Functions
2.19 Undervoltage and Overvoltage Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
364
Compounding is only available if address 137 is set to Enabl. w. comp.. In this case the calculated voltage
at the other line end is also indicated in the operational measured values.
Note
Compounding is not suited for lines with series capacitors.
The voltage at the remote line end is calculated from the voltage measured at the local line end and the flowing
current by means of a PI equivalent circuit diagram (refer also to Figure 2-174).
with
U
End
the calculated voltage at the remote line end,
U
Meas
the measured voltage at the local line end,
I
Meas
the measured current at the local line end,
C
L
the line capacitance,
R
L
the line resistance,
L
L
the line inductance.
Figure 2-174 PI equivalent diagram for compounding
Overvoltage negative sequence system U
2
The device calculates the negative sequence system voltages according to its defining equation:
U
2
=
1
/
3
·(U
L1
+ a
2
·U
L2
+ a·U
L3
)
where a = e
j120°
.
The resulting negative sequence voltage is fed to the two threshold stages U2> (address 3742) and U2>> (ad-
dress 3744). Figure 2-175 shows the logic diagram. Combined with the associated time delays T U2> (address
3743) and T U2>> (address 3745), these stages form a two-stage overvoltage protection for the negative se-
quence system. Here too, the drop-out to pickup ratio can be set.
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