5.4.2
Function block
TRIP
IG
HIZ
BLOCK
CB_CLOSED
CB_OPEN
GUID-C3405080-34F8-466A-8C2F-214B852164EE V1 EN
Figure 397:
Function block
5.4.3
Functionality
A small percentage of ground faults have a very large impedance. They are comparable to
load impedance and consequently have very little fault current. These high-impedance
faults do not pose imminent danger to power system equipment. However, they are a
substantial threat to humans and properties; people can touch or get close to conductors
carrying large amounts of energy.
ABB has developed a patented technology (US Patent 7,069,116 B2 June 27, 2006, US
Patent 7,085,659 B2 August 1, 2006) to detect a high-impedance fault.
The high-impedance fault detection function HIZ also contains a blocking functionality.
It is possible to block function outputs, if desired.
HIZ is limited to be used in 60 Hz electrical networks with efficiently
grounded or isolated neutral.
5.4.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
HIZ uses a multi-algorithm approach. Each algorithm uses various features of ground
currents to detect a high-impedance fault.
Although the HIZ algorithm is very sophisticated, the setting required to operate the
function is simple. The
Security Level
setting, with the setting range of 1 to 10, is set to
strike a balance between the extremes of security and dependability which together
constitute the reliability of any system. The setting value “10” is more secure than “1”.
The higher the
Security Level
setting, the lower the probability of false detection, but the
system might miss out some genuine fault. On the other hand, a lower setting would make
the system operate more dependably for high-impedance faults in the line, but the
operation is more likely for other transients in the system. There are events in electrical
1MAC059074-MB A
Section 5
Protection related functions
615 series ANSI
789
Technical Manual
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