Determining actual power output and derating factor of electric motors that drive oil well pumping units

ELECTRIC MOTORS that drive oil well pumping units cannot deliver an average horsepower output equal to name-plate rating without the effective or rms current exceeding rated current. Expressed another way, motors that drive pumping units must be derated if they are to operate without being thermally overloaded. A method is presented for determining the per cent of rated power output that electric motors can deliver when driving oil well pumping units. This requires a determination of average power output under actual operating conditions. A procedure for determining the average power output is developed that only requires measurements which can be made in the field by engineers and field testers.