THE TRANSFORMER. 21$ 



decrease of secondary terminal voltage is due almost entirely to 

 magnetic leakage, and when the receiving circuit is a condenser 

 the effect of magnetic leakage is to cause the secondary terminal 

 voltage to increase with increase of load. The theory of trans- 

 former regulation is developed in Chapter XL 



106. Transformer rating. An increase of the current output 

 of a transformer, with given value and frequency of E f , causes 

 a decrease of secondary terminal voltage and an increased gener- 

 ation of heat in the transformer coils. Increase of E f or de- 

 crease of frequency, on the other hand, causes an increase of 4> 

 according to equation (25), Art. 101, and this increase of <1> 

 causes an increase of iron loss according to equations (26) and 

 (27), Art. 103. 



The voltage rating, frequency rating, and current rating of a 

 transformer are therefore determined by the allowable heating 

 and by the required degree of constancy of secondary voltage, 

 and usually the allowable heating is the determining factor. 



A transformer is usually rated by specifying the value and fre- 

 quency of the primary voltage with which it is intended to be 

 used, and by specifying its ratio of transformation and the power 

 it can deliver steadily (at rated voltage) to a non-inductive receiv- 

 ing circuit. 



The rating of a transformer is by no means rigid and it is allow- 

 able to use a transformer under conditions differing very greatly 

 from the conditions specified in its rating, but when so used a 

 transformer should be watched so that it may be disconnected if 

 its temperature becomes excessive. 



107. The constant current transformer. When a number of 

 arc lamps (or other receiving units) are operated in series, indi- 

 vidual lamps must be short-circuited to cut them out of service, 

 and in order that the lamps may be independent of each other, 

 the circuit must be supplied with a constant current. When alter- 

 nating current is used to operate arc lamps in series, the constant 

 current transformer is used. This transformer takes current from 



