ABB Relion REG670, Applications Manual

Page: 242 / 780

particular protection function to best suit its specific characteristics and expectations
on dependability and security. The line side VT can for example be used by the
distance protection and the bus side VT by the directional residual OC earth fault
protection.
Apparent impedances and MOV influence
Series capacitors reduce due to their character the apparent impedance measured by
distance IEDs on protected power lines. Figure
115 presents typical locations of
capacitor banks on power lines together with corresponding compensation degrees.
Distance IED near the feeding bus will see in different cases fault on remote end bus
depending on type of overvoltage protection used on capacitor bank (spark gap or
MOV) and SC location on protected power line.
en06000612.vsd
~
E
A
0%
33 %
50 %
66 %
K
C =
80% 33% 33 % 50 %
Z<
100 %
80 %
IEC06000612 V1 EN
Figure 115: Typical locations of capacitor banks on series compensated line
Implementation of spark gaps for capacitor overvoltage protection makes the picture
relatively simple, because they either flash over or not. The apparent impedance
corresponds to the impedance of non-compensated line, as shown in figure
116 case
K
C
= 0%.
en06000613.vsd
jX
R
KC = 0%
KC = 80%
LOC = 0%
KC = 50%
LOC = 50%
jX jX
R R
KC = 2 x 33%
LOC = 33%, 66%
KC = 80%
LOC = 100%
jX jX
R R
IEC06000613 V1 EN
Figure 116: Apparent impedances seen by distance IED for different SC
locations and spark gaps used for overvoltage protection
Section 8
1MRK 502 071-UEN -
Impedance protection
236 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual