ABB RELION REX640 Technical Manual page 404

Protection and control

Hide thumbs Also See for RELION REX640:

Table of Contents

Protection functions

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.

LOFLPTUC Input signals

Table 460: LOFLPTUC Input signals

LOFLPTUC Output signals

Table 461: LOFLPTUC Output signals

1MRS759142 F

Three-phase currents

Block all binary out-

puts by resetting

Technical Manual