EUP Lot 11 Motors Final Report – DRAFT –October 2007 59 of 109 3.1.7 Company motor specifications Many larger organisations have their own specification of motors, which may limit choice by either insisting that all motors are designed for operation in their worse case application, or trivial considerations such as colour. 3.1.8 Repair of failed motors For maintenance personnel, the need for rapid vital plant to be brought on line again as soon as possible, will mean that when a motor fails they will do whatever is quickest. Very often it will be quickest to have the failed motor repaired rather than replaced, and as well documented elsewhere this will very likely lead to a decrease in efficiency. This is technically the lowest risk option too, an important consideration when the costs of downtime are high. 3.1.9 Economical factors Generally, it does not economically compensate to substitute motors until they fail. So, although personnel are aware of the problems that come with the use of, for example, oversized or older “imperial” motors, it is not realistic to change them. 3.2 Real load efficiency (vs. nominal) The nominal efficiency represents the average value of a representative sample of manufactured motors for each product category. The motor real full load efficiency can deviate from the nominal efficiency, due to several effects, namely the following: -Testing errors. Round-robin tests with that same motors performed in different laboratories, using direct test methods (e.g. IEEE 112-B), lead to maximum errors of near 10% -Different characteristics of raw materials (particularly magnetic steel) and manufacturing tolerances can lead to a variation of up to 10% in the motor losses. In USA NEMA allows a maximum 20% tolerance in the losses, which applied to the nominal efficiency, leads to the minimum guaranteed efficiency. The induction motor efficiency also varies with the load, as it can be seen in the next figure. Motor efficiency drops sharply below 50% load due to the constant load losses (mechanical and magnetic losses show little change with the load). Sometimes, and for short periods, motors can be operated above 100% load. Over this point, a slight decrease in efficiency is observed. Typically, a service factor of 1.15 (this represents a 15% overload) is permitted, without damage to the motor.

(1許多大型的組織機構都有他們自己馬達規範，這些規範可能會限制選擇機會，要不堅持馬達的設計都要以能運轉依他們最差的設備，或是堅持一些像是馬達的顏色等微不足道的考量。)

(2對維修保養人員來說，就是需要能快速的讓重要的工廠重新生產運作，也就是說當馬達故障時，他們要盡量想方法來解決。因為把故障的馬達修好要比重新替換一台馬達來的快，但是也如同其它文件上所記錄的，這通常也會造成馬達效率的衰退。然而就技術上來說，這也是風險最低的選擇，另一個重要的考量即是停工的成本更高。

(3一般說來，除非馬達壞了，否則替換馬達是相當的不划算的補償。因此人員都知道使用框號過大的馬達或是舊型英制的馬達隨之而來的麻煩是什麼，但更換馬達是相當的不實際。)

(4所謂宣稱的效率值是指每個型錄上各別找一個製造出的典型的樣品的平均值。馬達的實際全載效率值會和宣稱的效率值有所差異，幾個原因如下:

(5--錯誤測試. 相同的馬達在不同的實驗室循環測試，使用直接耦合測試法(例如IEEE 112-B)，等，可能造成最大錯誤差距達10%.)

(6不同的原物料的特性(特別是矽鋼片)及製造公差都可能造成馬達損失計算的的差異達10%. 在美國NEMA標準裡是容許損失差異最大到20%，也可應用在宣稱效率值上，導致成為最小保証效率值.感應馬達的效率值也是會因負載而有所不同,如下圖所示。馬達效率在負載只有50%時會急遽下降，因為有些負載損失是固定的(機械及電磁的損失則只有依負載表現些微的變化) 有時，馬達可以在短時間內超載運轉。但一旦超出負載運轉時，可以觀察到在效率上有些微的衰退。一般來說，在SF1.15(代表15%的超載運轉)是允許的,且不會對馬達造成損害。