[Electric engineering.] . such cases, the equalizer switch is usually mounted on apedestal near the machine, as shown in Fig. 62. 86. So far, in all that has been said, the machines weresupposed to be alike in size and general design. Under suchcircumstances, there is generally no great difficulty in get-ting compound-wound machines to operate properly in par-allel. Trouble is often experienced, however, when it comesto operating machines of different construction and size. 76 ELECTRIC TRANSMISSION. 15 Some field magnets will respond to changes in field excita-tion much more quic
[Electric engineering.] . such cases, the equalizer switch is usually mounted on apedestal near the machine, as shown in Fig. 62. 86. So far, in all that has been said, the machines weresupposed to be alike in size and general design. Under suchcircumstances, there is generally no great difficulty in get-ting compound-wound machines to operate properly in par-allel. Trouble is often experienced, however, when it comesto operating machines of different construction and size. 76 ELECTRIC TRANSMISSION. 15 Some field magnets will respond to changes in field excita-tion much more quickly than others, and other differencesin design may have considerable effect on the performanceof the machines when they are run in parallel. When run-ning two machines of different size in parallel, the problemis to get the load to divide between them in proportionto their size. For example, suppose we have a largemachine A connected in parallel with a smaller machine B,as shown in Fig. 63. Each machine is supposed to be. Fig. 63. adjusted so that it gives the same degree of compoundingwhen operated by itself. Also, when each machine isdelivering its proper share of the load, the drop between a bmust equal the drop between c d. For example, if C is thefull-load current of A, R the resistance between a and b, Cthe full-load current of B, and R the resistance betweenc and d, then C X R must equal Cx R? Now, the resist-ance of the series coils cannot very well be altered in order § 15 ELECTRIC TRANSMISSION. 11 to bring about the required condition of affairs, so that theonly thing to do is to insert resistance of some kind in theleads c b or f d until the above drops become equal. Thisresistance will, of course, be very small and may be made upof a short piece of heavy German-silver strip or even anextra amount of cable in one of the leads. In the figure,this small additional resistance is indicated at x. though itmay be necessary to insert it in the main lead of machine r
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