impedance faults do not pose imminent danger to power system equipment. However,
they are a considerable threat to people and property. The IEEE Power System Relay
Committee working group on High Impedance Fault Detection Technology defines High
Impedance Faults as those that 'do not produce enough fault current to be detectable by
conventional overcurrent relays or fuses.
High-impedance fault (HIZ) detection requires a different approach than that for
conventional low-impedance faults. Reliable detection of HIZ provides safety to humans
and animals. HIZ detection can also prevent fire and minimize property damage. ABB has
developed innovative technology for high-impedance fault detection with over ten years
of research resulting in many successful field tests.
5.4.6
Signals
Table 264:
HIZ Input signals
Name
Type
Default
Description
I_G
SIGNAL
0
Ground current measured using SEF CT
BLOCK
BOOLEAN
0=False
Block signal for activating the blocking mode
Table 265:
HIZ Output signals
Name
Type
Description
TRIP
BOOLEAN
Trip
5.4.7
Settings
Table 266:
HIZ Group settings
Parameter
Values (Range)
Unit
Step
Default
Description
Security Level
1...10
1
5
Security Level
Table 267:
HIZ Non group settings
Parameter
Values (Range)
Unit
Step
Default
Description
Operation
1=enable
5=disable
1=enable
Operation Disable / Enable
System type
1=Grounded
2=Ungrounded
1=Grounded
System Type
Section 5
1MRS240050-IB C
Protection-related functions
336
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Technical Manual
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