S-A] STUDY AND OPERATION. I3 1 



4. In the majority of cases transformers are used on con- 

 stant potential systems, the primary and the secondary potentials 

 being substantially constant. The secondary current, accord- 

 ingly, varies with the load. The primary current varies nearly 

 in proportion to the secondary current and to the load. Trans- 

 formers connected in different parts of a constant potential 

 system are in parallel, i. e., the primary of each transformer is 

 connected directly across the line so as to receive the full line 

 voltage. It will be seen (compare Appendix II.) that a constant 

 potential transformer is essentially a constant flux transformer. 

 Other usesf of the transformer may be considered special. 



Commonly, transformers are made for single-phase currents, 

 there being a single primary and a single secondary winding. 

 On polyphase circuits, several single-phase transformers are used 

 (see Exp. 6-A), one on each phase. A special 3-phase trans- 

 former, with three primary and three secondary coils is frequently 

 used (see 26, Exp. 6-A). 



5. Object and Apparatus. The object of this experiment is 

 to familiarize one with the structure and general behavior of a 

 transformer and with some of the more important relations be- 

 tween the different quantities involved in its operation. Sub- 

 sequent experiments go more fully into test methods (Exp. 5~B) 

 and theory (Exp. 5~C), parts of which can be read to advantage 

 in connection with the present experiment. 



A transformer with several coils having the same number of 

 turns is well suited for the purposes of this experiment. The 



f (43). Here may be mentioned the series or current transformer, with 

 primary in series with the line and secondary supplying current for an 

 ammeter or wattmeter; the constant current transformer for supplying 

 (constant current) arc lights from a constant current series circuit, one 

 time of importance; arc-light transformers for supplying (constant cur- 

 rent) arc lights from a constant potential primary circuit, depending for 

 their operation on magnetic leakage, the present form being the "tub" 

 type with movable secondary which is repelled by the primary and counter- 

 balanced by weights. 



