396 ELEMENTS OF ELECTRICAL ENGINEERING. 



revolutions per minute at zero load to 147 revolutions per minute at full load of 75 

 horse power. The station output is such as to require a total of 125 horse power to 

 be delivered by the engines. What power is delivered by each engine, and what is 

 their common speed? Ans. (a) 55.6 H. P., (b] 69.4 H. P., (c] 147.22 r. p. m. 



84. An alternator J3, of which the electromotive force is 1,000 volts, takes 75 

 kilowatts from alternator A. To what value must the electromotive force of A be 

 adjusted, so that the efficiency of transmission may be maximum, and what is the cor- 

 responding value of the current, resistance of circuit being I ohm and reactance of cir- 

 cuit being 0.58 ohm? Ans, 1,076 volts, 75 amperes. 



85. The electromotive force of alternator A in problem 84 is 1,076 volts. To 

 what value must the electromotive force of alternator B be adjusted to give maximum 

 efficiency of transmission, and what is the corresponding value of the current, intake 

 of B being 75 kilowatts? Ans. 1,002 volts, 74.9 amperes. 



86. The electromotive force of alternator A is 1,100 volts, and that of alternator 

 B is 1,000 volts, resistance of circut is I ohm and reactance of circuit 0.58 ohm. 

 What is the angular lag of B behind A, for which power is most efficiently trans- 

 mitted from A to B, what is the intake of B under these conditions, what is the 

 output of A y and what is the efficiency? Ans. 1 8 1. 8, P f/ = 92 kilowatts, 

 P' = IOI.8 kilowatts, efficiency 91.3 per cent. 



87. What is the angular lag of B behind A, in problem 81 for which power 

 is most efficiently transmitted from B to A | what is the intake of A under these 

 conditions, what is the output of B, and what is the efficiency? Ans. 159.47 

 P f = 36.4 kilowatts, P" = 148 kilowatts, efficiency 23.2 per cent. 



88. The electromotive force of A is 900 volts, that of B is 800 

 volts, resistance of circuit is I ohm, and reactance of circuit is I 

 ohm. What is the maximum intake of machine B as a synchro- 

 nous motor? Ans. 189. i kilowatts. 



89. What is the greatest value of B (A, uL, and R being as in problem 84) 

 which will permit machine B to act as a synchronous motor. Ans. 1,243.9 volts. 



90. What value must B have in order that the maximum intake of machine B 

 (problem 89) maybe the greatest possible, and what is this intake? Ans. 621.9 

 volts, 289.4 kilowatts. 



91. Given A = 800 volts, J?= I ohm, uL = I ohm, P // = 30 kilowatts ; plot a 

 curve showing different values of / corresponding to different values of B. Result 

 similar to Fig. 143. 



92- An alternator of which the electromotive force is 150 volts is to be run as a 

 motor from no-volt mains. The resistance of the alternator armature is I ohm. 

 What is the minimum amount of inductance required in the circuit, the frequency be- 

 ing 60 cycles per second ? Ans. 0.00246 henry. 



93. Suppose a condenser were to be connected in series with two alternators A 

 and B so that the total reactance of the ciruit will be 0.58 ohm ; the resistance of the 

 circuit being I ohm, the electromotive force of machine A I,ioo volts, and the elec- 

 tromotive force of machine B I,OOO. Plot curves showing the values of P f and 

 / J// , and AV 2 for various values of 0. 



