Water and wastewater treatment plants run around the clock, and electric motors account for the bulk of their energy use. In a treatment plant, blowers (aeration blowers), lift pumps, return-activated-sludge pumps, mixers and aerators often operate 24 hours a day, thousands of hours per year, in continuous (S1) duty. Under such loads, even a few percentage points of efficiency add up to a significant line on the annual electricity bill. This is where IE5 synchronous reluctance (SynRM) motors stand out, with the highest efficiency class defined by IEC 60034-30-2. In this article we explain where, why and how to select an IE5 SynRM motor in a water/wastewater plant, how it works with a variable frequency drive (VFD) under continuous energy-intensive load, and the savings logic it offers in the water sector. (This article is conceptual; it makes no fixed-price or numeric promises.)

IE5 synchronous reluctance motor application for blower and pump in a water and wastewater treatment plant

Where Does the Motor Load Come From in a Water and Wastewater Plant?

A large share of a treatment plant's electricity goes to aeration, namely the blowers and aerators that supply oxygen to the biological treatment tanks. Raw and treated water lift pumps, sludge return pumps, mixers and dosing pumps add a considerable load as well. What these share is that they almost never stop: because the process is continuous, the motors run in S1 (continuous) duty for up to 7,000-8,000 hours a year.

For a motor running continuously, efficiency is the most critical purchasing criterion. The purchase price is small next to the electricity the motor consumes over its life; for a continuously running motor, energy makes up the bulk of the total cost of ownership. To see this logic in more detail, review our IE5, IE4 and IE3 total cost of ownership (TCO) comparison.

Blower and Aerator: The Biggest Energy Consumer

In activated sludge systems, blowers with diffusers or surface aerators meet the oxygen demand of the microorganisms. Because this equipment is usually high-power and runs continuously, it is the plant's single largest energy item. Pairing an IE5 SynRM motor with a VFD in a blower application allows the airflow to be matched to the instantaneous process demand (dissolved-oxygen control). For the selection logic of high-airflow blowing equipment, our centrifugal and turbo blower motor selection article is a complementary resource.

Lift Pump and Mixer

Lift pumps move water from one stage to the next; mixers keep sludge from settling in the tanks. Both run under long, continuous load. For correct power and flow-head matching on the pump side, our centrifugal pump motor selection: flow, head and power matching article is a guide. For wastewater transfer applications with clogging risk, also consider submersible drainage and sewage pump motor selection.

What Do IEC 60034-30-2 and the IE5 Class Mean?

Electric motor efficiency classes are defined by the IEC 60034-30 series of standards. While the efficiency classes (IE1-IE4) of classic squirrel-cage induction motors are set by IEC 60034-30-1, the broader framework that covers drive-fed motors and different technologies (such as synchronous reluctance), including IE5, is defined by IEC 60034-30-2. IE5 (Ultra Premium) is the highest efficiency class commercially available today and aims to reduce losses by roughly one further step compared with IE4.

You can find a detailed explanation of why an IE5 SynRM motor cannot run without a drive in why an IE5 synchronous reluctance motor cannot run without a drive. Our IE5 and synchronous reluctance motors: the efficiency class of the future? article addresses the forward-looking position of this technology.

Why Synchronous Reluctance Suits the Water Sector

SynRM motors carry neither magnets nor conductor bars in the rotor; they turn on the reluctance principle. A magnet-free rotor offers an advantage in both cost and supply, and because there is no current generating losses in the rotor, the motor runs cooler. In continuous loads such as water plants, this cooler operation benefits bearing and winding life. For the supply advantage of the magnet-free rotor, see magnet-free rotor in IE5 synchronous reluctance motors: supply and cost advantage. We compare SynRM with permanent-magnet motors in IE5 synchronous reluctance vs permanent-magnet (PM) motor difference.

IE5 motor running efficiently with a VFD under continuous S1 load in a treatment plant

Why Is IE5 SynRM Advantageous Under Continuous S1 Load?

In a plant that runs continuously the motor almost never stops, so the efficiency difference accumulates every hour. An IE5 motor runs with lower losses than IE4, and when this difference adds up over a year it turns into tangible savings. The part-load efficiency behavior of SynRM motors is more stable than that of induction motors; since flow changes frequently in treatment plants, this is important. We explain this part-load advantage in the IE5 synchronous reluctance motor efficiency curve: why is it superior at part load?.

For how annual energy savings are calculated for continuous loads such as pumps, fans and compressors, the logic in energy savings with IE5 motors in pumps, fans and compressors under continuous load can be applied directly to water-sector applications.

Operating With a VFD and Commissioning

SynRM motors are driven by a VFD by design; they cannot start on their own when connected directly to the grid. For a water plant this is actually an advantage: thanks to the drive, blower airflow and pump speed are matched to process demand, avoiding wasted energy. For drive and installation compatibility, our drive and installation compatibility when switching to an IE5 motor: commissioning checklist is useful; for drive parameterization and autotune, our IE5 synchronous reluctance motor drive parameterization is a practical guide.

Thermal Behavior and Correct Sizing

In motors running continuously at low speed via a drive, the air delivered by the cooling fan also drops; therefore thermal behavior must be considered when sizing. We addressed this in thermal behavior and cooling in IE5 synchronous reluctance motors. For correct frame and drive matching, our frame-power table (IEC) for IE5 synchronous reluctance motors helps at the ordering stage.

Switching to IE5 in a Water/Wastewater Plant: Decision Steps

When deciding on IE5, the motor's power, annual operating hours and the efficiency class of the existing motor are evaluated together. On high-power blowers and pumps that run many hours, the switch pays back faster. We examined whether the efficiency difference between IE5 and IE4 justifies the investment in IE5 or IE4? Does the efficiency difference justify the investment?. Our IE5 ultra premium electric motor transition guide summarizes which application makes the switch to IE5 sensible.

