If a start command is output while the motor is being stopped, this process is aborted and the motor is started up again using the specified starting mode.
Note
If guided stopping is selected as stopping mode (soft stop, pump stop or braking), it may be necessary to select a larger dimensioned branch (soft starter, wiring, branch protection elements and motor), since the current exceeds the motor rated current while the motor is being stopped
Coasting Down
Coasting down means that when the on command to the soft starter is removed, the energy feed to the motor via the soft starter is interrupted. The motor will coast down freely, only driven by the mass reactance (centrifugal mass) of the rotor and the load. This is designated as a natural run-down. A larger centrifugal mass means a longer coasting-down.
Typical applications for coasting down
Coasting down is used for loads with no special requirements in terms of stopping behavior, e.g. large fans.
Torque Control and Pump Stop
In "Torque-controlled" and "Pump stop" mode, the coasting down process/ natural run-down of the load is extended. This function is set if abrupt stopping of the load is to be prevented. This is typical in applications with small mass reactances or high counter torques.
For optimum torque control during the stopping process, the motor data of the motor connected to the soft starter should be entered in the selected parameter set. This can be specified using the "Setting" menu item.
Stopping time and stopping torque
The "Stopping time" parameter of the soft starter can be used to specify for how long power should be fed into the motor after removal of the switch-on command. Within this stopping time, the torque generated in the motor is continuously and linearly reduced to the set stopping torque and the application is smoothly stopped.
Pump stop
In pump applications, so-called water hammers may occur if the drive is stopped abruptly without using pump stop. These water hammers are caused by the sudden break in the flow and the accompanying pressure deviations in the pump. They cause noise and a mechanical impact on the piping as well as on the flaps and valves inside the system.
Typical applications for soft stop / pump stop
Use soft stop / pump stop
• In pumps to prevent water hammers.
• In conveyor belts to prevent goods from toppling.
DC Braking / Combined Braking
In DC braking or combined braking, the coasting down / natural run-down of the load is shortened.
The soft starter imposes a (pulsating) DC current in phases L1 and L3 on the motor stator. This current creates a permanent magnetic field in the stator. Since the rotor is still rotating due to its mass reactance, currents are induced into the short rotor winding, creating a braking torque.
Note
The pulsating DC current loads the network asymmetrically and the motor and the branch must be dimensioned accordingly for the higher current load during the stopping procedure. A larger dimensioned soft starter may be necessary.
Stopping mode: combined braking
If combined braking is selected, the dynamic braking torque, DC braking torque and stopping time parameters can be configured on the starter.
Dynamic braking torque
The dynamic braking torque determines the extent of the braking effect at the start of the braking process in order to reduce the rotational speed of the motor.
The braking process is then continued using the DC braking torque function.
DC braking torque The height of the DC braking torque determines the brake force of the motor.
If the motor accelerates again during DC braking, the dynamic braking torque must be increased.
Stopping time
The stopping time determines how long braking torque is applied to the motor.
The braking time should be long enough to bring the load to a complete standstill.
To achieve a sufficient brake effect until standstill, the centrifugal mass (J) of the load should not exceed that of the motor. The stopping time should be selected such that the motor comes to a standstill. The soft starter has no standstill recognition; if required, this must be accomplished using external measures.
Note
The real stopping time can vary during braking processes when the combined braking function is applied.
If the DC braking function is selected, the stopping time and DC braking torque parameters can be configured on the starter. With this braking type, one output of the soft starter must be switched over to DC braking to control an external brake contactor. Please refer to Chapter 9 for wiring suggestions. The optimum parameters must be adjusted on the machine under appropriate load conditions.
DC braking torque
The DC braking torque determines the brake force of the motor.
Stopping time
The stopping time determines how long braking torque is applied to the motor.
The braking time should be long enough to bring the load to a complete standstill.
To achieve a sufficient braking effect until standstill, the load's mass moment of inertia should not be higher than 5 times the motor's mass moment of inertia.
(JLoad ≤5 x JMotor).
The soft starter has no standstill recognition; if required, this must be accomplished using external measures.
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