4.1.2
Three-phase non-directional long-time overcurrent protection
51LT
4.1.2.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Three-phase non-directional long time
overcurrent protection
PHLTPTOC
3I>
51LT
4.1.2.2
Function block
GUID-64BF56CE-B585-46A5-AD6D-5DE762D107A9 V1 EN
Figure 60:
Function block
4.1.2.3
Functionality
The three-phase long-time overcurrent protection 51LT is used as one-phase, two-phase
or three-phase non-directional overcurrent and short-circuit protection for feeders.
The operation of this function is very similar to the 51P function except that inverse curves
operating times are 10 times that of 51P.
The function also contains a blocking functionality. It is possible to block function
outputs, timers or the function itself, if desired.
4.1.2.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
The operation of 51LT can be described by using a module diagram. All the modules in
the diagram are explained in the next sections.
1MRS240050-IB C
Section 4
Protection functions
REF615R
131
Technical Manual
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