Fifth harmonic blocking
The inhibition of TR2PTDF operation in the situations of overexcitation is based on
the ratio of the fifth harmonic and the fundamental component of the differential
current (Id5f/Id1f) . The ratio is calculated separately for each phase without
weighting . If the ratio exceeds the setting value of
Start value 5.H
and if blocking is
enabled through the
Restraint mode
parameter, the operation of the biased stage
of TR2PTDF in the concerned phase is blocked. The fifth harmonic ratios I_5H_RAT_x
are given in Monitored data.
At dangerous levels of overvoltage, which can cause damage to the transformer,
the blocking can be automatically eliminated. If the ratio of the fifth harmonic
and the fundamental component of the differential current exceeds the
Stop value
5.H
parameter, the blocking removal is enabled. The enabling and disabling of
deblocking feature is also done through the
Harmonic deblock 5.H
parameter.
Figure 270: The limits and operation of the fifth harmonic blocking when both
blocking and deblocking features are enabled using the Harmonic deblock 5.H
control parameter.
The fifth harmonic blocking has a hysteresis to avoid rapid fluctuation between
"TRUE" and "FALSE". The blocking also has a counter, which counts the required
consecutive fulfillments of the condition. When the condition is not fulfilled, the
counter is decreased (if >0).
Also the fifth harmonic deblocking has a hysteresis and a counter which counts
the required consecutive fulfillments of the condition. When the condition is not
fulfilled, the counter is decreased (if >0).
Waveform blocking
The biased low stage can always be blocked with waveform blocking. The stage can
not be disabled with the
Restraint mode
parameter. This algorithm has two parts.
The first part is intended for external faults while the second is intended for inrush
situations. The algorithm has criteria for a low current period during inrush where
also the differential current (not derivative) is checked.
Protection functions
1MRS757644 H
526 620 series
Technical Manual
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