ABB REG670 Applications Manual page 249

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
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
= + +
I I I I
1 2 3
EQUATION1915 V1 EN
I
F
(
= + ⋅
X X X
1 1
DA A C
I
1
A
EQUATION1916 V2 EN
I
F
(
= + ⋅
X X X
2 2
DA A C
I
A 2
EQUATION1917 V2 EN
I
F
(
X = X + ⋅ X
DA 3 A 3 C
I
3
A
EQUATION1918 V2 EN
A1
jX
1
I
A2
A1
jX
2
I
A3
A2
jX
3
I
D A3
A1
D
A2
D
A 3
IEC06000621 V1 EN
Figure 123: 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
118 to 121.
)
−
X
11
)
−
X
11
)
− X
11
B
-jX
C
jX
11
F
I
F
D
B
en06000621.vsd
Section 8
Impedance protection
(Equation 118)
(Equation 119)
(Equation 120)
(Equation 121)
243