Hello!

I have a 200kW motor with a rated current of 345A installed for a Fluidized Bed Cooler (FBC Fan Circulation) application. Currently, the motor is started using a direct-on-line (DOL) starter. However, we've experienced mechanical stress at the motor feeder jaws and heat marking on our LV bus bar. Given this, I'm considering whether a soft starter or a Variable Frequency Drive (VFD) would be more suitable for the motor, especially since the motor speed does not need to change during operation.

Additionally, after installing either a soft starter or VFD, are there any best practices we should follow to minimize electrical and mechanical stresses on the motor feeders?

 

Ramp time parameter is required to adjust during commission in order to have enough Torque to driving the fan to reach synchronous speed ( Power=2x3.1416xTx N/60 ). Suggest to have Power electronic module at one step bigger size than motor rated due to It is taking higher current to maintain load at lower voltage( cold air is laways heavy than hot air) otherwise it will be tripped by over current at first start especially long ramp time adjustment. If you have many operating conditions to operate Boiler at any capacities. I would like to suggest to use VFD rather than Soft start, You can adjust Fan's speed( air flow ) to cope with Boiler capacity at any turndown capacity to save Fan 's power significantly.

 

Would prefer vector control over VFD which will provide huge energy saving over the other two, even though the capital cost is slightly higher by 15 to 20% when compared to VFD. With proper tuning you can reduce huge cost of maintenance.
Strongly prefer to add line filters for VFD / Vector control since the PWM is causing lots of stress on winding and insulation.

In the past I had experience for changing the DOL to VFD to Vector for a exhaust stack of banburry rubber mill, where found significant advantages for 15 KW blower with Vector control, where we had to skip multiple natural frequencies during ramps and ever 30 minutes the blower switches on and off (Backup and primary). 3 decades back we use Eurotherm 605C for this. The ambient was extremely corrosive and contaminated with chalk powered and electrically conductive carbon dust. Still we did see huge savings.