OPERATION
8.6
Soft Start Methods
Constant Current
Constant current is the traditional form of soft starting, which raises the current
from zero to a specified level and keeps the current stable at that level until the
motor has accelerated.
Constant current starting is ideal for applications where the start current must be
kept below a particular level.
Cur
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700%
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10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
1
3
2
1:
Initial Current
(parameter 2C)
2:
Current Limit
(parameter 2D)
3: Full voltage current
Rotor speed (% full speed)
Constant Current with Current Ramp
Current ramp soft starting raises the current from a specified starting level (1) to a
maximum limit (3), over an extended period of time (2).
Current ramp starting can be useful for applications where:
•
the load can vary between starts (for example a conveyor which may start
loaded or unloaded). Set the initial current (parameter 2C) to a level that
will start the motor with a light load, and the current limit (parameter 2D)
to a level that will start the motor with a heavy load.
•
the load breaks away easily, but starting time needs to be extended (for
example a centrifugal pump where pipeline pressure needs to build up
slowly).
•
the electricity supply is limited (for example a generator set), and a slower
application of load will allow greater time for the supply to respond.
Cur
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m
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fu
ll l
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d
cu
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700%
600%
500%
300%
100%
400%
200%
1
4
3
2
1:
Initial Current
(parameter 2C)
2:
Start Ramp Time
(parameter 2B)
3:
Current Limit
(parameter 2D)
4: Full voltage current
Time
48 |
EMX4e User Manual (710-18433-00C)
