US2384025A - Motor starting circuits and resistance unit for use therein - Google Patents

Description

l 1945 H. J. GRAHAM 2,384,025

MOTOR STARTING CIRCUIT AND RESISTANCE UNIT FOR USE THEREIN Filed March 4, 1943 2 Sheets-Sheet 1 171110711370 2". [[0230 Z12 Jlk'aharn.

Sept. 4, I945. 'H. J. GRAHAM 2,384,025

MOTOR STARTING CIRCUIT AND RESISTANCE UNIT FOR USE THEREIN Filed March 4, 1945 2 Sheets-Sheet 2 Patented Sept. 4, 1945 MOTOR STARTING CIRCUITS AND RESIST- AN CE UNIT FOR USE THEREIN Harold J. Graham, Boston, Mass. Application March 4, 1943, Serial 'No. 477,956

Claims.

My invention relates to motor starting circuits and to resistance units particularly adapted for use in such circuits.

The invention will be best understood from the following description when read in the light of the accompanying drawings. the scope oi the invention being more particularly pointed out in the appended claims.

In the drawings- Fig. 1 is a vertical sectional elevation, on the line II of Fig. 2, of the resistance unit according to the invention;

Fig. 2 is a section on the line 22 of Fig. 1;

Fig. 3 is a schematic diagram of a motor starting circuit and associated mechanism;

Fig. 4 is a view'showing the valve of Fig. 3 in a diflerent operative position; and

Fig. 5 is a schematic diagram showing a modification of part of the circuit of Fig. 3.

As will be understood by those skilled in the,

art, it is common practice in starting motors to place in series with the motor when it is initially energized either an ohmic resistance or an impedance, depending upon whether the motor being started is a D. C. or an A. C. motor, for

reducing the voltage applied to the motor, which I resistance or impedance is gradually cut out of circuit as the motor is brought to speed.

With large size motors, extreme difiiculty has been encountered in dissipating the heat gener ated by the resistance or impedance, making it necessary in instances where the motor is frequently stopped and started to employ resistances which structurally are of very large size.

To avoid the defects of prior installations, the

7 present invention comprehends a resistance, by

which term is herein included an impedance as well as an ohmicresistance,- immersed in a body of liquid with provision for cooling the same. it having been found that by such an arrangement the resistance unit and associated parts may be of relatively small dimensions with assurance that the resistance will not overheat or burn out under severe operating conditions.

Referring to the drawings showing a selected embodiment of the invention, there is provided a liquid container I, which conveniently may be in the form of a rectangular steel can. As shown, the can is provided with a cover 3 removably secured by bolts 5 to a flange 1 which surrounds the upper periphery of the can. Conveniently, a

, gasket 9 is placed between the cover and the flange to render the cover fluid-tight.

The can above described is filled with liquid to about the level L. Immersed in this liquid is a bare helical resistance coil II, the helix being rectangular transverse to its axis as illustrated in Fig. 2 and its turns being fairly widely spaced, the conductor'forming the coil in the illustrated embodiment of the invention being ribbon-like.

Extending through the cover are shown'a plurality of conductors in the form of rigid rods, The upper end of the coil is electrically connected to the lower end of the rod [3, while the lower end of the coil is electrically connected to the lower end of the longer rod l 5. As shown, the ends of the rods are slotted as indicated at ll (Fig. l), the ends of the coil being placed in these slots and soldered thereto as, for example, w t hard silver solder.

The remaining rod l9, 2 .23, 25, 2.1 and 29 shown are of progressively increasing length, their lower ends bein tapped to the resistance coil at different oints along its length. For Connecting the ends of these rods to the coil, Pieces of the same material as the resistance wire are bent to provide bracket members having the less 3| and 33, the legs 33 being laid against the conductor forming the resistance coil and soldered thereto, While the legs 3| are connected to the ends of the rods in the ways above mentioned in connection withthe rods I3 and I5.

The upper ends of the rods mentioned are screw threaded to form terminals, the rods extending through and tightly fitting insulating bushings 35 extending through and having driving fits with the openings 31 in the cover 3.

As shown, immersed in the body of liquid in the container I between the circumferential walls of the container and the resistance coil, is a cooling coil 39, the latter having relatively widely spaced turns and being conveniently'formed of copper tubing,-as shown, the upper and lower ends of the cooling coil have extensions ll and 43, respectively forming the outlet and inlet connections to the coil. As shown, the ends of each of these extensions is received in a socket in the lower end of a fitting 45, conveniently being sweated to the Walls of said socket. As shown, the fitting extends through an opening 41 in the cover and is secured thereto by a nut 49, the upper end of the fitting forming a nipple 5| for connec-' value. Preferably a pressure relief valve 53 carried by the cover is provided for relieving any excess pressure generated interiorly of the container, the container being otherwise sealed to avoid both escape of the oil fumes and so-called breathing of atmospheric air.

