Table 852: Special conditions
Condition Description
U3P connected to real measurements The function requires that at least two volt-
age channels are connected as the the third
channel can then be derived. However, it is
recommended that all three voltage channels
are connected.
Improper analog channel configuration causes a validation error if the analog
channels are not completely configured or they do not match with certain settings.
For troubleshooting, check the contents of this chapter and also the preprocessing
blocks in this document. The configuration can be written to the protection relay
once the mismatch is corrected.
4.5.8.5 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.
BLOCK
U3P
OPERATE
START
LVRT
curve
monitoring
U_AB
U_BC
U_CA
U_1
Figure 503: 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.
1MRS759142 F
Protection functions
REX640
Technical Manual
901
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