2.3 General features of protection
stages
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Hysteresis or dead band
When comparing a measured value against a pick-up value,
some amount of hysteresis is needed to avoid oscillation near
equilibrium situation. With zero hysteresis any noise in the
measured signal or any noise in the measurement itself would
cause unwanted oscillation between fault-on and fault-off
situations.
Figure 2.3-3. Behaviour of a greater than comparator. For example in
overcurrent and overvoltage stages the hysteresis (dead band) acts
according this figure.
Figure 2.3-4. Behaviour of a less than comparator. For example in under-
voltage and under frequency stages the hysteresis (dead band) acts
according this figure.
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