5.4.4
Measuring speed droop
DEIF recommends that the speed droop for each genset in the system is 4 %.
A lower speed droop gives a faster dynamic control loop. However, if the dynamic control loop is too fast, the system is
unstable. A higher speed droop gives a slower (maybe too slow) dynamic control loop.
Measuring the speed droop
To measure the speed droop for a genset:
1. Make sure that you can connect a load or loads to the genset that are up to 100 % of the genset nominal power.
• At the very minimum, you need to be able to load the genset up to 40 % of the genset nominal power.
2. Activate switchboard control.
3. Start the genset, with no load connected. Check that the generator power is zero. Record the generator power and speed.
• The generator power and speed are shown under Live data on the display unit.
4. Connect a load. Record the generator power and speed.
5. Connect or adjust the loads until the generator power is 100 % of the genset nominal load. Record the generator power
and speed.
• At the very minimum, you need three measurement points, to confirm that the droop is linear. With more than two
points, you can also identify measurement errors.
6. Calculate the speed droop using the equation below.
Droop = (Speed
low load
- Speed
high load
) / (Power
high load
- Power
low load
) × Power
nominal
/ Speed
nominal
× 100
INFO
You can use either the engine speed or the generator frequency to calculate the speed droop, since the generator
frequency is proportional to the engine speed. However, using the speed may make the droop calculations more
accurate. This is because the engine speed shown on the display may have more significant digits than the
frequency.
Example of speed droop
A 1000 kW genset runs at a nominal speed of 1500 rpm. The following measurements are taken:
# Power [kW] Speed [rpm]
1 0 1500
2 309 1481
3 650 1461
4 975 1442
PPU 300 Commissioning guidelines 4189341106 UK
www.deif.com Page 41 of 75
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