ABB Relion 611 Series, Technical Manual

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GUID-4A6308B8-47E8-498D-A268-1386EBBBEC8F V1 EN
Figure 64: Functional module diagram
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.
4.1.5.5 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
Section 4
1MRS757454 D
Protection functions
142 611 series
Technical Manual