Unleash High Efficiency Performance & Energy Savings with Permanent Magnet Technology

08/16/2022

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By Bob Lilland and Brandon Schumm

Being good stewards of natural resources like water and energy, while still delivering water where it’s needed, is an ever-growing challenge for groundwater professionals. That’s why high efficiency solutions have become more critical than ever. Evaluating the merits of these systems is also important. Users across a variety of industries, including the industrial, commercial, municipal and agricultural sectors, want to understand how high efficiency systems will work for their application needs. Will these systems not only deliver financial savings but also perform reliably with steady operation – using water more intelligently without sacrificing pump life, maintenance and other operational concerns? 

A growing solution for delivering higher efficiency with proven reliability is a system built around a permanent magnet (PM) motor, and submersible pumping systems are evolving to take advantage of the PM motor designs that have become popular in other industries. PM rotors are magnetized at all times due to the raw material selection and require no electrical power, making them more efficient, especially at reduced speeds and partial loads. PM motors operate more efficiently using rare earth magnets that perform with no slip. This translates into lower input power for the same output power, saving on operational costs every time the motor runs. In fact, running these in specific applications can provide energy savings that quickly offset additional initial investment costs. Motors with a 90% efficiency rating provide an investment payback of less than two years in typical duty rate systems. Also, lower current means that specific components of the system—including variable frequency drives (VFDs), motor cables and filters—might result in smaller size requirements and, consequently, become less costly. 

How do permanent magnet motors perform in submersible applications? 

PM motors provide considerable benefits in submersible applications over induction motors. If you are currently running an induction motor in a submersible pump and replace it with a PM motor, the PM motor will win every time in terms of less overall cost of ownership, more efficient operation, better performance and less downtime. Consider:

  • Permanent magnet motors run with an efficiency rate of about 90 to 94%. 

  • Permanent magnet motors deliver better performance across a range of speeds for longer motor life and better overall performance.  

  • Permanent magnet motors operate with no slip: in contrast with standard induction construction, their speed is constant regardless of load, delivering consistent water distribution at all times. 

  • When paired with a pump in submersible installations, PM motors offer higher efficiency operation and speed compared to other pumping systems that rely on induction motors.  

These are just the beginning of the benefits owners and operators experience with PM motor technology. It is also an efficient alternative to vertical line shaft turbines (VLSTs) and submersible systems powered by traditional induction motor designs. 

Continuous run vs. partial run: do the benefits still add up? 

PMM Size Weight ComparisonPM motors run with an efficiency rate of about 90% which is 10 to 12% greater than standard induction motor energy consumption. The Hydraulic Institute rates this type of interior permanent magnet construction as the best peak efficiency available when compared to surface-mounted or even induction motors. Consider the savings on a pump that runs 24/7: PM motor-driven pumping systems save you more the more you use them. 

Not running constantly? PM motors still offer benefits. They run more efficiently since their rotor does not need to be magnetized. This concentrates all the power into motor shaft rotation. Because of this power concentration, PM motor systems can run at a synchronous speed, providing improved hydraulic performance. With no slip, the motor speed is consistent and will not vary regardless of load. They also run on a lower line voltage than a standard induction system at rated speed, providing better performance for lower voltage systems. 

A PM motor may hold a higher initial price point than a submersible induction motor, but operational costs and efficiency savings can offset this. According to field trial data, typical high-duty rate systems can have a payback of one to two years. Paired with a variable frequency drive (VFD), your system is guaranteed to optimize performance and maximize system life while relying on real-time monitoring, protection and customizable application-specific programming software as needed to cover all customer requirements. These efficiency savings also position owners and operators for the future. Energy efficiency across a broad range of operations and infrastructure-related equipment is continuing to be prioritized at both the national and local levels. PM motors assure energy saving benefits to meet compliance considerations now and as regulations evolve. 

Permanent magnet motors as part of the entire system.  

Moving water takes tremendous power. To innovate, companies must look to technologies throughout the entire pumping system, including VFDs. 

If your current system is already running with a VFD, there’s more good news that comes from PM motor technological advancements: select VFDs have been enhanced to seamlessly be paired and perform with PM motors. In the past, variable frequency for these types of installations frequently led to an intimidating and complex setup process; now, new solutions have been engineered to deliver ease-of-use. It's not only easier to upgrade from a traditional system to one that is compatible with PM technology for more efficient operations, but it’s also a less involved process to setup a VFD overall. In some cases, you might experience a setup that feels as intuitive as installing a plug-and-play drive. 

VFDs are the most popular electronic device used to vary the speed of a pump, and for good reason. A PM motor paired with a VFD delivers not only energy savings but also advanced speed control. An induction motor will run at the slip speed at its rated voltage. If you try to increase the speed of an induction motor above 60 hz, it will run in a weakened field, thereby lowering your efficiency. In contrast, PM motors are designed to run with a synchronous speed at their rated voltage. This means you are not compromising speed for efficiency. When running a PM motor with a VFD, you can enhance and expand your pump envelope by gaining optimized efficiency. 

When the pump-motor assembly and VFD are designed and built together, they work together more effectively. Maximum efficiency is engineered into the entire system. This benefits the user in terms of energy cost savings, ease of installation and streamlined maintenance. 

Permanent magnet motors offer installation and maintenance benefits: from power density to increased environmental protection. 

Permanent magnet motor systems also offer maintenance advantages and noise-reduction benefits, along with cost savings in both installation and maintenance. PM motors are substantially smaller in footprint to an induction motor. In fact, the Hydraulic Institute labels PM motors as superior to all other types of motors in terms of size and weight and as having better power density over induction motors. When it comes to submersible pumping systems, the overall installation features fewer moving parts than those required for jobs with VLSTs, such as grounding rings or ball bearings. Fewer parts often leads to a smaller overall size: saving owners on installation time, shipping expenses and other costs —not to mention an overall more user-friendly operation and less scheduled maintenance over time. 
PMM Installation Comparison

PM motors used in submersible applications offer more silent operation than their surface-mounted counterparts as well — reducing noise pollution. Environmental or natural damage are also less of a concern with submersible motors since they are protected underground and away from heavy equipment, lightning and other potential hazards. In contrast, VLST installations would require a pump house to protect their aboveground motor from weather, environmental conditions or vandalism.   

One final, often overlooked, benefit is the ability of PM motors to work in complex or unique applications where submersible pumps are preferred. For example, if you’re installing a pump in a misaligned well, a submersible pump is typically better than a VLST system which will experience wear, tear and reduced longevity. Do you need high flow from a reduced diameter borehole? Submersibles are typically operated at higher speeds since the pump and motor are close-coupled, enabling them to move more water with a slimmer diameter pump. This changes the pump size and therefore can offer the opportunity to drill a smaller borehole for the installation of the smaller diameter pump and motor. Since a PM motor delivers more efficient operation plus better overall performance you deliver a win-win in applications such as these. 

Conclusion 

PM motor technology enhances today’s submersible pumping systems — delivering an efficient resource for power plus overall installation and maintenance benefits. This technology is a strong and cost-effective alternative to pumping solutions consisting of VLSTs or submersible systems powered by traditional electrical induction motor designs. As engineering advances, this technology will continue to become more accessible and adaptable, whether your pumping challenge is to service new or existing installations.