[Electric engineering.] . e of the load, itis, of course, necessary to have their voltages equal. Thereis another important condition that must also be fulfilled; themachines must be in synchronism. By this is meant that 15 ELECTRIC TRANSMISSION. 79 the E. M. F. of A must come to its maximum value at justthe same instant as the E. M. F. of B, or in other words,the electromotive forces of the two machines must vary inunison or be in phase with each other. This means thatboth machines must run at exactly the same frequency, forif this were not the case, they would get out of step. Beforetwo alte
[Electric engineering.] . e of the load, itis, of course, necessary to have their voltages equal. Thereis another important condition that must also be fulfilled; themachines must be in synchronism. By this is meant that 15 ELECTRIC TRANSMISSION. 79 the E. M. F. of A must come to its maximum value at justthe same instant as the E. M. F. of B, or in other words,the electromotive forces of the two machines must vary inunison or be in phase with each other. This means thatboth machines must run at exactly the same frequency, forif this were not the case, they would get out of step. Beforetwo alternators are thrown in parallel, equality of frequencyis the most important condition to be fulfilled. A slight dif-ference in phase will cause an exchange of current betweenthe machines, but they will pull each other into phase if thefrequencies are equal. 91. Synchronizing-.—The state of synchronism is usu-ally ascertained by means of synchronizing- lamps placed onthe switchboard and connected as shown in Fig. 64. T, T. ^Is&mJT,
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