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15.8.4.1
Identification
GUID-F5F76C4D-DD25-4695-9FF1-6B45C696CC5E v1
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Compensated over and undervoltage
protection
COUVGAPC
-
59_27
15.8.4.2
Application
GUID-49CDDFEF-DB8F-4733-AD7C-0A87E0F6BAA1 v1
Compensated over and undervoltage protection (COUVGAPC) function calculates the remote
end voltage of the transmission line utilizing local measured voltage, current and with the help
of transmission line parameters, that is, line resistance, reactance, capacitance and local shunt
reactor.
For protection of long transmission line for in zone faults this function can be incorporated
with other local criteria checks within direct transfer trip logic to ensure tripping of the line
only under abnormal conditions and to avoid unnecessary tripping during healthy operation of
the line (for example, lightly loaded or unloaded).
Long transmission line draws substantial quantity of charging current. If such a line is open
circuited or lightly loaded at the remote end, the voltage at remote end may exceeds local end
voltage. This is known as Ferranti effect and is due to the voltage drop across the line
inductance (due to charging current) being in phase with the local end voltages. Both
capacitance and inductance are responsible for this phenomenon. The capacitance (and
charging current) is negligible in short line but significant in medium line and appreciable in
long line. The percentage voltage rise due to the Ferranti effect between local end and remote
end voltage is proportional to the length of the line and the properties of the transmission line.
The Ferranti effect is symmetrical between all three phases for normal balanced load
condition. The overvoltage caused by Ferranti effect can be reduced by drawing larger load
through the line or switching in the shunt reactor (connected either to line or to remote bus) at
the remote end. The calculated compensated voltage at the local end can detect such
overvoltage phenomenon.
The vector representation of local end and remote end voltages are shown below:
R
L
U
s
U
R
1
2
C
1
2
C
O
M
N
P
C
U
r
U
s
I
c
R
I
c
X
I
c
IEC09000774-1-en.vsd
IEC09000774 V1 EN-US
Figure 389: Vector diagram for local end and remote end voltage at no power transfer
conditions
Where:
OM
Remote end voltage Ur
OP
Local end voltage Us
OC
Current drawn by capacitance (Ic)
MN
Resistance drop (IcR)
NP
Inductive reactance drop (IcX)
Section 15
1MRK 505 343-UEN B
Scheme communication
624
Application manual
Summary of Contents for Relion 670 series
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