Hany Zakhary, Seth Gilstrap, Walter Dinkins, Levare USA
Christopher DeWaal, CPH Corp.
In an effort to address safety concerns, PMM manufacturers and operators have worked together and developed API 11S9 Recommended Practice that covers many of the safety issues relative to PMM operations. The PMM is a very good generator due to “always on” permanent magnet rotor so presents a risk of electric shock and arc flash (AF) hazards if rotation occurs when service personnel handle the ESP cable conductors at surface. The primary methods to avoid these hazards is to insure an EquiPotential Zone (EPZ) is created at surface and to shunt the ESP cable leads. A proper risk analysis can help to determine if additional engineering controls are required to mitigate risks.
It is not possible to de-energize the PMM so an Energized Electrical Work Permit (EEWP) may be required under Article 110.4(B) of NFPA 70E. The methodology centers on creating an EPZ tailored for PMM cable splicing/wellhead connector operations and testing its effectiveness through actual on-site evaluation of the process. Shunting or shorting the ESP cable at surface is a very good “dynamic brake” preventing rotation. However, there are certain operations where the shunt must be removed as part of regular procedures so strategies are developed to deal with those conditions.
Arc Flash calculations are presented for when there is motor rotation with the potential for high voltage generation and high incident energy values. This data provides guidance necessary due to the variability in motor sizes and potential flow rates, which aids service personnel in choosing appropriate PPE for the job. Incorrect, or worse-case PPE selection may lead to the arbitrary choice of Cat 4 ARCs which might be over-rated and lead to added risks.
Of the 20,000+ permanent magnet motor (PMM) electric submersible pump (ESP) installations in the past 15 years, almost all were safely installed without devices intended to prevent inadvertently rotating the motor. These engineering control devices, e.g. tubing flow plugs and mechanical locks, are described along with explanation of the complications they bring to installing, operating, troubleshooting and pulling a PMM. The paper concludes with a summary risk assessment, procedures and implemented training.