21 in the end of the stator. An elongated shell or casing 22 surrounds the motor in spaced relation from the stator 11 so as to provide an annular fluid passage 23 which receives at its lower end (not shown) the discharge fluid from the pump. The upper end of the shell 22 is rigidly connected to a flange portion 24 on the end bell 18 with a seal ring 26 being interposed therebetween. As is customary in gasoline pump-motor units, the pumped fluid thus passes over the exterior of the operating parts of the motor and is discharged from the annular passage 23 through a plurality of radial ports 27 into a tubular extension 28 on the bell 13 which provides a fluid discharge or outlet from the unit. The extension 28 may have a threaded connection (not shown) with a pipe or tubular casing extending from the unit upwardly to the ground level.

The end hell 1% is also constructed to provide an inverted generally cup-shaped lower portion having a cylindrical wall 29 and a plurality of inwardly extending radial flange portions 30 which seat against the upper end of the stator 11 with a resilient ring 31 being interposed between the fianges 3t) and the elements 14. One of the flanges 3i; has an enlarged opening 32 for accommodating a cable connection or other electrical connection, indicated schematically at 33, between the stator windings and an electrical conductor means 34. The lower cup-shaped portion of the end bell 18 also has an upper end wall 35 with an internally threaded tubular ear-arcs extension 36 which projectsupwardly into the fluid outlet extension 28. As is customary in pump-motor units of this type, a conduit or cable (not shown) carrying suitable line conductors extends downwardly from the ground level and is threadedly connected to the extension 36.

' Coming now to the principal feature of the present invention, a partition 3% depends from the upper end wall 35 of the end bell structure into the hollow interior or cavity, designated at 37, and defines with part of the cylindrical wall 29 a separate recess 39 in which is mounted a protective device designated generally at 41. As will hereinafter appear, the protective device 41 is preferably mounted in the recess 39 by embedding the same in fluid-tight relation in a body 42. of electric potting and insulating material, such as an epoxy resin, which fills the recess 39 and extends upwardly into the extension 36. It will be understood that the electrical conductors in the conduit which connects to the extension 36 pass through the seal provided by the resinous mass 42 into the cavity 37 for connecting the motor to the line. As will be clear from Fig. 1, at least a portion of the protective device it projects downwardly from the resinous mass 42 in exposed relation within the hollow cavity 37. In accordance with the operating principle of the invention as hereinafter described in detail, it isessential that the exposed portion of the protective device ll he in contact with the fluid being pumped, and in the illustrated embodiment of the invention this contact is made possible by means of a passage or bore 43 in the upper end wall 35 of the end bell structure and a bore 4-4 extending through the element 14. As will readily be apparent, the passage 43 provides fluid communication between the inner cavity 37 and the pumped fluid which passes through the annular discharge passageway 23 and outlet 28. Likewise, the bore 44 provides fluid communication between the cavity 37 and the stator bore, it being understood that a certain portion of the pumped liquid will thus pass through the interior of the motor so that there is continuous circulation of pumped fluid through the cavity 37.

In the preferred embodiment of the invention, the protective device 41 comprises a combination of a conventional overload protector and an auxiliary shunt heating element. Thus, in Fig. l the overload protector, designated at 46, is of a well known type having a plastic body portion with a depending skirt 47 containing the sulating tube 58 is disposed at the bottom of the cup 48 operating elements of the overload protector, and a cupshaped member 48 containing the auxiliary shunt heater has a telescopic frictional fit around the skirt portion 47' of the overload protector. The interfitted body of the overload protector 46 and the cup 4-8 for the auxiliary shunt heater comprise together with the embedding or potting resin 42 a fluid-tight enclosure or sealing means so that the protective device is eifectively sealed from the fluid in the cavity 37.

Referring now to Figs. 2, 3, and 4, the body portion of the overload protector 46 has mounted thereon within the confines of the skirt 4'7 a pair of

stationary contacts

49 and 50 and a bimetallic disk 51 supported at its center by a screw 52 and having radially extending movable contact portions 53 which overlie the

stationary contacts

49 and 56 so that the coacting pairs of contacts are opened and closed in response to heating or cooling of the bimetallic disk 51 to certain predetermined temperatures. A low resistance heating element 54 is located closely adjacent the disk 51 and is connected in series relation between the stationary contact 56 and a terminal 556 which is in turn connected to the motor windings.

