io-C] SYNCHRONOUS CONVERTER. $2? 



PART H. OPERATION AND TESTS. 



14. Synchronizing. A synchronous converter can be brought 

 up to speed and synchronized by any of the means used for start- 

 ing and synchronizing a synchronous motor (Exp. IO-A). It 

 can also be brought to speed as a direct-current shunt motor 

 (Exp. 2-A) by means of direct current supplied to the commu- 

 tator end of the converter, a starting resistance being used in 

 series with the armature to limit the starting current; the field 

 rheostat regulates the field current and so controls the speed in 

 synchronizing. In the laboratory, direct current starting is usually 

 the most convenient. 



In practice, alternating current starting with low starting volt- 

 age is most common ; a " break-up " switch is used for separating 

 the field spools (see n, Exp. IO-A). A D.C. voltmeter on the 

 D.C. side shows when synchronism is reached by ceasing to beat 

 and by assuming a steady reading, either positive or negative. If 

 the polarity is not the one desired, the machine must be synchron- 

 ized again or allowed to slip a pole by opening and closing the 

 main switch. Another way to slip a pole is to reverse the field 

 connections and, after the D.C. voltmeter has come to rest near 

 zero, to again reverse the field; the converter then locks in step 

 with the proper polarity. 



15. Voltage Ratio. On open circuit, measure the A.C. and 

 D.C. voltage and compare their ratio with the calculated ratios, 5. 



16. Tests (Without Series Reactance). On the A.C. side, 

 connect* a circuit-breaker, voltmeter, ammeter and wattmeter; 

 on the D.C. side, connect an ammeter and voltmeter and a variable 

 resistance for a load. No reactance X is in the line; otherwise 

 the connections are as shown in Fig. 2. Line voltage should, if 

 possible, be kept constant. The following scheme of tests may be 

 followed or modified as seems desirable. 



17. No-load Excitation Test. Take the same no-load exci- 



*For a polyphase machine, see 2ia, Exp. lo-A. 



