Siemens SIPROTEC 4 7VK61 Manual page 109

•
If U is connected with U
4
System Data 1 (see Section
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
voltage triangle is fully displaced, the voltage will be √3 times the phase-to-phase voltage.
•
If any other voltage is connected to U
set in the Power System Data 1 (refer also to Section
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
U + U + U
L1 L2
to-phase voltage.
•
If any other AC voltage is connected to U
in the Power System Data 1 (Section
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
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.
SIPROTEC 4, 7VK61, Manual
C53000-G1176-C159-5, Edition 05.2018
voltage of the set of voltage transformers and this is set as with the Power
en
2.1.3.1 Setting Notes
which is not used for voltage protection, and if this was already
4
|. When the voltage triangle is fully displaced, the voltage will thus be √3 times the phase-
L3
2.1.3.1 Setting Notes
. Note that with a sensitive setting, i.e. close to operational values that are to be
4
2.5 Under and over-voltage protection (optional)
at margin heading "Voltage Connection", address 210
2.1.3.1 Setting Notes
which is used for voltage protection, and if this was already set
4
at margin heading "Voltage Connection", U4
Functions
= 3·U . When the
en 0
at margin heading "Voltage
= |
0
109