. Electric traction and transmission engineering . KILOWATTS. Fig. 73. 400 sum of the transformer and reactance voltages is greaterthan the former and therefore the slip-ring voltage is raisedwith load. The converter with such an arrangement issaid to be compounded, and may maintain a constant direct-current voltage under wide variations of load. It isusual to provide for each phase a reactance coil of acombined kilo volt-ampere capacity equal to 15 % of therated kilowatt capacity of the corresponding 74 shows a General Electric Company air-blast reac-tance set and starting swit
. Electric traction and transmission engineering . KILOWATTS. Fig. 73. 400 sum of the transformer and reactance voltages is greaterthan the former and therefore the slip-ring voltage is raisedwith load. The converter with such an arrangement issaid to be compounded, and may maintain a constant direct-current voltage under wide variations of load. It isusual to provide for each phase a reactance coil of acombined kilo volt-ampere capacity equal to 15 % of therated kilowatt capacity of the corresponding 74 shows a General Electric Company air-blast reac-tance set and starting switches for a , six-phaseconverter. The operating characteristics of the SUBSTATIONS. 173 converter previously mentioned, with added series ampere-turns at full load amounting to 64 % of the shunt ampere-turns, are shown in Fig. 75. With proper adjustments ofthe series and shunt field coils it is possible to make theconverter take a lagging current on light loads and a leadingcurrent on heavy loads. It therefore increases the power. Fig. 74- factor of the transmission circuit on heavy loads. Thismethod of regulation, however, fails to give satisfactoryresults when the line resistance drop exceeds 10 % of theimpressed line voltage or even less; and yet on large trans-mission systems and with long transmission lines it is desir-able and often economical to have a drop greater than motor-generators, however, the direct-current volt-age can be as easily and satisfactorily regulated as with 174 TRACTION AND TRANSMISSION. plain generators, and the regulation is in nowise dependentupon the drop in the transmission line. Furthermore, bythe use of series coils on a synchronous motor field themotor-generator set may be adapted for power factor correc-tion to the same extent as with converters. Cost. — The cost of converters per se is less than that ofmotor-generators of the same capacity. Compound con-
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