Alternator Parellel Operation

Simple! It will try to "swallow" more kW load from the infinite bus. In the process its speed will "droop" and its frequency will fall. This will happn until the alternator frquency is equal to the bus frequency.

in which form the excessive energy consumes? u saying bus will swallows the energy,but in which form,and what abt load sharing?and frequency of the other alternators?

The generators frequency (or the speed) is controlled by the prime mover's governor which controls the input power (generally fuel) of the prime mover. The governor has two types of control mode: Isochronous mode and Droop mode with a droop setting. With isochronous mode, the governor always keeps the frequency constant with increasing or decreasing the fuel (and thus shares the load), while the droop mode shares the load based on the system frequency. See the thread http://cr4.globalspec.com/thread/42805/Electrical-Governor-Settings for more detail.

If your generators run in parallel with the utility supply, they are generally set in droop mode. When you said, one of the alternator frequency increases, I assumed you do it by manually applying the increase signal to its governor. In this case, the generator will deliver more power to the system and if the load remains constant, the same amount of power will be decreased from the utility supply. Other two generators load will remain constant. However, the load sharing philosophy will be different if the governor of one of the other two generators is set in isochronous mode.

- MS

If the connected bus is truly infinite and actually running at 50Hz, nothing any of the three alternators does can affect the frequency. Typically the machines are running in droop and if this is the case, the machine with the higher setpoint will pickup proportianately more load than the machines with lower setpoints.

Have FUN!

TT3