Hi,
I understand that by using a soft start on a slip ring motor, the lock rotor torque is very poor and this is not a convenient way to start high inertia load even by adding extra resistance to the rotor circuit. I have heard that some soft starters are able to produce 400-500 % starting torque. How far this is true ?
Regards.
Bob

Alternative To Liquid Starter
Started by bob, May 27 2008 07:27 AM
2 replies to this topic
#1
Posted 27 May 2008 - 07:27 AM
#2
Posted 27 May 2008 - 06:46 PM
Hello Bob
The major advantage of the secondary resistance starter, is that you can alter the slip of maximum torque by altering the rorotr resistance. By doing so in a number of steps, you can achieve a high torque from zero speed to full speed at a relatively low starting torque. With sufficient well placed steps, you can have in the order of 200% torque at less than 250% current right through to full speed.
The only other way that you can achieve this, is by using a shorted rotor and an appropriate variable frequency drive. Note: Most drives will not produce the high torque at less than 5 - 10 Hz!
If you use a soft starter and a single stage of resistance, you essentially make the slip ring motor emulate a standard cage motor and so you have a high start current for a nominal start torque, for example 400% current and perhaps 100% torque.
I do not know of any way that a soft starter can give you 400% start torque. This is higher than the motor will produce DOL or with a secondary resistance starter.
Best regards,
The major advantage of the secondary resistance starter, is that you can alter the slip of maximum torque by altering the rorotr resistance. By doing so in a number of steps, you can achieve a high torque from zero speed to full speed at a relatively low starting torque. With sufficient well placed steps, you can have in the order of 200% torque at less than 250% current right through to full speed.
The only other way that you can achieve this, is by using a shorted rotor and an appropriate variable frequency drive. Note: Most drives will not produce the high torque at less than 5 - 10 Hz!
If you use a soft starter and a single stage of resistance, you essentially make the slip ring motor emulate a standard cage motor and so you have a high start current for a nominal start torque, for example 400% current and perhaps 100% torque.
I do not know of any way that a soft starter can give you 400% start torque. This is higher than the motor will produce DOL or with a secondary resistance starter.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#3
Posted 29 May 2008 - 09:40 AM
Thanks Mark. This subject is very well explained in the soft starter topic on your site.
Kind regards.
Bob
Kind regards.
Bob
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