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Chapter 10 - Voltage Protection Functions
4
COMPENSATED OVERVOLTAGE
The Compensated Overvoltage function calculates the positive sequence voltage at the remote terminal using the
positive sequence local current and voltage and the line impedance and susceptance. This can be used on long
transmission lines where Ferranti Overvoltages can develop under remote circuit breaker open conditions.
The Compensated overvoltage protection function can be set in the VOLT PROTECTION column under the sub
heading COMP OVERVOLTAGE. The remote voltage is calculated using line impedance settings and the line
charging admittance in the LINE PARAMETERS column.
The IED uses the [A,B,C,D] transmission line equivalent model given the following parameters:
●
Total Impedance Z = zÐq ohms
Total Susceptance Y = yÐ-90°
●
Line Length l
●
The remote voltage is calculated using the following equations:
Vr
D C
−
=
×
BA
Ir
−
where
●
V
is the voltage at the receiving end
r
I
is the current at the receiving end
●
r
V
is the measured voltage at the sending end
●
s
I
is the measured current at the sending end
●
s
A= D = cosh(y.l)
●
B = Z
.sinh(y.l)
●
c
C = Y
.sinh(y.l)
●
c
y.l = Ö(Z.Y)
●
= Ö(Z/Y)
●
Z
= 1/Y
c
c
Y = total line capacitive charging susceptance
●
Z
= characteristic impedance of the line (surge impedance)
●
c
There are two stages to provide both alarm and trip stages where required. Both stages can be set independently.
Stage 1 can be set to IDMT, DT or Disabled, in the V1>1 Cmp Funct cell. Stage 2 is DT only and is enabled or
disabled in the V1>2 Cmp Status cell.
The IDMT characteristic on the first stage is defined by the following formula:
t = K/(M - 1)
where:
K = Time multiplier setting
●
●
t =Operating time in seconds
M = Remote Calculated voltage / IED setting voltage
●
230
Vs
Is
P54A/B/C/E
P54xMED-TM-EN-1
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