Functions
2.8 Undervoltage and Overvoltage Protection 27/59 (Optional)
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
126
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
V
2
=
1
/
3
·|V
A
+ a
2
·V
B
+ a·V
C
|. For symmetrical voltages and two swapped phases the amplitude is equivalent to
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.
