2.9 Second harmonic O/C stage
If2>(51F2)
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2.9. Second harmonic O/C stage I
f2
>(51F2)
This stage is mainly used to block other stages. The ratio
between the second harmonic component and the fundamental
frequency component is measured on all the phase currents.
When the ratio in any phase exceeds the setting value, the
stage gives a start signal. After a settable delay, the stage gives
a trip signal.
The start and trip signals can be used for blocking the other
stages.
The trip delay is irrelevant if only the start signal is used for
blocking.
The trip delay of the stages to be blocked must be more than 60
ms to ensure a proper blocking.
Figure 2.9-1 Block diagram of the second harmonic stage.
Setting parameters of second harmonic blocking 2.Ha(51F2):
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