soft starter

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sukumar75 Associate Join Date: Oct 2009 Posts: 26 Good Answers: 1	soft starter 10/19/2009 1:04 AM
	How many times more current will take the ind. motor while starting through soft starter
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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 804	#1 Re: soft starter 10/19/2009 1:51 AM
	As much as it takes to accelerate. I don't mean to be sarcastic, but there really is no good answer to that question without knowing a lot of details and preforming a complex tansient motor starting analysis. A motor provides two types of torque: Accelerating torque and Load torque. When a motor s at a dead stop, you need to provide BOTH the Accelerating torque and the Load torque, then after the load is a full speed, you only need to provide the Load torque. In some types of loads, for example centrifugal pumps and fans, the load torque starts off very low and increases only as the motor speed increases. In high inertia loads, such as machinery with large flywheel masses like a rock crusher, a great amount of the Load torque is present at the very outset. So without knowing all the details of the load, the power system supplying it and how much voltage drop you are willing to live with, there is no way to know what the starting current will be in advance. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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Current Maarey Power-User Join Date: Aug 2008 Location: East Posts: 117 Good Answers: 6	#2 Re: soft starter 10/20/2009 1:57 AM
	It all depends upon the system capabilities being used for feeding the motor. Additionally you need to keep in mind that you are able to accelerate the driven equipment with the soft started condition. __________________ Atlas Shrugged - JGD
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electricalexpert65 Guru Join Date: Oct 2009 Posts: 2061 Good Answers: 169	#3 Re: soft starter 10/20/2009 7:15 AM
	As much minimum as to enable the motor to accelerate the load. A soft starter is used for reducing the starting current. Right? So, one would like to set the starting current to the barest minimum possible. Say, only 100% of the rated motor current. But, a soft starter too is only a reduced voltage starter and if the starting current is kept very low, then only a very low starting voltage is applied to the motor. As starting torque is proportional to the square of the applied voltage, the motor would not be able to develop sufficient starting torque or accelerating torque. More problem, if the connected mechanical load is of a high inertia type, like a blower or a fan. So, to enable the motor to develop sufficient starting torque, a certain minimum voltage has to be applied. And, this will decide the magnitude of the starting current. I have commissioned certain applications where even a starting current as low as 150% of the motor rated current was possible.
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sukumar75 Associate Join Date: Oct 2009 Posts: 26 Good Answers: 1	#4 In reply to #3 Re: soft starter 10/22/2009 3:55 AM
	Thak you so much, exactly I want to know this one only
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