The effect of this is the same as shifting the brushes except that no sparking results.
The other part is arranged so that its excitation may be varied, thus shifting the resultant plane of the field with respect to the direct current brushes.
One of these parts is permanently excited and it produces near its edge the fringe of field necessary for sparkless commutation.
Regulating Pole Method.—As applied to the rotary converter regulating poles fulfill the same functions as commutating or interpoles (see page 385) on motors and dynamos, that is, they insure sparkless commutation from no load to heavy overloads with a fixed brush position.
Fig. 2,054.—General Electric regulating pole rotary converter. The field structure is divided into two parts, a main pole and a regulating pole. The ratio between the voltages on the direct current and alternating current sides may be readily varied by varying the excitation of the regulating poles, the only auxiliary apparatus required being a field rheostat for controlling the exciting current. Where automatic regulation is required, machines may be provided with compound windings, or automatic field regulators may be used responsive to either voltage or current. These converters are adapted for a variety of purposes where a variable conversion ratio is required, either to maintain constant D. C. voltage with varying A. C. voltage or to vary the D. C. voltage as required. Converters may be operated inverted where it is required to furnish constant or variable A. C. voltage from a D. C. source. Where converter and inverted converter operation are desired, an opposite direction of rotation is required for the inverted operation. Converters of this type are built in capacities from 300 kw. up to 3,000 kw., and constructed to give a voltage range between 240 and 300 volts, to cover the usual lighting circuit requirements. In design, they are similar to standard rotary converters, with the exception that the regulating poles are located next to the main pole pieces and a slightly different form of pole piece bridge is used for the main poles, in order to allow the auxiliary poles to be readily removed or assembled.
The regulating poles are used in order to vary the ratio between the alternating current collector rings and the direct current side without the use of auxiliary apparatus such as induction regulators or dial switches which involve complicated connections and many additional wires. The regulating poles are arranged with suitable connection so that the current through them can be raised, lowered or reversed.
