METHOD AND APPARATUS FOR SLOWING BACK SPIN OF A ROD STRING OF A PROGRESSING CAVITY PUMP POWERED BY AN ELECTRIC MOTOR WHEN POWER IS LOST

摘要

A method and apparatus for slowing back spin of a rodstring of a progressing cavity pump powered by an electricmotor when power is lost. Pulse direct current voltage intothe windings of the electric motor powering the progressingcavity pump to magnetize a stator of the electric motor therebyreducing the rotational speed of a rotor of the electric motorand consequently the rotational speed of the back spinning rodstring of the progressing cavity pump.