Star or Delta for Differing Motor Pump Requirements 3

[JohnnyHS]

Hi Guys,

i am a little green with regard to the motors and the connection required to work them efficiently and correctly. I had a question to my supplier as to why the motor they supplied me was wired star as opposed to delta.

I got this reply from my questions. Can anyone eleborate as to why 63 frame up to 112 frame is 230v – Delta and 400v – Star. Above this frame size the voltage then is 400v – Delta and 690v – Star?

Sorry for the large amount of text but its best to give the whole picture!!


ME
Another question regarding the 3 motors now for the pumps you supplied to us on this order. The windings were in star or wye configuration. For this application can you confirm why these weren’t delta? Just out of interest as they work (well ones been tested so far) fine

SUPPLIER
Working against your PO 16917 these motors would be 230v Delta or 415v in Star.

ME
Can you confirm why these were 415V Star and not Delta then.

SUPPLIER
Why, did you want 415 Delta? 415v Delta in this frame size would be a special voltage, and need to be rewound specially.

ME
Having only dealt briefly with motor windings (usually I just like the plug it in and play in a complete system!) the question has been posed by the customer and I was hoping you would justify the star configuration for me with some technical justification/information to back it up.

SUPPLIER
The standard is 63 frame up to 112 frame is 230v – Delta and 400v – Star. Above this frame size the voltage then is 400v – Delta and 690v – Star.
This is due to the kW of the motors and the power required to run them.

The only real contentious issue is that some motor suppliers make the voltage change on 100/112 frame sizes, others 132 and a few 160 frames.

As you motors were 63 framed this is at the lowest end possible.

More the question, what voltage did you want to run them in?

ME
415V was the voltage we are running them on.

So the star or delta connection choice is done from the frame size?

SUPPLIER
Yes, and frame size is determined by power and speed, i.e. the larger kW of the motor the larger the frame.

So guys

Thanks for any help received! Laymans terms reply please LOL



Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[itsmoked]

As the supplier stated the more the power requirement,(bigger frame), the higher the voltage normally desired. As the voltage increases the current decreases. This reduced current allows more easily installed wiring,(less expensive), and more importantly, much less expensive protection devices like circuit breakers. Note that circuit breaker prices go up almost exponentially with current rating in the larger sizes.

Because of the way motors are designed and built it is fairly easy for the maker to design them to be run in two standard voltage situations. This allows them to use one design for two different customer groups.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I thought that your supplier explained the issue very well. What more do you want?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[EdDanzer]

I think the reason for the connection difference between Star and Delta is because Delta will have one leg that is high to ground. Most adjustable speed drives will not work on Delta 3 phase. I cost me over $30,000.00 to find this out.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[waross]

You are talking about the fairly rarely used corner grounded delta transformer bank, Ed D. This has nothing to do with start (wye) or delta connections in motors.
6 lead motors and 12 lead motors may be connected in either delta or star with no ill effects. The choice in connections is so that the motor may be used on either of two voltages. The ratio of the two allowable voltages is 1:1.73 (root 3)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JohnnyHS]

ok firstly, thanks for your replies guys.

I usually integrate these pumps within systems so i'll give the details of my requirements. dp required, flow rate required etc and the pump/motor specialist will (hopefully!!) supply the correct motor and pump for the system with the wiring connections supplied so forgive me i am inexperienced with the electrical hook up of motors.

Itsmoked can you help me out by telling me which connection Star or Delta leads to "more easily installed wiring" and "less expensive protection devices" and in which case you would go for the more expensive option?

I am probably being thick but its not logical to me to have 230v – Delta and 400v – Star for smaller physical frames and then change back to 400v for delta and 690V for star. I would have thought it would be for example 230V for delta then 390V and above is star. rather than the chop and change?

I guess what i am asking waross is why star is chosen and why delta is chosen with particular applications.

any assistance gratefully received!




Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[itsmoked]

I think you are a bit confused. The facility you're installing the motor in usually has a single voltage already installed. Now you come along with your motor. You then look at your motor to see if it needs to be wired in star or delta to run at the available voltage.


The voltage existing is usually the most logical for the place. If it is place with lots of motors, or perhaps large air conditioning loads it may be 480V. You would likely have to set up your motor(s) to be in their 460V mode which will be wye,(but you don't care). If the place is 240V then you would set the motors up to be 230V delta,(but, again you don't care).

