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Sophisticated VFD enhances PM Top Drive Motor performance in progressive cavity pump applications

The history of oil prices is very cyclical, behaving much like any other commodity, with wide price swings in times of shortage or oversupply. During times of abrupt swings, global concern typically builds that the calculus of oil pricing has changed for good, and that the existing marketplace paradigm is no longer valid.

Despite the complex political and technological infrastructure of the global oil supply chain, history has shown that extreme pricing movements invariably stabilize, and, over time, the market behaves within the boundaries of established cycles.

Companies that get oil out of the ground try to manage their costs very carefully. Equipment that costs more initially but lowers operating costs in the long run can be a tough sell.  This is especially true during pricing downturns, as companies are reluctant to make incremental capital investments for fear of further impacting the short term bottom line.

One company that is trying to break this mindset is General Magnetic (GM) of Calgary, Alberta, Canada.  Founded in 2008, GM has developed, gained initial market acceptance for, and begun to place in oil fields throughout western Canada, a large 85-horsepower MagnoDrive Permanent Magnet PCP Top Drive Motor (MagnoDrive) that drives progressive cavity pumps (PCPs).

PCPs have been primarily powered by top drives with conventional induction motors driving the top drive through speed reduction equipment.  More recently permanent magnet motor driven top drives developed and manufactured by GM and a small group of other manufacturers are being adopted by progressive oil field operators.  Though the MagnoDrive is more expensive initially, it utilizes significantly less electrical energy, allowing the initial cost differential to be offset early in its life cycle.

In considering the positive benefits of the MagnoDrive, Al Duerr, GM founder and CEO, and mayor of Calgary from 1989 to 2001 asks, “In the oil industry the challenge is how do you transform what tends to be financially-driven, shorter term thinking into a long term value proposition?  What could operating costs be if we had an overall 10% reduction in electrical energy? How would that drive to the bottom line?”

The progressive cavity pump and other pump types


A PCP is one of the three main pump types used to extract oil out of the ground.  The other two main types are the highly recognizable pump jack, which looks much like a large horse head methodically bobbing up and down, and the electrical submersible pump (ESP), which strikes far less a visual on the open plain.

A PCP extracts fluid from the ground through the progress of a sequence of small, fixed shape cavities as the pump rod is turned.  It is the lower cost, medium flow member of the three, compared to the medium cost pump jack, and the higher cost, higher flow ESP.

In addition to the energy consumption savings and the reduced greenhouse gases that result, there are other environmental and cost-of-ownership advantages of a PCP powered by a MagnoDrive.
The advanced motor’s direct drive operation eliminates the high maintenance hydraulic equipment, mechanical brakes, and speed reduction equipment, including gearboxes, belts and sheaves, required with conventional PCP top drives.   The absence of these external moving parts reduces the general maintenance required to operate the MagnoDrive, makes it much safer for field operators and maintenance crews to work on when maintenance is needed, and makes it noticeably quieter in the field.

“I joined General Magnetic because they were interested in doing product better.  For Progressive Cavity Pumps there is conventional equipment and then there is our equipment,” said Aaron Brassard, GM vice president of engineering and development.  “I was attracted by the chance as a citizen of our society to do something just a little bit better, to improve our environmental sustainability and ideally reduce operating costs as well. I have always believed you can achieve both objectives.”
Added Duerr, “There is a need for the energy industry to up its game, and I'm excited that General Magnetic can make a significant, long term bottom line impact while also lessening the environmental footprint.  When you consider electrical energy consumption, that's the biggest single operating cost for energy companies trying to get oil out of the ground.”

Full torque over the entire speed range


The main operational benefit of the MagnoDrive Permanent Magnet Top Drive motor over the conventional PCP drive is that the speed and torque envelop is available throughout the entire speed range; able to run full torque at 30 rpm, at 450 rpm, and anywhere in between, with approximately equal efficiency.

The vast majority of conventional PCP drives use AC induction motors. They have very good efficiency from 70% to 110% of their rated speed, but outside those speed ranges there are significant challenges. Permanent magnet motors are able to produce higher torque than the same size induction motors, providing greater operating efficiency.

The operating component of a MagnoDrive that enables the motor to run at any speed and torque within its operating envelope is a variable frequency drive (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.

A VFD is also essential in managing the motor in the event of a brownout or a blackout, and, depending on owner policy, restarting the motor when full energy is restored without operator intervention.

