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Old October 21st, 2018, 12:05 PM   #1
roxusa
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Star-Delta Starter

Without going into a lot of detail, 150 hp motor with a Star/Delta Start how much time on Star before switching to Delta. This is a compressor, I google it says as much time is needed to come up to full speed. I don't know what that would be. Is there a generic value.
Thanks
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Old October 21st, 2018, 12:31 PM   #2
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Quote:
Originally Posted by roxusa View Post
Without going into a lot of detail, 150 hp motor with a Star/Delta Start how much time on Star before switching to Delta. This is a compressor, I google it says as much time is needed to come up to full speed. I don't know what that would be. Is there a generic value.
Thanks
It is load dependent, so there is no "standard" time value that we can tell you. The critical issue is that the motor must get to 90% speed or greater before you transition, otherwise your motor will slow down during the open transition enough to be out of sync with the line frequency when it reconnects in delta, which can result in a very dangerous spike in current and torque, sometimes strong enough to twist the shaft off of the motor (I've seen that happen several times). That's why I never use Star-Delta any more, I always use Solid State Soft Starters now, they are almost the same cost and have none of those issues.


the alternative to having that torque / current spike issue is to use a Closed Transition Star-Delta starter, but that adds a 4th contactor and a resistor bank, so it ALWAYS ends up more expensive than a SS starter.
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Old October 21st, 2018, 12:51 PM   #3
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I have a 150 hp Atlas Copco we got from one of our plants closing, We put it in as a back up to our 200 hp. I replaced the Elektronikon® controller and had OEM go over unit. It worked fine and is a very clean looking unit for 2001 model. We never really ran much since 150hp barely makes it (need to fix a lot of pant air issues) needless to say after about 2 years only running a dozen times or so the Elektronikon® controller module failed again and OEM said replace again $$ . We just left it. I am playing with the Idea of a PLC & HMI and see it is Star Delta start. Our 200hp is just a big starter.
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Old October 21st, 2018, 12:58 PM   #4
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In going over the Schematic for the unit, more of a line diagram, I don't see any way they determine they are up to speed to change to Delta. They are only monitoring Pressure and temperature.
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Old October 21st, 2018, 01:05 PM   #5
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What would you recommend replacing this with. You mentioned soft start, would that incorporate easily, there is room in panel. Would that be more to control or work like a normal starter, curious I never worked with one.
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Old October 21st, 2018, 01:13 PM   #6
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We run three Atlas compressors at 600psi in our industry. Have upgraded two of them to ABB soft starters and have been running well. We contacted an ABB rep for recommendation. There not much different to wire up than a regular starter. If ethernet is ran to it, can pull quite a bit of data from it also.
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Old October 21st, 2018, 01:22 PM   #7
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Thanks, Ill look into the soft start option and do some more research, have enough $ invested in putting unit in and is a waist to not have running. No one cares until the day the 200hp fails.
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Old October 21st, 2018, 08:58 PM   #8
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+1 for Soft Starter. Solid State Starters are the way to go, if you are not going variable speed. Just make sure you size it for Heavy Duty (450% starting current minimum), or you could be in trouble with a newer 'High Efficiency' motor. The current/torque ratio is much higher on the newer motors, until you get up over the hump.
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Old October 22nd, 2018, 07:41 AM   #9
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Dependent on the compressor, maybe a VFD would be more suitable.

Could be used to save energy when the plant isn't using as much air.
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Old October 22nd, 2018, 07:56 AM   #10
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I looked at cost and don't think it would be approved since machine is not utilized only a back up that has been off line 2 years. Would be a big savings if the Main 200 hp was VFD
since it runs 24/6
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Old October 22nd, 2018, 08:45 AM   #11
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Then a Softstart would be the way to go.

As already stated earlier, make sure you get one the correct size, and rated for heavy duty.

Also be aware that when starting the SS will give off a decent amount of heat. Providing the cabinet it is installed in is big enough this shouldn't be a problem. However if it's cramped or has other items that give off a lot of heat, some form of forced cooling (fans and filters would be cheapest) is something you should look into.
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Old October 22nd, 2018, 08:55 AM   #12
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I am looking into the SS, not being a motor guy I will contact my local motor shop to see how this would apply to my motor and what the wiring would consist of. There looks to be ample space in the enclosure (not knowing the dimensions of SS) and it could easily be ventilated or fan cooled if needed. Thanks for the input.
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Old October 22nd, 2018, 12:24 PM   #13
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Just an update-OEM has the "Motor running time on Star" Factory set at 10 seconds with it adjustable from 10-20 seconds.
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Old October 22nd, 2018, 02:11 PM   #14
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If you have a clamp meter, turn the star timer up to max.

Measure current drawn when starting and set a stop watch, once it settles (fans run up to speed) stop the watch. This is what you should set the time too.

Too short a time is just as bad as too long a time on an open transition SD starter.
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Old October 22nd, 2018, 02:28 PM   #15
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Thank you That is what I needed
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