Switching Dynamo Into and Out of Parallel.--In order to put an additional dynamo in parallel with those already working, it is necessary to run the new dynamo up to full speed, and, when it excites, regulate the pressure by means of a hand regulator until the voltmeter connected to the terminals of the machines registers one or two volts more than the voltmeter connected to the lamp circuit, and then close the switch. The load upon the machine can then be adjusted to correspond with that upon the other machines by means of the hand regulator.
Ques. In connecting a shunt dynamo to the bus bars, must the voltage be carefully adjusted?
Ans. There is little danger in overloading the armature in making the connection hence the pressure need not be accurately adjusted.
It is, in fact, common practice in central stations to judge the voltage of the new dynamo merely by the appearance of its pilot lamp.
Ques. How is a machine cut out of the circuit?
Ans. When shutting down a machine, the load or current must first be reduced, by gradually closing the stop valve of the engine, or inserting resistance into the shunt circuit by means of the hand regulator; then when the ammeter indicates nine or ten amperes, the main switch is opened, and the engine stopped.
By following this plan, the heavy sparking at the switch contacts is avoided, and the tendency for the engine to race, reduced.
Ques. What precaution must be taken in reducing the current?
Ans. Care must be taken not to reduce the current too much.
Ques. Why is this necessary?