13.8.3.2 Principle of operation
Compensated over and undervoltage protection (COUVGAPC, 59_27) function is
phase segregated and mainly used for local criteria check in Direct transfer trip. The
principle is to utilize local measured voltage and current to calculate the voltage at the
remote end of the line.
The main measured inputs to COUVGAPC (59_27) are three-phase voltage and
current signals. COUVGAPC (59_27)uses line resistance, reactance and line charging
capacitance to calculate the remote end voltage. It also takes the input for local shunt
reactor, connected at the line side of the line breaker, reactance value. The calculated
voltage is referred to as compensated voltage.
ANSI09000782-1-en.vsd
Compensated
voltage calculation
V3P
I3P
59_PU_x
27_PU_x
AND
SWIPOS
EnShuntReactor
Over voltage
comparator
Under voltage
comparator
t
59_Trip_x
t
27_Trip_x
59 Trip
27 Trip
59 PU
27 PU
ANSI09000782 V1 EN
Figure 417: Logic diagram of Compensated over and undervoltage protection
(COUVGAPC, 59_27)
The formula used for calculation of compensated voltage is as follows:
V
remote
= V
local
– (I
local
– j x V
local
/X
sr
+ j x V
local
/X
cp
) x Z
setting
Where:
V
remote
calculated voltage at the opposite side of line
V
local
measured local voltage
I
local
measured local current
X
sr
reactance of local line connected shunt reactor, if applicable
X
cp
half of equivalent reactance of line distributed capacitor
Above calculated compensated voltage is compared to preset over and under voltage
levels set as percentage of base voltage VBase. If the calculated voltage exceeds setting
1MRK505222-UUS C Section 13
Scheme communication
835
Technical reference manual
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