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Motor Starting

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#1 electricalexpert65


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Posted 14 August 2010 - 08:04 AM

What is teh maximum permissible voltage drop at the three phase squirrel cage induction motor terminals during (a) Normal Running with full rated load and (cool.gif during acceleration? Can you also trace your answers to some National and/or International Standards?

#2 marke


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Posted 14 August 2010 - 10:19 PM

Hello electricalexpert65

The major consideration is usually the voltage during run as any continuous voltage drop is power loss.
Commonly in Australia and New Zealand, the standards call for a maximum of 5% but many target 2% voltage drop during run.

The major concern with voltage drop during start is the effect on other equipment.
Most equipment designed to operate on a 50Hz supply can tolerate a minimum voltage of Vnom - 15%.
If we allow for a 3% drop in the line voltage (bottom end of allowable supply voltage, then you would want to restrict the voltage drop during start to 12%.

Note most motors starters are of areduced voltage type so voltage drop during start does not hame a negative impact on the motor unless you require full DOL torque at start.

Best regards,

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