As best seen in Fig. 4, the lower cup-shaped enclosure 48 comprising the other half of the protective device 41 is fitted tightly around the lower end or" the skirt 47 of the overload protector, and a high resistance cartridge type shunt heating element 57 contained within .an inin physical proximity to the bimetallic disk 51 so as to be capable of actuating the latter. A pair of

electrical conductors

59 and 61 extend from the opposite ends of the heater 57 for connecting the heater in shunt relation across the line. As hereinafter explained in greater detail, the cup 48 is preferably made from a material having relatively low heat conductivity, and controlled heat conduction is provided between the shunt heater 57 and the exterior of the protective device 41 by means of a special heat conducting element which, in this instance, is in the form of an elongated strip 62 of material having relatively high heat conductivity. One end of the strip 62 is curled, as at 63, to provide a sheath around the insulating tube 58 and the strip extends through the bottom wall of the cup 48 with the outer end of the strip being folded several times upon itself, as at 64, for the sake of compactness. A fluid-tight seal such as a soldered connection 66 is provided where the strip 62 extends through the bottom of the cup 4-8.

Before describing the operation of the protective device, brief reference will be made to Fig. 5 which illustrates the preferred circuit connections. The motor is of the single phase alternating current type having a run ning winding 67 and a starting winding 68 in axially displaced relation with a squirrel cage induction rotor indicated at 6% The supply line comprises a pair of conductors 71 and 72, the latter being connected directly to one end of the running winding 6'7 and having a parallel branch 73 connected through a switch 74 and a capacitor 76 to one end of the starting winding 68. It will be understood that as thus illustrated the motor is of the split phase capacitor start type and the switch 74 is adapted'to be opened at a predetermined speed, either centrifugally or electrically, for cutting the capacitor 76 and the starting winding 63 out of circuit. The conductor 71 is connected to the stationary contact 49 of the overload protector, and the opposite stationary contact 50 is connected through the heating element 54 and the terminal 56 by means of a conductor 77 to the opposite ends of both

windings

67 and 68. Of course, the bimetallic disk element 51 with its contact ends 53 is arranged to bridge the

stationary contacts

49 and 50 in the usual manner, and in the case of certain types of overload protectors, the series heating element 54 may be omitted provided the resistance of the bimetallic disk 51 is sufficient to provide the desired heating effect under overload conditions. The auxiliary shunt heater 57 is connected by the

conductors

59 and 61 across the line, such connection being between the supply source and the overload protectores so that the shunt heater 57 is always energized regardless of the condition of the overload protector 46.

As heretofore briefly mentioned, the lower portion of the cup 48 and the projecting folded end 64 of the heat conducting strip are exposed within the motor cavity 37 so as to be contacted by the pumped fluid which fills the cavity 37 and flows therethrough as long as the pump is discharging fluid. Consequently, although the shunt heater 57 is always. energized, the cooling effect of the liquid in contact with the cup 48 and particularly the strip end 64 is suificient to dissipate substantially all of the heat evolved by the heater 57. In other words, during nor- 'rnal operation of the unit, the heater 57 has no significant effect on the bimeta lic element 51 since it is rendered ineffective by the cooling action of the circulating liquid. However, if at any time the supply of working fluid for the pump is exhausted so that the pump runs dry, the motor cavity 37 Willbe emptied rapidly and the cooling effect will be lost. Because of the markedly decreased heat dissipation in air as compared with liquid, the heat from the shunt heating element 57 will very quickly actuate the bimetallic disk 51 so as to disrupt the circuit and stop the'motor.

It is, of course, quite important to'achieve a proper balance between the capacity of the shunt heater 57 and the cooling effect of the liquid passing through the motor cavity 37' so as to obtain normal operation when the pump is operating with an adequate supply of working fluid while at the same time obtaining rapid and reliable stoppage of the motor as soon as the working fluid is exhausted. Obviously, the size of the shunt heater required in any given instance will depend on the surroundings, the manner in which the protective device is potted in the resin, and other factors. An effective degree of control over the rate of heat dissipation may be obtained by variations of the extent to which the lower casing portion 48 of the protective device projects from the resinous body 42, or in other words by varying the amount of surface of the protective device 41 which is exposed to contact with liquid in the motor cavity 37. However, for more sensitive control over the rate of heat dissipation from the protective device, I prefer the arrangement shown in Figs. 1 and 4 wherein the cup portion 48 may be of a material having very low thermal conductivity, e.g. stainless steel, and the strip 62 is preferably a metal having a very high degree of thermal conductivity such as copper. By such choice of materials and by regulating the extent of the externally projecting end portion 64 of the copper strip, heat is conducted from the heater 57 to the liquid in the motor cavity 37 primarily by means of the heat conducting element or strip 62.

