Usage:
This section is a general description of the function of the engine governor in relation to load division between parallel electric sets. For detailed information on governor controls and adjustments, see the Operation Guide and Service Manual for the engine.
It is very important that two basic facts be understood concerning load division between generator sets 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 a 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.
Governors furnished with Caterpillar Powered Electric Sets can be either of two types, governors with fixed speed droop or governors with adjustable speed droop. 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.
- 1. Two 3% governors.
- 2. One 3% governor and one 0% (isochronous) governor.
Example 1-Two 3% Governors
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.
The governor speed droop characteristics of these two units are similar. This is shown by lines "A" and "B" coinciding in Figure 1. If both units are started, 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.
PERCENT OF LOAD
Figure 1-Paralleling two units with similar speed droop characteristics.