US 3778694 A
An electric motor-control system. The motor load is a beam-type pumping unit which has an upstroke and a downstroke in each cycle. Loss of normal load during the downstroke only is detected by comparison with a preset normal-load signal and the motor is shut down.
Description (OCR text may contain errors)
[4 1 Dec. 11, 1973 3,509,824 5/1970 Schmidly, 3,413,535 11/1968 Hubby ELECTRIC MOTOR CONTROL SYSTEM FOR A BEAM-TYPE PUMPING LOAD  Inventors: Laurence M. Hubby, Bellaire;
Herbert J. Mayer, Houston, both of Tex.
Primary Examiner-T. E. Lynch AttorneyThomas H. Whaley et al.
 Assignee: Texaco, Inc., New York, NY.
Filed: June 5, 1972 ABSTRACT Appl. No.: 259,890
 U.S. 318/474, 318/476 n elec ri m tor-control sy tem. The motor load is a  Int. Cl. H02p 1/04 beam-type pumping unit which has an upstroke and a  Field of Search............................. 318/474, 476 ownstroke in each cycle. Loss of normal load during the downstroke only is detected by comparison with a 1 preset normal-load signal and the motor is shut down.
References Cited UNITED STATES PATENTS Hubby 318/474 3 Claims, 5 Drawing Figures E 74 l I l l PATENTEB na: 1 1 1975 I saw 1 er 3 a? 1 l P I l AMPZ/F/EP 25%: I
ELECTRIC MOTOR CONTROL SYSTEM FOR A BEAM-TYPE PUMPING LOAD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns an electric-motor-control system in general. More specifically, it relates to a system for use with an electric-motor-driven beam-type pumping unit. The arrangement is for shutting down the motor upon loss of pumping load.
2. Description of the Prior Art In the area of electric-motor-driven pumping units where a beam-type reciprocating pump is employed, there have been various proposals for shutting down the pump under pump-of conditions. Among such earlier arrangements are those shown and described in two patents of one of the joint applicants, i.e., U.S. Pat. No. 3,413,535] Hubby, Nov. 26, 1968, and US. Pat. No. 3,440,512] Hubby, Apr. 22, 1969. It had previously been thought that a most sensitive shutdown control would involve the comparison of the load upon the pump motor between each upstroke and downstroke of the pumping cycle. However, it has been found that the upstroke load is an unreliable indication of pumping conditions in the well and, consequently, the earlier control arrangements often were found to be unreli able.
Consequently, it is an object of this invention to provide a pump-off motor-control system that employs only the motor-load conditions during each downstroke while making a comparison with a predetermined normal-load signal.
SUMMARY OF THE INVENTION Briefly, the invention concerns a combination that is in combination with a beam-type pumping unit which has an electric motor for driving said unit. It also has a first control circuit for shutting down said motor under pump-off conditions, and said first control circuit comprises a power-supply circuit for connecting a source of electric energy to said motor in addition to a switch connected in said power-supply circuit for disconnecting said motor from said source of electric energy. The improved combination comprises a relay for controlling actuation of said switch and an impedance in said power-supply circuit for carrying motor-load current therethrough. It also comprises means for developing a signal proportional to said motor-load current and means for comparing said signal amplitude with a predetermined normal amplitude signal only during the downstroke of said beam-type pumping unit.
It also comprises means for actuating said relay whenever said comparing means indicates below normal, which shows pump-off conditions, whereby said motor is disconnected.
Again briefly, the invention concerns a combination as described above, wherein said means for comparing comprises a field-effect transistor, a capacitor, and circuit means for connecting said capacitor to said field-effect transistor. The arrangement being provided so as to pass said motor-load signal when the fieldeffect transistor is in one state, and to block same when it is in another state. In addition, the means for comparing" comprises a pair of mercury switches mounted on said beam, and circuit means for connecting said switches to said capacitor for charging and discharging same at the beginning of the upstrokes and the downstrokes of said pumping unit.
