Figure "A" of the illustration represents a constant frequency system. At load condition "1" machine A has a 40 kW load and machine B has a 120 kW load as shown. If load is to be transferred manually to achieve load condition "2" with machine A having a load of 100 kW and machine B having a load of 60 kW, how is this accomplished? See illustration EL-0025.
• Parallel generator load sharing in a constant frequency system • Effect of raising vs lowering governor speed setting on how much kW a generator carries when paralleled • Need to keep bus frequency at 60 Hz while shifting load between machines
• When two generators are in parallel at constant frequency, what happens to each machine’s kW load if you slightly raise only that machine’s speed governor setting? What if you lower it? • To move 60 kW of load from machine B to machine A while keeping system frequency at 60 Hz, do you need to move one governor, or both governors in opposite directions? Why? • Look at points A1/B1 (condition 1) and A2/B2 (condition 2) on Figure A: along which direction on the droop lines do you move each machine to get from the first pair of points to the second?
• Make sure you understand that raising the speed setting of a paralleled generator tends to make it pick up more kW and shed kW from the other unit(s). • Verify on the graph how moving along the droop line for machine A from 40 kW to 100 kW relates to a change in governor setting (up or down). • Check how the system can go from condition 1 to condition 2 without changing the overall bus frequency shown on the vertical axis.
No comments yet
Be the first to share your thoughts!