Question

Sketch a lamp bright, lamp dark system configuration for synchronizing lamps

Fig.—Schematic Diagram of Synchroscope and Synchronising Lamps for "Lamps Bright" System

In the "lamps bright" method a one-to-one ratio transformer is connected so that its secondary can be connected, with reversed polarity, in series with the secondary of the transformer connected to the running generator. Thus, when the two supplies are in synchronism double normal voltage is imposed on the lamps.

Fig..—Schematic Diagram of Synchroscope and Synchronising Lamps for "Lamps Dark" System

In practice it is almost impossible to adjust the speeds exactly so that the pointer remains stationary at 12 o'clock, and it is best practice to have the pointer rotating not faster than one revolution in 5 seconds in the "fast" direction, and to close the switch when the pointer is at about 11 o'clock. In this way with the machine slightly fast it will immediately assume load, whereas if switched when running slow it would take a motoring load which might possibly operate the reverse power relays. It is in view of this possibility that the latter should be provided with time lag.

Two voltmeters are necessary, one connected to the busbars and the other to the incoming machine. In practice a 10 per cent difference in voltage might be considered tolerable.