Strides in Motor Technology

When AutomationDirect was looking to provide customers with a high-performance, cost effective drive/motor package to complement their growing line of AC variable speed drives, they turned to Marathon Electric – a well-recognized, well-respected name in the industry. Marathon manufactures a full line of general purpose, inverter-duty, vector-duty and NEMA premium efficiency motors to meet the needs of a wide range of customers, and specializes in severe duty and explosion-proof motors for chemical washdown applications and hazardous applications.

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Marathon’s manufacturing and logistics operations are ISO9001:2000 certified, which contributes to the superior quality of all their products. Marathon Electric received the highest overall customer satisfaction index values for their product category in a customer satisfaction survey conducted by Control Engineering magazine in 2004.

To help address customer questions about inverter-duty motors and motor/drive applications, we talked to Tom Matyas, AutomationDirect’s Drives, Motors, and Motion Product Manager, about Marathon’s history of product development and recent advances in motor and drive technology.

When did Marathon Electric start to develop “inverter duty” motors?

About twenty-five years ago, customers started to approach Marathon Electric with applications that required motor speed to be altered with variable speed devices known as “drives” or “inverters”. Since many of the original drive manufacturers were located in the upper Midwest and Marathon is headquartered in Wisconsin, the company became a logical and convenient location to help develop those manufacturers’ products. Marathon accommodated these manufacturers by providing outstanding test facilities for them to test their products with Marathon motors. The rewards were twofold: drive manufacturers saw how their products functioned with Marathon motors and Marathon engineers learned how those drives affected their motors. This led to several generations of drive-compatible motors that are now named Blue Max®, Black Max®, Blue Chip XRI®, and microMAX™. With the advent of the IGBT drive, several new parameters were introduced to the motor. Changes in firing speed and carrier frequencies highlighted the need for further motor developments, and vector duty applications made even more refinements necessary. Through all these changes, Marathon has continued to improve the capability of its products. In fact, Plant Engineering magazine named Marathon’s microMAX “Product of the Year” in 2001.

Why do motors operate more efficiently when connected to a Variable Frequency Drive (VFD)?

To some degree, a motor operates more efficiently, and certainly with greater dependability, when teamed with a VFD. This is particularly true at lower operating frequencies, where iron losses are lower. Any time a particle is magnetically charged in one polarity (i.e. “north”), and then must reverse its polarity (i.e. “south”), energy is expended. Think of this phenomenon as “magnetic friction”. At lower frequencies, this polarity reversal occurs less frequently, thus “magnetic friction” is reduced. The lower losses allow the motor to run cooler. Unfortunately, the laws of physics operate in the same manner at higher frequencies; therefore, motors typically run a little warmer above 60 Hz.

With regards to efficiency, the real issue is not component (or even the motor/drive system) efficiency. It is really more a matter of improving the efficiency of the process that is powered by the drive/motor system. An example is a fan or pump application, where at lower frequencies, the HVAR system’s airflow or the pump’s fluid flow may be more appropriately matched to the requirements of the user. Reducing motor (and thus fan and pump) speed, versus using dampers or valves, utilizes power more efficiently, thus improving system efficiency. Machinery or conveyors become more efficient as they operate at optimal speeds.

Also, motors operated by VFDs are not adversely affected by “inrush” current, as are their line-started counterparts. This high current, typically six to seven times full load, causes more stress on the endturns of the motor than the program-controlled ramp-up of a VFD, which upon startup, acts much like a soft-starting device. As a result of lower mechanical insulation stresses (if you installed plexiglass in the motor’s endbell, you would actually see physical movement of the endturns in a motor that was line started) the insulation life of the motor is lengthened when operated with a VFD.

What is the history behind the Blue Chip XRI product?

The Blue Chip XRI motor line was originally developed to meet the efficiency and performance demands of the chemical process industry. Companies like Dow Chemical were among the first customers to recognize the important role of energy in the production of their products and demanded that motor manufacturers improve the efficiency and life of their offering. Through extensive cooperative engineering research and development, Marathon Electric has developed a line of premium efficiency motors that meet or exceed the rigorous requirements of all major processing manufacturers. These industries include petrochemical, mining, pulp and paper, pumping, and automotive.

