difference must exist in the magnitudes of the zero sequence currents for close-up forward
and reverse faults, that is, it is a requirement that |U0| >> |k · I0| for reverse faults, otherwise
there is a risk that reverse faults can be seen as forward.
AngleRCA
0
0
U
k I e
-
+ × ×
EQUATION1638 V2 EN-US
(Equation 243)
The negative-sequence voltage polarization with negative-sequence current compensation (-
U2Comp) compares correspondingly I
2
ensured that |U
2
| >> |k · I
2
| for reverse faults.
AngleRCA
2
2
U
k I e
-
+ × ×
EQUATION1639 V2 EN-US
(Equation 244)
7.7
Mho impedance supervision logic ZSMGAPC
SEMOD153841-1 v3
7.7.1
Identification
GUID-030C086A-8301-481E-BA0A-6550A9C1482E v2
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Mho Impedance supervision logic
ZSMGAPC
-
-
7.7.2
Application
SEMOD154555-4 v3
The Mho impedance supervision logic (ZSMGAPC) includes features for fault inception
detection and high SIR detection. It also includes the functionality for loss of potential logic as
well as for the pilot channel blocking scheme.
One part of ZSMGAPC function identifies a loss of phase potential that is the result of a long
term (steady state) condition such as a blown fuse or an open voltage transformer winding or
connection. This will block all trips by the distance protection since they are based on voltage
measurement.
In the pilot channel blocking scheme a fault inception detected by a fast acting change
detector is used to send a block signal to the remote end in order to block an overreaching
zone. If the fault is later detected as a forward fault the earlier sent blocking signal is stopped.
The blocking scheme is very dependable because it will operate for faults anywhere on the
protected line if the communication channel is out of service. Conversely, it is less secure than
permissive schemes because it will trip for external faults within the reach of the tripping
function if the communication channel is out of service. Inadequate speed or dependability
can cause spurious tripping for external faults. Inadequate security can cause delayed tripping
for internal faults.
ZSMGAPC function also includes functionality for blocking the sample based distance
protection due to high SIR. SIR directly influences the fault voltage level for a given voltage
level, and this is the major factor that affects the severity of CVT transients. Therefore, in
cases where the SIR value is too high, further filtering of the measured signals will be needed.
Section 7
1MRK 505 343-UEN B
Impedance protection
262
Application manual
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