DC Motor Testing - Supply Switched from MG Set to Drive and PLC System

Please give us a sketch of your system.

The DC motor frame type. Is it a laminated construction or does it have cast poles. etc.

Dear Sir

DC supply system in place of MG SET it will be 12 pulse PLC System supply to be given after 15 years service life in Steel industry motors having folloiwing description

If the magnetic path is partly through the cast frame you may find additional losses.

There may be some commutation issues with the waveform, but the 12 pulse operation does help mitigate this.

For some applications additional series armature reactors are used to smooth the waveform.

The entry and mill sections often see momentary impact loadings as the material hits the stands. You should see improved performance with the phase control system.

Steel mill applications often specify 200% to 250% OL capabilities. Verify if you are actually using this range. If you are not using this capacity you may decide not to install the capacity and save a few $.

I would present these issues to your supplier and have a plan in place to handle the situation.

This is quite normal to switch over from OLD MG set and relay logic to state of the art DC Drives and PLC system for better performance and reliabilty.

When you feed the old existing DC motors with 12pulse Dc Drives/Converter system, the following needs to be taken care-

1. There will be additional losses due to PWM output from the converter system which will result in heating and temperature rise. So winding temperature needs to be monitored with the help of RTD sensors on motor windings and temperature scanners. If required restrict/limit the maximum voltage output of the converter to avoid insulation failure.

2. Install DC output chokes at the converter output to avoid spikes and smoothen the output to some extent.

3. In some cases for Mill motor to meet the additional overload Flywheels were install with the MG set which stores additional energy during light load and suppliment the additional energy during overload, in that case you may require field forcing (additional voltage to motor field) to meet the torque demand. Before doing this check the motor field insulation voltage.

Regards,

Dear Sir

Thank you for your sugesstions for precaution to be taken when switched over from MG Set DC supply to Drive and PLC System to DC Motors

Sadasivam

Regards