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Motor Starter For Drives With Different Rating


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I have a storm tank mixer with a 9.5KW starter - star delta and I intend to change these to 11.8KW drives - soft starts. But by my programme, I have to install the new drives before receiving the a new starter. I am considering using the 9.5KW star delta starter to run the new drives pending a later date when I receive a new 11.8KW soft starts.


What can I do to achieve this? i.e can I run the drives using the star delta configuration? Will I need to modify the starter capacity to be able to start the 11.9KW drives? Will this have any particular effect on the drive or the supply.


I will be glad to learn from the expertise of members.

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The life expectancy of the contactors is a thermal problem.

If you overload the contactors, the temperature of the contact surfaces will increase and the life will be shortened.

The important factor to look at is the AC3 current rating of the contactors compared with the current being controlled. Some manufacturers will give the number of operations expected with different AC3 current ratings.

If the starter is operated frequently, it will have higher contact temperatures than if if operates very infrequently.

The temperature rise for a given operation, is proportional to the square of the current so a ten percent current rise leads to a 20% temperature rise.


Check the AC3 current rating of the contactors and compare this with the motor ratings. NB with a star delta starter, the main and delta contactors only see 57% of the motor rating and the star contactor is rated at 33% of the motor rating.


Best regards,

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