112 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



V = 1020 volts, 7=1. 136 amperes, P = 351 watts. If the second- 

 ary terminal voltage is 440 volts when there is a single-phase 

 load taking 40 kw. at 0.8 power factor connected across one phase 

 of the secondary, what will be the percentage rise in this voltage 

 when the load is thrown off? 



43. (a) On the basis of the same heating loss compare the 

 full-load kilowatt output at unit power factor of two single-phase 

 transformers connected in open delta with their name-plate 

 rating, (b) On the basis of the same heating loss compare the 

 full-load kilowatt output at 0.87 power factor both lagging and 

 leading of two single-phase transformers connected in open delta 

 with 87 per cent, of their name-plate rating. In each case the load 

 is balanced. 



44. (a) Three single-phase transformers with both primaries 

 and secondaries connected in delta supply a balanced load of 100 

 kw. at unit power factor. If it is necessary to remove one of these 

 transformers from the line by what per cent, will the copper 

 loss in each of the other two transformers be increased? (b) 

 If the load had been a balanced one taking 87 kw. at 0.87 power 

 factor both leading and lagging -what would have been the 

 per cent, increase in the copper loss in each of the other 

 transformers? 



45. (a) On the basis of the same copper loss in each trans- 

 former compare the full-load kilowatt output at unit power 

 factor of two equal single-phase transformers connected in T 

 with their name-plate rating, (b) On the basis of the same copper 

 loss in e^ch transformer compare the full- load kilowatt output 

 at 0.87 power factor of two equal single-phase transformers 

 connected in T with 87 per cent, of their name-plate rating. 



46. On the basis of the same copper loss in each transformer 

 compare the full-load kilowatt output of two equal single-phase 

 transformers connected in open delta with the full-load output ot 

 the same transformers connected in T (a) at unit power factor, 

 (b) at 0.87 power factor both lagging and leading. 



47. Compare the regulation of three lOO-kv.-a. transformers 

 whose primaries and secondaries are connected in delta with 

 that of two 100-kv-a. transformers whose primaries and second- 

 aries are connected in open delta when a single-phase load of 

 lOOkw. at 0.8 power factor is delivered on the secondary side. 

 The secondary or low-tension voltage under load conditions is 2200 

 volts and the ratio of transformation is 5 to 1. The short-circuit 



