CR4 - The Engineer's Place for News and Discussion®

Previous in Forum: Specification for Damaged Shielding   Next in Forum: Shunt Reactor for 11kV system
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







11 comments
Member

Join Date: May 2012
Posts: 5

Motor Control Center/Transformer Specifications

05/14/2012 7:10 PM

3rd year electrical engineering student currently on a co-op work term.

My supervisor has 'thrown me to the wolves' so to speak and given me something I know relatively little about. He's given me a week to get this done, so I'm hoping someone can give me some advice.

Basically I need to determine the specifications for a power pole transformer and for a MCC (motor control center).

Here's what I know.

2 pumps are being installed, each with an Installed Power of 300HP, and absorbed power of 257HP. The starting method is a VFD for each pump.

drive type: Piggy-back belt drive

electricity supply: 575V/3ph/60hz

Motor SPeed 1150 RPM

Pump SPeed : 340 RPM

Max Duty SPeed: 350 RPM

I was told that the MCC needs to control both drives, a 120/208V lighting panel, and 2 heaters.

There will be a 13.8KV line going to the transformer, which then needs to reduce down to 600V.

I was told this was pretty straightforward and easy, and my supervisor already knows which transformer and MCC to use.

Any advice on how to proceed and what steps to take would be much appreciated.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru
Hobbies - Automotive Performance - New Member Popular Science - Weaponology - New Member

Join Date: Oct 2008
Location: Want to be: 34° 34' 21.60" N, 92° 55' 42.28" W Really am in Arizona
Posts: 28936
Good Answers: 1086
#1

Re: Motor Control Center/transformer specifications

05/14/2012 7:20 PM

Sounds like he's given you a simple task. To which he already knows the answer.

Figure the amount of energy required for the installation and get on with it.

__________________
Luck comes and goes. Skill is forever.
Register to Reply
Member

Join Date: May 2012
Posts: 5
#2
In reply to #1

Re: Motor Control Center/transformer specifications

05/14/2012 7:30 PM

Oh I know it's a simple task. For someone who has done this before..

I didn't even know what an MCC was until yesterday, and have not yet got into any of the high power courses at University. So this is all new to me, so cut some me slack. I'm sure it's nice being a guru at this.

So yes, i know I need to calculate energy usage. And for the past couple of hours I've just been reading up on MCC's trying to learn about them.

Register to Reply
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 3776
Good Answers: 551
#3
In reply to #2

Re: Motor Control Center/transformer specifications

05/14/2012 7:45 PM

If he has already decided which MCC he wants you to use, contact that company and ask them for their MCC design software. Almost all of them have it available. The issue is, you cannot guess at the size of the unit space they will need for the big VFDs, no two manufacturers are exactly the same and you cannot simply "force" them to fit a space you pick out, because it may not be UL/CSA listed that way.

MCCs have their own UL/CSA design and test criteria that is different from other electrical equipment, and it's fairly rigid. So if mfr ABC puts a 250HP drive in a 25" wide cabinet, and mfr DEF puts it in a 36" wide cabinet, you will not be able to force DEF to squeeze theirs into 25" without them losing their listing, which in Canada means failing inspection. So since you already know the brand, don't waste a lot more time, just get the CD or the link to download their software, plug in your load data and let it design it for you.

What brand is it anyway?

__________________
** All I every really wanted to be, was... A LUMBERJACK!.**
Register to Reply
Guru
Hobbies - Automotive Performance - New Member Popular Science - Weaponology - New Member

Join Date: Oct 2008
Location: Want to be: 34° 34' 21.60" N, 92° 55' 42.28" W Really am in Arizona
Posts: 28936
Good Answers: 1086
#4
In reply to #2

Re: Motor Control Center/transformer specifications

05/14/2012 7:47 PM

I'm honestly not sure you are up to the task.

I'm certainly not up to trying to walk you through this.

Maybe someone else.

[Edit] JRaef is going to educate you, you're lucky. He is an authority.

__________________
Luck comes and goes. Skill is forever.
Register to Reply Off Topic (Score 5)
Member

Join Date: May 2012
Posts: 5
#5
In reply to #4

Re: Motor Control Center/transformer specifications

05/14/2012 7:53 PM

I'm honestly not sure you are up to the task of helping people.

I'm certainly not interested in any more of your responses.

Maybe someone else is better suited to be a guru.

