Functions
2.8 Undervoltage and Overvoltage Protection 27/59 (Optional)
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
125
Overvoltage Phase-to-Ground
The phase voltage elements can be switched
ON
or
OFF
in address
3701
59-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.
The setting
V>Alarm V>>Trip
creates in addition also a trip command only for the 59-2 element (V>>).
The settings of the voltage threshold and the timer values depend on the type of application. To detect steady-
state overvoltages on long lines carrying no load, set the
59-1-Vph PICKUP
element (address
3702
) to at
least 5 % above the maximum stationary phase-to-ground voltage expected during operation. Additionally, a
high dropout to pickup ratio is required (address
3709
59-Vph RESET
= presetting). This parameter can only
be set in DIGSI at
Display Additional Settings
. The time delay
59-1-Vph DELAY
(address
3703
) should be
a few seconds so that overvoltages with short duration do not cause tripping.
The 59-2 phase (V
ph
>>) element (address
3704
) is provided for high overvoltages with short duration. Here an
adequately high pickup value is set, e.g. the 1
1
/
2
-fold of the nominal phase-to-ground voltage. 0.1 s to 0.2 s are
then sufficient for the time delay
59-2-Vph DELAY
(address
3705
).
Overvoltage Phase-to-Phase
Basically, the same considerations apply as for the phase undervoltage elements. These elements may be
used instead of the phase voltage elements or be used additionally.. Accordingly set address
3711
59-Vph-
ph Mode
to
ON
,
OFF
,
Alarm Only
or
V>Alarm V>>Trip
.
As phase–to–phase voltages are monitored, the phase–to–phase values are used for the settings
59-1-Vpp
PICKUP
(address
3712
) and
59-2-Vpp PICKUP
(address
3714
).
For the time delays
59-1-Vpp DELAY
(address
3713
) and
59-2-Vpp DELAY
(address
3715
) the same con-
siderations apply as above. The same is true for the dropout ratios (address
3719
59-Vpp RESET
). The latter
setting can only be altered in DIGSI at
Display Additional Settings
.
Overvoltage Positive Sequence System V
1
The positive sequence voltage elements can be used instead of or in addition to previously mentioned over-
voltage elements. Accordingly set address
3731
59-V1 Mode
to
ON
,
OFF
,
Alarm Only
or
V>Alarm
V>>Trip
.
For symmetrical voltages an increase of the positive sequence system corresponds to a logical AND combina-
tion of the phase voltages. These elements are particularly suited to the detection of steady-state overvoltages
on long, weak-loaded transmission lines (Ferranti effect). Here too, the
59-1-V1 PICKUP
element (address
3732
) with a longer time delay
59-1-V1 DELAY
(address
3733
) is used for the detection of steady-state ov-
ervoltages (some seconds), the
59-2-V1 PICKUP
element (address
3734
) with the short time delay
59-2-
V1 DELAY
(address
3735
) is used for the detection of high overvoltages that may jeopardize insulation.
Please note that the positive sequence system is established according to its defining equation
V
1
=
1
/
3
·|V
A
+ a·V
B
+ a
2
·V
C
|. For symmetrical voltages the amplitude equivalent to a phase-to-ground voltage.
The dropout to pickup ratio (address
3739
59-V1 RESET
) is set as high as possible with regard to the detec-
tion of even small steady-state overvoltages. This parameter can only be set in DIGSI at
Display Additional
Settings
.
Overvoltage Negative Sequence System V
2
The negative sequence voltage elements detect asymmetrical voltages. If it is desired that such voltages cause
tripping, set address
3741
59-V2 Mode
to
ON
. To only signal such states, set address
3741
59-V2 Mode
to
Alarm Only
. If only one element is desired to generate a trip command, choose the setting
V>Alarm
V>>Trip
. With this setting a trip command is output by the 2nd element only. If negative sequence voltage
protection is not required, set this parameter to
OFF
.