2 Functions
164
7SD610 Manual
C53000-G1176-C145-4
The zero-voltage stages feature a special time stabilisation due to repeated measure-
ments allowing them to be set rather sensitive. This stabilisation can be disabled in
address 3728 3U0>(>) Stabil. if a shorter pickup time is required. This parameter
can only be altered in DIGSI at Display Additional Settings. Please consider that
sensitive settings combined with short pickup times are not recommended.
The dropout to pickup ratio 3U0>(>) RESET can be set in address 3729. This pa-
rameter can only be altered in DIGSI at Display 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 = 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.
Phase-earth under-
voltage
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 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.
The dropout to pickup ratio Uph-e<(<) RESET can be set in address 3759. This pa-
rameter 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 exam-
ple, 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 ob-
served. With induction machines undervoltages have an effect on the permissible
torque thresholds.
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