By forming the cup 48 from a metal such as stainless steel having low thermal conductivity as described above, it is also possible to avoid excessive heat dissipation from the unit 41 through the resinous body 42 to the motor frame. Consequently, the rate of cooling or heat dissipation from the heating element 57 is controlled for the most part by conduction from the heater 57 through the strip 62 to the fluid contained in the cavity 37. This arrangement makes it possible to maintain an adequate operating differential between the strip current with fluid present and with no fluid present in the cavity 37. Although materials other than stainless steel and copper may be used for the

elements

48 and 62, these particular materials are especially useful because they are readily available and because the thermal conductivity of stainless steel is approximately & of the thermal conductivity of copper.

When the pump-motor unit is operating under normal load conditions it will be seen that the ambient temperature of the bimetallic disk 51 of the protective device 41 is determined primarily by the heat of the shunt heating element 57 and by the presence or absence of fluid in the cavity 37. As long as fluid is present in the cavity 37, the thermal output of the heating element 57 is dissipated rather completely and the circuit remains closed through the over oad protector 46. However, when the pump ceases to discharge fluid and the cavity 37 empties, the cooling effect of the fluid is lost and the heat of the shunt heater 57 is suflicient to actuate the bimetallic element 51- of the overload protector so that the latter also functions as a protector against loss of liquid. In the preferred circuit arrangement shown in Fig. 5, the auxiliary heater 57 is always connected across the line in shunt relation with the motor windings and the output of the heater 57 does not vary with the load so that full protection against low liquid is provided at all times regardless of the load on the pump and regardless of the condition of the overload protector 46. Of course, it

will be understood that the overload protector 46 also functions in its usual manner so that under normal load conditions the thermal output from the low resistance series heater 54 is insufficient to open the circuit but under overload conditions (even with liquid present in the cavity 37) the heating element 54 heats up sufliciently to actuate the bimetallic disk 51 and disrupt the motor circuit thereby providing overload protection in the usual man- Although it has been the practice heretofore to include a simple heat responsive device suchas a bimetallic element and cooperating contact means in the motor circuit for purposes of protecting the motor against an abnormally high ambient temperature, e.g., to prevent ignition of gasoline, I have found that the use of a thermostat alone is completely inadequate to provide protection against loss of liquid. Tests have shown that a considerable length of time such as an hour or more is required under no load conditions for the motor to heat up sufliciently to trip the thermostat and by this time the bearings and pump parts are frequently destroyed or badly damaged. Even if the thermostat is located as close as possible to the windings of the motor, any arrangement by which the thermostat will trip rapidly under no load or low liquid conditions will result in unwanted tripping under normal operating conditions. Thus, to obtain the combined overload and low liquid protection features of the present invention the use of a heating means in conjunction with the bimetallic or heat sensitive means is absolutely essential, and the preferred arrangement for maximum effectiveness of the protective device embodies the use of two heating elements in the manner heretofore described in connection with Figs. 1 to 5.

Another advantage of the protective arrangement of the present invention is the fact that the overload protector 46 is located within the motor cavity and is, therefore, normally inaccessible so that the overload protector cannot be deliberately rendered ineffective or inoperative by imprudent operating practices. Furthermore, with the protective device 41 located in the motor cavity as herein described, it will be seen that the protector is located above the pump portion of the pump-motor unit so that both the motor and the pump are protected at all times against operation without an adequate supply of workiug fluid.