Also, the invention concerns the combination according to the foregoing summary, where said means for actuating said relay comprises a difference amplifier having two input circuits with one of said input circuits being connected to said electronic means and the other being connected to an adjustable normal-load signal. The system also comprises a second electronic means which includes a transistor, a second capacitor, and circuit means for connecting the last-named transistor to said second capacitor to discharge same and start a time period of a timing circuit. The system also comprises third electronic means connected to said timing circuit which includes a unijunction transistor and a second transistor as well as circuit means for connecting said unijunction transistor to said second capacitor and to said second transistor, in order to cause said second capacitor to trip said unijunction transistor when the charge has reached a predetermined amplitude and to cause said second transistor to conduct when said unijunction transistor has been tripped.
In addition, the third electronic means comprises additional circuit means for connecting said second transistor across the winding of said relay. This acts to deenergize the relay by short-circuiting action when said second transistor conducts.
BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and benefits of the invention will be more fully set forth in connection with the best mode contemplated by the inventors of carrying out the invention, and in connection with which there are illustrations provided in the drawings wherein:
FIG. I is a schematic showing of a beam-type pumping unit with electric motor-shutdown controls, according to the invention;
FIG. 2 is a schematic circuit diagram illustrating a preferred embodiment for an electric system that is applicable to the motor-control system schematically indicated in FIG. 1;
FIG. 3 is a front elevation of an alternative switch structure which may be used to replace a portion of the circuit of FIG. 2;
FIG. 4 is a top plan view fo the FIG. 3 structure; and
FIG. 5 is a side elevation of the FIG. 3 structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates schematically a system according to the invention. There is a beam-type pumping unit 11 that is driven by an electric motor 12 (shown separately in the electrical schematic portion). Motor 12 has power supplied thereto by any feasible electric power source that would be connected to a set of input terminals 15. This power source may supply three-phase AC power, and there is a timing unit 16 that is connected across one phase, as illustrated. This timing unit controls a switch 17 that is connected in a circuit for energizing a winding 18 of a solenoid switch 19 that has a set of contacts 20 actuated thereby.
As will appear more fully hereafter, the switch 17 is periodically actuated by the timing unit 16 in the event that the pumping unit 11 has been shut down. This is arranged so that the pumping unit 11 may automatically be started again after the pump-off has occurred.
In parallel with the switch 17, there is pump-off shutdown-control switch 23. This switch 23 is actuated by a relay which has a winding 25 that is energized under the control of a schematically indicated amplifier 26.
The arrangement so far described is similar to motorshutdown controls generally employed for the same purpose as the systems described in the abovementioned Hubby patents. Therefore, it will be understood that there is a motor-starting arrangement (not shown) that energizes the switch 19 during starting conditions but thereafter drops out to leave the switch 23 effective for de-energizing the winding 18 of the switch 19 whenever it is opened, except during such starting period.
Also, as in the earlier systems, there is a current winding that is connected in series with one phase of the supply for motor 12. This is in order to provide a signal at the secondary of a transformer 31, which signal is proportional to the motor load. The transformer 31 has a secondary, or output winding 32 that provides a motor-load signal for the control system.
In this invention it is desired to compare the motorload conditions, during downstroke only, with a predetermined normal-load signal that may be developed for any given pumping well. Consequently, as is schematically indicated in FIG. 1, there is another transformer 35 that has an input winding 36 with an adjustable resistor 37 in series therewith. This is provided so as to be able to set a predetermined normal-load signal that will be developedacross an output winding 38 of the transformer 35.
It should be emphasized that the FIG. 1 illustration, and particularly that part just described, is entirely schematic but indicates the principles involved. These principles include the additional arrangement with a switch 41 connected into the output circuit of the winding 32. The switch contacts of switch 41 are actuated under control of the beam element of the pumping unit 11, as indicated by a dashed line 42. The arrangement is such that switch 411 will be closed only during the downstrokes of the pumping unit. Consequently, a comparison of the motor-load amplitude signal (indicated by a rectangle 45) will be made with a predetermined norm al-load signal (indicated by another rectangle 46). However, this is only carried out while the switch 41 is closed, i.e., during each downstroke of the pumping unit 11. During each upstroke switch 41 will be open, and no comparison of the signals will be made.
