Motor Control Center/Transformer Specifications

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.

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.

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?

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?

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.

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..

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?

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.