national grid codes. The LVRT curve can be defined accurately according to the
requirements by setting the appropriate time-voltage coordinates.
The function contains a blocking functionality. LVRTPTUV can be blocked with the
BLOCK
input. Blocking resets timers and outputs.
4.5.9.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of LVRTPTUV is described using a module diagram. All modules in the
diagram are explained in the next sections.
Figure 358: Functional module diagram
LVRT curve monitoring
LVRT curve monitoring starts with detection of undervoltage. Undervoltage
detection depends on
Voltage selection setting. All selectable options are based
on fundamental frequency components.
Function uses phase-to-earth voltages when
Voltage selection is set to “Highest
Ph-to-E” or “Lowest Ph-to-E” and phase-to-phase voltages when
Voltage selection is
set to “Highest Ph-to-Ph” or “Lowest Ph-to-Ph”.
When the
Voltage selection setting is set to “Highest Ph-to-E”, “Lowest Ph-to-E”,
“Highest Ph-to-Ph” or “Lowest Ph-to-Ph”, the measured three-phase voltages are
compared phase-wise to the set
Voltage start value. If the measured value is lower
than the set
Voltage start value setting in number of phases equal to that set Num
of start phases, the
START
output is activated.
The setting options available for
Num of start phases are “Exactly 1 of 3”, "Exactly
2 of 3", and “Exactly 3 of 3”, which are different from conventional setting options
available in other functions. For example,
Num of start phases is set to "Exactly
2 of 3", any two voltages should drop below
Voltage start value within one cycle
network for the
START
output to activate. Even if more than two voltages drop
below
Voltage start value,
START
output is not activated.
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
.
Protection functions
1MRS757644 H
688
620 series
Technical Manual