in Fig. 6 I have illustrated a modification of the invention Which can be employed in some circumstances with effective results. T he same reference numerals are used in Fig. 6 for the parts which are identical with the Fig. 1 embodiment. in this instance, the combined overload and low liquid protective device is designated generally at 72% and comprises essentially the same electrical elements except that the auxiliary shunt heater 57 of the first embodiment has been omitted. The overload protector elements comprising a bimetallic disk 79 having contact portions 31, a pair of stationary contacts 82, and a low resistance heating element 83 are connected in series between the line and the motor windings by means of conductors S4, The entire unit is enclosed in a metallic cup or can 86 having a tight fitting cover portion 87 through which the conductors 84 extend. The enclosure 8687 and its contents are sealed in fluid-tight relation within the recess 39 by a body 42 of potting resin or like electrical insulating material so that the circuit components of the protective device are fully protected from contact with pumped fluid. As before, the lower portion of the can 36 projects to a predetermined extent from the resinous body 42 so as to be contacted by the cooling fluid in the cavity 37. in this embodiment, the value of the resistance heating element 83 is selected with due regard to the operating requirements of the motor and other environmental factors so that under normal load conditions the thermal output of the heater 83 is dissipated by the cooling effect of the fluid in contact with the exposed portion of the can 36. However, if liquid is lost from the cavity 37, the heat from the element 83 is suflicient to actuate the bimetallic disk 79 and disrupt the motor circuit thereby providing protection against loss of liquid. At the same time, even under full liquid operating conditions, the cooling effect of the liquid in the cavity 37 is insuflicient to dissipate all of the heat of the element 83 when the pump encounters an excessive load and thus the device 78 functions as an overload protector in the usual manner. Of course, it will be understood that a correct balance estates 7 inserts provided between the heating element 83 and the extent of the cooling effect by the liquid in the cavity 37 as determined by the proportion of the surface f the can SG WlIlCil is exposed to contact with the liquid and also as determined by the material from which the can 36 is made.

In the arrangement shown in Fig. it will be understood that under low liquid conditions the auxiliary shunt heater 57 will keep the motor circuit open until liquid returns to the cavity 37 and cools the heater 57. In other words, there will be no cycling of the bimetallic disk 51 under low liquid conditions. However, it will also be seen that the overload protector is will cycle in the usual mannor for ordinary overload conditions of the motor such as are encountered when sand or other foreign material enters the pump. In other words, when an overload current causes the'heater 54 to heat up, the disk Sll opens and breaks the circuit. The 'deenergized heater 54 then 'cools'off and the disk 51 returns to closed position. If the cause of the overload has been corrected, normal operation is resumed, but if the overload condition persists, the heater 54 heats up again and the same sequence is repeated in a cyclic'manner until the situation has been remedied.

In Fig. 7 a modification of the circuit is shown wherein the auxiliary heater is in efifect in two parts, as designated at 83 and 89, with one part being connected across the line in shunt relation by conductors @l. and 92, and the other part 89 being connected across the contacts 49, 55 and heater 54 by means ofthe conductor 91 and a condoctor 93. With this circuit arrangement when a low liquid condition is encountered, the heater section 88 which-is always across the line will keep the motor circuit open without cycling until liquid returns in the same manner as in Fig. 5. Under normal load conditions the heater section 89 is short-circuited and is not effective, but under overload conditions the heater 54 eitects initial opening of the

thermostat contacts

49, 50 and at the same time the heater section 85B is thereby energized. Dependbut upon the selected size or capacity of the heater section 89, the thermal output will be sufiicient to hold the disk 51 open immediately or will build up to such point after a few cycles. Thus, by appropriate selection of the heater section 89 the circuit arrangement of Fig. 7 can provide only a limited extent of recycling or none, as desired, under overload conditions. Of course, with this arrangement it will also be understood that when the disk 51'is held open by the heater section 89 it will be necessary to reset the overload protector as by momentarily opening the main line switch (not shown) so as to deenergizc the heater and return the protective device to its original operating condition. If desired, the heater section 83 may be provided with a sheath as in Fig. 4 but the section 89 should be unshielded so as to affect the disk 51 promptly.

Although the invention has been described with particular reference to certain specific embodiments thereof, it should be understood that various alternative arrangements and equivalents may be resorted to without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In a submersible pump-motor unit, an electric motor having a frame portion with at least one winding; end structure at one end of said frame portion providing a housing for an electrical connection between the winding and a line, said endstructure being formed with an internal recess adapted to receive fluid being pumped; a protective device interposedin the motor circuit at said electrical connection and comprising contact means in series with said winding and operative for disconnecting the winding at a predetermined temperature, a bimetallic element arranged to sheet opening and closing of said contact'n'ieans, and electrical heating means in physical proxiinityto'said bimetallic element and'connected in circuit with the motor, said heating means including a heating element connected in series with said winding whereby to provide overload protection for the motor; enclosure means containing said contact means, said bimetallic element, and said heating means and disposed within said recess; and a body of electrical insulating material retaining said enclosure means in said recess in fluid-tight embedded relation therein, said enclosure means including a metallic heat conducting portion projecting from said body and adapted to be contacted by the fluid in said recess for conducting heat from said heating means to the fluid whereby said heating means is normally cooled by the fluid in said recess but is adapted to actuate said bimetallic element to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

