lamps are dark; then, while the lamps are still dark, close the main circuit breaker and turn off the synchronizing switch.

After the main breaker has been closed, check and adjust the load distribution by adjusting the governor speed control. Maintain approximately one-half load on the master machine by manually adding or removing the load from the slave machine(s). The master machine will absorb all load changes and maintain correct frequency unless it becomes overloaded or until its load is reduced to zero.

The operator also must ensure that all generating sets operate at approximately the same power factor (PF). PF is a ratio, or percentage, relationship between watts (true power) of a load and the product of volts and amperes (apparent power) necessary to supply the load. PF is usually expressed as a percentage of 100. Inductive reactance in a circuit lowers the PF by causing the current to lag behind the voltage. Low PFs can be corrected by adding capacitor banks to the circuit.

Since the inductive reactance cannot be changed at this point, the voltage control rheostat has to be adjusted on each generator to share the reactive load. This adjustment has a direct impact on the generator current, thus reducing the possibility of overheating the generator windings.

PF adjustment was not discussed in the "Single Plant Operation" section because a single generator has to supply any true power and/or reactive load that may be in the circuit. The single generator must supply the correct voltage and frequency regardless of the power factor.

INFINITE BUS OPERATION. - Paralleling generator sets to an infinite bus is similar to the isolated bus procedure with the exception that all sets will be slave machines. The infinite bus establishes the grid frequency; therefore, the governor of each slave machine has to have speed droop to prevent constant load changes.

Emergency Shutdown

In the event of engine overspeed. high jacket water temperature, or low lubricating oil pressure, the engine may shut down automatically and disconnect from the main load by tripping the main circuit breaker. In addition, an indicator may light or an alarm may sound to indicate the cause of shutdown. After an emergency shutdown and before the engine is returned to operation, the cause of shutdown should be investigated and corrected.

NOTE: It is important to check the safety controls at regular intervals to determine that they are in good working order.

Basic Operating Precautions

The order that you post in the station for the guidance of the watch standers should include a general list of operating rules and electrical safety precautions. BE SURE YOU ENFORCE THEM!

The important operating rules are relatively few and simple. They are as follows:

1. Watch the switchboard instruments. They show how the system is operating; and they reveal overloads, improper division of kilowatt load or reactive current between generators operating in parallel, and other abnormal operating conditions.

2. Keep the frequency and voltage at their correct values. A variation from either will affect, to some extent at least, the operation of the electrical equipment of the base. This result is especially true of such equipment as teletypewriters or electrical clocks. An electrical clock and an accurate mechanical clock should be installed together at the generating station so that the operators can keep the generators on frequency.

3. Use good judgment when reclosing circuit breakers after they have tripped automatically; for example, generally the cause should be investigated if the circuit breaker trips immediately after the first reclosure. However, reclosing of the breaker the second time may be warranted if immediate restoration of power is necessary and there was no excessive interrupting disturbance when the breaker tripped. It should be kept in mind, however, that repeated closing and tripping may damage the circuit breaker as well as the overload vault area, thus increasing the repair or replacement work.

4. Do not start a plant unless all its switches and breakers are open and all external resistance is in the exciter field circuit.

5. Do not operate generators at continuous overload. Record the magnitude and duration of the overload in the log; record any unusual conditions or temperatures observed.

6. Do not continue to operate a machine in which there is vibration until the cause is found and corrected. Record the cause in the log.