Toshiba GR200 Series Instruction Manual page 47

Centralized busbar protection ied

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As cited earlier, the discriminating-zone-protection can have up to six protection-zones,

but the setting of the minimum operating current (minDIF-I) is common to each protection-

zone. The user can set minDIF-I using the setting [DIFCH-I] and [DIFDZ-I].

When DIF trip and DIF transfer-trip need to operate securely, set On for setting [DIFTP-

FS]; then the DIF trip will be issued with the Fail-safe operation (FS). On the other hand, DIF

trip and DIF transfer-trip operate without the FS operation when Off is set for the setting

Point for deciding about [DIF**-I] setting value

To seek the [DIF**-I] setting value, the user should follow on the Step1 to the Step4:

Step 1: Minimum fault current (I Fmin )

The DIF operation should be ruled to be less than a minimum fault current multiplied

by 0.8. As a result, the DIF relay is able to operate on the minimum fault current. Equation

(2.1-6) illustrates the relation between the I Fmin and the [DIFCH-I] and [DIFDZ-I].

The DIF relay operates faster when the large fault current flows. Therefore, the value of

the I Fmin should be considered to be more than 300% of setting [DIF**-I], as shown in Equation

Step 2: Operation accuracy in the DIF relay

The operation accuracy depends on the primary value of the CT. The user should note

that the operation accuracy gets worse when the operating value in the DIF relay is small and

Setting [ DIF**-I ]

CT primary value

depends on the number of CHs.

Setting [DIF**-I] ≤ 0.8 × I

Setting [ DIF**-I ] ≤

is small, as shown in Figure 2.1-12; the operation accuracy

Centralized GRB200

(Soft: 030, 031, 032, 033, 034)

6F2S1931 (0.20)

deteriorates

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