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3 comments
Anonymous Poster

Liquid Rotor Starter

08/20/2007 5:22 AM

what is liquid rotor starter?

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Anonymous Poster
#1

Re: liquid rotor starter

08/20/2007 5:24 AM
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Associate
New Zealand - Member - New Member

Join Date: Aug 2007
Location: Christchurch, New Zealand
Posts: 38
Good Answers: 1
#2

Re: Liquid Rotor Starter

08/21/2007 3:01 AM

A variant of the induction motor, is the slip ring, or wound rotor motor.

The induction motor has a "squirrel cage" rotor which is in effect a short circuited winding in the rotor. The start and run characteristics are influenced by the resistance and inductance of the rotor circuit. One of the problems of the induction motor, is that the start current is very high (600 - 900%) and the start torque is relatively low (120 - 200%) compared to the start current drawn. The induction motor has a speed at which maximum torque is produced and this is very close to full speed.

By altering the resistance in the rotor design, we can alter the speed at which maximum torque is produced. Below this speed, the current goes high and the torque goes down. Above this speed, the current drops with the torque.

The wound rotor motor, has a winding on the rotor that is not short circuited, but is brought out to slip rings. This enables the effective rotor resistance to be altered.

By varying the rotor resistance while the motor starts, we can cause the speed of maximum torque to shift from zero speed up to very close to full speed in a number of steps. The big advantage of this, is that the motor is able to provide a high start torque (around 200%) and a low start current (around 200%) from zero speed to full speed. This is very god for starting high inertia and difficult start loads on relatively weak supplies.

The rotor resistors can be cast resistors, wound resistors, or liquid resistors. With standard resistors, the stages are switched in and out by contactors to alter the resistance. With liquid resistors, the resistance can be varied by varying the immersion of probes in the electrolyte. This can be achieved by raising and lowering the probes, or the liquid level.

Best regards,

Mark Empson

http://www.LMPhotonics.com | http://www.LMPForum.com

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Anonymous Poster
#3
In reply to #2

Re: Liquid Rotor Starter

04/17/2009 12:45 PM

Thank you! This has been useful for me too. Mamadi VSD commissioning Engineer

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