ARM ASSEM. (L.H.) 8J6650 - Caterpillar

used with generators can vary from none to very complete instrumentation. Single unit operation can be accomplished without instruments. This is very common. The engine governor is adjusted for the high idle speed which will result in rated speed at full load. The generator regulator is normally adjusted for zero voltage droop. The regulator voltage level control may be set for rated voltage with a very precise regulator or for a slightly higher voltage if there is some inherent voltage spread in the regulator characteristic. The unit is then connected to the load lines. As long as the governor and voltage control settings are not changed, the unit can be operated without instruments.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