Electrical motors are very often oversized for the real load they have to run. Motors rarely operate at their full-load point. In the European Union, field tests indicate that, on average, motors operate at around 60 % of their rated load.
The maximum efficiency is obtained for the motors of between 60 to 100 % full load. The induction motor efficiency typically peaks near 75 % full load and is relatively flat down to the 50 % load point. Under 40 % full load, an electrical motor does not work at optimised conditions and the efficiency falls very quickly. Motors in the larger size ranges can operate with reasonably high efficiencies at loads down to 30 % of rated load.
Proper sizing：
●improves energy efficiency, by allowing motors to operate at peak efficiency
●may reduce line losses due to low power factors
●may slightly reduce the operating speed, and thus power consumption, of fans and pumps.

電動馬達的規格經常是超過其應有運轉的真正負荷。馬達很少在其全載點運轉。在歐盟實地測試結果顯示，平均而言大概在其額定負載的60%左右運轉。
馬達在其全載時的60~100%運轉可得到最大效率。感應馬達的最高效率約為全載的75%左右，而後平降至50%的負載點。如在全載40%時，電動馬達將無法有較佳的運轉條件，而且效率下降很快。
使用較大規格的馬達即使負荷降到額定負荷的30%時仍可有較合理、高效率的操作。
合適的馬達規格有下列好處：
●讓馬達在最高效率運轉可增進能源效率
●因為低電功率可減少線損
●可稍微降低風扇及泵浦的轉動速度而減少電力耗用

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.

●運轉控制器形成的諧波造成馬達和變壓器損失
●高效型馬達生產時需耗用更多的自然資源(銅、鐵)

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.

只要在有電力可用的地方，用電動馬達作為動力帶動在產業界是相當普遍的。
電動馬達的應用性及節省的成本要看設施的特性和規模而定。針對整體設施及系統需求評估，以決定其引入方法之可行性及價值。這項評估可由品質管理系統服務機構或由公司內部工程部門人員進行。
尤其是像變速設備(VSD)和能效型馬達(EEM)的使用有能耗更大而無法省能的風險，因此必須慎重。在更換現有設備零件時有必要採用新驅動設備。評估結果可用來研判何種方法可應用於系統中，及投入成本、節省成本、回收年限等資訊。
例如高能效型馬達(EEM)要用比低效型馬達更多的銅鐵材料，結果EEM雖有較高效率，但同時會有較低的轉差頻率(slip freq.)造成馬達轉速加快，以及比標準型馬達需要更大的起動電流。
以下有些例子說明不適合使用EEM的情況：
●當一套全載運轉的空調系統換裝EEM會因為低轉差頻率而增加通風器的轉速，進而增加轉動扭矩負荷。因此，使用EEM反而較標準型馬達更耗能，這設計不應該用來增加最後的轉速。
●如果設備每年運轉時數少於1000~2000小時，裝設EEM無法有顯著的節能效果。
●若設施必須經常性起停，可能會因EEM需要高起動電流而無法節省費用。
●若設施主要運轉模式為長時間半載運轉(如泵浦)，使用EEM的節省幅度微乎其微，還不如用VSD可以省能。

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.

能效型馬達較傳統型價格高約20%，其使用年限、操作成本如圖3.30。
當考慮要新購或修理馬達時要慎重地考量能效和下列事項：
●交流驅動馬達的回收年限可低於一年
●高效率馬達在能源節省上需要較長的回收年限

Energy Efficiency (2009) 3.6.2