The requirement is now according to equation 121.
step1 0I 1.2 3I (remote busbar with one line out)³ ×
EQUATION1200 V3 EN (Equation 121)
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 104.
ANSI05000152_2_en.vsd
One phase-to-ground fault
67N
ANSI05000152 V2 EN
Figure 104: 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.
EQUATION1201 V3 EN
(Equation 122)
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 506 334-UUS A Section 7
Current protection
211
Application manual
To Next Page
Loading...
