Siemens SIPROTEC 7SD80 Manual page 126

Functions
2.8 Undervoltage and Overvoltage Protection 27/59 (Optional)
This protective function also has two elements, one being 59-1-V2 PICKUP (address 3742) with a greater
time delay 59-1-V2 DELAY (address 3743) for steady-state asymmetrical voltages and the other being 59-
2-V2 PICKUP (address 3744) with a short time delay 59-2-V2 DELAY (address 3745) for high asymmetrical
voltages.
Please note that the negative sequence system is established according to its defining equation
1 2
V = / ·|V + a
2 3 A
the phase–to–ground voltage value.
The dropout to pickup ratio 59-V2 RESET can be set in address 3749. This parameter can only be set in DIGSI
at Display Additional Settings.
Zero Sequence System Overvoltage
The zero sequence voltage elements can be switched ON or OFF in address 3721 59G-3V0 (or Vx). They
can also be set to Alarm Only, i.e. these elements operate and send alarms but do not generate any trip
commands. If a trip command of the second element is still desired, the setting must be V>Alarm V>>Trip.
This protective function also has two elements. The settings of the voltage threshold and the timer values
depend on the type of application. Here no general guidelines can be established. The element 59G-1-
3V0PICKUP (address 3722) is usually set with a high sensitivity and a longer time delay 59G-1-3V0 DELAY
(address 3723). The 59G-2-3V0PICKUP element (address 3724) and its time delay 59G-2-3V0 DELAY (ad-
dress 3725) allow to implement a second element with less sensitivity and a shorter time delay.
The zero-voltage stages feature a special time stabilization due to repeated measurements allowing them to
be set rather sensitive. This stabilization can be disabled in address 3728 59G-3Vo Stabil. if a shorter
pickup time is required. This parameter can only be set in DIGSI at Display Additional Settings. Please con-
sider that sensitive settings combined with short pickup times are not recommended.
The dropout to pickup ratio 59G RESET can be set in address 3729. This parameter can only be set in DIGSI
at Display Additional Settings.
Undervoltage Phase-to-Ground
The phase voltage elements can be switched ON or OFF in address 3751 27-Vph-g Mode. In addition to this,
you can set Alarm Only, i.e. these elements operate and send alarms but do not generate any trip command.
You can generate a trip command for the 2nd element only in addition to the alarm by setting V<Alarm
V<<Trip.
This undervoltage protection function has two elements. The 27-1-Vph PICKUP element (address 3752) with
a longer setting of the time 27-1-Vph DELAY (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 27-2-Vph PICKUP element (address 3754) with the delay 27-2-Vph DELAY (ad-
dress 3755) becomes active
The dropout to pickup ratio 27-Vph RESET can be set in address 3759. This parameter can only be set 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 thresholds.
If the voltage transformers are located on the line side, the measuring voltages will be absent when the line is
disconnected. To avoid the undervoltage levels picking up, the current criterion CURR.SUP 27-Vph (address
3758) is switched ON. With bus—sided voltage transformers it can be switched OFF. However, if the busbar is
dead, the undervoltage protection will pick up and expire and then remain picked up. It must therefore be
ensured that the protection is blocked by a binary input.
126
·V + a·V |. For symmetrical voltages and two swapped phases the amplitude is equivalent to
B C
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011