5.4.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
High-impedance fault detection
PHIZ
HIF
HIZ
5.4.2
Function block
Figure 431: Function block
5.4.3
Functionality
A small percentage of earth 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 PHIZ also contains a blocking
functionality. It is possible to block function outputs, if desired.
PHIZ 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 "On" and "Off".
PHIZ uses a multi-algorithm approach. Each algorithm uses various features of
earth currents to detect a high-impedance fault.
Although the PHIZ 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 networks which can cause similar current
waveforms like high-impedance faults. These events could then be detected by
Protection related functions
1MRS757644 H
820
620 series
Technical Manual
