Connections and Circuit Control Apparatus.—When a storage battery is used in an electric lighting plant, provision must be made for feeding the lamps, etc., from either the dynamo or battery separately, or from the two working in parallel, and it should be possible to charge the battery at the same time the lamps are being supplied. To accomplish these results requires three switches, for the following connections:
1. To connect the lamps to the dynamo;
2. To connect the lamps to the battery;
3. To connect the battery to the dynamo.
Fig. 1,182.—Diagram showing action of storage battery as a reservoir of reserve power. The figure shows an actual load curve from an Edison station for 24 hours. A sudden storm caused the load to be thrown on very quickly, the peak of the load being higher than usual.
In some plants, the first switch is omitted, because the lamps are always fed by the battery alone, the latter being charged during the day, when no lamps are in use.
It is desirable, however, to have all three switches in every plant in order to be able to supply lamps and charge the battery at any time.
In the battery circuit there should be an ammeter having a scale on both sides of zero, to show whether the battery is being charged or discharged, as well as the value of the current. Another similar ammeter is required in the circuit between the dynamo and the battery, to show the direction and amount of current. A third ammeter is desirable in the lamp circuit, to show the total current supplied to the lamps, but it need only indicate on one side of zero, since the current there always flows in the same direction.
