RECTIFIED*: Till-: SYNCHRONOUS CONVERTER 359 



below normal and the voltage ratio and the power-factor cannot 

 be adjusted independently. 



Series Reactance. It was shown in Par. 133, page 326, that the 

 voltage at the terminals of a synchronous motor can be raised 

 by over-excitation and lowered by under-excitation, provided 

 there is sufficient reactance in the circuit between the motor and 

 <>urce of constant voltage. As the converter is operating 

 on its alternating-current side as a synchronous motor, it has 

 excitation characteristics similar to those of the synchronous 

 motor. That is, over-excitation causes it to take a leading curn n t , 

 and unilrr-cxcitntion causes it to take a lagging current. There- 

 fore, with series reactance in the alternating-current line, the 

 alternating voltage may be raised and lowered by changing the 

 excitation .see Par. 133, page 326). This may be accomplished 

 by hand regulation of the shunt-field rheostat, or automatically 

 by moans of a regulator, or by compounding the machine. 



Instead of using special series reactances, the transformers, 

 which are usually necessary with a converter, may be designed 

 to have sufficient leakage reactance for this purpose. 



The disadvantage of this method of voltage control is that a 

 change of voltage is accompanied by a change of power-factor. 

 ring the power-factor by any considerable amount is not 

 :lle, because of the decreased efficiency and output which 

 result. The voltage and power-factor cannot be changed inde- 

 jM'iideMtly. Therefore, this method is usually limited to less 

 than 10 per cent, variation above and below the normal voltage. 

 Inilin'iion Regulator. The induction regulator has already 

 been described in connection with the induction motor. (See 

 page 275.) This type of regulator may be connected between the 

 and the converter, and the alternating voltage 

 impressed on the converter terminals may be raised and lowered 

 thereby. This changes the direct-current voltage by a cor- 

 responding amount, t'nder these conditions the voltage maybe 

 i independently of p. 'tor, but the extra equipment 



i objection to the use of the induction regulator. 



\ l<>\v-\Mlt, -me alternator is often connected to 



the -haft of i h- converter. This alternator has t he same number 



of poles a> tip ; the all. |fl con- 



Illl the - : g rill rent 1 1 1 n > HI p| )l\ i ng the 



