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Large Motor Starting 103: Motor Starting Methods – How to Choose the Right One

This is the third post in our series on motor management covering various aspects of motor integration in an electrical network and the industrial process.

In the first, the electrical, thermal and mechanical constraints necessary to consider for large motor starting have been presented in detail. In the second post the typical application constraints have been introduced.

Motor Management

In this post we will try to answer the question: how to select the right motor starting solution for a concrete application?

There are several motor starting solutions that we can compare simply through the next table:

More detailed comparison of motor starting solutions can be found in this white paper: “Modeling of Motor Starting Methods in EMTP-ATP“.

By looking on the table we can decide that a variable speed drive is the solution for each case. And this would be right in the principle. However, the final decision will depend on several installation criteria which is related to:

  • Economical interest – the cost of the solution
  • Engineering simplicity – the efforts to evaluate this solution and to commission it
  • Maintenance easiness – which is also related to the cost of the maintenance
  • Footprint
  • Weight
  • Energy saving – the possibility to reduce energy consumption for some applications, for example when the operation is integrating idle cycles or reduced flow rate
  • Flexibility of adaptation – for varying operational conditions of flow, pressure, operating cycle

The next table provides a relative comparison of the above solutions for these installation criteria. It shows that the basic, contactor-based starting methods are also the most cost effective and easier for maintenance; but from the previous table we can see that these also cause the most stress on the network and the load:

You can find more information about large motor starting in the PCIC Conference tutorial here.

Learn more about motor management here.

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  • Starting is more stressful than running of a motor. Particularly if the no of starts and stops are very high. Every start results in rotor temperature going up to 400°C. No two motors are alike and therefore motors have to be selected based on starting and applied without indiscriminately on to other loads.

    • Delcho Penkov

      5 years ago

      Hello Srinivasan, yes starting is stressful and thermal stress is important. In practice, starting solution has to be selected with respect to the thermal stress. Motor data is critical here and indeed, from one motor to another the locked rotor time can be quite different and impacts the selection of the starting solution. However, starting time and prospective heating are also impacted by the load, in terms of load torque and inertia. It means that the process of definition of the optimal solution has ideally to include the application, the motor and the starter in the iterations. As this is often concerning two or even three manufacturers, the approach is to preview some extra performance which to maintain multiple possibilities for starting.

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