142 ELECTRICAL MACHINERY 



full load rating and consequently the efficiency would be 

 rather low. (See Chapter V). 



Typical Installation. The proper installation to supply 

 a load curve as given above would consist of two 2500 kw. 

 machines and one 1000 kw. machine. Then from 12 

 o'clock until 6 o'clock the 1000 kw. machine would be 

 running and the other two would be shut down. During 

 most of the day one 2500 kw. machine would be used and 

 during the two hours of peak load the two 2500 kw. machines 

 would be used, or one 2500 kw. and the one 1000 kw. machine 

 would do because a generator will carry 30% overload 

 for a short time. 



In such a station it is to be noticed 1st, that whatever 

 generators are running are operated at practically full load 

 under which condition the efficiency is a maximum and 2d, 

 any two generators of the three which are installed have suf- 

 ficient capacity to carry the station load. Therefore con- 

 tinuity of service is guaranteed and the station operates 

 efficiently; of course the first cost of the station would be 

 considerably higher for the three-generator equipment 

 than for the one-generator equipment. 



Parallel Connection of Generators. In a station only 

 one set of bus-bars is used, no matter how many generators 

 there may be in the station. Bus-bars is the name given 

 to the heavy copper bars which run the length of the switch 

 board (behind it) and to which all generators and feeders 

 are connected. The positive bus connects to the positive 

 terminals of all machines in operation and all negative 

 terminals are connected to the negative bus. Such a con- 

 nection is called a parallel connection of generators; all 

 generators send their power into the one set of bus-bars 

 and the load, supplied by various feeders, is taken from 

 them, as shown in Fig. 91. 



Division of Load. The question naturally arises as to 

 how these generators will divide the total load. Will each 

 take half or what will the division be and how is it deter- 



