Section 4
1MAC050144-MB C
Protection functions
214
615 series ANSI
Technical Manual
The operation of loss of load protection can be described by using a module diagram. All
the modules in the diagram are explained in the next sections.
Figure 100:
Functional module diagram
Level detector 1
This module compares the phase currents (RMS value) to the set
Pickup value high
setting.
If all the phase current values are less than the set
Pickup 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
Pickup 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
Pickup value low
setting. If
any of the phase current values is less than the set
Pickup value low
, a signal is sent to block
the operation of the timer.
Timer
Once activated, the timer activates the
PICKUP
output. The time characteristic is
according to DT. When the trip timer has reached the value set by
Trip delay time
, the
TRIP
output is activated. If the fault disappears before the module trips, the reset timer is
activated. If the reset timer reaches the value set by
Reset delay time
, the trip timer resets
and the
PICKUP
output is deactivated.
The timer calculates the pickup duration value PICKUP_DUR which indicates the
percentual ratio of the pickup situation and the set trip time. The value is available through
the Monitored data view.
The
BLOCK
signal blocks the operation of the function and resets the timer.
4.1.11.5
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
PICKUP
TRIP
Level
detector 1
BLOCK
I_A
Timer
t
Level
detector 2
I_B
I_C
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