US2947931A - Motor control systems - Google Patents

Description

Aug. 2, 1960 L. M. HUBBY 'MOTOR CONTROL SYSTEMS 2 Sheets-Sheet 1 Filed Dec. 24, 1956 m A v. v A

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lf i m iiiil Aug. 2, 1960 L. M. HUBBY 2,947,931

MOTOR CONTROL SYSTEMS Filed Dec. 24, 1956 2 Sheets-Sheet 2 MOTOR CONTROL SYSTEMS Laurence M. Hubby, Bellaire, Tex., assignor to Texaco Inc., a corporation of Delaware Filed Dec. 24, 1956, Ser. N0.-630,384

1 Claim. (Cl. 318-447) This invention relates to motor control systems and more particularly to systems for automatically controlling the pumping operation in an oil-producing well.

In many wells the quantity of fluid entering the borehole from the formation is often less than that which can be readily handled by the pumping equipment installed at the well. A sustained pumping operation by such equipment results in pumping the well substantially dry and in operating the pumping equipment at only a fraction of its normal or full load. Pumping operations under such conditions are accompanied by a decrease in efficiency and excessive wear of the pumping unit and motor. Consequently, it is customary to shut down the pumping equipment when a well runs dry and to pump intermittently so that the fluid is permitted to accumulate in the borehole during shutdown periods and is exhausted from the well during alternate pumping periods.

The intermittent pumping operation may be controlled either manually or automatically. Automatic devices which are adjusted to shut ofi and stop the pump only after the elapse of a certain time interval are well known in the art. However, if the time interval is not accurately and continuously determined for each well, the pumping period may be prematurely cut 013? at a time when considerable oil remains in the borehole or the pumping period may be cut ofi long after the borehole has been pumped substantially dry.

Pump control devices have been built which utilize a check valve or flapper in the well flowline and which are responsive to fluid flow. Such devices are difficult to install and are subject to failure through parafiinic accumulations which render the control mechanism inoperative. Furthermore, such devices are unable to distinguish between the flow of oil and the flow of gas; and usually, after the flow of oil has stopped the flow of gas begins quickly, by keeping the unit in operation as if it were still pumping oil. This occurs if the fluid oil level is, for any reason, pumped down to a point below the entry into the pump. When this happens, the gas, which is above the fluid level, will enter the pump as bubbles and frothy oil and the control device will not recognize the difference.

Accordingly, it is an object of the present invention to provide a control system for automatically shutting down well pumping equipment when the well has been pumped substantially dry.

A further object of this invention is to provide a control system for automatically terminating a pumping period when a well has been pumped substantially dry and for automatically starting another pumping period at a predetermined instant of time.

It is also an object of this invention to provide a well pumping control system wherein the duration of the pumping period is automatically adjusted to the amount of liquid available for pumping during the pumping period.

Another object of this invention is to provide a con- Unite States atet trol system which responds to load changes in a prime mover.

Still another object of this invention is to provide a control system which responds to a decrease in load in a prime mover.

In accordance with this invention, a control system is provided which is responsive to changes in energy consumed by a prime mover.

In order that the invention may be more clearly understood and readily put into effect, it will now be described more fully with reference to the accompanying drawing in which: Fig. 1 is a diagrammatic sketch illustrating the component parts of an embodiment of a pumping unit including a circuit diagram of an alternating current motor control system in accordance with the invention, and

Fig. 2 illustrates a circuit diagram of a system which may be used to control a direct current motor.

As shown in Fig. l the pumping unit includes a reciprocating well pump 19 located in a production tubing 12 which extends through the length of a borehole 14 lined with a casing 16. The pump 10 is shown disposed in a column of oil 18 below the gas-oil interface 20. The pump 10 is actuated in a well-known manner by means of a string of sucker rods 22 connected to a polished rod 24 which passes through a stuffing box 26 of a well head 28. Connected to the well head 28 is an outflow pipe 30 which may have a flow meter 32. A source of me chanical power 'for driving the pump 10 is supplied by an electric motor 34 through a shaft 36, a speed reducing mechanism 38 and means coupled to the polished rod for converting rotary motion to translatory motion, which means includes a crank 40 having a suitable counterweight 42 and a pitman 44 connected to a walking beam 46. On one end of the walking beam 46 disposed over the well head 28 is a horse head 48 and at the other end of the walking beam there is disposed a suitable counterweight 50. The polished rod 24 is connected to the horse head 48 by a bridle 52.

The pumping unit also includes an electric motor control system which is connected between terminals 54,

and 56 of electric motor 34 and terminals 58, 59 and 60 of an electrical power source 62, preferably a threephase alternating current source having a frequency of 60 cyclesper second. The system includes a main relay having a main coil 64 connected in series with a periodically actuated control switch 66 between terminals 58 and 59 of power source 62 and main switches 68, 69 and 70 interposed in conductors 72, 73 and 74 respectively which connect terminals 58, 59 and 60 of power source 62 to terminals 54, 55, and 56 respectively of electric motor v34. The primary winding 76 of a first transformer 78 is connected between conductors 72 and 73 at points intermediate the main switches 68 and 69 and the tenninals 54 and 55 of electric motor 34. A secondary winding 80 of transformer 78 is connected across the terminals of a potentiometer 82 having an adjustable tap 84. A primary winding 86 of a second transformer 88 is interposed in conductor 72 intermediate the main switch 68 and terminal 54- of electric motor 34, A secondary winding 90 of transformer 88 is connected serially with the secondary winding 80 of transformer 78 so as to provide a voltage of opposite phase to the voltage produced by winding 80. A voltmeter 94 is connected between the one terminal of the secondary winding 90 and the tap 84 of potentiometer 82 to measure the resultant voltage across the secondary winding 90 and a portion of potentiometer 82 determined by the position of tap 84. The control system also utilizes a first timedelay relay having a coil 96 and a-switch 98 and a second time-delay relay having coil 100 and a switch 102. The coil 96 of the first time-delay relay is connected between terminals 58 and 59 of power source 62 through main switches 68 and 69. The switch 98 of the first time-delay relay is connected in series with the coil 100 of the second time-delay relay and secondary winding 90 of transformer 88 and secondary winding 80 of transformer 78 through tap 84. The switch 102 of the second time-delay relay is connected between the terminal of the main coil 64 remote from terminal 58 of power source 62 and terminal 55 of the electric motor 34.

