More answers on motors and drives: Examples of how to optimize industrial energy usage

Manufacturing and industrial facilities can save energy in many ways, and improving efficiency of electric motors, drives and related systems remains a huge opportunity. Electric motor-driven systems are estimated to consume more than 70% of electricity in U.S. industrial plants. Reducing this electrical use is key to optimizing energy.

The European Union regulation on electric motors and variable speed drives 2019/1781 entered into application as of July 1, 2021, replacing the regulation on eco-design for electric motors (No. 640/2009). The regulation on electric motors and variable speed drives was updated again on July 1, 2023.

U.S. Code of Federal Regulations at 10 CFR, Part 431 — Energy Efficiency Program for Certain Commercial and Industrial Equipment was last amended in June 2023.

Plant managers, system integrators and electrical engineers should understand these regulations, and how to implement them in their facility on various types of equipment.

In an October 30, Control Engineering webcast, “Motors and drives: How to optimize industrial energy use,” Michael Lyda, technical supervisor at Advanced Energy, discussed basics of energy conservation standards for industrial applications of motors, variable frequency drives (VFDs), fans, pumps and compressors. Questions submitted by the audience that were not answered during the live event are addressed below.

Can you discuss using a VFD to reduce disturbance on the utility system, as well as using a VFD with a single-phase power supply for a three-phase motor, and the effect this has on energy efficiency?

Answer: VFD design principles allow for isolation of grid power from the load the VFD is serving. One issue that may arise is the impact of power quality events on the VFD itself. Three-phase induction motors are not very susceptible to transient voltage events, but VFDs are and may need special programming to ride through those events. In certain applications, VFDs are an effective way to get single-phase power to a three-phase motor, with the benefit of using three-phase motors being that they are typically more energy efficient than an equivalently sized single-phase motor.

We see VSD’s installed in many applications, not all of which have energy savings potential. For example, it has been very difficult for us to see energy savings with conveyor belts. What other applications can you think of that are similar?

Answer: Crushers, elevators and some load sharing applications like hydraulic pumps or deep well pumps.

Please explain the role of energy efficiency standard like ISO 50001: 2018 for improving overall energy efficiency.

Answer: Standardizing energy use in a facility and making energy management a protocol promotes an energy efficient organization from the inside out. Getting certified and setting goals for improvement requires organizations and employees to take energy management and energy efficiency more seriously, similar to the push/requirement of ISO 9001 and 14001 in certain industries.

What processes can be used to achieve better energy efficiency?

Answer: Energy audits, periodic assessments of significant energy users, energy treasure hunts, energy awareness training, standardization of energy management via ISO 50001 or similar program, using tools like DOE’s 50001 Ready Navigator, and participation in DOE cohorts around strategic energy management specific to your industry.

Is there a timeline for the DOE setting minimum efficiency requirements for fans?

Answer: A new test procedure was released May 2023 with an effective date of October 2023. Since then, 180-day extensions were granted to many fan manufacturers who now have until April 29, 2024 to adhere to the requirements.

What is the future of motor and drive technology?

Answer: Induction motors aren’t going anywhere. They are reliable, resilient and cost effective. However, there are newer motor technologies that could challenge the induction motor in some industries, especially those that are very carbon conscious or energy density focused and are willing to pay up for a higher efficiency product.

In the late 90’s, we had a number of drives in service that were putting noise onto the conductors and harming bearings. We installed line reactors to negate this problem. Has drive design changed in 25 years to minimize the effect of noise on the lines?

Answer: Line reactors and DC chokes are still very common methods to mitigate electrical noise and distortion produced by drives. The use of double-shielded VFD cable can also mitigate electrical noise seen at the motor terminals.

What does SNEM mean?

Answer: Small non-small-electric-motor electric motor. The official US DOE definition can be found here: https://www.govinfo.gov/content/pkg/FR-2022-10-19/pdf/2022-21891.pdf on page 63599.

Are there any motors NOT covered by U.S. DOE regulations?

Answer: All covered motors are defined in 10 CFR Part 431.12: https://www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part-431/subpart-B. I cannot possibly list them all, but a few motor types not covered include direct-current (dc) motors, motors rated over 750 horsepower, motors rated over 600 volts, motors rated at speeds slower than 8 magnetic poles, NEMA Design D rated electric motors, component sets of an electric motor, liquid-cooled electric motors and submersible electric motors.

Is the improvement in efficiency gained through IE4 significant, considering that it is much more costly than IE3?

Answer: Stepping from one efficiency level to the next is typically around a 20% reduction in losses. So, in theory, IE4 level efficiency is a 20% reduction in losses as compared to IE3. This will not be the case for every motor, but is a good rule of thumb. If you would like to compare a specific motor (output and speed rating), the efficiency levels are covered in standard IEC 60034-30-1.

