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Soft starter selection

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#1 Guest__*

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Posted 28 January 2005 - 07:02 AM

Sir , i hv to select the soft starter for 500kw SQCAGE Induction motor of 400 volts Ac 3 pH, 920 Amps Full load current please give me uour suggession.

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Posted 30 January 2005 - 11:28 PM

Hello anonymous,

Before any advice can be given, you need to state what the application is, eg. pump, fan, compressor, conveyor etc etc.


#3 marke


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Posted 31 January 2005 - 06:00 PM

Soft starters are given a number of different ratings by different manufacturers. At this stage, there is no real consistancy.
Some manufacturers rate for heavy duty starts as standard and you can use their ratings on almost any application, while others rate for very light duty starts and you need to goo to larger model sizes for heavier duty starts. This enables them to supply a lower cost starter for easy start applications such as pumping.

To select a starter for an application, you need to determine the functionality that you require, and there is a vast range of offerings, and you need to determine the starting duty.

The driven load determines the required start torque and start time. A High inertia load is going to require quite a lot of torque for a long time to get to full speed.
The motor design then determines the starting current to develop that torque and there are big variations in motor starting characteristics.
There are pages on this web site going into more detail on this.
Once you have determined the start current and time, you can select a starter for that duty, or, you can select a heavy duty rated starter for any application. The only disadvantage with using the heavy duty rating under all conditions, is the cost. It will have larger SCRs and heatsinks and will cost more.

If you provide us with more details of the driven load, we can make better suggestions.

Best regards,

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