2. In a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavity in said motor with means permitting the circulation through said cavity to be of tluid being pumped, and a combined overload and low liquid protective device for the unit located in said cavity in contact with fluid flowing therethrough, said protective device com prising heat sensitive means in series with said winding and operative for disconnecting the winding at a predetermincd temperature and electrical heating means in physical proximity to said heat sensitive means and connected in electric circuit with the motor winding and having a portion in series with said winding to be re-- sponsive to overload current flow through the motor, said heat sensitive means being adapted to open the motor circuit in response to an overload current therethrough whereby to provide overload protection for the motor, and said heating means being normally cooled by the fluid flowing through said cavity but being adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

3. in a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavity in said motor adapted to receivetluid being pumped, and a combined overload and low liquid protective device for the unit located in said cavity to be in contact with the fluid therein, said protective device comprising heat sensitive means in series with said winding and operative for disconnecting the winding at a predetermined temperature, said heat sensitive means being electrically connected to open the motor circuit in response to an overload current therethrough whereby to provide overload protection for the motor, and an electrical heating element in physical proximity to said heat sensitive means and connected in shunt relation with said winding, said element being normally cooled by the fluid in said cavity but being adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

4. In a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavityin said'rnotor-adapted to receive fluid being pumped, and a combined overload and low liquid protective device for the unit located in said cavity to be in con-tact with the fluid therein, said protective device comprising heat sensitivemeans in series with said winding and operative for disconnecting the winding at a predetermined temperature, 'an elmtrical heating element in physical. proximity to said heat sensitive means and connected in series with said winding whereby to provide overload protec'tion'for the motor, and an auxiliary heater in physical proximity to saidh'eat sensitivemeaiis and connected in shunt relation with said winding, said 9. auxiliary heater being normally cooled by the fluid in said cavity but being adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

5. The device of claim 4 further characterized in that the motor comprises a single phase alternating current motor with a running winding and a starting winding connected in parallel and having means to disconnect the starting winding at a predetermined motor speed, and said heating element is connected in series with both of said windings.

6. In a submersible pump-motor unit, an electric motor having at least one winding, means within said motor providing an internal cavity adapted to receive fluid being pumped, protective means for the unit including heat sensitive means in series with said winding and operative for disconnecting the winding at a predetermined temperature and electrical heating means in physical proximity to said heat sensitive means and connected in circuit with the motor, said heating means including a low resistance heating element connected in series with said winding whereby to provide overload protection for the motor and a high resistance shunt heating element connected in parallel with said winding, and sealing means mounting said heat sensitive means and said heating means in said cavity in fluid-tight relation, said sealing means including a heat conducting portion closely adjacent said shunt heating element and exposed to a predetermined extent to the fluid in said cavity for conducting heat from said shunt heating element to the fluid whereby said shunt heating element is normally cooled by the fluid in said cavity but is adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

7. In a submersible pump-motor uni-t, an electric motor having a frame portion with at least one winding; end structure at one end of said frame portion providing a housing for an electrical connection between the winding and a line, said end structure being formed with an internal recess adapted to receive fluid being pumped; a protective device interposed in the motor circuit at said electrical connection and comprising contact means in series with said winding and operative for disconnecting the winding at a predetermined temperature, a bimetallic element arranged to effect opening and closing of said contact means, and electrical heating means in physical proximity to said bimetallic element and connected in circuit with the motor, said heating means including a heating element connected in series with said winding whereby to provide overload protection for the motor and an auxiliary heater connected in shunt relation with said winding; enclosure means containing said contact means, said bimetallic element, and said heating means and disposed within said recess; and a body of resinous material retaining said enclosure means in said recess in fluid-tight embedded relation therein, said enclosure means including a metallic heat conducting portion closely adjacent said auxiliary heater and projecting from said body and adapted to be contacted by the fluid in said recess for conducting heat from said auxiliary heater to the fluid whereby said auxiliary heater is normally cooled by the fluid in said recess but is adapted to actuate said bimetallic element to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

