ABB REL670 2.2 IEC, Applications Manual

Page: 191 / 908

protection far away from the faulty line can maloperate by its instantaneous
operating distance zone, if no precaution is taken. Impedances seen by distance
IEDs on adjacent power lines are presented by equations
65 to 68 .
1 2 3
= + +
I I I I
EQUATION1915 V1 EN-US
(Equation 65)
X X
I
I
X X
DA A
F
A
C 1 1
1
11
= + ⋅ −
( )
EQUATION1916 V2 EN-US
(Equation 66)
X X
I
I
X X
DA A
F
A
C 2 2
2
11
= + ⋅ −
( )
EQUATION1917 V2 EN-US
(Equation 67)
X X
I
I
X X
DA A
F
A
C
3 3
3
11
= + ⋅ −
( )
EQUATION1918 V2 EN-US
(Equation 68)
en06000621.vsd
B A1
A2
A3
D
B
D
A3
D
A2
D
A1
jX
11
I
A1
I
A2
I
A3
I
F
-jX
C
jX
1
jX
2
jX
3
F
IEC06000621 V1 EN-US
Figure 94: Distance IED on adjacent
power lines are influenced by
the negative impedance
Normally the first zone of this protection must be delayed until the gap flashing has
taken place. If the delay is not acceptable, some directional comparison must also
be added to the protection of all adjacent power lines. As stated above, a good
protection system must be able to operate correctly both before and after gap
flashing occurs. Distance protection can be used, but careful studies must be made
for each individual case. The rationale described applies to both conventional spark
gap and MOV protected capacitors.
Special attention should be paid to selection of distance protection on shorter
adjacent power lines in cases of series capacitors located at the line end. In such
case the reactance of a short adjacent line may be lower than the capacitor
reactance and voltage inversion phenomenon may occur also on remote end of
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 185
Application manual