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6 F 2 S 0 8 4 2
Fuse
GRD150
Figure 2.1.7
Feeder Protection Coordinated with Fuses
Configuring the inverse time element OC1 (and EF1) and time graded elements OC2 and OC3 (or
EF2 and EF3) as shown in Figure 2.1.8, the characteristic of overcurrent protection can be
improved to coordinate with the fuse characteristic.
Time (s)
OC1
OC2
OC3
Fuse
Current (amps)
Figure 2.1.8
Staged Definite Time Protection
2.1.1.5 Scheme Logic
Phase overcurrent protection
Figure 2.1.9 and Figure 2.1.10 show the scheme logic of the phase overcurrent protection OC1 and
OC2 with selective definite time or inverse time characteristic.
The definite time protection is selected by setting [MOC1] and [MOC2] to "DT". Definite time
overcurrent elements OC1D and OC2D are enabled for OC1 and OC2 phase protection
respectively, and trip signal OC1 TRIP and OC2 TRIP are given through the delayed pick-up
timer TOC1 and TOC2.
The inverse time protection is selected by setting [MOC1] and [MOC2] to any one of "IEC",
"IEEE", "US" or "CON" according to the IDMT characteristic to employ. Inverse time
overcurrent elements OC1I and OC2I are enabled for OC1 and C2 phase fault protection
respectively, and trip signal OC1 TRIP and OC2 TRIP are given.
ICD is the inrush current detector ICD, which detects second harmonic inrush current during
transformer energisation, and can block the OC1D and OC2D elements by the scheme switches
[OC1-2F] and [OC2-2F] respectively. See Section 2.1.7.
OCHS element is used for blocked overcurrent protection. See Section 2.1.1.9.
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