It will be observed by the above described construction, that both the resistance coil and cooling coil are effectively suspended from the cover of the container out of contact with the container bottom, and that ample provision is made for expansion and contraction of the two coils, further that both coils may be removed from the container with the cover for inspection and repair, and can be conveniently assembled on the cover when the same is detached from the container.

In Fig. 3 is shown one form of motor starting circuit in which the resistance unit above described is adapted to be employed. As illustrated, the terminals afiorded by the upper ends of the rods I3, I5, I9, 2|, 23, 25, 21 and 29 of the resistance unit are connected to corresponding terminals 55 of a rheostat having a contact arm 51, which arm may be manually swung around a pivot 59 by a handle GI against the resistance of a torsion spring 63. As shown in Fig. 3, by moving the handle GI to the left from its full line position the rheostat arm 51 will place the resistance II in series with the motor 65 to be started, and as the handle is gradually moved to the left the arm will cause the resistance to be gradually cut out of circuit, until when the .handle is in its dotted line position shown in Fig.

3 the resistance will be entirely out out of circuit. As shown, the rheostat arm 51 is conveniently provided with an armature 51 which cooperates with the holding coil 69 to retain the handle BI in its dotted line position against the effort of the torsion spring 63 tending to return the handle to its full line position.

As schematically shown in Fig. 3, the inlet extension 43 of the cooling coil of Fig. l is supplied with water from a pipe 1I controlled by a valve 13 of the rotary plug type, which valve is provided with an exterior arcuate groove 15 for establishing communication between the pipe 11 and the inlet extension of the cooling coil when the valve handle 11 is out of its left hand position shown in Fig. 3. As schematically illustrated in Fig. 3, the valve handle 11 is connected by a link 19 to the handle GI of the rheostat. When the handle BI is in its dotted line posi: tion of Fig. 3 it will have moved the valve handle 11 into its position shown by Fig. 4 to again interrupt the flow of cooling water to the cooling coil. As a result of this construction, moving the handle 6| to place the rheostat arm 51 on the right hand rheostat contact 55 to place the resistance II in series with the motor will initiate a supply of cooling water to the cooling coil. This supply will remain established until the rheostat arm is moved to the left hand contact 55 to out the resistance I I out of circuit. By this arrangement considerable saving of cooling fluid cffected because normally the cooling fluid will flow only when the resistance is in circuit, that is to say, while the motor is being started.

As shown in Fig. 1, immersed in the body of liquid in the container is a so-called heat sensitive tube 8I of known construction consisting of a small sealed container filled with a liquid or other fluid adapted to expand when heated, a pilot tube 83 being provided for transmitting to the exterior of the container the pressure so generated. As shown, the pilot tube is provided with the usual protective covering 85 and extends through an opening in the cover 3, being firmly secured thereto by a push fitting 81 or in any other way commonly employed in connection with heat sensitive tubes.

As schematically illustrated in Fig. 3, the pilot tube 83 is connected to a chamber 89 closed by a flexible diaphragm 9I. Upon excess heating of the liquid in the container i the diaphragm will be flexed to the right against the resistance of the compression spring 93 and move the rod 95 connected to the diaphragm to the right to cause it to engage with the swinging latch 91 pivoted at 98. The latch normally holds the switch 99 closed against the tension of the spring IOI, release of the latch by movement of the rod 95 permitting the spring IOI to open this switch. When the switch 99 is opened it will break the circuit through the solenoid I03 with which cooperates an armature I95 normally holding the circuit breaker I01 in closed position against the effort of the spring I09. When the circuit through the solenoid is broken the spring I09 will open the circuit breaker and deenergize the motor 65. By manually closing the switch 99 the latch spring I I0 will normally cause the latch to reengage to retain the switch 99 in closed position.

