3 phase kiln questions?

[Darkwood]

We need to see the wiring config of the elements, you have the wiring plan there so we can then use ohms law to establish the demand of the elements per phase.

 

[pc1966]

True, it might have a contactor, but they stopped making these in the early 80s I think so SSR very unlikely. At around 18A/element it might even be a basic bimetallic operated switch as for domestic cookers, but the schematic should reveal this.

 

[Darkwood]

@pc1966 Domestic cooker loads are suitably small enough to work off simmerstats, this is an industrial kiln and I have yet to see one that works off such rudimentary control methods, I would favour contactors here simply because of the current been switched, also the fact it is changeable between single and 3 phase would mean some kind of 3 phase switching mechanism, normally the stat's however they are configured be it load passing or control circuit operation don't do 3 phase switching although I will stand corrected as there are certainly machines etc out there that have bespoke items in them purposely designed for them.. however, this is a very expensive solution to use if we have off the shelf alternative methods like contactor control and such alternative bespoke solutions are only really used to save space for more compact design, a issue I doubt needs to be applied to a kiln.
I will add here that some modern domestic ovens do indeed give both 1 an 3 phase options yet do not house contactors, this is where bespoke comes in and given the much lower loadings in domestic ovens it may be the case they use a 3ph simmer stat.

 

[HappyHippyDad]

I do have the complete wiring diagram, but it is a mismatch of many pictures, which would be just be chaotic to look at. I've just texted the customer for one full picture.

 

[westward10]

See all that ohms law stuff at college wasn't a waste of time???

 

[HappyHippyDad]

We need to see the wiring config of the elements, you have the wiring plan there so we can then use ohms law to establish the demand of the elements per phase.

The best I can do!

 

[westward10]

You have four elements per phase. What you need to do is access that contactor.

 

[pc1966]

Yes, it is contactor controlled just as @darkwood said.

Elements seem to be 3 identical sets of 4 in series, star-connected. If you can access the contactor out-going terminals you should easily manage to measure the resistance of each set and they ought to be very similar.

 

[westward10]

According to that schematic the elements are all the same so if it easier to access the elements you only need the resistance of one.

 

[Darkwood]

Measure any element 2 elements to confirm duplicate readings (wires disconnected) and not a faulty element you picked by chance, take this common value and we can tell you the rating with ohms law, taking measurements further upstream may not give accurate reading if any of the elements are failing and or loose connections so only do that if access restricted from getting to the elements.
If you need to take reading further upstream then get the ohms readings between every phase to phase option and they all should match give or take a few ohms, if they do we can rely on that value with confidence.

PS you can ignore the N in testing.

 

[HappyHippyDad]

Would it possible to do an example now? Its quite interesting!

If we assume the kiln is 12kW.....

Still cant see how its as simple as v = I x R though as V could be 230 or 400, giving us varying results of R if we assume 12kW.

 

[loz2754]

Would it possible to do an example now? Its quite interesting!

If we assume the kiln is 12kW.....

Still cant see how its as simple as v = I x R though as V could be 230 or 400, giving us varying results of R if we assume 12kW.

V=230 as the elements are wired line to neutral.

 

[HappyHippyDad]

I need numbers!

V = 230

I = 12000

R = ? single element. (Is this a reading literally of one element, if so what will the equation look like?)
R = ? group reading Ph to Ph (what is a group reading? L1 + L2 + L3 to N?)

 

[Darkwood]

V=230 as the elements are wired line to neutral.

Be careful we have a duel voltage system here, we are discussing testing the 400v approach if testing multiple elements at once, he is using 3ph here so lets not confuse matters.

 

[loz2754]

I need numbers!

V = 230

I = 12000

R = ? single element. (Is this a reading literally of one element, if so what will the equation look like?)
R = ? group reading Ph to Ph (what is a group reading? L1 + L2 + L3 to N?)

I is not 12000

 

[pc1966]

P = 12kW = 12,000 W
V = 230V
I = 12,000 / 230 = 52.2A for single-phase (excluding control circuit, fans, etc)
I per phase = 52.2 / 3 = 17.4A
R = V / I = 230 / 17.4 = 13.2 ohm per set of elements
In practice elements R will increase as they heat, so cold measurmenets will give you the switch-on current and that ought to drop by a small amount as it heats up (off hand don't know by home much though).

 

[loz2754]

Be careful we have a duel voltage system here, we are discussing testing the 400v approach if testing multiple elements at once, he is using 3ph here so lets not confuse matters.

Thanks. I understand that. But the aim is to connect to the available single phase supply. I had that in mind.
So we have a series/parallel resistance to calculate, 3 parallel groups of 4 series resistances.

 

[Darkwood]

Group reading

L1 to L2
L1 to L3
L2 to L3

Each reading should be more or less the same.


I = V/R
Amps = 400/resistance.



L - N of 1phase

Amps= 230/resistance of element group

multiply by 3 banks to get single phase load.

 

[pc1966]

If measuring phase-phase then you will see twice the resistance (of a single element of star-connected load) on a DC test.

 

[HappyHippyDad]

I is not 12000

Of course not! I'm rushing and coffee overloading. I = 52.2A