SEAL AS 6L8792 - Caterpillar

Parallel operation of mechanical and hydraulic governors will be described; the electric-hydraulic and electronic governors will not be covered here.When paralleling A.C. Generators, the engine governors must have the same speed droop characteristics if the sets are to divide the load in proportion to their ratings throughout the entire operating range.It is very important that two basic facts be understood concerning load division between generators operating in parallel. First, the power supplied to the generator and thus to the load is a function of the engine. The engine governor settings and the positions of the governor controls determine the amount of power delivered by the engine and the KW load carried by the generator. If the governor control setting is advanced, the engine and generator will assume more KW load. Likewise, decreasing the governor control setting will result in a reduction of load on the unit. Any other units on the line will, conversely, either reduce or gain load at the same time, assuming no change in total load or no change in the governor settings of the other units has taken place. Second, the division of power is not determined by generator excitation or terminal voltage. The Power Factor at which an generator will operate when paralleled with other generators is determined by its excitation. For more discussion on this subject, refer to the section on Parallel Operation of generators.As mentioned previously, governors furnished with Caterpillar Powered Electric Sets can be either of two types, governors with fixed speed droop (mechanical) or governors with adjustable speed droop (hydraulic). The values of speed droop used are commonly 3% and 0%. Governors with adjustable speed droop can be adjusted so their characteristics match quite closely the characteristics of governors with fixed speed droop. The operating characteristics of the following combinations of governors on paralleled electric sets will be described.
Two 3% mechanical governors
One 3% mechanical or hydraulic governor and one 0% (isochronous) hydraulic governorIn the diagrams that follow, the per cent of rated load of one unit will be shown across the bottom. The system capacity will, however, be the sum of the capacities of the units operating in parallel. Percentage is used in the general cases discussed. For any particular installation this can be converted to kilowatts as shown in the following:
Illustration 1 g01059009
Load Division - 3% Mechanical Governors
The governor speed droop characteristics of these two units are similar. This is shown by lines "A" and "B" coinciding in 2. If both units are stated, set for high idle speed and paralleled at no load, the system frequency will be 61.8 cycles or 103% of rated frequency. As load is applied to the system, the frequency will decrease along the speed droop characteristic until the frequency at full load is 60 cycles.
Illustration 2 g01059016
Paralleling two units with similar speed droop characteristicsIf Unit A had been operating alone carrying full load, the system frequency would be 60 cycles as shown by Line "A" at 60 cycles and 100% load. Now, if the