Finding the right Variable Frequency Drive


Not all 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.
In the development stages of their MagnoDrive, General Magnetic noticed a problem when conducting field tests with an initial VFD it had selected.

“We were using a leading manufacturer's drive, and we were having some tuning issues. Our field test crew noticed that the MagnoDrive didn’t run very well between 70 and 150 rpm.  It would start to get some strange vibrations, become unstable and the VFD would lose control,” said Brassard.
“We 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.”

The ABB variable frequency drive


In search of a VFD more compatible with the MagnoDrive and the PCP application, GM contacted ABB about a new VFD they had heard ABB recently developed.

“We got into the partnership with General Magnetic through a general website inquiry stating that they had interest in our drives, and what did we have available that would be appropriate for the permanent magnet PCP application,” said Glen Wilson, a regional LV Drive technical support rep for ABB, Canada.
“We made some visits and did some research, and in early 2014 we offered to put in a demo drive, to test the performance of our drive against the competitor's drives, and see if the performance GM was looking for was in our drive.”

Wilson and the ABB team worked with GM to specify the most appropriate drive for their MagnoDrive in a PCP application, and an ACS880 VFD was soon delivered for testing. “During our testing we had it running at all speeds and torques the afternoon that it arrived. It required a very tiny little tweak, and, in essence, it was basically perfect from day one. So, it really did establish itself as a great product for us. It's just very easy for us to use,” said Brassard. “So this is when we moved to the ACS880. We knew from the test stand that the low rpm issue was not a problem with the ABB drive. We have put out somewhere between 8 and 12 systems since working with ABB and we haven't had a single field call.”

Superior product support


The support the ABB Alberta, Canada technical team provided during the evaluation stage and beyond was equally important as the performance of the ACS880.
“The ABB VFD has been a great product for us, one of the easiest VFDs to use with our technology.  We tried many VFDs, and it is clearly one of the best we have tried,” said Duerr.  “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.”

“We have been able to pass the benefit of the ABB support on to our customers. With our complete understanding of the product and all it can do, we can deliver a much more robust package into the field. When we started understanding field application issues in more detail, we realized that it wasn't just the motor, but having a superior drive system was just as important.”

A very bright future


GM’s current installation base of MagnoDrives is in Alberta and Saskatchewan in Canada, in California in the United States, and in Indonesia.  They are actively cultivating further installations in the United States, South America, and the Middle East.  Locations with higher energy costs, like California in the US, are especially viable targets due to the increased savings the motor can provide.  Locations where there are high maintenance costs due to extreme environmental conditions are also ideal markets for the MagnoDrive.

Approximately half of GM’s new business is on new wells, with the other half being retrofit replacements of conventional PCP drive motors on existing wells.

The retrofits are often for customers with maintenance issues like belts that are wearing out too often, or situations where they might have a power cap with their utility. With a 100 kW power cap for example, the MagnoDrive with its superior energy efficiency can get more fluid out of the ground with the same energy.

A customer putting a MagnoDrive on a new well can often pay for the entire system in three to five years just from the power savings alone on a fully-utilized 85 horsepower system.  As a general example, at 14 cents a kWh and a fully-utilized 85 horsepower system, a customer will pay for the difference in the cost between a MagnoDrive and a conventional PCP drive in a little more than a year.
The GM MagnoDrive is designed to have a lifespan in excess of ten years, and can be easily moved from one well to another.

Speaking of the future prospects for General Magnetic’s PM Top Drive, Duerr concludes, “We have had growing interest within the industry because the operators, the field engineers, the guys on the frontline have found that our permanent magnet motors and the VFDs allow them to do things, to create opportunities, and to manage complex wells in a way that they couldn't before. Add the savings on energy, the single biggest operating cost in oil extraction, and we have a very compelling story to tell.”
Added Brassard, “While we are officially drive agnostic and want to enable customers to use any manufacturer’s VFD they might prefer, I really like the ABB ACS880. If I had one choice, that would be the drive that I would use. It's a fabulous VFD.”

 

GM founder and CEO Al Duerr is excited what the new MagnoDrive can provide to the energy industry.

MagnoDrives utilize significantly less energy than conventional motors, providing 10% savings on the single largest operating expense for oil field owners.

With a MagnoDrive and the appropriate VFD, the full torque envelop is available throughout the entire speed range.

GM has numerous MagnoDrive installations on PCP pumps throughout western Canada.

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