MOTOR EFFICIENCY LABELING

Thursday - 08/11/2018 09:37
Coincident with the NEMA test program: it was determined that a more consistent and meaningful method of expressing electric motor efficiency was necessary.
MOTOR EFFICIENCY LABELING
MOTOR EFFICIENCY LABELING
The method should recognize that motors, like any other product, are subject to variations in material, manufacturing processes, and testing that cause variations in efficiency on a motor-to-motor basis for a given design.

No two identical units will perform in exactly the same way.

Variance in the electrical steel used for laminations in the stator and rotor cores will cause variance in the magnetic core loss. Variance in the diameter and conductivity of the magnet wire used in the stator winding will change the stator winding resistance and hence the stator winding loss.

Variances in the conductivity of aluminum and the quality of the rotor die casting will cause changes in the rotor power loss. Variances also occur in the manufacturing process. The quality of the heat treatment of the laminations for the stator and rotor cores can vary, causing a variance in the magnetic core loss.

The winding equipment used to install the magnet wire in the stator can have tension that is too high, stretching the magnet wire and thus increasing the stator winding resistance and resulting in an increase in the stator winding loss I2R.

Similarly, other variances, such as dimensional variances of motor parts, will contribute to the variation in motor efficiency.
It is a statistical fact that a characteristic of a population of a product will generally be distributed according to a bell-shaped or gaussian distribution curve.

The height of the curve at any point is proportional to the frequency of occurrences.
 
Normal frequency distribution


In the case of electric motors, the variation of losses for a population of motors of a given design is such that 97.7% of the motors will have an efficiency above the minimum efficiency defined

Normal frequency distribution by a variation of motor losses of ±20% of the losses at the nominal or average efficiency. Figure 2.10 illustrates the efficiency distribution for a specific value of nominal efficiency of 91%.

It is possible as motor manufacturers gain experience with this procedure that variations in losses will be lower than ±20%. In this event, the spread between nominal efficiency and minimum efficiency can be reduced.

Consequently, NEMA adopted a standard publication, MG1-12.54.2, recommending that polyphase induction motors be labeled with a NEMA nominal efficiency (or NEMA NOM EFF) when tested in accordance with IEEE Standard 112, dynamometer method, with stray loss smoothing. In addition, a minimum efficiency value was developed for each nominal efficiency value.
Normal efficiency distribution

Table 2.7 is a copy of the NEMA efficiency Table 12-6a. It is recommended that this method of labeling efficiency and testing be specified whenever possible.

Normal efficiency distribution.

In instances in which guaranteed efficiencies are required, it is recommended that the preceding test method or an appropriate test method including the method of loss determination and the losses to be included in the efficiency determination be specified.
 Key: Manufacturers

Total notes of this article: 0 in 0 rating

Click on stars to rate this article

  Reader Comments

Security Code   
online
  • Support

    Sales Manager

    +(84)923.886.133

    dolin@dolin.com.vn

    Sales 01

    +(84)918.26.11.44

    dolinvn@dolin.com.vn

    Sales 02

    +(84)941.976.189

    info@dolin.com.vn

    Sales 03

    +(84)987.246.757

    sales@dolin.com.vn

    Sales 04

    +(84)949.380.913

    dolinsales@dolin.com.vn

    Sales 05

    +(84)934.008.489

    dolinvn@dolin.vn

Bestsellers
Software
Laws
CNC Machine
Construction and Land
Counter
  • Online57
  • Search engine12
  • Guest45
  • Today19,418
  • This month205,068
  • Total17,191,755
DOLIN

(+84)287.309.9639

You did not use the site, Click here to remain logged. Timeout: 60 second