ABB RELION RET670, Applications Manual

Page: 345 / 1016

Larger overreach than the mentioned 80% can often be acceptable due to fault current
infeed from other lines. This requires however analysis by means of fault calculations.
If any of the above indicates a zone 2 reach less than 120%, 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 161 , the IED at point A senses the impedance:
Z
V
I
Z
I I
I
Z
I I I
I
R Z
I
I
Z
AF
A
A
AC
A C
A
CF
A C B
A
F
AC
C
A
C
= = +
+
⋅ +
+ +
⋅ = + +





 ⋅
1
F F
C B
A
F
I I
I
R
+ +
+





 ⋅
1
EQUATION302 V5 EN-US
(Equation 221)
A
B
21
C
I A
IB
Z AC
Z CB
Z CF
IA+ IB
ANSI05000457-2-en.vsd
F
ANSI05000457 V2 EN-US
Figure 161: Setting of overreaching zone
8.9.3.4 Setting of reverse zone
GUID-0EDCDC8F-A2C9-4625-A6BD-0E7D2B4B1F04 v1
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 IED for the telecommunication
purposes.
Consider the possible enlarging factor that might exist due to fault infeed from adjacent
lines. Equation
222 can be used to calculate the reach in reverse direction when the
zone is used for blocking scheme, weak-end infeed etc.
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 339
Application manual