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In Words How Does Starting Of Induction Motor Cause Voltage Dip?


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#1 mithu

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Posted 24 January 2011 - 01:34 AM

Please explain how induction motors cause voltage sag when they start up, refering to their equivalent circuit!

#2 AB2005

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Posted 24 January 2011 - 07:37 AM

QUOTE (mithu @ Jan 24 2011, 06:34 AM) <{POST_SNAPBACK}>
Please explain how induction motors cause voltage sag when they start up, refering to their equivalent circuit!


When we start induction motor via DOL starter from steady state condition, it draws 600-800% current for a moment. If motor is large and the power distribution system (transformer, cables from traffo to distribution board, bus bars) is weak, then voltage dip problem occurs. Only one way to remove this voltage dip is to install VFD or soft starter to accelearte the motor. other way is to use Star Delta starter which also reduces the starting current by the factor of 1/1.73.

"Don't assume any thing, always check/ask and clear yourself".

#3 johnbose

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Posted 05 March 2011 - 11:13 AM

Any Motor is effectively a load with R&L components. Till back EMF develop it offer a very low pf load drawing 500% to 800% of the normal operating current. The IZ( Impedence ) drop in the circuit ( bus, cables etc till motor)cause the large voltage to dip unless the network is sized enough to reduce this. Or as indicted before limit the starting current using special starter.




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