4160 soft starting

[greco]

Hello everyone,

I would like to know if there is a majority use of soft starters for 900HP 4160V induction motors or across the line. When I first saw they want to start 900Hp across the lin I may have jumped to a conclusion that you can't do that but as the 4160 fact set in I started rethinking. I have been researching but have not seen anything that looks like a clear cut best practice.
I do realize that our infrastructure will determine what we need to do ( plus the utility will have something to say ) but it has me wondering if across the line is common for this size and voltage. We are in town with malls, hospitals, residential nearby. I am assuming our utility will want some form of controlled start but maybe I am off base. Any inputs or experiance would be great.

greco

 

[kingpb]

900Hp @ 4160V; across the line starting is very common. If this is being added to a existing system, then you need to do a little up front analysis to make sure it won't be an issue when it starts.

Static motor starting analysis should suffice, unless that analysis determines there may be a problem, than transient analysis may be required.

 

[Jraef]

Hello everyone,

I would like to know if there is a majority use of soft starters for 900HP 4160V induction motors or across the line. When I first saw they want to start 900Hp across the lin I may have jumped to a conclusion that you can't do that but as the 4160 fact set in I started rethinking. I have been researching but have not seen anything that looks like a clear cut best practice.
I do realize that our infrastructure will determine what we need to do ( plus the utility will have something to say ) but it has me wondering if across the line is common for this size and voltage. We are in town with malls, hospitals, residential nearby. I am assuming our utility will want some form of controlled start but maybe I am off base. Any inputs or experiance would be great.

greco

From an electrical/voltage drop perspective, you may not find a clear cut best practice because the ONLY reason to do this from that electrical standpoint is if the utility (or your own generator) restricts you on starting power and/or voltage drop. That often comes down to a simplified formula that is something like max. kVA per HP (or kw) before requiring some sort of RV starting, or a simplified limit to the VD it will cause, then it's up to you to figure out how to get there. Then from there, you often have a variance process by which you can argue that you do not need it because of how seldom it will be starting, blah blah blah...

However from a MECHANICAL perspective, soft starting is always going to allow your machinery to last longer by avoiding torque shock, torsional and lateral stresses on drive train components, belt slipping and damage, water hammer in the case of pumps, blade warping in the case of fans and in many cases product damage from jerking. Most people who buy MV soft starters do so more for those reasons.

 

[templdl]

From an electrical/voltage drop perspective, you may not find a clear cut best practice because the ONLY reason to do this from that electrical standpoint is if the utility (or your own generator) restricts you on starting power and/or voltage drop. That often comes down to a simplified formula that is something like max. kVA per HP (or kw) before requiring some sort of RV starting, or a simplified limit to the VD it will cause, then it's up to you to figure out how to get there. Then from there, you often have a variance process by which you can argue that you do not need it because of how seldom it will be starting, blah blah blah...

However from a MECHANICAL perspective, soft starting is always going to allow your machinery to last longer by avoiding torque shock, torsional and lateral stresses on drive train components, belt slipping and damage, water hammer in the case of pumps, blade warping in the case of fans and in many cases product damage from jerking. Most people who buy MV soft starters do so more for those reasons.

Oh how this subject brings back some very painful memories before they had a SS means to start medium voltage motors.
The very first medium voltage motor that I had sold was a 2300v 800hp wound rotor motor for a cheese factory way back in 1982. The POCOnsaid that it was imperative that the voltage sag be kept within a give percentage when starting the motor. Thus using a wound rotor motors an controlling the resistance applied to the rotor while starting the motor controller the starting current by using a stepping resist bank. My engineer Larry, did a most awesome job of engineering the stepping resistors while my motor designers not so hot.
It was an awesome ODP motor base upon a 4p motor but the designer used TENV enclosure to house the collector rings and brushes and that's where my education began. Carbon dust from the brushes that build up in the TENV enclosure caused arcing to issue between the rings. By default I then learned that there were countless grades of carbon brushes and much, much more. My engineering service in their infinite wisdom decided that simply removing the resistors and brushes the jumpering the rings the could start the the motor that way. But I think that they forgot their motor basics and the motor did not have any starting torque. This was onle part of the story. This motor had to be removed and installed through the roof with a crane. My company must was lost more money than the motor was with.