An approach to the computation of motor loading for a pumping unit

Design calculation of the motor loading will reduce the electrical cost and increase equipment life. The instantaneous gearbox torque was determined by combining the counterbalance effect with the calculated dynamometer cards and torque factors. Then the motor power was computed by combining the pumping speed with motor and drive efficiencies. The results show that the static load plays a major role in coalbed methane (CBM) wells while the dynamic load is relatively small. For balanced operation, the net torque load usually has two maximum peaks and the magnitudes of them are just within 50% of unbalanced gearbox loading. In a rotating system, torque and power are directly related, and the negative motor power results from the combination of moments of the various moving elements and the motor is operating in a “regenerative power” mode. While the net gearbox torque is maintained in balance, the motor power usually has two approximately equal peaks, the peak torque on motor and gearbox are lower, and the peak power delivered by the motor is less. Consequently, balance torque loadings can reduce the size of the prime mover and gearbox, load the motor more uniformly, and reduce the power cost.