FIG. 2 illustrates a practical embodiment for a circuit to carry out the system that isschematically illustrated in FIG. 1. Thus, there is shown, at the left end of FIG. 2, the transformer 31 with its input winding 30 and output, or secondary winding 32.
In FIG. 2, there is a resistor 50 connected to the output winding 32 in series with a diode 51. There is a Zener diode 52 connected across the winding 32, so that there is a bypass, or protective circuit for absorbing loverload signals which will occur during starting of the motor 12 (FIG. 1).
The motor-load signals that are developed in output winding 32 are connected to a difference amplifier 55 via the illustrated circuit which includes field-effect transistor 56. This field-effect transistor is controlled to permit passage, or not, of the signals, depending upon the state of charge of a capacitor 59. Capacitor 59 is connected in a series circuit between a common grounded circuit 68 and the field-effect transistor 56. This circuit includes a diode 61 and a resistor 62.
The state of charge or discharge of the capacitor 59 is controlled by a pair of switches 65 and 66. These are preferably mercury-capsule type switches that are mounted on the rocker arm, or beam of the pumping unit 11 (FIG. 1). They are so mounted that switch 65 will be momentarily closed at the beginning of every upstroke and switch 66 will be momentarily closed at the beginning of the downstrokes of the pumping unit.
Thus, at the beginning of each upstroke, switch 65 is momentarily closed, and the capacitor 59 will be charged. 0n the other hand, at the beginning of each downstroke, switch 66 is momentarily closed and capacitor 59 will be discharged.
It may be noted that the charging of the capacitor 59 is effected when switch 65 is closed, by reason of a circuit connector 70 and a resistor 74 that lead to the ungrounded side of a full-wave rectifier 73. These switch closings, i.e., switches 65 and 66, act to condition fieldeffect transistor 56 at the beginning of each up and downstroke, so that any power signals from output winding 32 will be transmitted or not, depending upon which of the switches 65 or 66 has been actuated.
During each downstroke, i.e., following the discharge of capacitor 59, the motor-power signal from the transformer winding 32 is delivered to one input of the dif: ference amplifier 55. The other input of this amplifier is connected via a circuit connector 77 to a potentiometer arrangement for applying an adjustable signal which may be set so as to represent the normal power signal for downstroke cycles of the paraticular well that is being pumped. This potentiometer circuit includes a variable resistor 78 that has one end connected to the common ground 60 and the other end to the input connector 77 via another circuit connector 79. The potentiometer circuit continues from a circuit-connection point 88 to one end of a resistor 81. The other end of resistor 81 is connected to a constant voltage point that is formed by Zener diode Maud a current-limiting resistor 82. Resistor 82 has the other end thereof connected to the positive, or ungrounded potential side of the rectifier 73, via a circuit connector 83.
The output of difference'amplifier 55 is connected via the illustrated circuit connections to the base electrode of a transistor 86. Transistor 86 is connected across another capacitor 87 which, in turn, is connected to act as part of a timing unit (to be more fully described below) which unit includes an RC circuit made up of the capacitor 87 in series with a resistor 88. Both the resistor 88 and capacitor 87 are connected across the constant voltage that exists between the point 75 and ground. This arrangement permits the controlling of initiation of timing cycles that depend upon the charging time of the capacitor 87 with its series resistor 88. Such timing circuit is commenced each time the capacitor 87 is discharged, which happens whenever transistor 86 conducts.
The timing circuit, including capacitor 87, has a connection thereto via a circuit connection 91 which leads to the uni-junction electrode of a unijunction transistor 92. This transistor 92 is connected with its other two terminals in a series circuit that includes a resistor 93 and another resistor 94, connected one on each side of the unijunction transistor. This unijunction circuit extends from the high potential at the constant voltage point 75 to the common ground connection 60.