Are there any concerns related to operating a VFD from a standby generator?

Answer: There are none that I’m aware of, unless the generator isn’t sized appropriately or there is a very low power factor. If the VFD is a nuisance tripping when run on the standby generator, then you may need to review the control parameters in the VFD itself.

What’s your opinion about AFE (active front end) technology for VFDs? What are the advantages and disadvantages?

Answer: These can be very useful if you want to keep harmonic distortion very low. We have tested a few and they mostly work as expected. These are also popular for regenerative applications, like those that have continuous braking during operation (conveyors mentioned above) or test benches. Of course, you will likely pay higher upfront cost for that additional functionality.

You dropped out while talking about which VFDs are good for air compressors. What was your recommendation?

Answer: VFD compressors are very common these days, especially if your base air load is higher than one compressor and you could add a VFD compressor as trim. I would recommend not retrofitting an existing compressor with a VFD (since some compressor types are not designed to run at partial loads), and if you want to use a variable speed compressor to purchase an all-in-one product.

What is the effect on a VFD of increasing or decreasing the PWM frequency?

Answer: The lower the PWM frequency, the better it is for the VFD because the IGBT’s aren’t working as hard. However, at lower PWM frequencies the VFD will make more audible noise, and it’s also not as good for the motor. As you increase the PWM frequency, the waveform seen by the motor becomes cleaner and the audible noise reduces, but the IGBT’s are having to work harder in the drive so it may self-regulate (derate) or trip off if the load is too high.

How do we estimate the programming cost of VFD?

Answer: If you don’t have experience in-house, then this should typically be done by your electrical contractor. Once wired and energized, it may take a few minutes for a simple, straightforward application; but it could take hours and troubleshooting if the application and control method is very complex.

If you are in an area with high Demand (kW) charges, it may pay to segregate kW and kWh charges. Right?

Answer: Most industrials will be on time-of-use rates so demand (kW) and energy usage (kWh) are separate charges on the electric bill. Depending on the application, adding a VFD may not impact your demand charge if the load still peaks at various times over your billing interval, but it will certainly help reduce the kWh usage if you can slow the motor down during some portion of operation.

How do you determine if a VFD will cause cooling issues on a fan cooled motor?

Answer: Review the motor nameplate for its inverter duty ratings. You should see the turndown ratio which indicates the lowest speed that motor could spin and still be adequately cooled by its fan alone. There may be a VT rating and CT rating. VT is for variable torque applications where the torque required reduces with the speed and CT is for constant torque applications where torque required is constant regardless of speed.

How are “VFD rated” motors different than older standard motors?

Answer: Inverter duty motors typically use 1000V rated wire insulation for the motor windings, whereas standard motors use 600V rated wire. This usually means the magnet wire has two extra coats of insulation applied during manufacturing to get to the higher voltage rating. There may be other design changes for a specific manufacturer like closed bearings or Class H insulation coming standard, but I would defer to the motor manufacturers on those items.

Do you recommend “VFD” specific cables over standard building wire?

Answer: Generally, yes, but I will defer to the VFD manufacturer on this. If the manual specifies VFD cable, then you should use it.

Would a soft starter work better for a loaded motor than a VFD?

Answer: A soft-starter only helps during motor start-up. A soft-starter will not allow for variable speed operation and does not offer energy savings potential. If the only goal is to limit in-rush current at motor start-up, then a soft-starter is the right product for that application.

How do we size VFDs for three-phase motors on a single-phase power supply?

Answer: VFD sizing should be based on rated motor current.

As a fan manufacturer should I request my motor supplier be certified by DOE? In other words. is it a requirement that I use a certified motor so that I can list my fans as certified?

Answer: For any covered products, the motor manufacturer should have listed a compliance certification number (CC#) on its motor nameplates. A comprehensive list kept by DOE can be found here: https://www.regulations.doe.gov/certification-data/products.html#q=Product_Group_s%3A*. If the motors you are using do not have a CC#, you could be held liable for illegally distributing those products into commerce.

Where can I get assistance on how to configure my single-phase to three-phase inverter?

Answer: We have tested some of these products at the lab, so I am remotely familiar. For the best advice, I would reach out directly to the manufacturer. If you’ve tried that and aren’t having any luck, shoot me an email.

Does the DOE have the authority to go into a plant/factory to inspect motors to see if they meet current regulations?

Answer: Not that I’m aware of. However, DOE does perform enforcement testing of products in the market and pulls products off the shelf. For that effort, DOE will review the motor nameplate, but is more interested in testing the motor and verifying if the resulting efficiency meets or exceeds minimum requirements.

Do you have experience and expertise with the topics mentioned in this content? You should consider contributing to our CFE Media editorial team and getting the recognition you and your company deserve. Click here to start this process.