Staged Definite Time Overcurrent Protection; Operate Time; Conjunction Of Inverse And Instantaneous Overcurrent Protection; Feeder Protection Coordinated With Fuses - Toshiba GRE110 Instruction Manual

6 F 2 T 0 1 7 2

Operate time

T
C
T
C
A B
C
Figure 2.2.1 Conjunction of Inverse and Instantaneous Overcurrent Protection
The current setting is set 1.3 to 1.5 times higher than the probable maximum fault current in the
event of a fault at the remote end. The maximum fault current for elements OC2 to OC4 is obtained
in case of three-phase faults, while the maximum fault current for elements EF2 to EF4 is obtained
in the event of single phase earth faults.

2.2.2 Staged Definite Time Overcurrent Protection

When applying inverse time overcurrent protection for a feeder system as shown in Figure 2.2.2,
well coordinated protection with the fuses in branch circuit faults and high-speed protection for the
feeder faults can be provided by adding staged definite time overcurrent protection with
time-graded OC2 and OC3 or EF2 and EF3 elements.
Fuse
GRE110
Figure 2.2.2 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 2.2.3, the characteristic of overcurrent protection can be
improved to coordinate with the fuse characteristic.
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