2 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



without changing its root-mean-square value or form factor, 2020 

 watts is supplied at no load. What is the division between the 

 eddy current and hysteresis losses at 25 cycles? 



7. With 440 volts at 50 cycles impressed on the low-tension 

 winding of a transformer 641 watts is supplied at no load. If 

 the frequency and voltage are each reduced 50 per cent, without 

 changing the form factor 278 watts is supplied at no load. 

 What is the division between the-eddy current and hysteresis 

 losses at 50 cycles? 



8. With 440 volts at 60 cycles impressed on the low-tension 

 winding of a transformer 371 watts is supplied at no load. If the 

 voltage is reduced 50 per cent, without changing the frequency or 

 the form factor 114 watts is supplied at no load. What is the di- 

 vision between the eddy current and hysteresis losses at 440 volts? 



9. If a simple harmonic electromotive force of 2200 volts at 

 60 cycles is impressed on the low-tension winding of a transformer 

 the core loss is 940 watts, 23 per cent, of which is due to eddy 

 currents, (a) What will be the core loss if an electromotive 

 force of the same effective value and frequency but with a form 

 factor of 1.05 1 is impressed on the low-tension winding? (b) 

 What will be the core loss if an electromotive force of the same 

 effective value and frequency but with a form factor of 1.2 2 is 

 impressed on the low- tension winding? 



10. The magnetic circuit of a transformer has a mean length 

 of 77.3 in. and an average cross-section of 34.4 sq. in. The 

 low-tension winding has 399 turns. Find the core loss, the no- 

 load current, and the power factor at no load when 2300 volts at 

 60 cycles is impressed on the low-tension winding. The curve of 

 core loss at 60 cycles and flux density, and the B-H curve are 

 given by the data on the following page: 



11. A magnetic circuit has a mean length of 69.5 in. and an 

 average cross-section of 30.0 sq. in. It is wound with a coil of 

 94 turns. A constant voltage of 440 volts at 50 cycles is im- 

 pressed on this coil. How long an air-gap would it be necessary 

 to cut in the magnetic circuit in order that the coil would take a 

 current 20 times as great? What is the power factor before and 

 after cutting the air-gap? Neglect the resistance of the coil and 

 use the magnetic data given in problem 10. Assume that the core 

 loss at 50 cycles is 80 per cent, of the loss at 60 cycles. 



1 Flat topped. 



2 Peaked. 



