2.5.1 Second Harmonic Blocking Implementation
Second harmonic blocking can be applied to the following overcurrent protection types:
• Phase Overcurrent protection
• Earth Fault protection
Second harmonic blocking is implemented in the GROUP (n) SYSTEM CONFIG column, where (n) is
the number of the setting group.
Second harmonic blocking is applicable to all stages of each of the elements.
The function works by identifying and measuring the inrush currents present at switch on. It does this
by comparing the value of the second harmonic current components to the value of the fundamental
component. If this ratio exceeds the set thresholds, then the blocking signal is generated. The
threshold is defined by the 2ndHarm Thresh setting.
We only want the function to block the protection if the fundamental current component is within the
normal range. If this exceeds the normal range, then this is indicative of a fault, which must be
protected. For this reason there is another settable trigger I> lift 2H, which when exceeded, stops the
2nd harmonic blocking function.
Each overcurrent protection element has a I>Blocking setting with which the type of blocking is
defined.
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