4.82
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
➤ An adaptive tuning feature that learns and tunes out feeder
ambient load conditions. (Note: A minimum of 0.05 • I
NOM
load current is expected for successful tuning.)
➤ Decision logic to differentiate an HIF condition from other
system conditions such as switching operations and noisy loads.
The HIF detection element derives a Sum of Difference current (SDI) that rep-
resents the total non-harmonic contents of the phase currents to detect an HIF
signature. An averaging filter generates a stable reference of SDI and adapts to
the ambient conditions of feeder loads. In turn, an adapted detection threshold
is established based on the trends of the measured SDI and you would use
decision logic to separate normal trending from the existence of an HIF on the
distribution system. The SEL technical paper, Detection of High-Impedance
Faults in Power Distribution Systems by Daqing Hou, details additional infor-
mation about this HIF detection method.
Additional HIF detection logic measures the total odd-harmonic content
(ISM), maintains long-term and short-term histograms of ISM, and generates
HIF alarms by comparing the difference between two histograms. When the
difference between the two histograms is not substantial, the long-term histo-
gram is updated through an IIR filtering process from the short-term histo-
gram. The long-term histogram therefore adapts to the feeder ambient load
conditions and increases the overall HIF detection security.
To Next Page
Loading...
