GUID-A97464D1-3085-4F27-B829-11EEC47CA654 V1 EN
Figure 251:
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.
Biased low stage
The current differential protection needs to be biased because the possible appearance of
a differential current can be due to something else than an actual fault in the transformer
(or generator).
In the case of transformer protection, a false differential current can be caused by:
•
CT errors
•
Varying tap changer positions (if not automatically compensated)
•
Transformer no-load current
Section 4
1MAC059074-MB A
Protection functions
508
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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