G120C Load surge when running at full speed

Hi,

I have induction motor to be driven with G120C 75kW. It will run continuously with defined speed. Load coupling to the motor to be done with pneumatic clutch. What happens if the applied load needs slightly higher than 200% of the rated current of the drive because of the load's moment of inertia? If we can control the clutch friction and transition time, the load requires 130% current @0,6sec to accelerate to motor speed. But the clutch operates instantly and coupling time is shorter so accelerating time of the load is very short that means it requires >200% current which the drive can't supply. Does the drive reduce the freq. in order to reduce the voltage(and current) and accelerates again? Or it trips instantly?

Regards...

Hakan

Can you provide the part number?

Tractor

h.yilmaz

Hi,

I have induction motor to be driven with G120C 75kW. It will run continuously with defined speed. Load coupling to the motor to be done with pneumatic clutch. What happens if the applied load needs slightly higher than 200% of the rated current of the drive because of the load's moment of inertia? If we can control the clutch friction and transition time, the load requires 130% current @0,6sec to accelerate to motor speed. But the clutch operates instantly and coupling time is shorter so accelerating time of the load is very short that means it requires >200% current which the drive can't supply. Does the drive reduce the freq. in order to reduce the voltage(and current) and accelerates again? Or it trips instantly?

Regards...

Hakan

 You have the High overload device 6SL3210-1KE31-4UF1, 75kW, 136Ampere.

After some reading here I cannot be certain, if the drive will 'current limit', or 'trip'. There is an indication that in U/F it will current limit, but that appears to be during acceleration, or ramping to setpoint.

Your application is exceeding the High Overload level 200% for 3 seconds, instantly, I think it will trip without current limiting.

To be sure you need another opinion here.

Tractor

zako_

You should do a trace of some parameters like r68 r80 r82 r63 r36 if one orsome parameters on the Limit.

 Unfortunately the machine is still in production. We manufactured the drive cabinet and sent to the plant. They later acquired the machine and connect, then we will go there for commissioning.

There are things you can do to improve the ability for your drive to handle the increased load.  The good ones are not free, nor easy.

For example, you can increase the voltage into the drive with a transformer, or if there is one there already, to change taps to increase voltage closer to the maximum input voltage according to the drive specs.  A new drive is less expensive for larger transformers.

You can increase the input frequency closer to the maximum allowed using a UPS or motor-generator set.  This is more expensive than a new drive - guaranteed.

You can add additional cooling and directed air flow to the drive, then alter parameters in the drive to allow it to run slightly longer in overload - really recommend working with Siemens Support on this one as it can void your warranty, burn up the drive, cause unhappy customers, and make for a bad day.

You can also put an additional load coupling into the system that causes the high inertia load to work fine when "clutched" into the system.  You can also put the motor in "coast" mode an instant before the high load is clutched in, then do a flying restart to catch the load after it has slowed down a little, or at least into the zone where the motor can do its job.

These ideas / suggestions may not be appropriate for your given situation, plus may be the wrong answer short / long term.  They are simply suggestions that might get you a few more % overload or fractions of a second more time in overload.

h.yilmaz

zako_

You should do a trace of some parameters like r68 r80 r82 r63 r36 if one orsome parameters on the Limit.

 Unfortunately the machine is still in production. We manufactured the drive cabinet and sent to the plant. They later acquired the machine and connect, then we will go there for commissioning.

Thanks guys,

Siemens Support have made it clear that it will trip with F7801 code immediately if the load surge makes the drive to reach the current limit set in p0640 which is certain in my case. I need to find the solution on the mechanics. Science Guy's suggestion looks as if the only way to overcome, making drive to coast at one instant before load surge then make it flying start but as the application is flying shear, uncertainty on the cut lengths makes the process very costly. Miliseconds means centimeters in production. Process speed is 11m/s. It is unclear how long will it take the drive to restart and whether the time lag will be repeatable.

Regards...

Hakan

For your specific application, definitely throw out that flying restart suggestion.

1. Best (electrical): New Drive - S120 with regen capabilities so it can absorb more energy (than DC braking resistors)
2. Increase voltage to drive closer to maximum by changing transformer taps for mains voltage 3 phase feed to the drive.  If your drive is a standard 400 VAC, it might allow close to 500 VAC and still be within specifications for the drive.  This higher voltage will help increase the power rating without increasing the current rating
3. New motor - select a motor more suited to this type of impulse load, and can accept higher power (perhaps higher AC voltage)
4. Mechanical redesign (best overall)

For something moving this fast and that high of an impulse load, I imagine the mechanical braking on the motor shaft / load must be pretty substantial.  Perhaps supplement that with a way to modulate the braking forces with a very fast control / response loop to maintain speed setpoint during the transition.

h.yilmaz

Thanks guys,

Siemens Support have made it clear that it will trip with F7801 code immediately if the load surge makes the drive to reach the current limit set in p0640 which is certain in my case. I need to find the solution on the mechanics. Science Guy's suggestion looks as if the only way to overcome, making drive to coast at one instant before load surge then make it flying start but as the application is flying shear, uncertainty on the cut lengths makes the process very costly. Miliseconds means centimeters in production. Process speed is 11m/s. It is unclear how long will it take the drive to restart and whether the time lag will be repeatable.

Regards...

Hakan