Fig. 2,022.—Delta-star connection of three transformers for low pressure, three phase, four wire system.
When lights only are used the neutral should be the same as the main conductors. The copper required in such a system for a given power and loss is about 33.3 per cent. as compared with a two wire single phase system or a four wire two phase system using the same voltage.
Fig. 2,023.—Diagram of transformer connections for motors on the monocyclic system.
Monocyclic Motor System.—Motors on the monocyclic system are operated from two transformers connected as shown in fig. 2,023. In the monocyclic system the single phase current is used to supply the lighting load and two wires only are necessary, but if a self-starting induction motor be required, a third or teaser wire is brought to the motor and two transformers used.
The teaser wire supplies the quarter phase current required to start the motor, which afterwards runs as a single phase synchronous motor and little or no current flows through the teaser circuit as long as the motor keeps in synchronism; in case it fall behind, the teaser current tends to bring it up to speed instead of the motor stopping, as would be the case of a single phase motor.
Fig. 2,024.—Moloney flaming auto type arc lamp transformer for 110 volts primary to 55 volts secondary. A hook in bottom of case provides means for suspension of lamp. The transformer may be operated on circuits from 100 to 120 volts primary, 50 to 60 volts secondary. The secondary capacity is 8 to 12 amperes.
The voltage of the transformers should be tested by means of a voltmeter or two incandescent lamps joined in series, before starting up the motor, to see if the proper transformer connections have been made and prevent an excessive flow of current.