It comes down to you not really caring one way or another. You hook the leads up the way the name plate tells you to for the voltage you are going to run it on. You can easily never even know which way you you're setting the motor up, wye or delta, as the user it doesn't matter normally to you.

As for cost there is none really to decide on. I was giving you the broader picture of generally the higher the voltage the smaller the breaker amperages needed and the smaller the copper($$) wire you need. This would be a choice made by the facility architect to set the plant voltage based on expected power consumption and typical loads.

If you have a motor over about 5hp and the facility has both 480V and 240V you would probably go with 460V setting just to save on copper expenses. It depends on each situation like the staff who maintains things.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ccjersey]

The motor star/delta reconnection is a way to match one motor to a wider range of facility voltages. It also allows a method of reduced voltage soft starting (which is rapidly disappearing with the proliferation of solid state soft starters and VFD's).

Another way to make a dual voltage motor is to use a series/parallel reconnection which result in a motor that will operate on two voltages X and 2X instead of X and 1.732X like the delta/star reconnection. Series/parallel designs can be either delta or star, but the arrangement stays the same for high/low reconnection.

As motor power increases, motor voltage usually increases because of the expense of the conductors and switchgear. The dual voltage motors are useful even at higher power/larger frame because of the variation and overlap in facility design/supply voltage. Many times older facilities will utilize a lower voltage than more modern ones, but both need new/replacement motors, so a single dual voltage design can fit in both.

 

[JohnnyHS]

Itsmoked and ccjersey thank you very much for your replies - From what I am reading it looks like if I’m not the manufacturer of the motor then I shouldn’t be worrying about it too much – I should just hook it up as to how the manufacturers supply it as they seem to manufacture their motors to suit wide application scenarios.

The question came up from the customer asking me why it was wye. I will essentially reply that the OEM motor characteristics require it to be hooked up for this particular application (and not to ask any more questions coz it doesn’t matter!! Lol).

As you can see from the attachment from the first post the L1 2 and 3 are supplied into the same terminals anyway (the top 2 diagrams). I posted the question on here because a) I know one of you lovely people would point me in the right direction to help my customer and b) I’m one of those annoying people just like kids who keep on asking why and get great satisfaction on knowing!! (yes I love the discovery channel and the program how do they do that!)

In my searches I found this link also. It may prove useful to other budding searchers and information hungry monsters for info reg. this.

http://www.phaseconverterinfo.com/phaseconverter_deltawye.htm

Thanks again




Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[itsmoked]

Ah, I know what else is bothering your customer.

Generally motors are three lead devices. You feed them the voltage they want on three leads. Yes inside there may be a bunch more leads but the external connection is three.

This outside power is going to be DELTA or WYE depending on the plant again. The motor only cares about the voltage between those three leads. It will be hooked to the plant thru three leads. So we are talking about the motor's internal connections and completely different - the plant's power scheme.

You are telling the customer, "You need to hook up the motor in a wye configuration to achieve the correct voltage for the motor. The customer can be thinking *#*($

&$^@ but my plant is DELTA!?!?"

It doesn't matter... Look at the plant voltage between the three power leads and then 'configure' the motor appropriately.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[EdDanzer]

You need to check each leg of the 3 phase to ground to determine if it is delta or wye three phase. Then you need to make sure the legs of the motor are not grounded in the wye configuration if you choose that connection. Anything less could be an embarrassment.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[waross]

Yes a 480 volt wye system will read 277 Volts to ground from any phase.
A 480 Volt delta system with balanced insulation impedances will read 277 volts to ground from any phase.
A 480 volt delta system with a grounding transformer or artificial neutral will read 277 volts to ground from any phase.
And don't connect a motor with a grounded leg to any system. It is faulty. have it properly repaired before using it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JohnnyHS]

Thanks to all once more!

My eyes are opening ever so slightly as to the star/delta question posed. i love it. I'm going to try and have a little delve into why (rather than when which the suppliers gave me) the motor manufacturers choose one over the other (but still pretend i dont care!)

Being newish to these particular forums and having posted, got lots of great replies (not all though lol) and read lots of other posts i must say it seems to be a fantastic community of technical minds round the world combining their great varied knowledge and experience for the common good and benefit of others. Makes you feel a little bit of faith in the human race after all *sigh* lol


Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.