Patent ID: 6599095
Filing Date: 2003-07-29
Classification: F04B

Abstract:
A system for pump off control of a pump jack drive system of induction motor drive comprising:means for detecting speed of the induction motor and an instantaneous value of secondary current of the induction motor; means for detecting down stroke time in every cycle of the pump jack; means for detecting each maximum value of the secondary current instantaneous values in each down stroke time of the secondary current; means for detecting and storing a time value from each down stroke reference point to said each maximum value of the secondary current instantaneous values; and means for setting a reference time value to be compared with the detected and stored time value, wherein the system is capable of comparing the detected and stored time value with the reference time value after the down stroke end every cycle and the system is further capable of detecting an occurrence of a pump off condition as a case where the time at which the instantaneous value of the secondary current reaches the maximum value lags behind the setup reference value.