1MAC309294-MB F Section 4
Protection functions
RER620 249
Technical Manual
4.5.3.2 Function block symbol
Figure 116: Function block symbol
4.5.3.3 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 high impedance fault.
The high impedance fault-detector function HIZ also contains a blocking functionality. It
is possible to block function outputs, if desired.
4.5.3.4 Principle of operation
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.
Figure 117: Electrical power system equipped with HIZ
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 decision logic to provide the detection decision. The decision logic can be
modified depending on the application requirement.
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