For those who want to convert an existing motor to IE5 together with a drive, replacing an old motor with IE5 + drive: retrofit steps guides on panels and payback. For the full set of treatment-plant equipment, our biogas and treatment plant electric motors and water treatment and wastewater plant motors articles offer a holistic view. You can review our product range under our IE4 electric motor and efficient electric motors categories, and reach more content from our home page.

The Savings Logic in the Water Sector: Why Is Efficiency So Valuable?

Because water and wastewater plants are a public service, they must run without stopping; a blower or lift pump being down for long is unacceptable for the process. This forced continuity means the motors turn almost without rest throughout the year. The bulk of a motor's total lifetime cost is not the purchase price but the electricity it consumes. In a continuously running motor this ratio is even more pronounced: the electricity bill paid over the years rises to many times the initial purchase price of the motor.

That is why, in the water sector, efficiency is not a luxury but the main factor determining the operating cost directly. The fact that an IE5 motor runs one step lower in losses than IE4 may seem small for a single motor, but in a plant with many motors running many hours, it adds up to meaningful total savings. You can find methods for measuring and verifying savings in annual savings measurement and documentation in high-efficiency motors. For the extra savings the drive provides in pumps and fans, our pump-fan savings with a VFD in high-efficiency motors can be applied directly to water-plant applications.

Affinity Law and Variable-Flow Operation

In pump and fan applications, the biggest gain the drive provides comes from the affinity law: when you reduce the flow of a pump or blower, the power it consumes drops much faster. So at moments when the process allows flow to be reduced, the IE5 + drive combination consumes noticeably less energy than a fixed-speed motor. Because the incoming water flow in treatment plants varies through the day and across seasons, this feature is very well suited to the water sector. We addressed the effect of the affinity law on pump and fan energy savings in VFD pump and fan energy savings: affinity law.

Correct Power and Speed Selection: Avoiding Oversizing

A common mistake when selecting a water-plant motor is choosing equipment larger than needed. An oversized motor runs continuously at low load, which lowers efficiency, because motors reach their highest efficiency when running near rated load. Although SynRM motors offer a more stable efficiency curve at part load than induction motors, correct sizing still matters. The power should be set according to the real flow and pressure demand, planning for future capacity growth with a reasonable margin. We examined how SynRM differs from induction in terms of rated current and panel selection in rated current and power factor in IE5 synchronous reluctance motors.

Treatment plants can also experience sudden load changes (for example a flow surge after rain). SynRM motors, together with a drive, can give a fast torque response to such impulsive loads; we addressed this behavior in torque response to sudden load change in IE5 synchronous reluctance motors. Quiet operation is also an advantage for treatment plants; you can find the sound level of SynRM motors in noise and sound level in IE5 synchronous reluctance motors.

Label Reading and Order Verification

In an IE5 SynRM motor order, because the motor will be paired with a drive, reading the label data correctly is especially important. To verify the rated values needed for drive matching, our nameplate and label reading in IE5 synchronous reluctance motors; for compatibility with different drive brands, our compatibility of IE5 synchronous reluctance motors with different drive brands is a practical resource. Considering all these steps together, the IE5 switch for a water plant should be planned not as a motor alone but as a motor-drive-panel-installation whole.

Frequently Asked Questions

Can an IE5 SynRM motor be connected directly to the grid in a water treatment plant?

No. Synchronous reluctance motors are driven by a VFD by design and cannot start on their own when connected directly to the grid. In a treatment plant this is actually an advantage: the drive provides extra savings by matching blower airflow and pump speed to the instantaneous process demand.

What is the difference between IEC 60034-30-2 and IEC 60034-30-1?

IEC 60034-30-1 defines the efficiency classes (IE1-IE4) of classic fixed-speed squirrel-cage induction motors. IEC 60034-30-2 sets efficiency classes for drive-fed motors and different technologies such as synchronous reluctance, covering a broader framework including IE5.

How quickly does switching to an IE5 motor pay back in a blower application?

The payback period depends on the motor's power, annual operating hours and electricity use. On high-power equipment such as blowers that run thousands of hours a year, the efficiency difference accumulates continuously, so the switch pays back noticeably faster than for equipment that runs less.

Maintenance and Long Life

The magnet-free, bar-free rotor of SynRM motors also offers a maintenance advantage. Because there is no loss-generating component in the rotor, the motor runs cooler, which extends the life of the bearing grease and winding insulation. In continuously running water plants, this long life reduces unplanned downtime. We addressed maintenance and fault management of SynRM motors in IE5 synchronous reluctance motor maintenance and fault management, and the concept of uptime and MTBF in operating life and MTBF in IE5 motors. All of this makes IE5 attractive in the water sector not only for energy savings but also for operational reliability.

Get a Quote

For your water or wastewater treatment plant, let us plan the correct power and drive matching together for IE5 synchronous reluctance, blower, pump and mixer motor supply. Our expert team is ready to offer a solution tailored to your application. You can reach us at +90 (532) 345 49 86 or via our contact page.

Purchasing Checklist

  • Has the equipment type been determined? (blower, lift pump, mixer, aerator)
  • Have the S1 (continuous) duty type and annual operating hours been clarified?
  • Have the required power (kW) and speed range been selected per the application?
  • Has a VFD suitable for the IE5 motor and its correct sizing been planned?
  • Have the IEC 60034-30-2 efficiency class and frame-power match been verified?
  • Have thermal behavior, cooling and low-speed conditions been assessed?
  • Has the plant's panel and installation compatibility (commissioning) been checked?