Kiln Conversion from 1Ph to 3Ph

[NamPotter]

Hi All - I have gotten a Top loading kiln which works on 220V (single Phase here in Namibia) rated at 45A. I have access to 3 Phase at the workshop and would like to convert the kiln to work on 3 Phase. I measured found the following information on our 3 Phase here in Namibia. Measured L1 to L2, L2 to L3, L3 to L1 is 380V. L1 to N, L2 to N and L3 to Neutral is 220. So the Kiln has 3 sets of elements. Is it possible to wire the elements: each set to one phase (Lx) and to Neutral. Thus element set 1 to L1 and N, set 2 to L2 and N, set 3 to L3 and N.

Obviously all through the proper contactor with the right rating etc etc etc. The elements are all 220-240V. So I dont need new elements?

The reason for reconfiguring is that there is no 45A 220V outlet.  And the 3 phase is much cheaper than running it on 220V.

Alternatively I touhg of keeping it on 220V normal outlet (single phase) but then reducing the element sets from 3 to 2 in order to bring down the total Amp rating. Presently 3 elements per set, 3 sets in kiln - total elements are 9 at 45 amps (5 amps per element) - - so only 6 would be 30. I do understand that the kiln would then not be efficient, fire longer etc etc etc.

[neilestrick]

@NamPotter You'll need to call the kiln manufacturer to find out what needs to be done to run it on 3 phase. It may or may not need new elements. There may also be other things in the kiln that need to be changed, like terminal blocks and such. Typically the neutral is not used in kilns, but in some rare cases it is, typically in smaller kilns. Again, the manufacturer will be able to tell you what needs to be done.

3 phase isn't any cheaper to fire. It'll pull the same watts either way, and watts are what you're paying for. 3 phase simply allows you to get the same wattage at lower amperage, so you don't max out your circuit box as quickly and can run smaller wires.

[Bill Kielb]

@NamPotter You have three phase wye service so your idea is correct. I am assuming you pay less per kWh for three phase so your electrician needs to wire as appropriate using the neutral and one single phase  of your service to just run this in single phase fashion.. This kiln is likely wired for single phase use right now or in the US we call two phase plus a neutral single phase. (Weird I know, just a North America grid thing but then we wire our single phase 220  - Actually now 240 -using both phases and no neutral) our two phases are 180 degrees apart as well so leg to leg is 240 V and leg to neutral is 120v. Our three phase service is 120 degrees apart and typically wye, but can be delta with a nominal leg to leg voltage of 480 v or 277v from neutral to phase. Oh, we also have 120 /208 three phase but that’s a whole story by itself. 

You can run this as a balanced three phase load (Or technically three balance single phase loads) , L1 -  neutral, L2- neutral, L3- nuetral)  But that likely requires three isolation relays and recalculating  your breaker requirements and the appropriate breaker based on three single phase loads.  At full load your neutral will have zero amps as long as all three loads are equal and in use.   Neutrals in  balanced  phase use never see anymore than the single leg maximum load because of the 120 degree phase offset.. At no time will you be able to use leg to leg voltage so getting this right is important.

 Definitely a job for a reasonably skilled electrician though, but common in these situations throughout the world. You will still need to bring an earth ground for safety though, no matter where you are on the planet and someone with skill with respect to kilns or heaters and wiring in elevated temperature environments always a plus. Finally your electrician needs to be versed enough to ensure everything inside is suitable for at least 380v isolation. 

[NamPotter]

Thanks Neilestrick and Bill for your inputs - much appreciated.

Well, I did it! I connected element ring 1 to L1 and N, element ring 2 to L2 and N and element ring 3 to L3 and N. also connected the earth to the body of the kiln to be on the safe side and gave it a go - All went fine. Did a SW firing to cone 6 with a controller I have never used before. It had a "Soft Soak" function which did not work too well. Most pots are under fired so I have to refire them again, possibly add a bit more glaze too. The cone at the bottom did not bend at all, the one in the centre touched the shelve and the top one just started bending. So the conclusion is that the kiln did not really soak on the "soft" mode. It simply slowed the ramp a bit.

Throughout the firing I often checked the cables to make sure they dont heat up or melt, nothing of that happened. The only part in the wiring that heated up a bit was the main switch (where the 3phase plug goes into the wall - was a bit warm. The power consumption for the 10h firing was about 54 Kw (or units as they are called here) which translates to a cost of about N$150 (approx 10US$) - that is pretty cheap - I have a tiny kiln at home (30x30x30cm inside) which I use for bisque only and runns of a normal stove plug (30A) and a bisque firing there costs me about N$75. (glazing in the tiny kiln - ha ha only 4 bowl at a time - not worth it).

I guess with the large round kiln at my disposal now it would have been great to have a seperate temp controller for each element ring - this would however be quite a costly outlay - although I see LL Kilns has such a device. Anyway I guess I will have to fire some more in it to get some experience in using it to the best.

Thank you for your interest and comments. Yes Bill, 3 phase power (in different countries) is a whole different story by itself - interesting none the less. The problem here in Namibia is that no one really knows anything about kilns. If you get an electrician to help - normally he does not know either and on top of it all charges a fortune - so for quite some time I have helped other potters here to fix minor kiln issues like broken bricks, replacing elements and the like. Would be great if one could get some more information on the topic and some tips etc.

[NamPotter]

Oh, am also going to raise the bottom shelve by another inch from the floor. Presently it sit on stilts about 1 inch off the floor. Hopefully this will allow some more heat to circulate below and possibly add to the successful firing.

[neilestrick]

@NamPotter Kilns with single thermocouples often fire unevenly as you have described, with the middle firing hotter than the top or bottom. The way to deal with that is to load the kiln more densely in the middle, and less dense at the top and bottom. So big bowls and vases at the bottom, small mugs and cups in the middle, and bigger pieces or pieces with low mass again at the top. 

[Bill Kielb]

50 minutes ago, NamPotter said:

Would be great if one could get some more information on the topic and some tips etc.

There are many videos on the net you may find useful. One idea is there are controllers made to control multiple zones which helps to even out kilns as yours. Here in the states Bartlett controls has made the V6CF multi zone kiln control with cone firing built in. Since you likely have three isolation relays you are already set up for multi zone operation really. You would need to add two more thermocouples of course but the hookup and wiring is fairly simple. Bartlett has since created a touch screen and the V6CF which has existed for a decade and still does a great job is slowly being replaced. I mention because you may find a suitable used controller for a very reasonable price. This would likely help you with balancing a bit.

Just a possibility 

[Hulk]

Half shelves - if you have any - allow a stagger, such that pieces at the top "see" more element, and denser pack in the middle, overlapping edges of flared pieces (like bowls). I'd leave the bottom shelf just off the floor, particularly if raising it even partially blocks an element.