SOFT STARTERS

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hawkeye23

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Are soft starters starting pattern ajustable or is it setup already before being puting in service ? I was ask once if the starting up speed was able to be changed and could not answer that question. I think it was about slowing down the startup current the motor pulled. They were siemans for [10hp 3 phase 480v motors ]that are not available anymore they did have some adjustable points but did not have any paper work to know what they were for.
Can someone with experience in this area answer this question. Thanks for the help .
 
hawkeye23 said:
Are soft starters starting pattern ajustable or is it setup already before being puting in service ? I was ask once if the starting up speed was able to be changed and could not answer that question. I think it was about slowing down the startup current the motor pulled. They were siemans for [10hp 3 phase 480v motors ]that are not available anymore they did have some adjustable points but did not have any paper work to know what they were for.
Can someone with experience in this area answer this question. Thanks for the help .
Click to expand...

Soft starters don't control speed, the ONLY thing they can actually control is the RMS voltage getting to the motor, from zero to 100%. Using voltage control, they can AFFECT the TORQUE getting to the motor and thus the acceleration time plus with proper feedback, they can be used to control current during acceleration, but that is all.

If it's a Siemens soft starter that's no longer available, it's probably a 3RW34 series, at 10HP, maybe a 3RW30 or 31. The 30s and 31s were basic voltage ramp starters, the 34s also included current limit. Your adjustments were usually Initial Torque (or Voltage) which for the Germans is abbreviated with a "U", Ramp Time, abbreviated with a "T" and if a 34, Current Limit, abbreviated with an "I". So to set it up, you start with the Initial Voltage set as low as possible, give it a Run signal and raise the setting until the motor just starts to turn. That gives you the softest starting without wasting time doing nothing but heating up the windings. Then see if it accelerates and if it seems smooth. If it is, leave it alone. If you need to keep the current lower (the factory default on the 34s was I think 300%) then turn it down, but know that it may stall. if it doesn't seem to accelerate fast enough, raise the current limit setting. If it's a 30/31, all you can play with is the ramp time to affect the acceleration; shorter time means higher current and vice versa.

Be careful by the way, those older units did NOT have Motor Overload Protection built-in, you are supposed to use an external OL relay.
 
Jraef said:
Soft starters don't control speed, the ONLY thing they can actually control is the RMS voltage getting to the motor, from zero to 100%. Using voltage control, they can AFFECT the TORQUE getting to the motor and thus the acceleration time plus with proper feedback, they can be used to control current during acceleration, but that is all.
Click to expand...
By the expression "starting up speed" maybe hawkeye23 meant the speed at which it is starting up i.e. acceleration?
 
Jraef said:
Soft starters don't control speed, the ONLY thing they can actually control is the RMS voltage getting to the motor, from zero to 100%. Using voltage control, they can AFFECT the TORQUE getting to the motor and thus the acceleration time plus with proper feedback, they can be used to control current during acceleration, but that is all.

If it's a Siemens soft starter that's no longer available, it's probably a 3RW34 series, at 10HP, maybe a 3RW30 or 31. The 30s and 31s were basic voltage ramp starters, the 34s also included current limit. Your adjustments were usually Initial Torque (or Voltage) which for the Germans is abbreviated with a "U", Ramp Time, abbreviated with a "T" and if a 34, Current Limit, abbreviated with an "I". So to set it up, you start with the Initial Voltage set as low as possible, give it a Run signal and raise the setting until the motor just starts to turn. That gives you the softest starting without wasting time doing nothing but heating up the windings. Then see if it accelerates and if it seems smooth. If it is, leave it alone. If you need to keep the current lower (the factory default on the 34s was I think 300%) then turn it down, but know that it may stall. if it doesn't seem to accelerate fast enough, raise the current limit setting. If it's a 30/31, all you can play with is the ramp time to affect the acceleration; shorter time means higher current and vice versa.

Be careful by the way, those older units did NOT have Motor Overload Protection built-in, you are supposed to use an external OL relay.
Click to expand...

Allen Bradley SMC-2 has the following programming option available:

Preset Slow Speed Option
The Preset Slow Speed option can be used on applications that require
a slow speed for positioning material. The Preset Slow Speed can be
set for either Low, 7% of base speed, or High, 15% of base speed.
Reversing is also possible through programming. Speeds provided
during reverse operation are Low, 10% of base speed, or High, 20%
of base speed.
 
weressl said:
Allen Bradley SMC-2 has the following programming option available:

Preset Slow Speed Option
The Preset Slow Speed option can be used on applications that require
a slow speed for positioning material. The Preset Slow Speed can be
set for either Low, 7% of base speed, or High, 15% of base speed.
Reversing is also possible through programming. Speeds provided
during reverse operation are Low, 10% of base speed, or High, 20%
of base speed.
Click to expand...
Yeah, but that's sort of an anomaly in the soft starter world. What they (we) do on that is to create a quasi cycloconverter where it is pulsing a series of phase angle fired sequences in such a way as to make an equivalent lower frequency than the fundamental, similar to the way a zero-cross variable time base SCR heating controller works. That's why the speed values are fixed, there are only so many combinations of pulses that will work effectively and you cannot do that to the motor for very long.
 
I like to say thanks to you guys for the help with this soft starter setup question , they were very helpfull.
After seeing those siemen 3rw numbers they appear to be right on . We are using these for 3phase 480v 7.5 and 10hp sump pump motors which we had in stock now we have none . We also used the thermal unit built into the motors for the protection .
All the infomation on the 3rw will be very helpful in checking for the best setup for this appl.
Thanks again.
 
hawkeye23 said:
I like to say thanks to you guys for the help with this soft starter setup question , they were very helpfull.
After seeing those siemen 3rw numbers they appear to be right on . We are using these for 3phase 480v 7.5 and 10hp sump pump motors which we had in stock now we have none . We also used the thermal unit built into the motors for the protection .
All the infomation on the 3rw will be very helpful in checking for the best setup for this appl.
Thanks again.
Click to expand...

Ah, a centrifugal pump. The interesting thing about this type of pump is that it doesn't start to pump until about 70% of the RPM as I understand. One application that I can remember is to a water hammering issue where when the pump did start to pump it causes water hammer. One answer was to uses a VFD to control acceleration, On of my OEMs though if he could control a one of my soft stars to ramp the voltage at the time the pump started to actually pump he could cause the motor to slip up to full RPM thus accelerating the pump much slower.
The thing about an induction motor is it tries to reach its synchronous speed regardless of the voltage that is applied because the voltage is based upon t 60hz. As such a motor would accelerate very quickly until with a centrifugal pump until resistance was reached at the point where it started to pump water. It is at that point where the start starts ability to control that would cause the motor to slip gradually ramping the voltage/current up to the point where the motor accelerated to full speed.
All my OM did was to customize the soft start control to provide the control that was need for his pumps.
It worked flawlessly.
 
JoeStillman said:
Soft starters for 7.5 and 10 Hp at 480V seems like overkill to me. Is there a reason why you don't just start these across-the-line?
Click to expand...

There may not be much benefit when it comes to effects on the source, but there could be many benefits to the driven load.
 
I am just maintaining the sump pumps , I did not design the setup. But I think they did the right thing with a soft starters. They are started by floats , which is often.
 
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