16 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
13%. The alternator in Question 155 is destined to supply high 
tension at a frequeney of 50 eyeles. What will be its 
peripheral density under these circumstances? 
138. Give the average peripheral densities of a 200, a 500 and 
an 800 KVA. single phase alternator, each generating 
current at 50 cycles. 
139. For a low speed 400 KVA. medium tension, 50 cycle, three 
phase alternator, the total armature conductor value has 
been found to be 85,540. What will be the approximate 
armature bore of this machine? 
140. State the limits of usual peripheral speeds of standard 
alternators. ; 
141. Give the formula for the peripheral speed of the magnet 
wheel of an alternator. 
142. State the formula which checks the leading dimensions of 
alternators in terms of their outputs. 
143. A 400 KVA. 500 revs. polyphase alternator, has an arma- 
ture bore of 55 inches and the iron length with its paper 
insulation measures 9.5 inches. Calculate the output fac- ~ 
tor of this alternator. 
144. Give the output factor of an 800 KVA. polyphase alternator 
by using the curve in Fig. 64 of the Instruction Book. 
145. What approximate output will be delivered by a 500 KVA. 
polyphase alternator, if the same ‘is designed for supply- 
ing a single phase current? } 
146. <A 500 KVA. polyphase alternator generates a phase pres- 
sure of 5,000 volts. What will be the obtainable output 
of the same type of machine when designed to deliver 
a phase pressure of 10,000 volts? 
147. What is the reason of the decreasing output with inereas- 
ing voltage? 
148. Which items are chiefly affected by the ratio between pole 
are and pole pitch? 
» P 
a Se 
