Star-Delta Starter: Open or Closed Transition? 2

[nightfox1925]

I went over the operation of these two starters and I find the closed transition starter to be better due to the elimination of switching transients. Are there any guidlines at hand available on when to apply either starters? Are there any recommended values of motor rating were either starters are effective and safe to apply?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[itsmoked]

Around here the general consensus is that open transitions cause more trouble then they're supposed to be preventing.

The time it takes them to transition is more than enough time for the motor, (with it's full magnetic fields intact), for the motors output to fall horribly out of phase with the power. When the close comes it's a 'crap shoot' as to whether the motor will be hooked up in phase, slightly out of phase or 180 degrees out of phase! Lots of problems are caused by open transition wye-delta starters. Most annoyingly you get this random aspect where 20 times things are fine then suddenly fuses are blown or other machinery on the network chokes, etc.

I think the general consensus is closed transition is excellent but a hassle and about the same price as a vastly more effective, flexible, and predictable soft starter these days.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[nightfox1925]

Thanks itsmoked, I will try to get pricing for closed transition star-delta against a softstarter? Do you have any recommended brands for s softstarter that provides an optimum price?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[itsmoked]

Wow.. As I see it the market is in great flux. Lots of buy-outs and consolidations and drop outs.

I have just been abused in this arena in the last two weeks.

I was looking for a 50hp SS. Prices range from $4.5k to $900 and everywhere in between. Essentially there are extremely robust units residing at the upper prices and rather more fragile units at the lower prices. It requires a little finesse to get the best solution.

If you are going to start essentially an unloaded motor, as was my case, and you aren't going to do it anymore often then 15 or 20 minutes you can go with the low end units.

In my case I'm starting the 50hp unit every few hours and the hydraulics are such that the driven pump with 2 inch pipe just returns directly to the tank during start up. No load. I also control the system so I can and MUST prevent loading of the motor before the SS completes. One screw-up and this cheap SS will likely toast. The customer is crazy, cheap, foolish, in this particular case.

Now if you're going to start something with say an inertial load the cheapest ain't gonna do it. You probably want a $2k ish model. The top end stuff often called "crusher duty" is for truly nasty loads where the motor has to start the load and the load will increase as the motor spools up like a rock crusher. Also if you have a light/no starting load but are going to be starting and stopping the motor frequently then again you want to head up the price curve.

You can Google or I guess the better thing these days is ask.com for VFDs and find quite a few online. You can find their prices too, often order them online.

What's your application?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[nightfox1925]

I have some fan motors for the boiler each rated around 75HP and 200HP. I have a lot of motors for the conveyor and cutter motors ranging from 30 up to 100HP for the Mill. We have initially though of making all motors greater than 15HP to be star-delta started since the distribution voltage being used for the small (3MW) plant is only 480VAC and to ease up system voltage drops whenever these motors are started.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[Walden]

As a matter of interest, how much are you out there paying for your closed transistion resistors? Here in the UK I have quotations from £275 to £321 for a three section resistor in a ventilated box suitable for 4 starts/hour for 2 seconds: motor current = 240A at 400V. Carriage costs extra.
Another motor at 760A = £476 same specification

 

[jraef]

General rules of thumb, which by the way support what has already been posted...

When to consider Open Transition: Only when the user is too cheap to do it right. It carries no advantage over any other form of reduced voltage starting other than price. In addition, as itsmoked said, the potential problems are typically worse than the cure.

When to consider Closed Transition: Only when the environment will allow its use (see below) and then only when the user is so backwards or afraid of technology as to insist on paying more for it than Solid State will cost. As a rule, even the heavier duty solid state starters are going to cost the same or less than a closed transition Y-D starter now. The move up from Open to Closed transition means adding another contactor, logic and most importantly, the transition resistors. These things all add to the cost and real estate, which takes away the only advantage Y-D starting has over solid state. In addition, the resistors will usually glow red hot during that transition time, making them unsuitable for inclusion into a sealed enclosure. Then if you mount them in an external cage, you must also be concerned as to potential ignition of flammable materials such as dust, lint etc. That's why you almost never see them used in sawmills or factories that work with fabrics, even non-classified areas of coal processing facilities.

Bottom line (exposing my prejudice here), there is no reason to specify either one. Use solid state or even Autotransformer if you must have bang-bang equipment.

As to brand of solid state starter, check with your local trusted sources. Any recommendation from us in this group is going to be biased by what we have experienced locally (or who signs our paychecks). But even if we recommend brand X over brand Y, but you have no local support for brand X, then it was not necessarily a good recommendation. A better way to do it is to see what you have available from trusted sources near you, then ask us for opinions on those choices.

 

[nightfox1925]

Thanks to all for your technical two cents. I already started contacting local distributors of Solid State Starters. As a matter of design improvement, I am recommending for a utility tie up with the plant and increased in-plant generation inorder to have a strong source wherein I will eventually end up reducing the nos of Solid State Starters.

I value your comments since it provides me the guidance and confidence on the technical approach I will decide on.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[jraef]

Point of order,
The best benefits of using reduced voltage starting are torque related, not just power supply related; i.e. allowing your machinery to last longer with less maintenance. Just because you increase your system capacity you should not automatically reduce the application of soft starters, they are going to save you more than their cost in the long run.

 

[nightfox1925]

Thanks to all for your comments and suggestions

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata