Techno-Economic Assessment of Retrofitting Line-Operated Induction Motors With an Optimized Rewinding Under Partial Load Conditions

Squirrel-cage induction motors (SCIMs) manufactured before adoption IE1 class or even after, which have been in operation for a minimum of 10 years within the industry, are being replaced with brand-new ones with higher efficiency classes such as IE3, or IE4 to comply with minimum energy performance standards (MEPS) adopted in most countries. This transition has been established as a profitable energy efficiency action (EEA), notwithstanding the elevated acquisition costs associated with such high-efficiency motors (IE3/IE4). When looking for new EEAs, optimized rewinding of oversized, line-operated, fixed-speed SCIMs of IE1, or IE2 class shows up as a cheaper option with excellent cost-effectiveness. It allows for upgrading the efficiency class to IE3 or IE4, as well as increasing the efficiency at loads lower than 50%, potentially leading to a reduction of the consumption of electrical energy. This paper shows how to upgrade the motor efficiency class through optimized rewinding and presents an economic framework based on the life cycle cost analysis (LCCA). Theoretical and experimental results show that rewinding a SCIM with a specific optimized winding configuration can increase its efficiency and be a cost-effective retrofitting measure compared to replacing the motor with a brand-new IE3 or IE4 class counterpart. In case studies conducted in the Portuguese industry, fixed-speed, variable-torque motors were rewound using an optimized rewinding strategy, leading to a significant reduction in both active and reactive power input. This approach also exhibited a superior cost-benefit ratio compared to replacing the motor with a brand-new one of IE3 or IE4 class.