ABB REL650 series, Applications Manual

Page: 249 / 516

A hydro turbine that rotates in water with closed wicket gates will draw electric power
from the rest of the power system. This power will be about 10% of the rated power. If
there is only air in the hydro turbine, the power demand will fall to about 3%.
Diesel engines should have reverse power protection. The generator will take about 15%
of its rated power or more from the system. A stiff engine may require perhaps 25% of the
rated power to motor it. An engine that is good run in might need no more than 5%. It is
necessary to obtain information from the engine manufacturer and to measure the reverse
power during commissioning.
Gas turbines usually do not require reverse power protection.
Figure 118 illustrates the reverse power protection with underpower protection and with
overpower protection. The underpower protection gives a higher margin and should
provide better dependability. On the other hand, the risk for unwanted operation
immediately after synchronization may be higher. One should set the underpower
protection (reference angle set to 0) to trip if the active power from the generator is less
than about 2%. One should set the overpower protection (reference angle set to 180) to trip
if the power flow from the network to the generator is higher than 1%.
Underpower protection Overpower protection
Q Q
P P
Operating point
without
turbine torque
Margin Margin
Operate
Line
Operate
Line
Operating point
without
turbine torque
IEC09000019-2-en.vsd
IEC09000019 V2 EN
Figure 118: Reverse power protection with underpower or overpower protection
7.15.2 Directional overpower protection GOPPDOP (32)
1MRK 506 334-UUS A
Section 7
Current protection
243
Application manual