In this manner, the timing circuit which consists of the capacitor 87 and the resistor 88, will determine the length of time that will pass before the unijunction transistor 92 is tripped. When transistor 92 is tripped, it will allow current flow to pass therethrough and, thus, actuate another transistor 98 and cause it to conduct. When transistor 98 conducts, it acts to short-circuit a parallel connected winding 100 of a relay 101. This relay 101 corresponds to the relay 24 with its winding 25, of the FIG. 1 schematic It will be observed that with the arrangement of FIG. 2, so long as the transistor 98 does not conduct, the winding 100 of the relay 101 will be energized. consequently, a switch contact 102 of the relay 101 will be held closed. Therefore, the circuit for controlling energization of the motor 12 (FIG. 1) will be maintained in the state to energize, so long as conditions during downstrokes of the pumping unit 11 remain normal.
It may be noted that there is another switch 103 illustrated. This corresponds to the switch 17 of the FIG. 1 schematic Switch 103 has its contacts connected in parallel with the contacts 102 of the relay 101. Also, in FIG. 2, there is an energization winding 106 which provides energy to the control circuit of FIG. 2 via a transformer 107, to the full-wave rectifier 73. In this manner, the control circuit which is illustrated in FIG. 2, will be de-energized along with the motor itself, whenever the conditions are such during one or more downstrokes of the unit that the power signal falls below the predetermined normal signal level.
FIGS. 3, 4 and 5 illustrate a switch structure that may be employed instead of the field-effect transistor 56 and its control circuits, i.e., resistor 62, diode 61, capacitor 59, plus switches 65, 66 and circuit connections 69, '70 and 74. In other words, a single-pole singlethrow switch like that illustrated in FIGS. 3-5 would be connected into the ciruit which connects the diode 51 to one input of the difference amplifier 55.
The switch structure would be mounted on the beam or rocker arm of the pumping unit-1l (FIG. 1) and it would be oriented and designed to provide the desired closing of the switch only during the downstrokes. It will be clear how this would be accomplished after the following description of the switch structure is considered.
As shown in FIGS. 3-5, there is a support plate 110 that has a shaft 111 extending out at right angles. This shaft 1 11 supports, in a freely rotatable manner, an arm 112 that is held on the shaft between a bushing 115 and a cotter pin 116, or the like.
The arm 112 extends vertically upward as shown in the drawings and may rotate freely in a limited arc as determined by two adjustable stops 119 and 120.
At the free end of the arm 1 12, there is a clip or other support 121 that holds the body of a mercury tubeor capsule-type switch 122. The switch 122 has a globule of mercury 125 inside and a pair of electrodes 126 at one end which will be electrically connected together whenever the mercury contacts them. There are also, of course, electrical circuit wires 127 that carry the electrical connection from the electrodes 126 to whatever circuit is to have the switch connected therein.
By mounting the plate 110 oriented vertically on the rocker arm of the pumping unit 11 (FIG. 1) when it is horizontal, and by designing the stops 119 and 120 so as to permit the proper degree of arc of the arm 112, the switch 122 will flop from one position to the'other at the beginning of the downstroke and upstroke, alternately. Consequently, it will close a circuit between the electrodes 126 during the downstroke and open it during the upstroke as the beam of the pumping unit oscillates.
OPERATION The operation of the FIG. 2 circuit may be briefly reviewed as follows:
After the motor 12 of the FIG. 1 has been started, the switches 65 and 66 will be each momentarily closed at the beginning of every upstroke and downstroke, respectively, and this will charge and discharge, respectively the capacitor 59. Consequently, during each downstroke, after capacitor 59 has been discharged, the signals representing the current being drawn (which are proportional to the power of the motor 12) will be developed from output winding 32 of the transformer 31. These signals will be transmitted via the field-effect transistor 56 to one input of the difference amplifier 55. Then, so long as the maximum amplitude of this power signal exceeds the preset normal signal amplitude existing on input connection 77 of the difference amplifier 55, there will be an output signal applied to the transistor 86, and it will conduct and provide a short-circuit path for discharging the capacitor 87. Consequently, each downstroke portion of a pumping cycle will cause a timing cycle of the RC timing circuit (capacitor 87 and resistor 88) to hold off while the transistor 86 is conducting. This timing circuit will ordinarily not permit the capacitor 87 to be charged sufficiently to trip the unijunction transistor 92 before the next succeeding downstroke signals are received in any event. Therefore, the relay 101 will remain energized under normal pumping conditions.
