4.1.8.6 Application
When a motor runs with a load connected, it draws a current equal to a value
between the no-load value and the rated current of the motor. The minimum load
current can be determined by studying the characteristics of the connected load.
When the current drawn by the motor is less than the minimum load current drawn,
it can be inferred that the motor is either disconnected from the load or the
coupling mechanism is faulty. If the motor is allowed to run in this condition, it
may aggravate the fault in the coupling mechanism or harm the personnel handling
the machine. Therefore, the motor has to be disconnected from the power supply as
soon as the above condition is detected.
LOFLPTUC detects the condition by monitoring the current values and helps
disconnect the motor from the power supply instantaneously or after a delay
according to the requirement.
When the motor is at standstill, the current will be zero and it is not recommended
to activate the trip during this time. The minimum current drawn by the motor
when it is connected to the power supply is the no load current, that is, the higher
start value current. If the current drawn is below the lower start value current, the
motor is disconnected from the power supply. LOFLPTUC detects this condition
and interprets that the motor is de-energized and disables the function to prevent
unnecessary trip events.
4.1.8.7 Signals
LOFLPTUC Input signals
Table 460: LOFLPTUC Input signals
Name Type Default Description
I3P SIGNAL - Three-phase currents
BLOCK BOOLEAN 0=False Block all binary out-
puts by resetting
timers
LOFLPTUC Output signals
Table 461: LOFLPTUC Output signals
Name Type Description
OPERATE BOOLEAN Operate
START BOOLEAN Start
Protection functions 1MRS759142 F
404 REX640
Technical Manual
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