Understanding motor applications to help design more efficient motors - part 1 of 2
September 2019
When it comes to designing better motor solutions, diving into the intricacies surrounding the specific motor application makes a huge difference. We sat down with Nidec Motor Corporation’s Application Engineering Manager, Patrick Hogg, to gain a clear picture of how understanding motor applications can help engineers design a better electric motor within a system.
With over 12 years of experience in the electric motor industry, Hogg has expertise in applications for everything from dishwashers and small fractional pumps up to 5,000-HP compressor motors. He says that there are several important questions to consider whenever he gets an initial inquiry from a customer. “When a customer requests a motor from us, there are certain aspects they should consider regarding the application involved. What features do they need to make sure are on the motor? What specific capabilities does the application require from the motor?”
Just the tip of the iceberg
He points out that specifying the required horsepower, RPM and voltage ratings are only the tip of the iceberg. “Someone might tell me they need a 5-HP, 1800-RPM, 230-volt motor. I might have hundreds of options that could technically fulfill those specifications but not be the most well-suited for the application. So, we need to dive into what the motor and application really needs to develop, and what solution the customer requires.”
This includes the necessary step of asking questions like: What torque does the motor need to generate? At what speed or speeds does it need to achieve this torque? Is the motor driving a variable or constant load? Hogg also recommends evaluating the speed torque curve of the application that will be required. “Once I have the load curve, I can fully understand how to design the motor to run a given application.”
Another important factor Hogg advises to think about is duty cycle of the application. “Does the application require high amounts torque for extended periods; short bursts of high torque and then long periods of lower torque requirements; a reciprocating load that could actually not require the motor to produce torque?” Knowing the answer to these questions provides crucial information for designing a motor that delivers the appropriate amount of power for the application at hand. One example is the starting of a large load that must overcome a high inertial load to start to turn. The motor must generate a high amount of torque to start this load, but once the load is spinning it requires much less torque until it comes up to speed. It is crucial to understand the load and system requirements of an application like this to give an optimal design that keeps the inrush current, which generates the starting torque, as low as possible for energy savings and still start the motor even if the voltage supply is lower than expected.
Environmental concerns
Environment also influences motor requirements. For instance, a compressor motor that is located outside during cold weather will require greater starting torque since its oil will be much more viscous than if it was a warm summer day. A couple other considerations for starting include voltage and current for the installation and the torque requirements necessary to drive the specific application.
Hogg illustrates this last factor by discussing two different applications. “If you think of a conveyor, it needs to move the same weight whether it’s running at 10 RPM or 400 RPM. This means I would design the motor to generate the same amount of torque at the maximum and minimum speeds and handle the heat that comes with it. A conveyor like this is an example of a constant load application and could require a special design to operate reliably.
“The second application example is with a rotodynamic pump and what is called a variable torque load. In most rotodynamic pumps there is very little torque required at low speeds because the pump is not moving much fluid, but as the pump speeds up more fluid is moved and more torque is required from the motor. This motor design can be much different than that of the constant torque system. Each application has its own set of considerations, but the more information we have on the overall system, the better the motor solution we can deliver.”
Hogg states that these pieces of information – the load type, the load curve, the duty cycle, and the starting requirements – form a helpful starting place to begin understanding what specific type of motor will help accomplish the application’s requirements, at least from an electrical design standpoint. In next month’s blog article, we will discuss the main mechanical considerations to keep in mind, as well as a few other factors.
Bio: Patrick Hogg is the Application Engineering Manager for general industry and pumping at Nidec Motor Corporation. He received his bachelor’s degree in Mechanical Engineering from Southern Illinois University and his MBA from the University of Missouri-St. Louis. Mr. Hogg has over 10 years of experience in the motor and pump industry and has been an active HI Member since 2013.
Sources: All info obtained from an interview with Patrick and Episode 21 of the Pumps & Systems Podcast (https://www.pumpsandsystems.com/podcasts).