2 Functions
336
7SD5 Manual
C53000-G1176-C169-1
This protective function also has two stages. The settings of the voltage threshold and
the timer values depend on the type of application. Here no general guidelines can be
established. The stage 3U0> (address 3722) is usually set with a high sensitivity and
a longer delay time T 3U0> (address 3723). The 3U0>> stage (address 3724) and
its delay time T 3U0>> (address 3725) allow you to implement a second stage with
less sensitivity and a shorter delay time.
Similar considerations apply if this voltage stage is used for a different voltage at the
measuring input U
4
.
Since the time delays of the zero sequence voltage stages are very stable due to the
measurement repetition, the sensitivity can be set quite high. This stabilization can be
deactivated at address 3728 3U0>(>) Stabil. if a shorter pickup time is required.
This setting is only possible via DIGSI
®
at "Additional Settings". Please keep in mind
that it does not make sense to combine a sensitive setting with a short pickup time.
The dropout to pickup ratio 3U0>(>) RESET can be set in address 3729. This pa-
rameter can only be altered with DIGSI
®
under Additional Settings.
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 2.1.2.1 under
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 2.1.2.1
under margin heading „Voltage Connection“, e.g. U4 transformer = Usync
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
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 2.1.2.1,
under 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“ then is, 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 greater, but also the reset ratio 3U0>(>) RESET
(address 3729) must be set as high as possible.
Undervoltage
Phase–Earth
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 in
addition to the alarm by setting .
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 un-
dervoltage 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.
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