CHAPTER XIX 



SINGLE-PHASE TRANSFORMERS : 



PARALLEL RUN, HEAT RUN, OVERLOAD, 



HIGH TENSION TEST 



Parallel Run 



The discussion of the parallel test is given here rather 

 than under the heading of "ratio" or "polarity," be- 

 cause the heat run is the next test, and excitation voltage 

 must therefore be provided. 



Having previously tested the ratio and polarity on 

 one of the transformers of the group, the parallel run 

 can be made and the polarity of the others checked with 

 the one tested; also the ratio of the remaining trans- 

 formers. If the transformers differ in ratio by one-tenth 

 of 1 per cent, the fact will be shown in the parallel run, 

 because the test is made at the full potential of the 

 transformer. If a transformer is one turn out, a dif- 

 ference of voltage between the two transformers of from 

 15 to 40 volts will be shown, depending upon the size 

 of the transformer. This potential gives quite a spark 

 and the exact amount of voltage difference may be deter- 

 mined by connecting a voltmeter between the two 

 transformers. 



The connections for the parallel run are shown in Fig. 

 49, No. 2 being the standard transformer the one on 

 which polarity and ratio have been taken. Only two 

 transformers must be connected at the same time, for 

 if voltage is on the entire set, there is more danger of 

 some one coming in contact with the primary leads. 

 Connect two of the transformers as shown in Fig. 49, 

 making one side of the primary connections permanent, 

 and arranging the other side so that the circuit may be 

 completed with a small fuse wire of not over 3 amperes 

 capacity. One end of this fuse wire should be carefully 

 fastened to one end of a clean dry stick about two feet 



[166] 



