ABB RELION 620 Series Technical Manual page 552

Section 5
Protection-related functions
546
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Figure 263: Electrical power system equipped with HIZ
Power system signals are acquired, filtered and then processed by individual high-
impedance fault detection algorithm. The results of these individual algorithms are further
processed by a decision logic to provide the detection decision. The decision logic can be
modified depending on the application requirement.
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Figure 264: Block diagram of HIZ
HIZ is based on algorithms that use line residual 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
1MAC504801-IB E
620 series ANSI
Technical Manual