Level detector 1
This module compares the phase currents (RMS value) to the set
Start value high
setting. If all the phase current values are less than the set
Start value high value,
the loss of load condition is detected and an enable signal is sent to the timer. This
signal is disabled after one or several phase currents have exceeded the set
Start
value high value of the element.
Level detector 2
This is a low-current detection module, which monitors the de-energized condition
of the motor. It compares the phase currents (RMS value) to the set
Start value low
setting. If any of the phase current values is less than the set
Start value low, a
signal is sent to block the operation of the timer.
Timer
Once activated, the timer activates the
START
output. The time characteristic is
according to DT. When the operation timer has reached the value set by
Operate
delay time, the
OPERATE
output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the
value set by
Reset delay time, the operate timer resets and the
START
output is
deactivated.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is
available in the monitored data view.
The
BLOCK
signal blocks the operation of the function and resets the timer.
4.1.9.5
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.
Protection functions
1MRS757644 H
356
620 series
Technical Manual
