Rectifiers

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Besoeker

Besoeker

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UK
TBH, I don't do much by way of estimating. Supply and installation of equipment is always a fixed price contract. So this may not be the right place for this

I've had a recent enquiry for four 250kA, 32V DC supplies.

It isn't rocket science. It's just a lot of fairly standard units for us.
The technical challenge is in working out the best vector arrangements of the various HV to LV, the LV to unit transformers, and the physical arrangement of the units to make best use of output conductors. The commercial challenge is just a little more difficult to judge.

I'll quote it as fixed price as requested. But it is a risk/reward balance.
Play safe and the chances you will be out of the frame on price.
Cut it fine, and you might win the contract and lose your shirt or a lot more.

I'm of a mind to take the more conservative approach. It isn't a field with many players and we do have some good reference installations.

I'm not making any particular point here. Just rambling on about something that has preoccupied me over the past few days.
 
chris kennedy

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Have a beer and relax Mac. Wait, what time is it there?:grin:

Since you didn't ask a question I'll ask one. What is the application of these power supplies?
 
Besoeker

Besoeker

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Location
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chris kennedy said:
Have a beer and relax Mac. Wait, what time is it there?:grin:

Since you didn't ask a question I'll ask one. What is the application of these power supplies?
Click to expand...
Chris

I'm fairly relaxed about the technical aspects.
And I have already sized and priced transformers and power components.
It is all pretty much around the ball park I had in mind.
Seven digits.
Small errors are big sums.

And, while contemplating this, I'm having a nice Merlot.
At around 11:pm local time.
And still working out best circuit configurations.

To answer your question, the application is annealing in a steel strip mill.
 
Besoeker

Besoeker

Senior Member
Location
UK
dbuckley said:
Two hundred and fifty thousand amps.

Besoeker does a lot of big DC supply projects

250KA at 32V = 800KVA x 4 = 3.2MVA...

Can you get trannies to go straight from 11KV? Save a whole load of intermediate metalwork?
Click to expand...

I have considered this in the past but a number of practical limitations generally don't make it an especially attractive proposition.

The 11kV transformers and switchgear usually have to be in a locked sub-station or outdoors (for the transformers). In many cases, this would make them distant from the production process which, for the magnitudes of the currents required, isn't desirable. Isolation proceedures and permits to work have to be handled by someone further up the tree etc.

Then, there is the consideration of the maximum current rating for the individual rectifiers. We generally use a hexaphase arrangement with individual SCRs on the LV side of the transformer. Paralleling SCRs is something best avoided in my opinion. There is a maximum practical limit for an individual hexaphase rectifier and we feed each from its own transformer to get a multi-pulse configuration. Obviously, this means a fair number of units. And everything is water-cooled. So not entirely suited to 11kV units.
 
Besoeker

Besoeker

Senior Member
Location
UK
StephenSDH said:
Thats why I thought it couldn't be. I can't imagine 3.2MVA of rectifiers. I would love to see the drawings.
Click to expand...
Your wish.....etc.
It's actually 32MVA.

This is one element of a system we did earlier:

C12273-twoLHSlimbs02.jpg


Electrically (taken from one of our drawings):
Hexaphase01b.jpg


Each element is phase displaced from the others to minimise supply current harmonics.
 
D

dbuckley

Senior Member
Location
Canterbury, New Zealand
[fx] Gulp [/fx]

The discussion on not using 11KV directly is interesting, and in fact iillustrates that as well as getting my sums wrong (schoolboy error, especially considering I used Calc to do it), I hadn't thought the full picture through adequately...
 
cadpoint

cadpoint

Senior Member
Location
Durham, NC
OK, I've thought about that picture and drawing, I even thought I'd wait till I thought about all the questions :cool:

Your bringing in all your electronic on the Line side? Or to say you control from this side to change for the desired results?

I assume you do all your work on this side?

Why are only five out of six legs, fused? Why only 2 out of 3, maybe CT'd.

Noting Center Feed as leg One, is that an EU practice?

How big is the Furnace?

What's the Plate or Rod size?

Is all this attached to rolls or just heat element, say between rolls?

That is some piece of equipment!
 
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