Starting a used 22KW motor

[Phreezzz]

Hi
I recently purchased an industrial blower (Roots) with a 22KW motor. I am located in a 415v 50 Hz territory.
No control system came with this purchase (OK, it was cheap) and I have a set of six labelled wires from the motor.

Cost of a new star delta starter is greater than I paid for the entire package, and needless to say hurts to have to fork out this much money.
I have found a 60KW starter used for military systems, but it is 60Hz. (Made by Whippell Electrical, England).
Would this device operate on 50Hz? I imagine only the contactors may be problematic, perhaps not have the full pulling power?

Another option I am considering is building a star delta starter from the various components. However this may prove even more costly. I noted another thread on this forum (back in 2004) that had links to various starter schematics.
One of these was for a two speed controller for a 3 phase motor. In effect, and as far as I can see, this is a star delta starter without the time controlled relay. In other words, low speed is the soft start position and high speed switches over to the full load position.

Is my assessment correct? Would a low high speed controller be in effect a 'manual' star delta starter, costing less as I no longer need the time controlled relay and providing me with a low speed motor option?

Apologies if either of above questions have been asked and answered before, but I have searched this forum before posting
Thanks in advance

Phil

 

[ScottyUK]

Why do you want a star-delta starter on such a small motor? You are likely to get better performance and have more money left in your wallet if you use a soft starter. There are numerous suppliers at this power level. If you actually want variable speed instead of just a soft start, consider a VSD instead.

If you are in the UK then there is a tax break which allows you to offset the capital investment on energy-saving plant against your company taxes. A fan with a VSD would almost certainly qualify if you can trun it at a reduced speed and load. The initiative is known as the ECA. Google finds a lot of hits, but this one is from the UK Government:

http://www.eca.gov.uk/

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Sometimes I only open my mouth to swap feet...

 

[Phreezzz]

Hi Scotty
Yes, I am in the UK, and thanks for your advice. The only reason I am looking for a star delta starter was because that we suggested to me by local electical engineer!
We are an RnD company and will not be running this thing on continuous basis, but will be starting and stopping quite a bit. Reducing this load will be good, thanks for the tax break links, will follow that up too.
I have little knowledge of the VSD option, but variable speed would be a great advantage. I presume this is a frequency converter of sorts? Sounds expensive! Any idea where to look for good prices or should I Google it?

Thanks again
Phil

 

[ScottyUK]

Yes, the VSD is a frequency converter which converts the fixed frequency fixed volatge mains into a variable voltage, variable frequency output to the motor. A 22kW drive will set you back about £2000, plus installation if you can't do it in-house. I'm not sure how much of that you can offset against tax, but the economics might get more attractive if our beloved Chancellor was feeling benevolent. A soft starter will cost about £200 - £300 plus an enclosure of some description but won't give you variable speed.

Since it is a fan application you might want to check out some of the Nola-type energy saving devices. In the right application they can save energy and give you a soft start from the same unit. I'm not an expert on these things but there are a couple of guys in the US who are just waking up about now and they know them inside out.

Does the fan have a very heavy rotor? The long acceleration time which is associated with a high inertia load can make things tough for a direct-on-line starter. The soft starter is well suited to this kind of application.

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Sometimes I only open my mouth to swap feet...

 

[Phreezzz]

Scotty
This motor drivers a blower, not a fan. A blower is positive displacement and unlike a fan, does not store so much energy in the form of angular momentum. Start up time of the blower is relatively short. it can also be started off load, ie with blower ducts open.
I have found one GE soft starter for a tad under £500, and several others up to £1000 but nothing so far as low as you indicate. Will continue looking
As an RnD company, to be able to adjust the motor speed would be a plus, we can better control th eariflow under differing conditions, so I will hunt for one of these guys, see what the price difference is compared to a soft starter.
Thanks for your help, if you can suggest a cheap source, dont hesitate to let me know
Phil

 

[ScottyUK]

Phil,

Something like RS part no 539-0156 has more than adequate capacity unless you have a really heavy rotor. It needs an enclosure and some form of circuit protection to finish it off. I know for sure that most wholesalers will undercut the RS price by a fair margin. Do you have anything on your machine which you can reuse, e.g. main circuit breaker, enclosure, etc? I guess you are working to a budget if you are in R&D!


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Sometimes I only open my mouth to swap feet...

 

[jraef]

OK, Scotty's right, I just woke up

A Roots blower takes a lot of torque to accelerate, I doubt that a star-delta would have worked for you anyway. You will likely need a soft starter capable of at least 400% current for 30 seconds. My experience with them is that anything less than 350% current will stall. For comparison, a star-delta starter would provide the equivalent of 200% current, so the motor would not fully accelerate in star, which means when you switch to delta it would be no different than starting DOL, maybe even worse! The problem with a soft starter or star-delta or any other form of reduced voltage start is that you will be limited in the number of starts the motor can handle in a given period, maybe as low as 1 or 2 per hour (depending on a lot of factors). Forget the "Nola energy saver" soft starters by the way, they will NOT save appreciable energy on a Roots blower.

