ABB REL650 series, Applications Manual

Page: 217 / 516

The requirement is now according to equation 121 .
step1 0
I 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
0
3I
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.
step1 0
I 1.2 3I
³ ×
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