Fig. 2,044.—Equalizer connections of Westinghouse rotary converter. The armature coils are cross connected at points of equal voltage and taps are led out from the winding at suitable points to the slip rings. This construction insures a uniform armature saturation below each pole piece and eliminates one cause of sparking at the commutator.
Ques. What is the general construction of a rotary converter?
Ans. It is built similar to a dynamo with the addition of suitable collector rings connected to the armature windings at points having the proper phase relations.
Standard rotary converters have been developed for 25 and 60 cycles. The standard railway machines are compound wound, the series field being designed for a compounding of 600 volts at no load and full load when supplied from a source of constant pressure with not more than 10 per cent. resistance drop and with 20 to 30 per cent. reactance in the circuit. The large size machines are usually wound for six phase operation.
Figs. 2,045 and 2,046.—Westinghouse pole construction for converters. Fig. 2,045, pole without windings; fig 2,046, pole with windings. Poles are built up of steel laminations held together with rivets. Projections on the inner ends of the poles form seats for the field coils and hold them in position. Copper dampers set in slots in the pole faces insure stable operation. Rotary converters for railway service are almost invariably compound wound. The series windings are formed of bare copper strap. The shunt windings are of insulated copper strap or wire. Spaces between coil turns and sections are provided for ventilation.
Compounding of Rotary Converters.—Compounding is desirable where the load is variable, such as is the case with interurban railway systems. The purpose of the compounding is to compensate automatically for the drop due to line, transformer, and converter impedance.
On account of the low power factor caused by over compounding, and the fact that substations are customarily connected to the trolley at its nearest point without feeder resistance, over compounding is not recommended. An adjustable shunt to the series field is provided with each machine.