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Speed And Torque Control


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I am a student engineer working on a project at a steel company. I need to find a suitable solution to control the acceleration and deceleration of an already existing slip-ring motor for a crane application. Hoist crane: 135 kW at 525 V. I have come across various soft-starters, variable speed and frequency drives as well as sensorless speed control drives. I do not have the experience to select the most appropriate. Could someone please help. I really appreciate it.



Sammy :)

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That is a very complex problem, one I would not leave to a student, unless they are just testing your critical thinking process and will not necessarily implement your solution without being reviewed by an experienced engineer.


Assuming that is the case, look at it from this angle. Don't get caught up in the technology yet. Look at all of the other factors going on. Here are some examples, there will undoubtedly be more that I will think of right away;

  • Accuracy. +-10% or +-.01% can may a huge difference in your choices.
  • Control response. How quickly, from a commanded speed or torque change, must the system be capable of responding? If it is only necessary to respond in 1 or 2 seconds to a step change in load, it may be a waste to spend a lot of money on a digital drive. But if the step-change response needs to be as fast as possible to avoid product problems, a liquid starter may be far too slow.
  • Operating environment, control equipment environment. Trying to use complex electronics in dirty nasty corrosive environments can be daunting, but using a liquid starter in a high ambient temperature area might be equally difficult.
  • Sophistication of the workforce that will be maintaining and operating the equipment. Using systems too advanced for the people who must operate and maintain them can be worse than doing nothing at all, but re-using outdated technology when you have a good qualified workforce can end up making people frustrated.
"He's not dead, he's just pinin' for the fjords!"
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