The requirement is now according to equation
.
step1
0
I
1.2 3I (remote busbar with one line out)
³
×
EQUATION1200 V3 EN
(Equation 39)
A higher value of step 1 might be necessary if a big power transformer (Y0/D) at remote
bus bar is disconnected.
A special case occurs at double circuit lines, with mutual zero-sequence impedance
between the parallel lines, see figure
ANSI05000152_2_en.vsd
One phase-to-ground fault
67N
0
3I
ANSI05000152 V2 EN
Figure 48:
Step 1, third calculation
In this case the residual current out on the line can be larger than in the case of ground fault
on the remote busbar.
step1
0
I
1.2 3I
³
×
EQUATION1201 V3 EN
(Equation 40)
The current setting for step 1 is chosen as the largest of the above calculated residual
currents, measured by the protection.
Step 2
This step has directional function and a short time delay, often about 0.4 s. Step 2 shall
securely detect all ground faults on the line, not detected by step 1.
1MRK 511 286-UUS A
Section 6
Current protection
115
Application manual
Содержание REC650 ANSI
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