Zero-Phase Current Differential Element Difg - Toshiba GRL100-701B Instruction Manual

Figure 2.16.1.2 Segregated-phase Current Differential Element (Iin-Iout Plane)
Characteristic A is expressed by the following equation:
I out ≤ (5/7)(I in - DIFI1)
Characteristic B is expressed by the following equation:
I out ≤ DIFI2
This figure shows the physical meaning of setting DIFI2, that is, DIFI2 defines the maximum
outflowing current in case of an internal fault which can be detected by the relay. This outflowing
current can be significant particularly in the case of a double-circuit three-terminal line or
three-terminal line with outer loop circuit. Depending on the fault location, part of the fault current
flows out from one terminal and flows in from another terminal. For details of the outflowing fault
current, see Sections 2.2.10 and 2.2.12.

2.16.2 Zero-phase Current Differential Element DIFG

The DIF element is not too insensitive to detect a high-impedance earth fault, but to detect such
faults under a heavy load current, the GRL100 is provided with a protection using a residual
current.
Figure 2.16.2.1 represents the percentage restraining characteristic of the residual current
differential element. Differential current (I d ) is a vector summation of the residual currents of all
terminals and restraining current (I r ) is a scalar summation of the residual currents of all terminals.
Figure 2.16.2.1 Zero-phase Current Differential Element (Ir-Id Plane)
The characteristic of the DIFG element is the same as that of the DIF element in the small current
region and is expressed by the following equation:
I out
I out = I in
DIFI2
A
DIFI1
0
I d
5/6 DIFGI
 133 
B
Operating
Zone
I in
Operating
Zone
I r
6 F 2 S 0 8 5 0