Setting Guidelines - Hitachi Relion 670 Series Applications Manual

1MRK511407-UUS Rev. N
Power to the power plant auxiliaries may come from a station service transformer connected to the
secondary side of the unit step-up transformer. Power may also come from a start-up service transformer
connected to the external network. One has to design the reverse power protection so that it can detect
reverse power independent of the flow of power to the power plant auxiliaries.
Hydro turbines tolerate reverse power much better than steam turbines do. Only Kaplan turbine and bulb
turbines may suffer from reverse power. There is a risk that the turbine runner moves axially and touches
stationary parts. They are not always strong enough to withstand the associated stresses.
Ice and snow may block the intake when the outdoor temperature falls far below zero. Branches and
leaves may also block the trash gates. A complete blockage of the intake may cause cavitations. The risk
for damages to hydro turbines can justify reverse power protection in unattended plants.
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 69
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
Operate
Line
Margin
Operating point
without
turbine torque
IEC09000019 V2 EN-US
Figure 69:
8.6.3

Setting guidelines

GlobalBaseSel: Selects the global base value group used by the function to define IBase, VBase and
SBase. Note that this function will only use IBase .
Operation: With the parameter Operation the function can be set Enabled/Disabled.
Phasor measurement unit RES670
Application manual
illustrates the reverse power protection with underpower protection and with overpower
Overpower protection
Q
Operate
Line
Margin
P
Operating point
without
turbine torque
Reverse power protection with underpower or overpower protection
© 2017 - 2023 Hitachi Energy. All rights reserved
Q
P
IEC09000019-2-en.vsd
Section 8
Current protection
SEMOD172134-4 v7
143