8. In a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavity in said motor adapted to receive fluid being pumped, and acombined overload and low liquid protective device for the unit comprising heat sensitive means in series with said winding and operative for disconnecting the winding at a predetermined temperature, said heat sensitive means being adapted to open the motor circuit in response to an overload current therethrough whereby to provide overload protection for the motor, an electric heating element in physical proximity to said heat sensitive means and connected in shunt relation with said winding, and enclosure means containing said heat sensitive means and said heating element and disposed within said cavity, said enclosure means including a generally cup-shaped portion of relatively low thermal conductivity having said heating element disposed therein, and a heat conducting element of relatively high thermal conductivity extending through said cup-shaped portion from the interior thereof into said cavity for conducting heat from said heating element to fluid in said cavity whereby said heating element is normally cooled by the fluid but is adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid for the pump is exhausted thereby protecting the unit against operation without an adequate:

supply of fluid.

9. The device of claim 8 further characterized in that: said cup-shaped portion comprises stainless steel and said heat conducting element comprises copper.

10. The device of claim 8 further characterized in that said heat conducting element comprises a strip extending through the base of the cup-shaped portion in sealed relation therewith, the innermost end of said strip being wrapped around said heating element and the outermost end of said strip being arranged compactly in said cavity for contact with the fluid therein.

11. In a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavity in said motor adapted to receive fluid being pumped, and a combined overload and low liquid protective device for the unit comprising heat sensitive means in series with said Winding and operative for disconnecting the winding at a predetermined temperature, an electrical heating element in physical proximity to said heat sensitive means and connected in series with said winding whereby to provide overload protection for the motor, an auxiliary heating element in physical proximity to said heat sensitive means and connected in shunt relation with said winding, and enclosure means containing said heat sensitive means and both of said heating elements and disposed Within said cavity, said enclosure means including a generally cup-shaped portion of relatively low thermal conductivity having said auxiliary heating element disposed therein, and a heat conducting element of relatively high thermal conductivity extending through said cup-shaped portion from the interior thereof into said cavity for conducting heat from said auxiliary heating element to fluid in said cavity whereby said auxiliary heating element is normally cooled by the fluid but is adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid for the pump is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

12. In a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavity in said motor adapted to receive fluid being pumped, and a protective device for the unit comprising an overload prJtector including a base with a depending annular skirt portion, heat sensitive means mounted on said base within said skirt portion and connected in series with said winding and operative for disconnecting the winding at a predetermined temperature, an electrical heating element mounted on said base within said skirt portion in physical proximity to said heat sensitive means and connected in series with said winding whereby to provide overload protection for the motor,

a cup-shaped member fitted on said skirt portion in substantially unitary relation with the overload protector, an auxiliary heater disposed in said cup-shaped member in physical proximity to said heat sensitive means and connected in shunt relation with said winding sealing means retaining said overload protector and the attached cup-shaped member in fluid-tight relation in said cavity, and heat conducting means extending from said auxiliary heater through said cup-shaped member into said cavity for conducting heat from said auxiliary heater to the fluid in said cavity whereby said auxiliary heater is normally cooled by the fluid but is adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid for the pump is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

13. In a submersible pump-motor unit, an electric motor having at least one winding, means providing an internal cavity in said motor adapted to receive fluid being pumped, and a combined overload and low liquid protective device for the unit located in said cavity in contact with the fluid therein, said protective device comprising heat sensitive means in series with said winding and operative for disconnecting the winding at a predetermined temperature and electrical heating means in physical proximity to said heat sensitive means and connected in circuit with the motor, said heating means including a first resistance heater connected in shunt relation with said winding and a second resistance heater connected around said heat sensitive means and normally short-circuited when the motor circuit is closed, said heat sensitive means being adapted to open the motor circuit in response to an overload current therethrough whereby to provide overload protection for the motor with said second resistance heater being energized when the motor circuit is thus opened whereby to limit or prevent cycling of the heat sensitive means, and said first resistance heater being normally cooled by the fluid in said cavity but being adapted to actuate said heat sensitive means to disconnect said winding when the supply of fluid being pumped is exhausted thereby protecting the unit against operation without an adequate supply of fluid.

