The Magnet Makes the Difference in These High-Efficiency Pump Motors from Franklin Electric

Pumps with permanent magnet motors and VFDs deliver attractive return on investment in high-duty-cycle applications.

High-efficiency equipment has become a focal point in the clean-water and drinking water sectors as utility leaders strive to be better stewards of energy and water resources.

That focus extends to the pumping systems that move wastewater through collection systems and into treatment processes, and that draw drinking water from wells and reservoirs and fill the tanks and towers that hold water for distribution.

The objective is to create pumping systems that deliver financial savings while performing reliably and intelligently, providing long service life, and saving on maintenance. Toward these ends, pump manufacturer Franklin Electric offers high-efficiency submersible pumping systems built around the company’s MagForce permanent magnet motors.

The company cites PM motors as a proven technology used in applications from industrial to residential. PM motors have rotors made with rare earth magnets that perform with no slip. Because the rotors require no electricity to become magnetized, the motors are more efficient.

The savings on energy can quickly offset the higher initial costs. For example, motors with a 94% efficiency rating can provide a payback of less than two years in long or continuous duty applications.

Brandon Schumm, product manager for large submersible motors with Franklin Electric, talked about the technology in an interview with Treatment Plant Operator. 

What was the market impetus for this type of pumping system?

Schumm: We had customers with high-duty-cycle applications running 24/7 or very close to that. They understood that if there was a way to get better efficiency out of the pump or motor, they could save on operating costs. PM motors were not new to the world, so we looked into that technology and incorporated it into submersible motors. The pump is still the same. The difference is the high-efficiency motor we’ve added to the system.

Was there any particular challenge to marrying PM motors to submersible pumps?

Schumm: The design was a little tricky because we’re confined to a certain diameter in submersible applications. In aboveground settings with a PM motor, you can change the geometry and get bigger, wider and longer. But working within a limited diameter for going down a well does pose a few design challenges. 

Is the efficiency advantage due to the use of the rare earth magnets?

Schumm: Yes. With traditional induction motors, you have to add energy as electricity to make that internal magnet. With PM motors, you eliminate that added energy because the magnet is already there.

Where would these high-efficiency pumps typically be found in drinking water or wastewater treatment plants?

Schumm: Municipal drinking water plants are our main focus, but these motors could be used in any high-duty-cycle application. PM motors are more expensive than induction motors, and you have to overcome that up-front cost. If you have an application where a pump is running 30-40% of the time or more, that’s a good opportunity to look at this solution.

How much more efficient are pumps with PM motors versus induction motors?

Schumm: It depends on the size of the pump, but anywhere from 8 to 12 percentage points more efficient. So where an induction motor might be 82-83% efficient, pumps with these high-efficiency motors can get into the low to mid-90s. 

Beyond energy efficiency, what advantages do these pumps have?

Schumm: Because you’re pulling less current for the system, you can look at downsizing other components. In wire sizing, for example, in the past you might have used a 6-gauge wire. Now, because the motor is pulling less current, you can use a smaller-gauge wire. You might even be able to downsize the variable-frequency drive or the filtering. Another benefit is the capacity for higher speed. Based on the frequency coming in, which in our market is 60 Hz, pumps and motors spin at about 3,450 rpm due to the slip that’s inherent with an induction motor where you have to create that internal magnet. With the magnet already present in the PM motors, you can get up to 3,600 rpm. We consider that a boost in performance.

Are there any benefits related to size or configuration?

Schumm: In some systems we can reduce the weight and the length by almost half. I was on an install recently where a customer was using one of our 250 hp motors. When the technician, who was rather short, went to bolt the motor to the pump, he said, “This is the first time I’ve been able to reach the bolts and not have to use a ladder.”

How do you relate the efficiency of these pumps to prospective customers?

Schumm: Many municipalities have had visits from energy consultants, and the first thing they do is look at the ceiling and say, “If you want to save energy, change all your lighting to high-efficiency LEDs.” So to better relate, we created a calculator showing that if you were to switch to a high-efficiency MagForce motor, it’s equivalent to replacing X number of lightbulbs with LEDs. The calculator can also show reduced carbon footprint.

What role do VFDs play in these high-efficiency pumping systems?

Schumm: You must use a variable frequency drive with this type of motor. When you go to start up the motor, you have to know the phase alignment. If you just applied energy over the line without a VFD in place, the motor would lock itself up. You need a VFD to get it spinning and to have that phase alignment when it is operating. 

Can you cite an example of an application where these pumps proved beneficial?

Schumm: A municipality in Germany was using an induction-motor-driven pump over the line. To get the correct flow, they would throttle the flow out of the pump. The motor was spinning all the time and they were essentially restricting it so as not to produce more flow than they needed. We set them up with a high-efficiency system with a VFD. They were able to downsize the pump, and with the VFD they could vary the speed depending on the flow requirement. We cut the power consumption in half. We attributed about 80% of the savings to the VFD, and the other 20% to the PM motor.

What is the size range for this line of motors?

Schumm: We run the whole gamut. We start out at 1.5 hp and go clear up to 300 hp. Our 8-inch and 10-inch designs are where we see municipal and industrial applications going. The 8-inch motors range from 75 to 175 hp, and 10-inch units from 250 to 300 hp.

As featured in Treatment Plant Operator's article: The Magnet Makes the Difference in These High Efficiency Pump Motors from Franklin Electric