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Universal Motor Controller
UMC100-FBP
V 6
Technical Description
Low Current Protection
The low current function is triggered when the motor current falls below a desired level. The function
detects loss of suction for pumps, broken belt for conveyors, loss of airlow for fans, broken tools for ma-
chines etc. Such states do not harm the motor but early diagnosis helps to minimise the extent of dam-
age to the mechanical installation and subsequent loss of production
The motors on underload draw mainly the magnetising current and a small load current to overcome fric-
tional losses. Therefore, the other reason to isolate the motors on underload is to reduce the reactive load
on the power system network.
The low current function signals a warning when the motor current falls below the warning level for a
conigurable period of time, after motor start-up. The low current function creates a trip when the motor
current falls below the trip level for a conigurable period of time, after motor startup.
Block Diagram:
Example:
The diagram above shows an underload situation of the motor after the startup time is over (T1). At T the
motor current falls below the undercurrent warning limit I
t
an undercurrent warning is set.
ucwd
Then at T3 the current also falls under the undercurrent trip level I
speciied undercurrent trip delay time t
the low current level and stays there. Therefore a trip is released and the motor stopped.
[%]
I/I
e
I
SE
I
e
I
lcwl
I
lctl
Low Current
---------------------------------------/===========================================================
Warning
Low Current
-------------------------------------------------------------------------------/===================
Trip
Relevant Parameters
•
Undercurrent Trip Level
•
Undercurrent Trip Delay
FieldBusPlug / Issue: 11.009
I<I
lcwl
I/I
[%]
e
I<I
lctl
After Start-up
. Therefore no trip happens. At T4 the current falls again under
uctd
T2
T1
t
lcwd
&
T
lcwd
&
T
lctd
. After the undercurrent warning delay time
ucwl
but only for a period shorter than the
uctl
T4
T3
t
lctd
•
Undercurrent Warning Level
•
Undercurrent Warning Delay
- 39 -
Low Current
Warning
Low Current
Trip
I
: Low current trip delay time
lctl
I
: Low current warning delay level
lcwl
t
:Low current trip delay
lctd
t
:Low current warning delay
lcwd
I
: Nominal current
e
I
: Current deining the end of the
SE
start-up period
t
lctd
UMC100-FBP
t
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