Setting Of Reverse Zone - ABB RELION RET670 Applications Manual

Section 8
Impedance protection
8.12.3.4
386
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 184, the IED at point A senses the impedance:
V I I
+
A A C
Z Z
= = +
AF AC
I I
A A
EQUATION302 V5 EN-US
A
I A
21
ANSI05000457 V2 EN-US
Figure 184: 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 IED for the telecommunication
purposes.
Consider the possible enlarging factor that might exist due to fault infeed from adjacent
lines. Equation 285 can be used to calculate the reach in reverse direction when the
zone is used for blocking scheme, weak-end infeed, and so on.
(
³ × -
Zrev 1.2 ZL Z rem 2
EQUATION1525 V5 EN-US
Where:
ZL is the protected line impedance
Z2rem is zone 2 setting at remote end of protected line.
I I I
+ +
A C B
Z R Z
⋅ + ⋅ =
CF
F
I
A
Z AC
Z CB
F
C
Z CF
I A+ IB
IB
)
1MRK 504 163-UUS A
  
I I
C C
1 Z 1
+ +  ⋅ + +
 
AC C F F
I
A
  
B
ANSI05000457-2-en.vsd
GUID-B633CF2C-28B2-4FDD-BE0E-D09CA434F01F v1
Transformer protection RET670 2.2 ANSI
Application manual

I
+
B
R
 ⋅
F
I
A

(Equation 284)
(Equation 285)