Thermal classes

Increased limiting overtemperatures are admissible for certain insulating materials of thermal class H according to an agreement between manufacturer and customer... 

Table 6.13 Part B Thermal classes according to IEC 60085 - examples for ...

An essential point considering e-motors is their thermal behaviour. For the simple case of permanent operation at rated power, the windings shall exceed neither the temperature limit of the corresponding temperature class (T1. .. T6) nor the limiting temperature due to the thermal class of insulating material given in Table 6.13, Part A. 

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... 

Table 6.21 tE values of cage induction motors (thermal class F, 50 cps, for temperature classes T1/T2 and T3) (by courtesy of Siemens AG, Standard Drives Division, Erlangen/Germany)... 

Number of poles 12, 4 Rated power 135 kW, 400 kW Rated voltage 1 kV, 1 kV Rated current 155 A, 267 A Rated speed 492 min-1, 1485 min-1 Rated frequency 50 cps, 50 cps Thermal class H, H Cooling water flow 3 15 litres/min Inlet temperature of cooling water =s+40°C Type of protection EEx dl as an option terminal compartment according to increased safety EEx de I Certificate BVS 91.B.1056X/2. N. 

Number of poles 2 Rated power 55 kW Rated voltage 1 kV Rated current 37 A Rated speed 2950 min-1 Rated frequency 50 cps Thermal class H ... 

The suitability of an enameled wire for a particular application depends to a very large extent on the thermal class to which it belongs. Classification of a wire according to the usual IEC standards is carried out primarily on the basis of its temperature index, breakdown voltage at nominal temperature, and the heat shock characteristics of the insulation. The IEC specifications are internationally binding. In many countries the national standards are completely IEC-harmo-nized. 

Performance is based on tests appropriate to the application. Perhaps the most widely used set of IEEE thermal ratings are those used in the magnet wire industry. The IEEE thermal classes are 105°C, 130°C, 155°C, 200°C, and 220°C. IEEE magnet wire standards are described in Appendix D. 

As temperature often is the dominant aging factor in electrical insulating systems, certain basic thermal classes have been recognized internationally (Table 8). 

Table 8. Thermal classes for electrical tapes for long-term service life at elevated temperature... 

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