Functions
6-234 7SA6 Manual
C53000-G1176-C156-2
6.16.2 Applying the Function Parameter Settings
The voltage protection can only operate if it has been set to Enabled during the con-
figuration of the device scope (see Section 5.1, address
137).
The overvoltage and undervoltage stages can detect phase–to–earth voltages,
phase–to–phase voltages or the symmetrical positive sequence system of the voltag-
es; the symmetrical negative sequence system can also be used for overvoltage. Any
combination is possible. Detection procedures that are not required are switched
Off.
Overvoltage
Phase–Earth
The phase voltage protection stages can be switched On or Off in address 3701
Uph-e>(>)
. In addition to that you can also set Alarm Only; i.e. these stages op-
erate and transmit signals. Without generating a trip command.
The settings of the voltage and time values depend on what they are used for. If
steady-state overvoltages are to be detected on long unloaded lines, the
Uph-e>
stage (address 3702) is set to at least 5 % above the maximum stationary phase–to–
earth voltage that is to be expected in operation. Additionally, a high drop-off to pick-
up ratio is required (address
3709 Uph-e>(>) RESET = 0.98 =presetting).This
setting can only be modified with DIGSI
®
4 under “Additional Settings”. The delay
time
T Uph-e> (address 3703) should be a few seconds so that overvoltages with
short duration may not result in tripping.
The
Uph-e>> stage (address 3704) is provided for high overvoltages with short du-
ration. Here, an adequately high pick-up value is set, e.g. the 1.5–fold of the nominal
phase–earth voltage. 0.1 s to 0.2 s are sufficient for the time delay
T Uph-e>> (ad-
dress
3705).
Overvoltage
Phase–Phase
Basically, the same considerations apply as for the phase voltage stages. These stag-
es may be used instead of the phase voltage stages or be used addionally. The ad-
dress
3711 Uph-ph>(>) is set to On, Off or Alarm Only.
As phase–to–phase voltages will be detected, phase–to–phase values are used for
the settings
Uph-ph> (address 3712)andUph-ph>> (address 3714).
The same aspects as mentioned above apply to the time delays
T Uph-ph> (address
3713)andT Uph-ph>> (address 3715) as well as to the drop-off to pick-up ratios
(address
3719 Uphph>(>) RESET). This setting can only be modified with DIGSI
®
4
under “Additional Settings”.
Positive Sequence
System Overvolt-
age U
1
The positive sequence voltage stages can be used instead of or in addition to previ-
ously mentioned overvoltage stages. The address
3731 U1>(>) is set to On, Off or
Alarm Only, accordingly.
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 (ad-
dress 3732) with a longer delay time is used for the detection of steady-state overvolt-
ages, the
U1>> stage (address 3734) with the short delay time T U1>> (address
3735) is used for high overvoltages that may jeopardize insulation.
Note that the positive sequence system is established according to its defining equa-
tion 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.
The drop-off to pick-up ratio (address
3739 U1>(>) RESET) is set as high as possible
with regard to the detection of even small steady-state overvoltages. This setting can
only be modified with DIGSI
®
4 under “Additional Settings”.
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