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•
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Adaptive control (ear-
ly acceleration)
Adaptive control
(late deceleration)
9.8 Soft Start Methods
9.8.1 Constant Current
Constant current is the traditional form of soft starting, which raises the current from 0 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.
500
300
100
400
200
10 20 30 40 50 60 70 80 90 100
Current (% motor full load current)
Rotor speed (% full speed)
Illustration 29: Example of Constant Current
Initial current (set in parameter 2-3 Initial Current)
Current limit (set in parameter 2-4 Current Limit)
9.8.2 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 (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 parameter 2-3 Initial Current
to a level that will start the motor with a light load. Then, set parameter 2-4 Current Limit to a level that will start the motor with a
heavy load.
The load breaks away easily, but starting time has to be extended (for example a centrifugal pump where pipeline pressure has
to build up slowly).
The electricity supply is limited (for example a generator set), and a slower application of load allows greater time for the supply
to respond.
AQ262141844215en-000401 / 175R1174 | 63Danfoss A/S © 2020.12
Operation
VLT® Soft Starter MCD 600
Operating Guide
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