486 ALTERNATING CURRENTS 



9. What effect have the two leakage fluxes upon the operation of the 

 transformer? 



10. In the complete vector diagram of the transformer, why are the 

 primary and the secondary induced voltages shown equal in magnitude and 

 in phase with each other? Why is a voltage equal and opposite to the 

 primary induced voltage necessary in order to find the voltage at the 

 terminals of the primary? 



11. Show that the total primary current is not equal and opposite to 

 the secondary current even when both windings have the same number of 

 turns. Resolve the primary current into two components explaining why 

 one of these components varies with the load on the transformer secondary. 



12. What is meant by transformer regulation and what assumptions are 

 usually made in obtaining it. 



13. Explain what approximation is made in obtaining the simplified 

 transformer diagram. What advantages result in so making the diagram? 



14. What is the relation ordinarily existing between the primary and 

 secondary resistances in a transformer?- What is meant by "equivalent 

 resistance referred to the primary" and how is this quantity used? 



15. Discuss the relation usually existing between the primary and the 

 secondary reactance, giving reasons for the existance of this relation. 

 What is meant by "equivalent reactance referred to the primary." How 

 is this quantity used in determining the transformer characteristics? 



16. What relation exists between the equivalent reactance referred to 

 the primary and that referred to the secondary? 



17. Show that if one side of a transformer is open and the other side is 

 connected to the line, practically the entire input goes to supply the core 

 loss. How does this core loss vary with the voltage? Why? 



18. Why do both the magnetizing current and the core loss increase 

 very rapidly after the rated voltage of the transformer has been reached? 

 Why is it practically impossible to operate transformers at voltages very 

 much in excess of those for which they are rated? How is the true magne- 

 tizing current found? 



19. When one side of a transformer is short-circuited and the other side 

 is connected to an alternating supply, show that the input goes almost 

 entirely to supplying the copper losses of the primary and secondary coils. 

 How is the equivalent impedance and the equivalent reactance referred to 

 either side determined from the short-circuit test? 



20. What losses exist in a transformer operating under load? How may 

 these losses be computed for different loads? Indicate the method of 

 calculating the efficiency over the working range of the transformer? What 

 are the advantages of this method over direct measurements of output 

 and input? 



21. In what way does the core type of transformer differ in construction 

 from the shell type? Compare the dimensions of the electrical and mag- 

 netic circuits in the two cases. Which type is better adapted for high 

 voltage and why? How is the leakage flux reduced to a minimum in the 

 two cases? 