I like the idea of a VFD as well, it will be capable of starting the motor with little thermal stress, so you can start and stop it as many times as you like if necessary. This may actually save you a lot more energy cost in the long run because if you had to leave it running longer due to limited starts-per-hour, you are wasting a lot of energy. There are a few things to think about on using a VFD however:

1) You will need to be aware of what the minimum speed you can run that blower is. Some have mechanical lubrication and if you go too slow, you lose it.

2) Because of the high starting torque requirements I suggest a "vector" drive (although most are providing that as standard now anyway). Open Loop (sensorless) vector would be fine.

3) Make sure you buy what is called a "constant torque" rated drive. Some ignorant vendors (and they are out there) will hear the word blower and try to sell you a variable torque rated drive. This is NOT a variable torque load.

A VFD will likely be 3-5 times the cost of a soft starter in that size range, but I seriously recommend it if variable speed has any value to you, I doubt you will regret it. Remember, going too cheap can ultimately be the most expensive option!

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[MikeHalloran]

Of course you'll put the blower in a sturdy outbuilding with noise suppressing ventilation louvers...

... or go deaf.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

V e r y d e a f..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Phreezzz]

OK, now you have all given me plenty to think about
Question, what if the roots blower is not working into a load on startup, ie, free input and output port
Once the motor has started, then load is applied
We used to run a 1000 CFM compressor at 150 psi, diesel engine, a Detroit, for our experimental work, however we never required more than 10 psi, it was CFM we were wanting
So the decision was made to go electric, go blower!
This will put out some 600 + CFM, but as for noise, I think this may be quiet compared to what we are used to?

What is it that limits the number of starts per hour, temperature rise? Of what?
What about a manual system (with contactors) two speed, low in star, high in delta?
If I read your comments correctly, the mismatch between blower and motor may be too far out for this setup
Lubrication of blower is important, I have the operating range of rpm, so cannot go too low in rpm

Variable speed is not so important, we can change gearing motor to blower quite easily!

Any more comments and ideas are very welcome

Thanks

 

[MikeHalloran]

I think later Detroit two-cycle Diesels have spiraled vanes on their Roots blowers. If the vanes on your blower are straight, as I suspect they are, it will make more noise than the Detroit ever could.






Mike Halloran
Pembroke Pines, FL, USA

 

[Phreezzz]

Someone better point me to the sound proof enclosure forum

 

[Phreezzz]

Anyone know anything about the Ralspeed soft starters
Tracked one down for my 22 KW motor for £100
Sounds a good deal if it is a good brand?

 

[itsmoked]

Skip the low in star high in delta thought. Bury it deep.

On a roots I believe the open exhaust does drop the load significantly. On a centrifugal the opposite is true.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Keith is right, opening the exhaust on a PD blower like a Roots does not help much, most of the starting torque requirement is to overcome inertia from the mass of the rotors and friction in the gearbox(es).

The starts-per-hour limitation comes from the rotor having to dissipate the heat from high starting current. Unlike the stator which has fins and maybe fans, the rotor can only dissipate through the shaft, and that takes time.

I have no direct experience with RalSpeed, they don't export to the US (415V max). Looking at the on-line specs for the Torq-Master it seems a decent product, no apparent deficiencies. But do NOT buy the "Versistart" or "DuoStart" products. They are 2-phase starters, meaning they only control 2 of the 3 phases, the 3rd is DOL all the time (even when off). This could be disastrous for your application.

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Phreezzz]

Thanks everyone for your excellent comments. I now have enough advise make an informed purchase and hopefully respolve my problem.
Additionally thanks for the warnings in relation to specific brands.
The last post referred me to an FAQ that details code of conduct, this I have re read. I am concerned that in some way this post breached one of the codes indicated in this FAQ, although I fail to see where this took place.
Please advise to avoid future mistakes

 

[itsmoked]

No it did not. Rest easy and good luck with your project.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Phreezzz,
LOL. At first I re-read all of the policies to try and figure out which one you thought you had violated, then I realized; you though that tag at the end of my post was directed at you!

Sorry for the misunderstanding. That is just a "signature line" added to the end of all of my postings (unless I un-click the box for it). Nothing personal, it just serves mainly as a warning to students who try to get homework answers by posting them here. The more you browse postings here, the more you will see this FAQ on sig-lines. I added that at a time when I was seeing a lot of student posting attempts and I would actually try to help them to understand why their posts were being deleted. They would get snotty with me because they never read the rules and thought I was being arbitrary. Now I just ignore and Red Flag them like everyone else does, so it''s probably time to change my sig-line.

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[itsmoked]

Yeah jraef.. "Electronics is my game - sausage is my gain."

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

LOL, you meant salami I suppose?


JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376