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Soft starter for high inertia load
A soft starter can be used to start a high inertia load provided that the motor is capable of starting that load, but a soft starter does not directly control the acceleration of the motor as the inverter.
A solid state soft starter is a reduced voltage starter and does not alter the frequency of the voltage applied to the motor. During start, the acceleration field is at line frequency and the torque is a function of the full voltage starting torque curve of the motor and the current reduction caused by the soft starter. The torque is reduced by the current reduction squared.
For a high torque start, the start current must be high, I have started many motors with a starting current as high as 450 - 500% of rated current.
The minimum start current is determined by the minimum start torque of the load and the motor current and torque/speed curves.
The best way to start a high inertia load is to set the starter up for a current limit only. There is nothing gained from a current ramp on a high inertia load.
The acceleration time is determined by the start torque (controlled by the start current) and the load inertia.
Try to start with the current limit set at 400% and see how long it takes to start. You can shorten the start time by increasing the start current and lengthen the start time by reducing the start current.
During start, there is high slip power loss in the rotor. The total rotor loss is basically equal to the full speed kinetic energy of the load. It is important that the rotor ha sufficient thermal mass to start the load inertia.
With the soft starter, set parameter 1 to equal the rated current of the motor, parameter 2 to 400%, parameter 3 to 400% and parameter 4 to 1. If the acceleration is too slow, increase 2 to 450% and try again.
We have started many high inertia rock crushers and chippers using soft starters with start times as long as 45 seconds.
If the requirement is truly to control the ramping time to full speed a RVSS (Reduced Voltage Soft Starter) is not the way to go. You will need a inverter which has capacity to control velocity over time. Having that knowledge tells you that if you continue on with a RVSS you want to have the starting current within that area to minimize the possibility of the motor sitting in a stall condition under current.
Once at that point of initial rotation you can set up the ramp time to 15 seconds, however it must be realized that you cannot control the velocity during this ramp period. Once at full speed the soft starter should have a bypass mechanism to shunt it to line power. The function of the soft starter is to minimize inrush current to the motor and shock loading to the mechanical parts of the system by ramping the current / voltage to the motor.
A solid state soft starter is a reduced voltage starter and does not alter the frequency of the voltage applied to the motor. During start, the acceleration field is at line frequency and the torque is a function of the full voltage starting torque curve of the motor and the current reduction caused by the soft starter. The torque is reduced by the current reduction squared.
For a high torque start, the start current must be high, I have started many motors with a starting current as high as 450 - 500% of rated current.
The minimum start current is determined by the minimum start torque of the load and the motor current and torque/speed curves.
The best way to start a high inertia load is to set the starter up for a current limit only. There is nothing gained from a current ramp on a high inertia load.
The acceleration time is determined by the start torque (controlled by the start current) and the load inertia.
Try to start with the current limit set at 400% and see how long it takes to start. You can shorten the start time by increasing the start current and lengthen the start time by reducing the start current.
During start, there is high slip power loss in the rotor. The total rotor loss is basically equal to the full speed kinetic energy of the load. It is important that the rotor ha sufficient thermal mass to start the load inertia.
With the soft starter, set parameter 1 to equal the rated current of the motor, parameter 2 to 400%, parameter 3 to 400% and parameter 4 to 1. If the acceleration is too slow, increase 2 to 450% and try again.
We have started many high inertia rock crushers and chippers using soft starters with start times as long as 45 seconds.
If the requirement is truly to control the ramping time to full speed a RVSS (Reduced Voltage Soft Starter) is not the way to go. You will need a inverter which has capacity to control velocity over time. Having that knowledge tells you that if you continue on with a RVSS you want to have the starting current within that area to minimize the possibility of the motor sitting in a stall condition under current.
Once at that point of initial rotation you can set up the ramp time to 15 seconds, however it must be realized that you cannot control the velocity during this ramp period. Once at full speed the soft starter should have a bypass mechanism to shunt it to line power. The function of the soft starter is to minimize inrush current to the motor and shock loading to the mechanical parts of the system by ramping the current / voltage to the motor.
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