•
If U
4
is connected with U
en
voltage of the set of voltage transformers and this is set as with the Power
at margin heading “Voltage Connection”, address 210
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
which is not used for voltage protection, and if this was already
set in the Power System Data 1 (refer also to Section
at margin heading “Voltage
Connection”, e.g.
U4 transformer
=
Usy2 transf.
or
U4 transformer
=
Not connected
), the
device calculates the zero-sequence voltage from the phase voltages according to its definition 3·U
0
= |
U
L1
+ U
L2
+ U
L3
|. When the voltage triangle is fully displaced, the voltage will thus be √3 times the phase-
to-phase voltage.
•
If any other AC voltage is connected to U
4
which is used for voltage protection, and if this was already set
in the Power System Data 1 (Section
at margin heading “Voltage Connection”,
U4
transformer
=
Ux transformer
), this voltage will be used for the voltage stages without any further
factors. This “zero-sequence voltage protection” is then, in reality, a single-phase voltage protection for
any kind of voltage at U
4
. Note that with a sensitive setting, i.e. close to operational values that are to be
expected, not only the time delay
T 3U0>
(address 3723) must be set high, but also the reset ratio
3U0>(>) RESET
(address 3729) must be set as high as possible.
Phase-to-earth undervoltage
The phase voltage stages can be switched
ON
or
OFF
in address 3751
Uph-e<(<)
. In addition to this, you can
set
Alarm Only
, i.e. these stages operate and send alarms but do not generate any trip command. You can
generate a trip command for the 2nd stage only in addition to the alarm by setting
U<Alarm U<<Trip
.
This undervoltage protection function has two stages. The
Uph-e<
stage (address 3752) with a longer setting
of the time
T Uph-e<
(address 3753) operates in the case of minor undervoltages. However, the value set
here must not be higher than the undervoltage permissible in operation. In the presence of higher voltage
dips, the
Uph-e<<
stage (address 3754) with the delay
T Uph-e<<
(address 3755) becomes active.
The dropout to pickup ratio
Uph-e<(<) RESET
can be set in address 3759. This parameter can only be
altered in DIGSI at Display Additional Settings.
The settings of the voltages and times depend on the intended use; therefore no general recommendations
for the settings can be given. For load shedding, for example, the values are often determined by a priority
grading coordination chart. In case of stability problems, the permissible levels and durations of overvoltages
must be observed. With induction machines undervoltages have an effect on the permissible torque thresh-
olds.
If the voltage transformers are located on the line side, the measuring voltages will be missing when the line is
disconnected. To avoid that the undervoltage levels in these cases are or remain picked up, the current crite-
rion
CURR.SUP. Uphe<
(address 3758) is switched
ON
. With busbar side voltage transformers it can be
switched
OFF
. However, if the busbar is dead, the undervoltage protection will pick up and expire and then
remain in a picked-up state. It must therefore be ensured in such cases that the protection is blocked by a
binary input.
If the 7VK61 is operated without current transformer connection, the current criterion is of no use and associ-
ated parameters are hidden.
Phase-to-phase undervoltage
Basically, the same considerations apply as for the phase voltage stages. These stages may replace the phase
voltage stages or be used additionally. Depending on your choice, set address 3761
Uph-ph<(<)
to
ON
,
OFF
,
Alarm Only
or
U<Alarm U<<Trip
.
As phase-to-phase voltages are monitored, the phase-to-phase values are used for the settings
Uph-ph<
(address 3762) and
Uph-ph<<
(address 3764).
The corresponding time delays are
T Uph-ph<
(address 3763) and
T Uphph<<
(address 3765).
The dropout to pickup ratio
Uphph<(<) RESET
can be set in address 3769. This parameter can only be
altered in DIGSI at Display Additional Settings.
Functions
2.5 Under and over-voltage protection (optional)
SIPROTEC 4, 7VK61, Manual
109
C53000-G1176-C159-5, Edition 05.2018
Содержание SIPROTEC 4 7VK61
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