: THI-: SYXCHKONOUS CONVERTER 373 



154. Starting Synchronous Converter from the Direct- 

 current Side. If sufficient direct -current power is available, 



inverter may be started from the direct-current side, starting 

 as a shunt motor. When started in this manner, the series field 

 should be short-circuited, as it will oppose the shunt field when 

 the machine operates as a motor and will therefore reduce the 

 starting torque. The transformer secondaries are short-circuits 

 on the direct -current armature at starting, as the frequency is 

 zero and their resistance is very low. This is particularly true 

 if the brushes happen to be resting on commutator segments 

 which are connected directly to the slip-ring taps. Therefore, 

 the transformers should be disconnected. The proper speed is 

 obtained by adjusting the shunt field. As there is practically no 

 voltage control in the simple converter when operating in this 

 manner, it is not always possible to adjust the alternating voltage 

 to a value equal to that of the line. To prevent any disturbance 

 which may result from synchronizing at a voltage other than 

 bus-bar voltage, some of the starting resistance is often left in 



i r mature circuit until after the machine has been 

 synchronised. 



155. Parallel Operation of Synchronous Converters. Syn- 

 chronous converters may be operated in parallel on the direct- 

 current side, just as shunt and compound generators are similarly 

 operated. If one series field winding be used on each machine, 

 only one equali/er is necessary. If the machine is a three-wire 

 converter and is compounded, there will be two series fields, as 

 shown in 1 iu. :i:jx. In this case two equali/er switches are 



sary. (See Vol. I, page 376, Fig. 338.) The loads are 

 shifted by changing the voltages of the converters, either by 

 field control or by any of the other methods already described. 



ter operation i> obtained if each converter has its own 



transformer bank, rather than by having a >ingle bank supplying 



Jill the converter-. This introduces more or ! ! :mce 



n and st:tbili/e< their operation. It may even 



cessary to in iefl reactSQOei in the iran>former leads. 



The alternating >ide of a converter may be accidentally opened 



by a circuit I while the direct-current -ide 



I to a source of power. BUOh 88 Other <,.[! vert - 



ry across the bus-bar.-. The convert 



