Ques. Explain how secondary connections are made for different voltages.
Ans. If, for instance, the secondary pressure of a transformer having two sections be 100 volts with the terminals in parallel, as in fig. 1,990, then connecting them in series will give 200 volts at the free secondary terminals, as indicated in fig. 1,991.
Ques. What precaution should be taken in connecting secondary sections in parallel in core type if the two sections be wound on different limbs of the cores?
Fig. 1,989.—Method of comparing instantaneous polarity. Two of the terminals are connected as shown by a small strip of fuse wire, and then touching the other two terminals together. If the fuse blows, then the connections must be reversed; if it does not, then they may be made permanent.
Ans. It will be advisable to make the connections ample and permanent, so that there will not be any liability to a difference between the current flowing in one secondary winding and that flowing through the other.
Two Phase Connections.—In the case of two phase distribution each circuit may be treated as entirely independent of the other so far as the transformers are concerned. Two transformers are used, one being connected to one primary phase and supplying one secondary phase, the other being connected to the other primary phase and supplying the other secondary phase as indicated in fig. 1,996, exactly as though each primary and secondary phase were an ordinary single phase system, independent of the other phase.
Figs. 1,990 and 1,991.—Methods of altering the secondary connections of a transformer having two sections in the secondary to obtain a different voltage. Fig. 1,990 shows the two sections in parallel giving say 100 volts; fig. 1,991 shows the two sections in series giving 200 volts.