Functions
6-2357SA6 Manual
C53000-G1176-C156-2
Negative Sequence
System Overvolt-
age U
2
The negative sequence system voltage stages detect asymmetrical voltages. If such
voltages shall cause tripping, set the address
3741 U2>(>) to On. If these states shall
be signalled only, set the address
U2>(>) to Alarm Only, in any other cases to Off.
This protective function also has in two stages, one being
U2> (address 3742)witha
greater time delay
T U2> (address 3743) for stationary 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 established according to its defining equa-
tion U
2
=
1
/
3
⋅|U
L1
+a
2
⋅U
L2
+a⋅U
L3
|. For symmetrical voltages and two exchanged
phases this is equivalent to the phase–to–earth voltage value.
The drop-off to pick-up ratio
U2>(>) RESET) can be set in address 3749. This setting
canonlybemodifiedwithDIGSI
®
4 under “Additional Settings”.
Zero Sequence
System Overvolt-
age
The zero sequence voltage stage can be switched On or Off in address 3721. In ad-
dition, this stage can also be selected to
Alarm Only i.e. these stages operate and
issue alarms only. This protection function can be used for any other single-phase
voltage which is connected to the fourth voltage measurement input U
4
.(Alsoreferto
Section 6.1.1 and see margin heading “Voltage Transformer Connection”).
The settings of the voltage threshold and the timer values depend on the type of ap-
plication. Here no general guidelines can be established. Generally, with a sensitive
setting of
3U0> (address 3722), i.e. close to operational values that are to be expect-
ed, not only the time delay
T 3U0 (address 3724) must be greater, but also the reset
ratio
3U0 Reset Ratio (address 3723) must also be as large as possible. Usually
the presetting is sufficient. This setting can only be modified with DIGSI
®
4 under “Ad-
ditional Settings
”.
Similar considerations apply if this voltage stage is used for a different voltage at the
measuring input U
4
.
When setting the voltage values please observe the following:
• If the U
en
-voltage of the set of voltage transformers is connected to U
4
and if this
was already set in the power system data 1 (refer also to Section 6.1.1 under mar-
gin heading “Voltage Transformer Connection”,
U4 transformer = Udelta
transf.
), the device multiplies this voltage by the matching ratio Uph / Udelta
(address 211), usually with 1.73. Therefore the voltage measured is √3 ·U
en
=
3.U
0
. When the voltage triangle is fully displaced, the voltage will be √3-times the
phase-to-phase voltage
.
•
If any other voltage is connected to U
4
,whichisnot used for voltage protection, and
if this was already set in the power system data 1 (refer also to Section 6.1.1, “Volt-
age Transformer Connection”, e. g.
U4 transformer = Not connected or U4
transformer = Usync transf.
), the device calculates the zero sequence volt-
age according to its definition: 3 · U
0
=IU
L1
+U
L2
+U
L3
I. When the voltage triangle
is fully displaced, the voltage will be
√3-times the phase-to-phase voltage.
•
If any other voltage is connected to U
4
, which is used for voltage protection, and if
this was already set in the power system data 1 (refer also to Section 6.1.1, “Voltage
Transformer Connection”, i. e.
U4 transformer = Ux transformer), this volt-
age will be used for the voltage stages without any further factors. This “zero se-
quence voltage protection” then is, in reality, a single-phase voltage protection for
any kind of voltage at U
4
.
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