ABB RELION 620 Series Technical Manual page 830

Section 5
Protection related functions
824
Transformer
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Figure 422: Electrical power system equipped with PHIZ
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 423: Block diagram of PHIZ
PHIZ is based on algorithms that use earth 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.
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1MRS757644 F
620 series
Technical Manual