Motor protection system and process

Abstract From the Canadian patent

Method and apparatus for providing an electric motor such as used on an oil well pumping unit with stall protection. The system comprises means for generating a signal representative of motor speed and for establishing at least two stall speed set points corresponding to upper and lower stall speeds of the motor. Upon the motor speed signal reaching the upper speed set point for one time duration or the lower stall speed set point for a second short time duration, a motor control function is generated. The system may be used for motors having a plurality of operating modes. In this case, at least two stall condition suites, comprising at least two upper and lower stall speed set points as …