It frequently happens in practice, especially when the motor is being started under load and comes up to speed very slowly, that the operator will keep the resistance I I too long in circuit and dangerously overheat it. However, by-the above described construction, involving use of the heat sensitive tube 9| and circuit breaker I01, the motor will be deenergized under such conditions. When the motor is deenergized upon opening of the circuit breaker I01, the latch 91 will be held in its released position by the rod until the liquid in the container I cools sufficiently to permit the compression spring 93 to move the rod 95 into its normal position and enable the operator to reset the latch by manually closing the switch 99. In other words, the latch cannot be reset to hold the switch 99 closed until the liquid in the container is cooled to below the predetermined temperature at which the latch is released; However, while the circuit breaker is open the handle SI of the rheostat may be moved by the operator to open the valve 13 to supply cooling liquid for cooling the overheated resistance II. Normally the circuit breaker I 01, the latch 91 and associated mechanism will be contained in the locked casing the key to which is in the hands of a. responsible person. It will be understood, however, that closing the control switch II for supplying the energizing current to the motor will not supply that current unless the latch 91 is in engaged position, under which conditions the solenoid I03 will automatically close the circuit breaker when the switch III is closed.

The mechanical release mechanism afforded by the latch 91 may, if desired, be replaced by an electrical release as illustrated in Fig. 5. As

shown in Fig. 5, movement of the rod 95 to the.

left upon excess heating of the liquid in the container I is effective to open the normally closed switch I I3 to break the current through the high resistance relay coil I I5. When the circuit is so broken the spring II1 will be effective to open the relay switch H9 and break the current through the solenoid I03 of the circuit breaker I01 to permit th spring I09 to open the circuit breaker. With the arrangement shown in Fig. 5,

when the switch I I l is closed the circuit breaker ill! will automatically close provided the tem perature of the liquid in the container l is sufficiently reduced to cause the rod 95 to permit the spring I2! to close the switch H3. Otherwise, and so long as the temperature of the liquid in the container l is above an undesired maximum, the switch H3 will be held open and the solenoid I03 of the circuit breaker [01 will be deenergized to cause the spring l! of the circuit breaker to hold the latter in open position.

It will be understood that, within the scope of the appended claims, wide deviations may be made in the forms of the invention above described without departing from the spirit of the invention.

I claim:

1. An electric resistance unit having, in combination, a liquid container, a resistance element in said container positioned to be submerged in the liquid therein, a fluid conducting cooling coil for the liquid in said container positioned to be submerged in the liquid therein, a removable cover for said container, said resistance element and cooling coil being secured to said cover and removable from said container with said cover.

2. An electric resistance unit having, in comfor said container, a conductor in the form of a vertically extending coil forming a resistance positioned in said container above th bottom thereof, a vertically extending fluid conducting cooling coil for the liquid in said container positioned in the latter above the bottom thereof, said conductor coil and cooling coil being suspended from said cover with one of said coils surrounding the other, said coils being removable from said container with said cover.

3. An electric resistance unit having, in combination, a liquid container, a removable cover for said container; a conductor in the form of a vertically extending coil forming a resistance in said container above the bottom thereof and positioned to be submerged in the liquid therein; a fluid conducting cooling coil for the liquid in said container above the bottom thereof and positioned to be submerged in the liquid therein; taps for said conductor coil carried by said cover and suspending said conductor coil from said cover; said' cooling coil having inlet and outlet connections carried by said cover and suspending said cooling coil from said cover, said coils being removable from said container with said cover.

4. An electric resistance unit having, in combination, a liquid container; a removable cover for said container; a group of vertically extending, laterally spaced, conducting rods operatively fixedly carried by and extending through said cover into said container; a resistance coil in said container above the bottom thereof and positioned to be submerged in the liquid therein, said coil surrounding said group of rods and being tapped at different points along its length to said rods severally, whereby said coil is supported through said rods solely by said cover; and a fluid conducting cooling coil in said container above the bottom thereof and positioned to be submerged in the liquid therein, said coo-ling coil surrounding said resistance coil and having vertically extending terminal inlet and outlet portions extending through and carried by said cover, whereby said cooling coil also is solely supported by said cover, and whereby both the cooling coil and resistance coil may be removed from said container with said cover.

5. An electric resisitance unit having, in combination, a liquid container; a removable cover for said container; a group of vertically extending, laterally spaced, conducting rods operatively fixedly carried by and extending through said cover into said container, which rods severally terminateat different distances above the bottom of said container; a resistance coil in said container above the bottom thereof and positioned to be submerged in the liquid therein, said coil surrounding said group of rods and being tapped at difierent points along its length to the lower end portions of said rods severally, whereby said coil is supported through said rods solely by said cover; and a fluid conducting cooling coil in said container above the bottom thereof and. positioned to be submerged in the liquid therein, said cooling coil surrounding said resisitance coil and having vertically extending terminal inlet and outlet portions extending through and carried by said cover, whereby said cooling coil also is solely supported by saidcover, and whereby both the cooling coil and resistance coil may be removed from said container with said cover.

HAROLD J. GRAHAM

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