ABB REL670 2.2 IEC, Applications Manual

Page: 283 / 908

• 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 dotted paragraphs above gives a zone2 reach less than
120%, the time delay of zone2 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 zone2 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 wit a simple example below.
If a fault occurs at point F, 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 204)
A
B
Z<
C
I A
IC
Z AC
Z CB
Z CF
I A+ IC
IEC05000457-2-en.vsd
F
IB
IEC05000457 V2 EN-US
Figure 144: Setting of overreaching zone
8.5.3.4 Setting of reverse zone
SEMOD154704-33 v3
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
205 can be used to calculate the reach in reverse direction
when the zone is used for blocking scheme, weak-end infeed and so on.
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 277
Application manual