The information on Achieved environmental benefits, Cross-media effects, Applicability, Economics, Driving forces for implementation, Examples, and Reference information for ENE techniques for electric motors is given in Section 3.6.7.
Energy efficient motors (EEMs) and high efficiency motors (HEMs) offer greater energy efficiency. The additional initial purchase cost may be 20 - 30 % or higher for motors of greater than 20 kW, and may be 50 - 100 % higher for motors under 15 k W, depending on the energy savings category (and therefore the amount of additional steel and copper use) etc. However, energy savings of 2 - 8 % can be achieved for motors of 1 - 15 kW.
As the reduced losses result in a lower temperature rise in the motor, the lifetime of the motor winding insulation, and of the bearings, increases. Therefore, in many cases:
●downtime and maintenance costs are reduced
●tolerance to thermal stresses increases
●ability to handle overload conditions improves
●resistance to abnormal operating conditions − under and overvoltage, phase unbalance, poorer voltage and current wave shapes (e.g. harmonics), etc. – improves
●power factor improves
●noise is reduced.
A European-wide agreement between the European Committee of Manufacturers of Electrical Machines and Power Electronics ( CEMEP) and the European Commission ensures that the efficiency levels of most electric motors manufactured in Europe are clearly displayed. The European motor classification scheme is applicable to motors < 100 kW and basically establishes three efficiency classes, giving motor manufacturers an incentive to introduce higher efficiency models:
●EFF1 (high efficiency motors)
●EFF2 (standard efficiency motors)
●EFF3 (poor efficiency motors).
These efficiency levels apply to 2 and 4 pole three phase AC squirrel cage induction motors, rated for 400 V, 50 Hz, with S1 duty class, with an output of 1.1 to 90 k W, which account for the largest sales volume on the market. Figure 3.27 shows the energy efficiency of the three types of motors as a function of their output.
The Eco Design (EuP) Directive is likely to eliminate motors in class EFF 3 and EFF 2 by 2011. The International Electrotechnical Comission ( IEC) is, at the time of writing, working on the introduction of a new international classification scheme, where the EFF2 and EFF# motors are together at the bottom, and above EFF1 there will be a new premium class.
An appropriate motor choice can be greatly aided through the use of adequate computer software, such as Motor Master Plus29 and EuroDEEM30 proposed by the EU-SAVE PROMOT project.
Appropriate motor solutions may be selected by using the EuroDEEM database31, which collates the efficiency of more than 3500 types of motors from 24 manufacturers.
Harmonics caused by speed controllers, etc. cause losses in motors and transformers ( see Section 3.5.2). An EEM takes more natural resources (copper and steel) for its production.
Electric motor drives exist in practically all industrial plants, where electricity is available.
The applicability of particular measures, and the extent to which they might save money, depend upon the size and specific nature of the installation. An assessment of the needs of the entire installation and of the system within it can determine which measures are both applicable and profitable. This should be done by a qualified drive system service provider or by qualified in-house engineering staff. In particular, this is important for VSDs and EEMs, where there is a risk of using more energy, rather than savings. It is necessary to treat new drive application designs from parts replacement in existing applications. The assessment conclusions will identify the measures which are applicable to a system, and will include an estimate of the savings, the cost of the measure, as well as the payback time.
For instance, EEMs include more material (copper and steel) than motors of a lower efficiency. As a result, an EEM has a higher efficiency but also a lower slip frequency ( which results in more rpm) and a higher starting current from the power supply than a motor of standard efficiency. The following examples s how cases where using an EEM is not the optimum solution:
●when a HVAC system is working under full load conditions, the replacement of an EEM increases the speed of the ventilators ( because of the lower slip) and subsequently increases the torque load. Using an EEM in this case brings about higher energy consumption than by using a motor of standard efficiency. The design should aim not to increase the final rpm
●if the application runs less than 1000 − 2000 hours per year (intermittent drives), the EEM may not produce a significant effect on energy savings (see Economics, below)
●if the application has to start and stop frequently, the savings may be lost because of the higher starting current of the EEM
●if the application runs mainly with a partial load (e.g. pumps) but for long running times, the savings by using EEM are negligible and a VSD will increase the energy savings.
The price of an EEM motor is about 20 % higher than that of a conventional one Over its lifetime, approximate costs associated with operating a motor are shown in Figure 3.30:
When buying or repairing a motor, it is really important to consider the energy consumption and to minimise it as follows:
●payback period can be as short as 1 year or less with AC drives
●high efficiency motors need a longer payback on energy savings.
Energy Efficiency (2009) 3.6.1