On the other hand, whenever a downstroke portion of the cycle fails to develop the normal power signal, there will not be an output from the difference amplifier 55 and, therefore, transistor 86 will not conduct so that the RC timing circuit will continue to permit capacitor 87 to be charged. Thus, as the capacitor approaches full charge, there will be sufficient potential applied to the emitter of unijunction transistor 92 to trip the latter and cause the other transistor 98 to conduct. Then, conduction of transistor 98 will shortcircuit the winding 100 of relay 101 and, consequently, the relay will be de-energized and its contacts 102 will drop open. This results in de-energizing the solenoid switch 19 of the pumping system shown in FIG. 1, and the motor will be shut down, and also power to winding 106 will be cut off.
While the invention has been described above in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention but merely as being descriptive thereof.
1. In combination with a beam-type pumping unit having an electric motor for driving said unit, and a first control circuit for shutting down said motor under pump-off conditions, said first control circuit comprising a power-supply circuit for connecting a source of electric energy to said motor, and
a switch connected in said power-supply circuit for disconnecting said motor from said source of electric energy, the combination comprising a. a relay for controlling actuation of said switch,
b. an impedance in said power-supply circuit for carrying motor-load current therethrough,
c. means for developing a signal proportional to said motor-load current,
dl electronic means for passing said motor-load signal when in one state, and blocking same when in another state,
d2 switch means actuated by said beam for setting the state of said electronic means,
el. a difference amplifier having two input circuits,
e2. one of said input circuits being connected to said electronic means (d1. and the other being connected to an adjustable normal load signal e4. second electronic means connected to the output of said difference amplifier (el) for controlling an electric timing circuit (e), and
e6. third electronic means connected to said timing circuit (e5) for de-energizing said relay (a) whenever said motor-laod signal (c) is not greater than said normal load signal (e3).
2. The invention according to claim 1, wherein said first electronic means (dl) comprises dla, a field-effect transistor,
dlb. a capacitor, and
dlc. circuit means for connecting said capacitor to said field-effect transistor (dla and wherein said switch means (d2) comprises d2a. a pair of mercury switches mounted on said beam, and
d2b. circuit means for connecting said switches (d2a to said capacitor (dlb for charging and discharging same at the beginning of the upstrokes and the downstrokes of said pumping unit, and wherein said second electronic means (e4) comprises e4a. a transistor,
e4b. a second capacitor,
e4c. circuit means for connecting said transistor (e4a to said second capacitor (e4b to discharge same and to start a time period of said timing circuit (c5), and wherein said third electronic means (e6) comprises e6a a unijunction transistor,
e6b a second transistor,
eec circuit means for connecting said unijunction transistor (e6a to said second capacitor (e4b and to said second transistor (e6b to trip said unijunction transistor (e6a when the charge has reached a predetermined amplitude and to cause said second transistor (e6b to conduct when 5 said unijunction transistor (e6a has been tripped, and e6d additional circuit means for connecting said second transistor (e6b across the winding of said relay (a) for de-energizing same by shortcircuiting when said second transistor (e6b) conducts.
3. In combination with a beam-type pumping unit having an electric motor for driving said unit, and a first control circuit for shutting down said motor under pump-off conditions, said first control circuit comprising a power-supply circuit for connecting a source of electric energy to said motor, and
a switch connected in said power-supply circuit for disconnecting said motor from said source of electric energy, the combination comprising a. a relay for controlling actuation of said switch,
b' an impedance in said power-supply circuit for carrying motor-load current therethrough,
0. means for developing a signal proportional to said motor-load current,
d3. electric switch means for passing said motorload signal when in one state, and blocking same when in another state,
d4. mechanical support means actuated by said beam for actuating said switch means (d3) from one said state to the other for electrically closing said switch only during downstrokes,
e7. a difference amplifer having two input circuits.
e8.one of said input circuits being connected to said electric switch means (d3), and the other being connected to an adjustable normal-load signal (e9),
e10. electronic means connected to the output of said difference amplifer (e7) for controlling an electrical timing circuit (ell), and
e12. second electronic means connected to said timing circuit (ell) for de-energizing said relay (a) whenever said motor-load signal (0) is not greater than said normal-load signal (e9).