High Capacity Motor Drive

  • Thread starter Luiz Antonio Dourado
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Thread Starter

Luiz Antonio Dourado

Dear Sirs

Our company is now working in a production capacity debottlenecking of one of our Polyethylene facilities. One of the main equipment's involved in the project is an extruder, driven by a DC motor.

We will need to increase the power capacity of the motor and we are now considering the alternatives to the use of a DC motor with
variable speed control. Motor power will be 2750KW. Supply voltage available is 6.9KV with option to use reducing transformer.

Basically we see 3 possibilities for this which are:

1) Keep using a DC motor
2) Use a induction motor with a frequency converter
3) Use a synchronous motor with a cycloconverter

We are aware of the higher maintenance requirements of a DC motor over other technologies.

I would appreciate your feedback regarding the advantages and disadvantages of each alternative.

Thanks in advance for your attention.

*** Luiz Antonio Dourado Goncalves - POLITENO Ind. Com. S.A.
Eng. de
Eletricidade e Instrumentacao (Electrical & Instrumentation
[email protected] http://www.politeno.com.br
Camacari -
Bahia - Brasil

David W. Spitzer


For general information, my book --- Variable Speed Drives: Principles and Applications for Energy Cost Savings, ISA --- may be helpful. Due to the large energy costs associated with a motor this size, a detailed analysis should be performed that may present other possibilities.

What size is the existing motor? Has the extruder been checked to ensure that it can handle torque from the larger motor?

I would caution that starting torque may be an issue in this application, so replacing the DC motor with any other type should be reviewed carefully. There also may be some energy savings associated with implementing one of these technologies. Remember that energy savings of only a few percent on a motor this size can represent substantial savings. Also, using a transformer will reduce efficiency by about a percent. Medium voltage drives are available.


David W. Spitzer (eu falo portugues fluentemente)