When the
Voltage selection
setting is “Positive Seq”, the positive-sequence
component is compared with the set
Voltage start value
. If it is lower than the set
Voltage start value
, the START output is activated.
Once START is activated, the function monitors the behavior of the voltage defined
by
Voltage selection setting
with the defined LVRT curve. When defined voltage
enters the operating area, the OPERATE output is activated instantaneously. The
pulse length of OPERATE is fixed to 100 ms. START also deactivates along with
OPERATE.
If a drop-off situation occurs, that is, voltage restores above
Voltage start value
,
before OPERATE is activated, the function does not reset until maximum recovery
time under consideration has elapsed, that is, START output remains active.
LVRT curve is defined using time-voltage settings coordinates. The settings
available are
Recovery time 1
…
Recovery time 10
and
Voltage level 1
…
Voltage level
10
. The number of coordinates required to define a LVRT curve is set by
Active
coordinate
settings.
When
Recovery time 1
is set to non-zero value, it results into horizontal
characteristics from point of fault till
Recovery time 1.
Two examples of LVRT curve are defined in
Figure 504
and
Figure 505
with
corresponding settings in
Table 853
.
It is necessary to set the coordinate points correctly in order to avoid
maloperation. For example, setting for
Recovery time 2
should be greater
than
Recovery time 1
.
Recovery time 1
…
Recovery time 10
are the
respective time setting from the point of fault.
Figure 504: Low voltage ride through example curve A
Protection functions
1MRS759142 F
902 REX640
Technical Manual
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