Pump control responsive to voltage-current phase angle
First Claim
1. A process of controlling an inductive, alternating current, electric motor of a well-pumping unit cyclically operating to reciprocate a subsurface pump by means of a sucker rod string, comprising:
- (a) during each reciprocation cycle, repeatedly measuring phase angle between voltage applied to and current drawn by the motor;
(b) producing a control function related to the measured phase angle for a predetermined portion of the reciprocation cycle;
(c) comparing a value of the control function with predetermined limit value; and
(d) if the value of the control function exceeds the limit value, shutting off the motor at least temporarily.
3 Assignments
0 Petitions
Accused Products
Abstract
A pump-off controller checks for pump-off by examining the relative phase relationship between AC voltage and AC current supplied to an inductive, alternating current, electric motor driving a cyclically operated mechanical system having a walking beam for raising and lowering a subsurface pump by means of a string of sucker rods. When the phase angle between AC voltage supplied to the motor and AC current drawn by the motor exceeds a predetermined value at selected points or regions of the pumping stroke, the pumping system is shut down for a predetermined time.
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Citations
20 Claims
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1. A process of controlling an inductive, alternating current, electric motor of a well-pumping unit cyclically operating to reciprocate a subsurface pump by means of a sucker rod string, comprising:
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(a) during each reciprocation cycle, repeatedly measuring phase angle between voltage applied to and current drawn by the motor; (b) producing a control function related to the measured phase angle for a predetermined portion of the reciprocation cycle; (c) comparing a value of the control function with predetermined limit value; and (d) if the value of the control function exceeds the limit value, shutting off the motor at least temporarily. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for controlling an inductive, alternating current, electric motor of a well-pumping unit cyclically operating to reciprocate a subsurface pump by means of a sucker rod string, comprising:
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(a) means for, during each reciprocation cycle, repeatedly measuring phase angle between voltage applied to and current drawn by the motor; (b) means for producing a control function related to the measured phase angle for a predetermined portion of the reciprocation cycle; (c) means for comparing a value of the control function with a predetermined limit value; and (d) means for shutting off the motor at least temporarily if the value of the control function exceeds the limit value. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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19. An apparatus for controlling an inductive, alternating current, electric motor of a well-pumping unit cyclically operating to reciprocate a subsurface pump by means of a sucker rod string, comprising:
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(a) a transducer configured to emit an electronic signal when a portion of the pumping apparatus passes at least one point during a reciprocation cycle; (b) a current transformer connected so as to measure the current drawn by the electric motor and transform it to an output voltage; (c) a first comparator coupled to the motor supply voltage and to the output of the current transformer that produces a signal proportional to the phase angle between the voltage applied to the motor and the current drawn by the motor; (d) a computing circuit that sums the signal produced by the first comparator; (e) a timer coupled to the transducer and to the computing circuits and configured to activate the summing during a predetermined portion of the reciprocation cycle; (f) a second comparator coupled to the computing circuit that compares the summed signal with a predetermined limit value and produces a signal on an output if the summed signal exceeds the limit value; and (g) a motor cut-off switch coupled to the output of the second comparator. - View Dependent Claims (20)
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Specification