In operation, the periodically actuated control switch 66 closes at a predetermined time to start the electric motor 34 by completing the circuit to the main coil 64 which causes the main coil 64 to become energized, hence, closing main switches 68, 69 and 70. As soon as switches 68 and 69 are closed, a voltage is produced across the secondary winding 80 of the first transformer 78 and current flows through conductor '72 from terminal 58 of the power source 62 to the motor 34 passing through the primary winding 86 of the second transformer 88 to induce a volt-age in the secondary winding 90. By

properly adjusting tap 84 of potentiometer 82, equal but opposite voltages canbe set up across the secondary Winding 90 of the second transformer 88 and a portion of potentiometer 82 which will produce a zero voltage across voltmeter 94 under given or normal pumping conditions. Therefore, under the given pumping conditions no current can pass through coil 100 of the second timedelay relay regardless of whether switch 93 of the first time-delay relay is in the open or closed position. The

switch 98 of the first time-delay relay is maintained in an open position until after a predetermined starting period has passed in order to protect coil 100 of the second time-delay relay from excessive transient voltages which may be set up during the starting period. At the termination of the starting period periodically actuated switch 66 is opened but the main coil 64 of the main relay now continues to be energized through normally closed switch 162 of the second time-delay relay.

When the well runs dry, that is, when the pump is pumping at substantially less than its full or normal capacity, the electric motor 34 loses a substantial amount of its load and therefore the electric motor 34 no longer demands the current that was demanded during the normal pumping operation. This decrease in current causes the voltage developed across the secondary winding 90 of second transformer 88 to decrease, thus increasing the resultant voltage across voltmeter 94 since the voltage across the secondary winding 80 of first transformer 78 remains substantially constant. The voltage across the voltmeter 94 energizes coil 100 of the second time-delay relay which after an elapse of time opens switch 102 to deenergize main coil 64, thus opening switches 68, 69 and 70 to cut off the supply of electric energy from the power source 62 to the electric motor 34. The switch 102 of the second relay recloses after switches 68, 69 and 7%} open but the electric motor 34 will remain inoperative since current will not pass through switch 102 to main coil 64 when switches 68, 69 and 70 are open. The electric motor 34 will not restart until the periodically actuated control switch 66 recloses to begin a new cycle.

The variable resistor 92 is connected in series with coil 100 of the second time delay relay in order tovary the percentage of the voltage across voltmeter 94 that is to be applied across coil 100, thus providing adjustable means for terminating the pumping action when the motor 34 is operating at any given load and for preventing minor disturbances from activating the second time delay relay. The variable tap 84 of potentiometer 82 provides adjustable means to compensate for changes in size of pump, in pumping strokes per minute or in well fluid, or for seasonal changes in motor load.

Electric motor 34, which is illustrated in Fig. 1 as hav ing three input terminals 54, 55 and 56 may be a threephase or two-phase motor. However, it should be understood that the control system of the present invention may also be used to control single phase motors. It should also be understood that the periodically actuated control switch 66 may be manually operated as well as automatically.

When a direct current motor is used as the prime mover the control system illustrated in Fig. 2 may be used. This system operates in a manner similar to that of the control system illustrated in Fig. 1 and diflers therefrom only in that the potentiometer 82 is connected directly across the power lines or between the electrical conductors 72 and 73' and a resistor 88' replaces the second transformer 88.

Obviously many modifications and variations of the invention as hereinabove set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claim.

I claim:

In a pumping unit for pumping fluid from a well,

an electric motor control system comprising means having first and second output terminals for supplying electric energy, an electric motor having first and second input terminals, first and second conductors each including a mainswitch interconnecting said first terminals and said second terminals respectively, a main relay having a main coil for actuating said main switches, a periodically actuated control switch connected serially with said main coil between said first and second output terminals, a potentiometer having a variable tap, a first transformer having a primary winding connected between the first and second input terminals of said electric motor and a secondary winding connected across said potentiometer, a second transformer having a primary winding interposed in said first conductor between the main switch of said conductor and said first input terminal and a secondary winding connected serially with and in phase opposition to the secondary winding of said first transformer, a voltmeter connected between the variable tap of said potentiometer and the terminal of the secondary winding of said transformer remote from the secondary winding of the first transformer, a first time delay relay having a switch and a coil connected between said first and second input terminals, a variable resistor, and a second time delay relay having a coil connected serially with said variable resistor and the switch of said first time delay relay across said voltmeter, and a switch connected across said periodically actuated control switch through one of said main switches.

References Cited in the file of this patent UNITED STATES PATENTS 1,199,936 Simon Oct. .3, 1916 1,983,429 Albright Dec.,4,.l934 2,180,400 Coberly Nov. 21, 1939 2,456,456 Smith Dec. 1 4, 1948 2,498,057 Winter Feb. 21, 1950 2,688,268 Hunter et al. Feb, 2, 1954 2,687,693 Hudson Aug. 31, 1954 2,754,763 Hofer July 17, 1956 2,774,929 Schaefer Dec. 18, 1 956 2,856,574 Schaefer Oct. 14, 1958

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