Optimizing Progressive Cavity Pump performance

Finding the right variable frequency drive enables the use of top drive motor's full torque potential throughout the entire speed range.

Not all variable frequency drives (VFDs) are created equally, and some applications are more demanding than others. It is critically important to find the best brand and model for a specific application.

General Magnetic (GM) of Calgary, Alberta, Canada recently found this to be the case regarding a large 85-horsepower MagnoDrive Permanent Magnet PCP Top Drive Motor it had developed. Though it could be adapted for other purposes, the MagnoDrive was designed to drive progressive cavity pumps (PCPs), one of three main pump varieties used to extract oil out of the ground.

The MagnoDrive offers several appealing advantages over the conventional induction motors that typically power PCPs, including reduced energy consumption, greenhouse gases and maintenance, and increased safety for field operators. The main performance advantage of the MagnoDrive, however, is that the speed and torque envelope is available throughout the entire speed range; able to run full torque at 30 rpm, at 450 rpm, and anywhere in between, with equal efficiency.

A variable frequency drive: the key Progressive Cavity Pump operating component

The operating component that enables the motor to run at any speed and torque within its operating envelope is a VFD (also known as a variable speed drive, VSD). A VFD is typically programmed to manage all possible situations, providing the advanced supervisory control that determines when to stop and start the motor, how fast it should go under varying loads, and how to most efficiently operate within any torque limits.

In the development stages of their MagnoDrive, GM noticed a problem when conducting field tests with an initial VFD it had selected.

GM was using a leading manufacturer’s drive, but noticed the MagnoDrive didn’t run very well between 70 and 150 rpm. It would start to get some strange vibrations, become unstable and would lose control. It especially had problems at low rpms, which are where many PCP operators typically want to run, between 100 and 150 rpm. So if the system doesn’t run really well at that speed, it is a pretty big problem.

As part of their effort to address the low rpm performance issue, GM contacted us to see if we had a potential solution.

Identifying the ideal VFD through research and testing

Our team made some visits and did some research to specify the most appropriate drive for the MagnoDrive in the PCP pump application. We determined that the relatively new ACS880 VFD appeared to be a very good fit, and offered to put in a demo drive to test its performance against the competitor’s drive.

We ran the ACS880 at all speeds and torques the afternoon it arrived, and after a very small tweak the problem was solved. The ACS880 allowed the MagnoDrive to operate at full torque at low rpm, high rpm and anywhere in between with equal efficiency. GM made the switch to the ACS880, and has put out a number of systems with the new drive and hasn’t had a single field call.

Al Duerr, GM founder, CEO and former mayor of Calgary recently told me, “We tried many VFDs, and the ACS880 is clearly one of the best we have tried. I think it is important that we have had great support from ABB. They have been totally engaged, and I, as a small developer and manufacturer, really appreciate their ability as a very large company to understand that there is the genesis here of something that is really exciting.”

By working closely with the customer and thoroughly understanding the nuances of their technology, we were able to find the optimal drive for their specific application.

In case you are interested to read the full story and watch a video of how General Magnetic boosted the PCP Top Drive Motor performance, please visit the case site here.