An elementary book on electricity and magnetism and their applications . es inthe primary equal the volt amperes in the secondary? 11. When no current is being taken from the secondary coil, whatprevents the impressed from sending an excessive currentthrough the primary coil? 12. What losses in a transformer may be reckoned as fixed losses? 13. Why do big transformers require some special means of cann-ing away heat in order to avoid excessive temperatures? 14. How can the input of a transformer be calculated? 15. What makes the all-day efficiency so much lower than theinstantaneous eff
An elementary book on electricity and magnetism and their applications . es inthe primary equal the volt amperes in the secondary? 11. When no current is being taken from the secondary coil, whatprevents the impressed from sending an excessive currentthrough the primary coil? 12. What losses in a transformer may be reckoned as fixed losses? 13. Why do big transformers require some special means of cann-ing away heat in order to avoid excessive temperatures? 14. How can the input of a transformer be calculated? 15. What makes the all-day efficiency so much lower than theinstantaneous efficiency ? 16. What is the essential difference between a constant-voltagetransformer and a constant-current transformer? 17. Why are auto-transformers not more generally used in distribut-ing systems? 18. WThat advantages has electric welding over other methods ofwelding? 19. What precaution should be taken in using a current transformer ? 20. What makes testing transformers so bulky? 21. What apparatus would you use to change the voltage on adirect-current system ? -. Fig. 264. — An induction motor, (a) rotor and (6) stator. CHAPTER XVIALTERNATING-CURRENT MOTORS Induction motor, its place and essential parts — rotatingmagnetic fields produced by two-phase currents and three-phase currents — rotor, squirrel-cage and wound types —starting and running characteristics — speed and slip — itscommercial uses. Single-phase induction motor, methodsof starting and its use. Synchronous motor, ways of starting and special uses. Series motor with commutator, special features and usefor railways. Wagner motor starts as repulsion motor andruns as induction motor. 263. Place of the induction motor. We have seen (Chap-ter XIV) that the alternating-current generator can be builtbigger and more cheaply than the direct-current generatorand that the alternating current is much cheaper for transmis-sion and gives a system of greater flexibility for varying these advantag
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