Robbie McElveen

Induction versus permanent magnet motors

It is clear that a premium will continue to be placed on energy efficiency in motors. The circumstances around global warming and the availability of future oil supplies only increase the focus on electric motors as key elements in the efficient utilization of energy resources. PMs offer an important tool in the quest for cost-effective ways to further increase motor efficiencies. The characteristics of PM motors are sufficiently distinct from that of induction motors that users need to understand their operation to ensure successful applications. The nonsalient PM rotor construction provides high efficiency and high-torque density, whereas the salient pole construction offers some distinct advantages, especially with regard to system issues. Full flexibility to use other than 50 or 60 Hz base frequencies to further optimize performance obviously requires application with an inverter. Once the decision is made to use an inverter, the variable-frequency degree of freedom, with regard to pole selection, works in favor of the PM motor design. The improving performance to cost relationship of PM materials is getting to the point where the increased power density of the PM motor can be large enough to offset the cost of the magnets. While the authors would not suggest that PM motors are going to replace the widespread usage of induction motors, the PM motors provide an interesting alternative, especially in the case where an inverter is to be used in the application. It is for those inverter-fed applications that the first usage is expected in the pulp and paper industry.

Permanent magnet motors for power density and energy savings in industrial applications

The present and future market for motors places high value on power density, operating efficiency, reliability, variable speed operation and low cost. Permanent magnet (PM) motors are now able to meet these market expectations. Compared to the prolific induction motor, PM motors provide the attributes of efficiency and reliability, plus have the additional advantages of higher power density (power per mass or volume), superior power factor (low current), low rotor temperature, and synchronous operation. Advancement in magnet technologies allows operation at higher temperatures without permanent magnetization loss. PM motors are now economically viable due to the availability of rare-earth magnets such as neodymium iron boron at lower prices. Performance comparisons between induction, surface permanent magnet, and salient pole permanent magnet motors are presented in this paper.

Electrical and mechanical differences between NEMA/IEEE and IEC ac low voltage random wound induction motors

The primary standard for low voltage, random wound, induction motors in North American countries is National Electrical Manufacturers Association (NEMA) MG 1-2011. In some other countries, the governing standard is International Electrotechnical Commission (IEC) 60034-1:2010. This paper compares performance, design and construction details of NEMA and IEC three phase, low voltage, random wound alternating current (AC) induction motors. Not only are there obvious mechanical mounting and dimensional differences, but design practices and electrical design norms are different as well. Users must recognize and provide for these variations as they manage projects in different parts of the world. Although testing standards have been fundamentally harmonized between IEEE, CSA and IEC in recent years, efficiency requirements in various countries are not uniform. Obtaining motors in compliance with common standards such as IEEE 841 or API 610 becomes difficult when considering IEC motor designs. This paper discusses the challenges that arise when trying to apply a NEMA based standard to an IEC motor design and vice versa.

Reliability of Cooling Tower Drives: Improving Efficiency with New Motor Technology

Cooling towers are used in many process applications in the petrochemical industry, so reliability of these towers is crucial. In many cases, redundant towers need to be installed to ensure that a process will not have to be stopped due to a cooling tower failure. The most prevalent cause of cooling tower downtime is failure of the right-angle gearbox or associated mechanical components, such as the driveshaft or disc couplings. The elimination of these components can reduce the losses in the drive system and offer the possibility for improved overall system efficiency. This article describes new developments in motor technology that allow for the replacement of high-speed motors, driveshafts, couplings, and gearboxes with a slow-speed permanent magnet (PM) motor. A case study is presented with provisions of maintenance and efficiency improvement data.

A new more reliable solution for cooling tower drives

Cooling towers are used in many process applications in the petrochemical industry. Reliability of these towers is crucial. In many cases, redundant towers are installed to ensure a process will not have to be stopped due to a cooling tower failure. The most prevalent cause of cooling tower downtime is failure of the right angle gearbox or associated mechanical components, such as the driveshaft or disc couplings. Further, the elimination of these components reduces the losses in the drive system and offers the possibility for improved overall system efficiency. This paper describes new developments in motor technology which allow for the replacement of the high speed motor, driveshaft, couplings, and gearbox with a slow speed permanent magnet (PM) motor. A case study is presented with maintenance and efficiency improvement data provided.

Electrical and mechanical differences between NEMA and IEC AC low voltage random wound induction motors

The primary standard for low voltage, random wound, induction motors in North American countries is National Electrical Manufacturers Association (NEMA) MG 1-2011. In some other countries, the governing standard is International Electrotechnical Commission (IEC) 60034-1:2010. This paper compares performance, design and construction details of NEMA and IEC three phase, low voltage, random wound alternating current (AC) induction motors. Not only are there obvious mechanical mounting and dimensional differences, but design practices and electrical design norms are different as well. Users must recognize and provide for these variations as they manage projects in different parts of the world. Although testing standards have been fundamentally harmonized between IEEE, CSA and IEC in recent years, efficiency requirements in various countries are not uniform. Obtaining motors in compliance with common standards such as IEEE 841 or API 610 becomes difficult when considering IEC motor designs. This paper discusses the challenges that arise when trying to apply a NEMA based standard to an IEC motor design and vice versa.