Functions
2.19 Undervoltage and Overvoltage Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
373
Overvoltage positive sequence system U
1
You can use the positive sequence voltage stages instead of or in addition to previously mentioned overvoltage
stages. Depending on your choice, set address
3731
U1>(>)
to
ON
,
OFF
,
Alarm Only
or
U>Alarm
U>>Trip
.
For symmetrical voltages an increase of the positive sequence system corresponds to an AND gate of the volt-
ages. These stages are particularly suited to the detection of steady-state overvoltages on long, weak-loaded
transmission lines (Ferranti effect). Here too, the
U1>
stage (address
3732
) with a longer delay time
T U1>
(address
3733
) is used for the detection of steady-state overvoltages (some seconds), the
U1>>
stage (ad-
dress
3734
) with the short delay time
T U1>>
(address
3735
) is used for the detection of high overvoltages
that may jeopardise insulation.
Note that the positive sequence system is established according to its defining equation
U
1
=
1
/
3
·|U
L1
+ a·U
L2
+ a
2
·U
L3
|. For symmetrical voltages this is equivalent to a phase-to-earth voltage.
If the voltage at the remote line end is to be decisive for overvoltage detection, you can use the compounding
feature. This requires that address
137
U/O VOLTAGE
is already set to
Enabl. w. comp.
(enabled with
compounding) when configuring the protection functions (Section 2.1.1.3).
In addition, the compounding feature needs the line data, which have been entered in the
General
Protection Data (Power System Data 2)
1111
x'
, address
1112
c'
and
address
1113
Line Length
and address
1105
Line Angle
. These data are vital to correctly calculate the
compounding. If the values provided here do not correspond to real conditions, the compounding may calculate
an excessively high voltage at the remote end, which will cause immediate pickup as soon as the measured
values are applied. In such a case, the pickup state can only be reset by switching off the measuring voltage.
Compounding can be switched
ON
or
OFF
separately for each of the U1 stages: for the
U1>
stage at address
3736
U1> Compound
and for the
U1>>
stage at address
3737
U1>> Compound
.
The dropout to pickup ratio (address
3739
U1>(>) RESET
) is set as high as possible with regard to the de-
tection of even small steady-state overvoltages. This parameter can only be altered in DIGSI at
Display Addi-
tional Settings
.
Overvoltage negative sequence system U
2
The negative sequence voltage stages detect asymmetrical voltages. If such voltages should cause tripping,
set address
3741
U2>(>)
to
ON
. Or you can set address
3741
U2>(>)
to
Alarm Only
. In this case the con-
dition will be reported but no trip signal will be generated. If only one stage is desired to generate a trip com-
mand, choose the setting
U>Alarm U>>Trip
. With this setting a trip command is output by the 2nd stage only.
If negative sequence voltage protection is not required, set this parameter to
OFF
.
This protection function also has two stages, one being
U2>
(address
3742
) with a greater time delay
T U2>
(address
3743
) for steady-state asymmetrical voltages and the other being
U2>>
(address
3744
) with a short
delay time
T U2>>
(address
3745
) for high asymmetrical voltages.
Note that the negative sequence system is calculated according to its defining equation
U
2
=
1
/
3
·|U
L1
+ a
2
·U
L2
+ a·U
L3
|. For symmetrical voltages and two swapped phases this is equivalent to the
phase-to-earth voltage value.
The dropout to pickup ratio
U2>(>) RESET
can be set in address
3749
. This parameter can only be altered
in DIGSI at
Display Additional Settings
.
