ABB RET670 - Page 282

• The impedance corresponding to the protected line, plus the first zone reach of the
shortest adjacent line.
• The impedance corresponding to the protected line, plus the impedance of the
maximum number of transformers operating in parallel on the bus at the remote
end of the protected line.
If the requirements in the bullet list above gives a zone 2 reach that gives non-
selectivity between the overreaching zone and the shortest outgoing line at the remote
end, the time delay of zone 2 must be increased by approximately 200ms to avoid
unwanted operation in cases when the telecommunication for the short adjacent line at
remote end is down during faults. The zone 2 must not be reduced below 120% of the
protected line section. The whole line must be covered under all conditions.
The requirement that the zone 2 shall not reach more than 80% of the shortest adjacent
line at remote end is highlighted in the example below.
If a fault occurs at point F (see figure
124, also for the explanation of all abbreviations
used), the IED at point A senses the impedance:
1
A B B
AF AC CF AC CF
A A
I I I
Z Z Z Z Z
I I
æ ö
+
= + × = + + ×
ç ÷
è ø
EQUATION302 V3 EN (Equation 189)
A
B
21
C
I
A
IB
Z
AC
Z
CB
Z
CF
I
A+
I
B
ANSI05000457-2-en.vsd
F
ANSI05000457 V2 EN
Figure 124: Setting of overreaching zone
Setting of reverse zone
The reverse zone is applicable for purposes of scheme communication logic, current
reversal logic, weak-end infeed logic, and so on. The same applies to the back-up
protection of the bus bar or power transformers. It is necessary to secure, that it always
covers the overreaching zone, used at the remote line terminal for the
telecommunication purposes.
Section 3 1MRK504116-UUS C
IED application
276
Application manual