Register to Reply Off Topic (Score 6)
Guru
United States - Member - New Member

Join Date: Jun 2008
Location: Alabama
Posts: 1625
Good Answers: 61
#6

Re: Motor Control Center/Transformer Specifications

05/14/2012 9:39 PM

1. first thing you can do is size the transformers. It sounds like you have 2 - 300 HP motors. So you need 3 transformers, since this 3 phase, that have the capacity for this load.

2. You will need the load amps for the MCC

3. need a source for the 120/208 ltg panel. need load to size Tr and panel.

4 .Do you need to size the service conductors from the transformers to the MCC?

Do this and come back. Where are you located?

Register to Reply Score 1 for Off Topic
Guru
Engineering Fields - Power Engineering - New Member

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 1739
Good Answers: 230
#7

Re: Motor Control Center/Transformer Specifications

05/14/2012 11:21 PM

Trent, you want advice, so here's the advice that I received from my school about co-op assignments. "...you do what ever you are asked to do with a smile and an inquisitive mind. Your supervisor knows that you don't know everything, but he does want to see how you handle yourself and how you interact with his team. Your goal is to learn as much as you can about the task as fast as you can by utilizing the resources available to you. It's what you'll be doing for the rest of your career as an engineer..."

If you were my co-op, and if I polled my team and found out that you didn't go to them for help, I'd be wondering who did the work for you. Worse than that, if you cut any of that attitude like you did here, then I would be on the phone to your co-op adviser asking for a replacement. A good engineer sees an assignment as a challenge, not as a chore.

__________________
Curious minds want to know, engineering minds get answers....
Register to Reply Score 1 for Good Answer
Member

Join Date: May 2012
Posts: 5
#8
In reply to #7

Re: Motor Control Center/Transformer Specifications

05/14/2012 11:37 PM

Oh I agree with you.. Problem is, I'm on my own, working with a bunch of civil co-op students who know nothing about electronics. I do talk to my supervisor a lot, and ask him a lot of questions, and he's a great help. But when he's unavailable for the afternoon...

And in regards to my attitude, I have a great positive attitude, until someone tries to belittle me in these forums. In my view, Lyn was trying to be antagonistic. If I read his/her comments wrong, then I apologize.

Register to Reply Off Topic (Score 5)
Commentator

Join Date: Sep 2009
Posts: 67
#9

Re: Motor Control Center/Transformer Specifications

05/15/2012 1:42 AM

as a 3rd year student to should be able to do this... why don´t you try and then post your answer and then we will advise.... don´t wait for someone to do all your work for you or you will never grow in your field..

Register to Reply
Member

Join Date: May 2012
Posts: 5
#10
In reply to #9

Re: Motor Control Center/Transformer Specifications

05/15/2012 11:08 AM

I appreciate everything everyone has said. Just going from theory to practical use is a bit of a learning curve.

Well I was told to work backwards. So here is what I've done. If my logic is off, please let me know. I figure if I can determine the total amount of current needed to power everything off the 600V line, then I can size the 13.8kv/600v transformer accordingly.

Figure out all the current loads on for the two VFD's of 300HP, I worked out the current needed for each one. As they both run off a 600V line, I converted HP into Watts, then used P=sqrt(3)*V*I*(pf of 0.85).

Gives me 254A in each line.

I was also told to add in two 30Kilowatt heaters, so 34A in each of those two lines.

I need a transformer to drop the 600V line down to 120V for the 120/208V panel. This is where I'm a bit confused at the moment. Trying to figure out how much current will be coming into the panel after the step-down transformer. I don't know much about these panels, and have been attempting to research it online. Are there standard spefications for these panels? Is there a way to figure out the current needed?

Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member United Kingdom - Member - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2010
Location: Under the Major Oak
Posts: 3577
Good Answers: 143
#11

Re: Motor Control Center/Transformer Specifications

05/15/2012 6:49 PM

First off is to up rate the calculated rating for the transformers for both the 600V and 208V.

You have to have a degree of tolerance for start up currents of the motors which you can get from the motor / VSD manufacturers data. Is there a possibility of the two drives starting simultaneously?

The ancillary supplies need to be capable of supplying the required load and any future additions, which you can guarantee will increase.

Once you have your estimated figures then look to the transformer manufacturers data. Your estimated load may be 567KVA. You could have one made to that exact specification, or you could buy a "standard" rated transformer off the shelf cheaper.

__________________
Pessimists are rarely disappointed.
Register to Reply
Register to Reply 11 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

JRaef (1); lyn (2); porky2009 (1); RAMConsult (1); TonyS (1); trentjr (4); wareagle (1)

Previous in Forum: Specification for Damaged Shielding   Next in Forum: Shunt Reactor for 11kV system

Advertisement