The Blue Chip XRI Ultra High Efficiency motor incorporates an all cast iron frame and end bells that provide the necessary strength and corrosion resistance for the most demanding industrial applications. They also feature 100% copper windings that offer lower resistance and lower temperature-rise for higher overall efficiency. Low-loss electrical grade steel laminations and longer stack lengths in the rotor and stator reduce electrical losses and improve heat transfer by lowering flux density and increasing cooling capacity. The Blue Chip XRI family boasts one of the highest overall efficiency levels in the motor industry and is inverter rated at 20:1 constant torque. XRI motors meet NEMA Premium efficiency levels, have a 1.25 service factor through 40 HP (1.15 above), and provide the eXtra Return onInvestment (XRI) expected of a high-efficiency motor.

Are these features incorporated in the Blue Max product line?

In addition to the features of the Blue Chip motors, the Blue Max motor line was engineered with several premium components that stand out from the competition. They include the MAXGUARD Class H insulation system, a patented low-stress winding design, normally closed thermostats (one per phase) and encoder provisions included on the opposite drive end. The Blue Max line offers constant torque operation from 0 to base speed (RPM) on vector drives and constant HP operation up to twice base speed (143-256 frame size). These motors are optimized for operation with IGBT inverters.

Why was the microMAX motor developed?

Originally, Marathon Electric wanted to develop a low cost replacement for Permanent Magnet DC (PMDC) motors. Combined with low cost digital micro drives, the microMAX provides exceptional performance throughout its rated speed range. This revolutionary design features up to a 1000:1 constant torque and 2:1 constant horsepower range, rivaling much more expensive variable speed motors. Other design features include linear torque characteristics, superior starting torque (up to 400%), excellent torque to inertia, and smooth low speed performance. To ensure long life, Marathon utilizes their exclusive CR2000 corona-resistant magnet wire. microMAX motors meet all applicable UL, CSA, and NEMA standards, including NEMA MG1-1998, Part 31.

In addition to initial acquisition cost savings, maintenance (cost of ownership) costs are virtually zero. With no brushes or commutators to maintain, the user can expect significant savings over the lifetime of the motor. As an example, the five-year cost of ownership of a ½ HP microMAX motor versus PMDC shows no brush replacements (as compared to 15 brushes @ $30), equaling $450 in savings; no commutator maintenance (as compared to 5 commutators @ $100), equaling $500 in savings; and energy savings (@ $0.8/KW) of $161. While the total physical savings is approximately $1,100, the improved productivity is even more valuable.

Why has Marathon Electric developed an association with AutomationDirect?

Marathon Electric believes that AutomationDirect offers a unique approach and access to the marketplace through its Internet site, and complete product support to assure customer satisfaction and reliable product quality and service. AutomationDirect has taken the time to extensively test and evaluate the Marathon Electric product offering to assure the reliability and compatibility of the Blue Chip XRI, Blue Max, Black Max, and microMAX products. AutomationDirect’s DURApulse and GS2 lines of AC drives have been tested at Marathon’s state-of-the-art lab facility, also to ensure interoperability and to validate performance requirements. The entire line of Marathon motors offered by AutomationDirect carries a 3-year warranty, complies with UL requirements and NEMA standards, and carries the CE mark.

These factors, combined with the unique features of AutomationDirect’s DURApulse drive line, make AutomationDirect the ideal source for serious drive application customers. Marathon Electric also realizes that AutomationDirect can reach those customers who understand the requirements of their application and can independently choose the most appropriate motor/drive package for their needs.

For complete technical specifications and pricing for the Marathon motors and DURApulse AC drives offered by AutomationDirect, visit www.automationdirect.com/drives.

By Tom Matyas
AutomationDirect Product Manager

Originally Published: Sept. 1, 2004