Motor stator critical

In continuous operation, rotor and windings asymptotically attain their permanent operating temperatures at different values Trotor, Tstator. For the steady state, a hotter rotor (compared with the stator windings), Trotor > T stator/ indicates a rotor critical motor, whereas hotter stator windings (compared with the rotor), Tstator > Trotor, indicate a stator critical motor. Normally, motors with a rated power exceeding 1. .. 2 kW, are rotor critical, smaller motors are stator critical. ... 

Figure 6.58 Thermal behaviour of an E class stator critical motor, stalled at to after steady state at rated power.

Temperature sensors as an alternative to or associated with current dependent protective devices are within the scope of e standards. Temperature measurements in stator windings are commonly used, but as an alternative to current dependent protective devices they are applicable in stator critical motors only. 

Another example is given in Fig. 6.59. A rotor critical motor (windings in thermal class F) is to be rated for T2 and T3 operation. The rotor (here, for simplification, considered as a thermal homogeneous component) passes the T3 class temperature limit (minus 5 K) after time tE3 at point 3, and somewhat later the T2 class or rotor temperature limit (+300°C minus 10 K) after time fEi at point 1. Meanwhile, the stator windings have passed the... 

Rotor critical motors with temperature sensors in the rotor require expensive data transmission techniques, e.g. Pt 100 resistances, data convertor with frequency modulator, and brushless data transmission to a stator-fixed... 

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