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 371 to 374.
EQUATION1915 V1 EN-US (Equation 371)
X X
I
I
X X
DA A
F
A
C1 1
1
11
= + ⋅ −
( )
EQUATION1916 V2 EN-US (Equation 372)
X X
I
I
X X
DA A
F
A
C2 2
2
11
= + ⋅ −
( )
EQUATION1917 V2 EN-US (Equation 373)
X X
I
I
X X
DA A
F
A
C3 3
3
11
= + ⋅ −
( )
EQUATION1918 V2 EN-US (Equation 374)
en06000621.vsd
BA1
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 212: 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
Section 8 1MRK 506 369-UEN B
Impedance protection
388 Line distance protection REL670 2.2 IEC
Application manual
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