Motors and motor-driven systems are huge consumers of electricity, accounting for around 65 per cent of the electrical energy consumed by the power industry. Thus, they are ideal for energy efficiency improvements. Low electricity consumption, better tolerance for thermal and electrical stresses, optimised performance at higher temperatures and reduction of greenhouse gas emissions are some of the key advantages of energy efficient motors (EEMs). The increasing government focus on EEMs and growing construction activity in the country are driving growth in this market.
EEM design and technology
In EEMs, design improvements are incorporated specifically to increase operating efficiency and reduce intrinsic motor losses. Other improvements are the use of lower-loss silicon steel, a longer core (to increase active material), thicker wires (to reduce resistance), thinner laminations, smaller air gap between stator and rotor, copper instead of aluminium bars in the rotor, superior bearings and a smaller fan, etc. The performance of EEMs is better than that of standard motors (STMs) under full, partial and no load conditions. As EEMs have lower losses, their slip is smaller than the STMs, which lowers the starting torque. Thus, EEMs are not suitable for those applications that require a higher starting torque. Further, EEMs operate at a higher power factor than STMs, thus saving on the amount spent in power factor correction.
A motor designed to achieve high efficiency and power factor is made of better material, and thus costs more than a STM. EEMs use more copper, higher grade laminations, and better insulating material. Despite the higher cost, an EEM is preferred because its running cost is much less than that of an STM for any given load.
An EEM requires more active magnetic and conducting material, optimum design of slots, air gaps and windings to achieve the maximum efficiency. Core losses can be reduced by using high grade silicon steel. Stator winding is designed such that the resistance is minimised. Stator copper losses are reduced by increasing the copper section of wire, which is to be wound on the core. In EEMs, improved bearings are used to reduce the friction loss while the optimum design of the fan reduces windage loss. Stray losses are minimised with the careful selection of slot numbers, tooth/slot geometry, air gap length, etc. Other design aspects include optimised air gap between stator and rotor to reduce the magnetising current and associated losses.
EESL, under the National Motor Replacement Programme, is accelerating motor replacement with IE3 motors. Under the programme, no upfront investment is required by the customer. Repayment to EESL is done through monetised energy savings. Motors have a three-year warranty. Large and medium industries and commercial establishments are being targeted under the programme. EESL has estimated that the annual energy saving potential of over 2 million motors produced in India is more than 5 billion kWh or $500 million per annum, which can lead to an avoided generation capacity of 600 MW. EESL aims to replace 120,000 motors in the first phase. According to EESL, almost 90 per cent of the installed stock of motors in India is at IE1 and sub-IE1 levels, resulting in huge inefficiency. Further, old and rewound motors have been running for more than 15 years.
Going forward, installing EEMs is a viable option as they can help save a significant amount of electricity in industrial motor systems. Industrial facilities will be able to significantly reduce their energy consumption as well as operations and maintenance costs by using new-generation electronic variable frequency drives and EEMs.