.1.2 Determination of unit rating
The unit rating of a motor can be determined according to various aspects, since
every application requirement is different. The outline in Table 4.3.1 indicates
which selection factors are important:
4.1.3 Catalog data
The degree to which an individual motor meets requirements can be determined
by comparison of the motor to the manufacturer's catalog data. Table 4.5.1 lists
the most important parameters to be observed, depending on the application.
Some of these parameters have been standardized, others are specific to the
manufacturer or can be selected by the customer, generally from several alternatives. Therefore the design engineer often has a certain freedom of choice in
defining the details of a motor. Many manufacturers offer modular motor
designs. The following specifications can usually be defined when ordering
• rotor design and thus the torque characteristic
• cooling system
• insulation class of the windings
• style
• type of installation
• degree of protection and protective devices as well as other data.
4.1.4 Operating conditions
For design purposes the operating conditions and the parameters of the driven
load are as important as the motor data.
Table 4.6.1 shows the most important data to be observed for design. In critical
cases the proper drive motor for the given motor task should be selected in
cooperation with the motor supplier.
4.1.5 Procedure for selecting motors
Most motors are operated in continuous duty S1. The first selection consideration is the output in continuous duty. Since the service life of electrical machinery depends largely on the continuous operating temperature, the choice must be
made carefully. As a second step, the suitability of the motor for the starting
conditions should be examined with respect to starting time or starting torque. In
motors with complex operating modes (S2 ... S9) basically the same considerations apply, whereas consultations with the suppliers are usually necessary due
to the changing load conditions and the fluctuating winding temperatures.