Operation Principle - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.5.8.5
818

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.
U_AB
U_BC
U3P
U_CA
U_1
BLOCK
GUID-12C20798-163F-4155-860A-F0385C1B0ADD V1 EN
Figure 444: 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.
OPERATE
LVRT
curve
START
monitoring
1MRS759142 C
REX640
Technical Manual