The global induction motor market is moving fast towards the higher efficiency classes, such as premium efficiency (IE3) and super-premium efficiency (IE4) classes. Despite that, the existing operating motor stock is still dominated by below-standard and standard motors, since, on average, induction motors, regardless their efficiency classes, can be repaired/rewound 2-4 times over their useful lifetime of 12-20 years. Hence, it is important that the repair/rewinding practices are of the highest quality possible, to ensure that the motor efficiency and reliability are maintained during that process, particularly in the case of motors of higher efficiency classes. In many cases, the motor efficiency and reliability can even be improved during the repair/rewinding process. In this paper, an overview of retrofitting options in induction motors to improve their efficiency and reliability is presented, and an international accreditation program for electric motor repair centers/shops is briefly described.

Nowadays the economic analysis of an induction motor’s life cycle is the clearest way to measure the viability of actions to promote energy-efficient technologies to the end user. The cost effectiveness in motors replacement by energy-efficient motors is a well-known practice that leads to energy savings, however this paper presents the cost-effectiveness of low-power induction motors which have their efficiency improved after rewinding. This process improves the investment viability and brings the greatest financial and energetic savings. In this paper, low-power induction motors are rewound and their efficiencies are measured by tests A and B from IEEE standard 112/2017. The rewound motors have better cost-effectiveness than replacement by IE3/Premium and even IE4/Super-Premium units. The rewound motors increase between 3 and 4 percentage points in relation to former efficiency and the payback is less than 2 years, regardless of the efficiency measurement method.

HVDC systems are becoming more common worldwide, specially in Brazil, since the adoption of such system for Itaipu’s hydroelectric complex in the 1980’s. Today, the country has the Xingu-Estreito bipole, with length of 2375 km. This system crosses a region with high lightning incidence, a phenomenon which causes faults in power systems. The most widely used model for the positioning of the arrestor cables over a transmission line is the electrogeometric model. This model, however, does not take into account the different potentials over the structure’s surface, and therefore presents significant inaccuracies when assessing the risk of lightning strikes on structures such as a HVDC line. This work then used the Electric Field Deflection (EFD) model with the aid finite elements. Four levels of lightning are assessed (I, II, III and IV), with current peaks of 3.9, 5.4, 10.1 and 15.7 kA. It was verified that the positive pole tends to attract most of the lightning with shielding failures width (SFW) of 12, 8, 4 and 0 m. It was then proposed to move the arrestor cables horizontally. The study indicates that this horizontal shifting of the cables in 5 and 8 m toward the side with larger chance of direct incidence reduces the shielding failure widths in 50% for peak current of 3.9 kA and almost eliminates the strikes for lightning with peak currents of 5.4, 10.1 and 15.7 kA.

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.

This paper presents a proper model and methodology to improve the efficiency class of a squirrel-cage induction motor during rewinding. The modeling approach is based on the finite element model, i.e. two-dimensional model coupled with the rotor equivalent circuit (first stage) and the stator equivalent circuit (second stage). Results obtained with finite element analysis are compared with those obtained with analytical calculations. It is demonstrated that, during rewinding, if an improved winding configuration is used, efficiency gains can be obtained, allowing to improve the efficiency class of the motor, from IE2 to IE3, respecting the specified limits of NEMA & IEC performance indicators, namely, breakdown torque, locked-rotor torque, and locked-rotor current. In 79% of the simulated cases the efficiency gain allowed the studied motor to reach the IE3 class.

The increasing concern about climate change has underpinned global efforts toward the reduction of greenhouse gas emissions (GHGs). In this sense, energy efficiency actions (EEAs) are interesting solutions that have been expanding over the years in the industrial sector. Replacing low-efficiency electric motors with high-efficiency counterparts is a ubiquitous action in this sense. However, they still have a high cost, making it necessary to perform a proper technical-economic analysis to determine the feasibility of the action. For this purpose, life cycle cost analysis (LCCA) has proven to be an excellent alternative for economic viability verification of EEAs because this methodology takes into account expenses throughout the entire life cycle of the project or equipment. Considering decision-making involving optimization, this work proposes a methodology to calculate the present residual value at the end of the life cycle, considering the service time of motors and the chosen study period for the project. Two case studies involving predicted theoretical situations are simulated, and the impact of service time on the replacement of a 50-CV, four-pole motor and, 40-CV in a local industry is assessed. It is observed that Net Savings are affected by the study period when replacement occurs in terms of a low-power high-efficiency motor since such action can lead to different service times. Overall, the improved LCC applied to induction motors replacement proves to be a good method for predicting the residual value, whereas the results show that different service times are necessary to maximize net savings and the residual cost in the same case.