ABB RELION 620 Series Technical Manual page 553

1MAC504801-IB E
5.4.5
620 series ANSI
Technical Manual
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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Figure 265: Validation of HIZ on gravel
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Figure 267: Validation of HIZ on sand
Application
Electric power lines experience faults for many reasons. In most cases, electrical faults
manifest in mechanical damage, which must be repaired before returning the line to
service.
Most of the electrical network faults are ground faults. Conventional protection systems
based on overcurrent, impedance or other principles are suitable for detecting relatively
low-impedance faults which have a relatively large fault current.
However, a small percentage of the ground faults have a very large impedance. They are
comparable to load impedance and consequently have very little fault current. These high-
Protection-related functions
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Figure 266: Validation of HIZ on
concrete
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Figure 268: Validation of HIZ on grass
Section 5
547