Parallel Operation of GovernorsThis section is a general description of the function ofthe engine governor in relation to load division betweenparallel electric sets. For detailed information ongovernor controls and adjustments, see the OperationGuide and Service Manual for the engine.It is very important that two basic facts be understoodconcerning load division between generator setsoperating in parallel. First, the power supplied to thegenerator and thus to the load is a function of theengine. The engine governor settings and the positionsof the governor controls determine the amount of powerdelivered by the engine and the KW load carried by thegenerator. If the governor control setting is advanced,the engine and generator will assume more KW load.Likewise, decreasing the governor control setting willresult in a reduction of load on the unit. Any other unitson the line will, conversely, either reduce or gain load atthe same time, assuming no change in total load or nochange in the governor settings of the other units hastaken place. Second, the division of power is notdetermined by generator excitation or terminal voltage.The Power Factor at which a generator will operatewhen paralleled with other generators is determined byits excitation. For more discussion on this subject, referto the section on Parallel Operation of generators.Governors furnished with Caterpillar Powered ElectricSets can be either of two types, governors with fixedspeed droop or governors with adjustable speed droop.The values of speed droop used are commonly 3% and0%. Governors with adjustable speed droop can beadjusted so their characteristics match quite closely thecharacteristics of governors with fixed speed droop. Theoperating characteristics of the following combinations ofgovernors on paralleled electric sets will be described.1. Two 3% governors.2. One 3% governor and one 0% (isochronous)governor.Example 1 - Two 3% GovernorsWhen paralleling A.C. Generators, the engine governorsmust have the same speed droop characteristics if thesets are to divide the load in proportion to their ratingsthroughout the entire operating range.The governor speed droop characteristics of these twounits are similar. This is shown by lines "A" and "B"coinciding in Figure 1. If both units are started, set forhigh idle speed and paralleled at no load, the systemfrequency will be 61.8 cycles or 103% of ratedfrequency. As load is applied to the system, thefrequency will decrease along the speed droopcharacteristic until the frequency at full load is 60 cycles.Figure 1 - Paralleling two units with similar speeddroop characteristics.17
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