Parallel unit operation cannot be accomplished without instruments because of the necessity of having equal voltages and frequencies before the units are paralleled. Minimum instrumentation would be a voltmeter for each unit and a set of synchronizing lamps. It is customary to provide an ammeter for each unit as a check on the output of each unit. The power output of each units not indicated by ammeters since currents for kilowatts and magnetizing power are indicated simultaneously by the ammeter. If the governor or voltage regulator adjustment is not correct, it is difficult to make the proper adjustment, particularly during operation. It is usually necessary to remove the load, take the units out of parallel, make the necessary adjustment, and re-parallel the units. Additional instrumentation makes this unnecessary.
The installation of a kilowatt meter for each unit is useful in setting governor controls, particularly when adding or removing units during continuous operation of an electric plant. The kilowatt meter indicates the power output of the unit. By varying the governor speed control setting, any unit can be made to furnish and desired amount of power up to its full rating. Loads can be divided equally between units of the same rating or proportionately for units of different ratings. Kilowatt meters are particularly useful if the power plant is operated with a lead unit adjusted for isochronous operation. The load on each unit is clearly seen. Overloading the system can be prevented by starting additional units before changes in total load cause overloading of the system.
Two other useful meters for power plant operation are the power factor meter and the kilovar meter. The power factor meter indicates the power factor of the power delivered by an generator. If there is not a set of load instruments, the power factor of each generator is the same as the load power factor if all the generator power factor meters indicate the same value. If these power factor meters show different values, the magnetizing power of the generators is not in proportion to their ratings.
Assume an .80 power factor load and two units on the line. If Unit One indicates .70 power factor and Unit Two indicates .85 power factor, Unit One is delivering too much magnetizing power and the excess is causing Unit Two to operate at a higher power factor; this is indicated by the power factor of Unit Two being less than the load and the power factor of Unit One being less than the load. Power factor can be equalized between the units by reducing the magnetizing power of Unit One. This is accomplished by reducing the voltage level setting of its generator. The power factor is decreased by increasing the voltage level setting of an generator. The power factor of all other units in the line will vary in the direction opposite to that of the unit being adjusted. If the three-phase load in a system is not balanced within ten percent, the indication of a power factor meter may be in error by approximately .05.
Magnetizing power is also called wattles or reactive power. It can be measured by a reactive kilovoltampere meter. This meter is similar to a kilowatt meter, but it measures reactive or magnetizing power instead of active power. Equal or proportionate indications by KVAR (kilovar) meters indicate equal power factors. Indications of KVAR meters are not influenced by unbalanced loads.