Pump control responsive to voltage-current phase angle
AssigneeAutomation Associates, Inc.
InventorsG. Wayne Westerman, Richard C. Montgomery, Gerald W. Pippin
Life of this patent
Estimating the term…
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.
Claims20
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.
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:
- (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.
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:
- (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.
Dependencies are inferred from the claim text.