In the introductory part of the paper a application review and achievements outline of high speed motors from the beginning of applying, i.e. from 40 years of XX century are presented. Then the attention was directed on issues concerning structure of high speed motors and additional phenomena connected with supplying from high frequency voltage source, i.e. mechanical stresses; skin effect; power losses and their increasing caused by non-sinusoidal shape of supplying voltage. The extends and supplements of calculation algorithm and computation program concerned: mechanical power losses calculations (friction and windage losses), calculations of winding resistances and reactances by increased frequency and air gap thickness are presented. Moreover are presented the general technological requirements connected with start of motors production in examined rated power and rotation speed range. The software presented in the paper enabled high speed motors calculations of rated power up to 100 kW. As an example the calculations are performed for five two-pole motors of synchronous rotating speed 18 000 rpm, i.e. of supply voltage frequency 300 Hz.
The cost of an unexpected failure of a large AC motor can be very high. Not only the cost of simple repair (or replace) of the failed motor, but the costs of production breakdown should be taken into consideration. Many of the motor failures may be avoided by careful and proper motor design, especially by propper design of stator winding and its insulation system, bearing housing and bearing selection, rotor squirrel cages. At Komel Centre evaluation and calculation methods of mechanical and thermal stresses occurred in rotor cages of different types (deep bar, double cage, idle bar) at motor starting period are developed. The calculation are verified by special bench tests. The objects of the tests were sample AC motors 315, 500 and 800 kW, 6000 V. The same was performed for stator winding overhangs for 2 and 4-pole 6000 V motors. Very helpful in design process of reliable AC motors are case studies and expert evidences of different motors breakdowns and failures occurred at their exploitation. At Komel Centre many expert evidences of failed large AC motors of variouos manufacturers were carried out (see table 1).
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