DC machines are used for many purposes because their rotor speed can be controlled easily. However, large DC motors such as those for driving rolling mills have often a problem called nospark zone drift between base and top speed. In such case, No-spark communtation is kept with the aid of an external commutation compensating apparatus, i.e. a diverter. It is desirable to omit this external apparatus, because it requires more space and maintenance.
Then, we invented new interpole structure to achieve a driftless no-spark zone for DC motors without the diverter, and their usefulness was confirmed by analysis and experiments. The form of the interpole structure and the compensating principle of the no-spark zone drift with diverterless DC motors are described ther. We clarified particular emphasis in order to obtain the effects of the structure for a 2, 000kW DC motor.
We applied the interpole structure to the machines rated from 470kW to 2, 900kW. We confirmed that these DC machines were able to compensate for no-spark zone drift singly without the diverter, and they had improved rotor speed regulation for a weak field. The measured reults were shown to have good agreement with the analytical results.
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