The Ultimate Solution in PMM Safety - Part III

Charles Booth

Patented Mechanical Shaft Lock Secures a Permanent Magnet Motor Simply and Securely 

In parts one and two of this three-part series, we discussed the fact that ESPs using highly efficient permanent magnet motors (PMMs) must have their shafts locked during installation and removal. This is because PMMs, unlike induction motors, can potentially generate lethal electrical charges if downhole conditions flow fluid through the ESP with enough force to rotate the shaft.

We covered in depth the dangers of an unprotected PMM, shunting (click HERE—please read this one first) and plugging the tubing (click HERE), along with the benefits of each option.

Though the benefits of both previous options are clear, they are countered by the drawback of not physically locking the shaft. Because safety is a key value at Extract, and our highest priority, we recognized a need for our clients to have a physical lock to permanently secure PMMs as they’re installed, removed or serviced.


The Mechanical Shaft Lock

Attached to the top of the pump before installation, the shaft lock secures the shaft from turning due to downhole pressures—yet it is released simply by starting the motor. There is no need to reconnect cables (as with shunting) or wait on a slick line crew to retrieve a tubing plug.

Being an external mount means, later, when the pump is removed, the shaft lock can be transferred to another ESP after the lock is redressed in the shop.

The oil and gas industry has been asking for something like this to improve safety, so we developed this mechanical shaft lock to answer those concerns.  This is the safest, most effective solution.

The heart of the lock is a shear pin inserted into two aligned slots—one attached to the shaft, the other attached to the shaft lock.This keeps the shaft from rotating, no matter the level of downhole pressure, assuring that the pump cannot generate voltage or current.

Once the PMM ESP is in place and everything is ready, we commission the unit. During the initial startup, horsepower from the motor releases the shear pin, allowing the pump to operate as normal. Only the ESP’s motor is strong enough to release the pin—no downhole forces are strong enough to shear the MSL.

The released shear pin is captured in a sealed compartment to protect the pump from shear debris (see diagram).


In this image you’ll see two shear pins (in yellow) pointing up at the bottom of the drawing. The left one is engaged, meaning this pump is ready to be installed.

This image displays the left pin is sheared off and captured, showing that the motor has run and released the MSL.

This final image shows the right-hand pins engaged, readying the ESP system for extraction from the well. To engage these pins a slick line with a 300-pound weight is lowered onto the top of the shaft lock.


To make sure the shaft cannot move, we still shunt the motor in addition to the shaft lock. Installing a tubing plug may not be required, but we apply the shunt because redundancy is always the safest course.


Further Safety Measures

We lock access to everything associated with our PMM systems to make sure those unfamiliar with them don’t get in and accidentally treat them like induction pumps. We lock the drive cabinets, the transformer sections and the junction boxes. Even after installation, if our equipment is accessed by someone only familiar with induction motors, they could accidentally interact with a connection that is hot - locking access prevents incorrect changes from being made.


Even within Extract, we operate with dedicated technicians that only work on PPM systems, who are specifically trained in PMMs. Everything is color-coded and locked with special locks to assure safety.


Click HERE to discuss our PMM ESPs with an Extract Expert.

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