API RP 11S9 First Edition 2023 PDF
This document serves to emphasize safety aspects and recommended practices concerning the handling, installation, troubleshooting, operation, and pulling of permanent magnet motors (PMMs) used in subsurface and surface artificial lift pumping systems.
In electrical submersible pump (ESP) systems, two motor technologies provide power to the pump: the AC induction motor (IM) and the permanent magnet motor (PMM). The IM has been the industry standard since 1916. It evolved over time with many improvements and is a mature technology in 2021. PMM, a younger technology originating in the 1990s, also evolved in the early 2000s and has gained global commercial acceptance since 2010. PMM requires more precautions due to the construction and physics of the motor and how it generates voltage.
In both IM and PMM, the poles on the rotating rotor cause an internal voltage to be generated in the stator winding, known as the electromotive force (EMF). In an IM, if the shaft rotates while the motor is disconnected from any external power source, only the residual magnetic field in the steel laminations is available to generate EMF. In most applications, this residual magnetism will be negligible such that there is no hazardous level of EMF generated, although it is known for back-spinning IMs to generate hazardous voltage. However, EMF will be generated in a PMM any time that the shaft is rotated as the rotor poles, which are magnetically strong, are always present. This EMF will be proportional to the shaft rotational speed regardless of the direction of rotation.
