Frequencies flux density limits

Table D-2 Recommended Flux Density Limits vs. Frequency ...

The power convertor must provide the AC motor with low-harmonic voltage waveform and simultaneously allow the amplitude to be adjusted. This avoids magnetic saturation of the motor as the frequency is adjusted. For constant torque, from maximum speed to base speed, the voltage is adjusted proportional to frequency. Above base speed, the motor is usually operated at constant horsepower. In this region the voltage is held constant and the flux density declines. Also, the convei tor must limit the starting current, ensure operation at favorable slip, and provide a path fitr reverse power flow during motor slowdown. 

It can be seen that the ICNIRP method effectively considers that a flux density that is 50% of the allowable limit at a given frequency has used 50% of the total allowance. A second occurrence at another frequency would consume the rest of the allowance, and any field, however small, at any other frequency would then cause a violation. Dutch regulations apply the same summation formulas as lO lIRP but use different values for the reference limits. In the United Kingdom, the National Radiological Protection Board uses its own values of reference limits and also applies its own summation formula [43]. 

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