TRANSFORMERS 15 



72. Calculate the regulation of the auto-transformer No. F for 

 a load of 510 kw. at 0.90 power factor on the low-tension side. 

 What is the efficiency of the transformer at this load? 



73. If the high-tension winding of the auto-transformer No. E is 

 short-circuited what voltage should be applied to the low-tension 

 winding so that there will be full-load current in the windings? 



74. If the high-tension winding of the auto-transformer No. F 

 is short-circuited what voltage should be applied to the low-ten- 

 sion winding so that there will be full-load current in the windings? 



75. An induction regulator is connected in a 2300-volt cir- 

 cuit as shown in Fig. 2. With no load on the line and with 2300 

 volts impressed on the circuit as shown in the h 



figure the voltage measured from a to c is 



2550 volts. If the winding b-c is short-eir- 



cuited and a reduced voltage of 210 volts is 



impressed on the winding a-6, the line current 



in (o-a) is 130 amperes and the power supplied FIG. 2. 



is 2.2 kw. (a) When the station supplies 250 



kw. at 0.78 power factor and a voltage of 2300 volts at a-6 what is 



the line voltage at a-cf (b) This regulator is adjusted to reduce 



the voltage so that with no load on the line and with 2300 volts 



impressed on the circuit (at a-6) the voltage at a-c is 2050. 



The short-circuit data are unchanged. What is the voltage at a-c 



when the station supplies 300 kw. at a leading power factor of 



0.92 and a line voltage of 2300 volts at a-bf 



76. An induction regulator is connected in a 6600-volt circuit 

 as shown in Fig. 2. With no load on the line and with 6600 volts 

 impressed on the circuit (at a-6) the voltage measured from a to c 

 is 7370 volts. If the winding, 6-c, is short-circuited, and a reduced 

 voltage of 600 volts is impressed on the winding, a-6, tho line 

 current (in o-a) is 76 amperes and power supplied is 4.2 kw. 

 (a) When the station supplies 430 kw. at 0.80 power factor and 

 a voltage of 6600 volts at a-6 what is the line voltage at a-cf 



b Thi- regulator is adjusted t< reduce the voltage so that 

 with no load on the line and with 6600 volts impressed on the 

 circuit (at a-6) the voltage at a-c is 5850 volts. The short- 

 circuit data are unchanged. What i> the voltage at a-c when the 

 station supplies a line curn-nt (in o-a) of 81 amperes at a leading 

 power factor of 0.83 and a line voltage of 6600 volts at a-6f 



77. A small experimental tran-tWim-r has four equal coils 

 which may be inter-connected in different ways. In the first case 



