ABB RER620 Technical Manual page 256

Section 4
Protection functions
250
Figure 118: Block diagram of HIZ
HIZ is based on algorithms that use ground current signatures which are considered non
stationary, temporally volatile, and of various burst duration. All harmonic and
non-harmonic components within the available data window can play a vital role in the
high impedance fault detection. A major challenge is to develop a data model that
acknowledges that high impedance faults could take place at any time within the
observation window of the signal and could be delayed randomly and attenuated
substantially. The model is motivated by extensive research, actual experimental
observations in the laboratory, field testing, and what traditionally represents an accurate
depiction of a non stationary signal with a time dependent spectrum.
Figure 119: Validation of HIZ on gravel
Figure 121: Validation of HIZ on sand
Figure 120: Validation of HIZ on concrete
Figure 122: Validation of HIZ on grass
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