Hawkins Electrical Guide v. 06 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

The horizontal line OA represents the alternating current voltage generated by the main poles, alone, with the regulating poles unexcited, that is, when delivering 250 volts direct current pressure.

For a six phase converter OA measures about 180 volts diametrically, that is, between electrically opposite collector rings.

If now the regulating poles be excited to full strength, to bring the direct current pressure up to 300 volts, the alternating current voltage generated by the regulating poles will be 90 degrees out of phase with that generated by the main poles (since they are placed midway between the main poles), and will be about 40 volts as shown by the line AB.

The resultant alternating current volts across the collector rings will be represented by the line OB with a value equal to 184.

Fig. 2,057.—Voltage diagram for regulating pole converter illustrating principles explained in the accompanying text.

Again, if the regulating poles be reversed at full strength, to cut the direct current pressure down to 200 volts, the alternating current voltage of the main and regulating poles will be OA and AC respectively, giving the resultant OC equal to OB with a value of 184 volts. Accordingly, the direct current pressure may be either 200 or 300 volts with the same alternating current pressure, and if the main field be kept constant, the direct current pressure may range between 200 or 300 volts, while the alternating current pressure varies only between 180 and 184 volts.

The alternating current pressure can be kept constant through the full range of direct current voltage by changing the main field so as always to give an equal and opposite flux change to that of the regulating field. A constant total flux may thus be obtained equal to the radius of the arc BC, fig. 2,057. In this case the line OA, representing the main field strength, will equal OB when the regulating field is not excited, and 250 volts can only be obtained at this adjustment.

This method of operation gives unity power factor with a constant impressed pressure of 184 volts alternating current with a range of direct current voltage from 200 to 300 volts.