Thus the synchronizing lamps may be arranged as in [fig. 2,581], which is simply an extension of the single phase method.
Ques. Are three lamps necessary?
Ans. Only to insure that the connections are properly made, after which one lamp is all that is required.
Ques. How is it known that the connections of [fig. 2,851] are correct?
Ans. If, in operation, the three lamps become bright or dark simultaneously, the connections are correct; if this action takes place successively, the connections are wrong.
If wrong, transpose the leads of one machine until simultaneous action of the lamps is secured.
Fig. 2,851.—Method of synchronizing three phase alternators with, three lamps, being an extension of the single phase method.
Ques. What is the disadvantage of the lamp method of synchronizing?