14-. in a submersible pump-motor unit, an electric motor having at least one Winding; means providing an internal cavity in said motor adapted to receive fluid being pumped; and a combined overload and low liquid protective device for the unit located in said cavity in contact with the fluid therein; said protective device comprising a bimetallic element, contact means in series with said winding and controlled by said bimetallic ele ment for disconnecting the winding at a predetermined temperature, and electrical heating means in physical proximity to said heat sensitive means and connected in circuit with the motor; said heating means including a low resistance heating element connected in series with said winding and said contact means whereby to provide overload protection for the motor, a first high resistance heating element connected in shunt relation with said winding, and a second high resistance heating element connected around said contact means and normally shortcircuited when the motor circuit is closed; said second high resistance heating element being energized when said contact means is open whereby to limit or prevent cycling of the bimetallic element, and said first high resistance heating element being normally cooled by the fluid in said cavity but being adapted to actuate said bimetallic element to open said contact means and disconnect said winding when the supply of fluid being pumped is exhausted-thereby protecting the unit against operation without an adequate supply or" fluid.

15. A combined overload and low liquid protective.

winding of the motor and operative for disconnecting the winding at a predetermined temperature, an electrical heating element in physical proximity to said heat sensitive means and also adapted to be connected in series with the motor winding whereby to provide overload protection for the motor, an auxiliary heating element in physical proximity to said heat sensitive means and adapted to be connected in shunt relation with the motor winding, enclosure means containing said heat sensitive means and both of said heating elements, said enclosure means including a generally cup-shaped portion of relatively low thermal conductivity having said auxiliary heating element disposed therein, and a heat conducting element of relatively high thermal conductivity extending through said cup-shaped portion from the interior to the exterior thereof for conducting heat from said auxiliary heating element to an external cooling liquid whereby said auxiliary heating element is normally cooled by the liquid but is adapted to actuate said heat sensitive means to disconnect the motor winding when no cooling liquid is present.

16. The device of claim 15 further characterized in that said cup-shaped portion comprises stainless steel and said heat conducting element comprises copper.

17. The device of claim 15 further characterized in that said heat conducting element comprises a strip extending through the base of the cup-shaped portion in sealed relation therewith, the innermost end of said strip being wrapped around said auxiliary heating element and the outermost end of said strip being arranged compactly at the outside of said cup-shaped portion.

18. A protective device for use with a pump-motor unit comprising an overload protector including a base with a depending annular skirt portion, heat sensitive means mounted on said base within said skirt portion and adapted to be connected in series with a winding of the motor and operative for disconnecting the winding at a predetermined temperature, an electrical heating element mounted on said base within said skirt portion in physical proximity to said heat sensitive means and also adapted to be connected in series with the motor winding whereby to provide overload protection for the motor, a cupshaped member of relatively low thermal conductivity fitted on said skirt portion in substantially unitary relation with the overload protector, an auxiliary heater disposed in said cup-shaped member in'physical proximity to said heat sensitive means and adapted to be connected in shunt relation with the motor winding, and heat conducting means extending from said auxiliary heater through said cup-shaped member to the exterior thereof for conducting heat from said auxiliary heater to an external cooling liquid whereby said auxiliary heater is normally cooled by the liquid but is adapted to actuate said heat sensitive means to disconnect the motor winding when no cooling liquid is present.

19. In a pump-motor unit combination of an enclosure in the unit adapted to receive liquid when being pumped by the unit, an electric motor, and protective means for the unit including a heat responsive switch connected in series with said motor to control the operation of the motor, electrical heater means adjacent said switch and connected in circuit with said motor to provide overload protection for said motor, said heater means having a portion connected in series with said motor to be responsive to overload current flow through the motor, and a container enclosing said heater means and said heat responsive switch and having a heat conducting portion mounted within said enclosure and exposed for contact with liquid therein, whereby said switch is maintained closed during normal operation but opens to stop said motor when either an overload on said motor occurs or when the liquid being pumped is exhausted and the cooling effect of the liquid on said heat conducting portion -is thereby withdrawn.

20. The combination according to claim 19, in which said heater means includes a heating element connected in shunt relation with said motor.

21. The combination according to claim 19, in which said heater means includes a first heater element connected in series with said switch and said motor and a second heater element connected in shunt relation with respect to said switch and said motor.

Boothby Apr. 16, 1935 Bonner Nov. 23, 1943 14 Clark Mar. 25, 1947 Ingels Nov. 30, 1948 Szwargulski Feb. 1, 1949 Ogden Feb. 14, 1950 Brooks Aug. 15, 1950 Morris Aug. 5, 1952 Hemphill June 22, 1954 Barrell Apr. 24, 1956 Schaefer Dec. 18, 1956 FOREIGN PATENTS Great Britain Apr. 20, 1955