Electric motors rated for use on a fixed frequency power supply, combinations of voltage variation and frequency variation are classified as being either zone A or zone B, in accordance with IEC 60034-1 Rotating electrical machines Part 1 Rating and performance.
- Zone A
- Electric motors shall be capable of performing continuously within Zone A but do not need to comply fully with the performance at rated Voltage and Frequency. The motors may exhibit some deviations. Temperature rises may be higher than at the rated Voltage & Frequency.
- Zone B
- Electric motors shall be capable of performing continuously within Zone A but do not need to comply fully with the performance at rated Voltage and Frequency. The motors may exhibit greater deviations. Temperature rises may be higher than those in Zone A. Extended operations at the limits of Zone B may shorten the life of the motor.
(IEC 60034-1 Figure 12)
In practical applications and operating conditions, an electric motor will sometimes be required to operate outside the perimeter of zone A. Such deviations should be limited in duration and frequency of occurrence. Corrective measures should be taken, where practicable, within a reasonable time, such as a reduction in output. Such action may avoid a reduction in machine life from temperature effects.
The temperature-rise limits or temperature limits in accordance with IEC 60034-1 apply at the rating point and may be progressively exceeded as the operating point moves away from the rating point. For conditions at the extreme boundaries of zone A, the temperature rises and temperatures typically exceed the limits specified in IEC 60034-1 by approximately 10 K.