Field Diverter Method of Speed Control of DC Series Motors:

The field flux can be reduced by shunting a portion of motor current around the series field, thus reducing the excitation mmf and weakening of field. This Field Diverter Method of Speed Control of DC Series Motors is illustrated in Fig. 1.72 (a).

This method provides speeds above normal because flux is reduced by this method. Lesser the divertor resistance, less the field current, less flux and, therefore, more the speed.

This method is convenient as well as economical and provides the speed control range usually not exceeding 2: 1. This method of speed control is used in electric drives in which the speed should rise sharply as soon as the load falls.