3 Phase Heating Element Problem.

Power = √3*V_line*I_line, irrespective whether it is Υ or Δ.

In Υ, V_line = √3*V_phase and I_line = I_phase

In Δ, V_line = V_phase and I_line = √3*I_phase

So, go by what the manufacturer says, don't worry.

As for the power consumption there would be no difference and the manufacturer's statement is correct however the situation is not the same in case one of the heaters breaks down.

In case of star connection with neutral conductor failure of one heater element does not effects the performance of the rest of the two good elements but please be aware that in case of delta configuration break in any one heater may burn the rest of the good elements.

...please be aware that in case of delta configuration break in any one heater may burn the rest of the good elements.

Can you please elaborate on how the two remaining resistors can burn ?

I was under the impression that if I connected the elements they sent me in a star configuration that the current drawn would then only be around 3A as opposed to the rated 9.11A they are rated at and that elements would give off less heat. If so what is the difference between the original elements I have which were connected in star and the new ones connected in delta if both of them are rated for 9.11A. Surely then the actually elements are constructed differently.

Yes it sounds like they are made differently to the orginal elements.

On a system where line to line is 380 Volts, line to neutral will be 220 Volts.

Your new elements sound like they are 220 Volt elements - hence the recommendation to connect them Star - each connected from line to neutral.

If you can see the wire they should look thicker as they are intended for lower voltage.

The 9.11 Amp rating is the line current on any 3 phase leg - which will remain the same for the same power rated elements.

If you measured the current through each element it would be higher (than the old ones) as they are intended to be fed by a lower voltage in Star configuration.

Crazy stuff 3 phase huh?

Your new elements sound like they are 220 Volt elements - hence the recommendation to connect them Star - each connected from line to neutral.

The new elements are 380v and they have asked me to connect in Delta.

Go for it.

Kvsridhar,

If the elements are rated at 380 volts and at this voltage are 6kW

So V/I = R 380/9.11 = 41.7 Ohms

P = I x I x R So 9.11 x 9.11 x 41.7 = 3460 Watts

This does not make any sense it is supposed to be 6000 Watts

Now if the elements are 380 volt rated and they are 6kW

P = V x I so P / V = I 6000 / 380 = 15.78 amps This I believe is the correct current.

And if R = V / I 380 / 15.78 = 24.1 Ohms this I believe is the correct resistance.

If this is the case, and I am sure it is, let us now have a look at your drawings.

In the Delta Con-fig P = V x I so 380 x 15.78 = 6kW

In the Star Con fig I = V / (Ra + Rb) 380 / 48.2 = 7.88 amps

So the power in the star con-fig is P = I x I x R 7.88 x 7.88 x 48.2 = 2992 Watts

So I think that your power calculation is incorrect

Sorry Mate, but you just cant get the same energy out of heating elements if you wire them is series, as I have shown.

To get full potential out of you heating you should follow the manufactures recommendation's and connect in delta if you line voltage is 380 volts

Cheers

Joe

Ok, now to look again at the question,

"I have a three phase heater 380v. It has 3 elements making up the heater all rated at 380v. Originally the heater was connected in star configuration with P=6kw and In=9.11A

I was thinking that the elements were 6kW each, but I now am thinking that the elements are 2kW each making a total of 6kW.

I think that I have misinterpreted the question, "SORRY GUYS"

So if the elements were connected in delta format the line current would be 9.11 Amps but if the same elements were connected in Star each element would be working at a reduced voltage 220 Volts and have a reduced power output to about 3.5kW.

The next part of the question was;

" I have recently received new elements and the drawing that came with them shows the connection in a delta configuration still with P=6kw and In= 9.11A. The company that sent them say this is the correct configuration for these elements".

This is correct, obviously the elements that he had before were only rated for 220 Volts and that is why they were wired in the Star con-fig, the new elements are 380 Volt elements.

Conclusion; The line current would still be the same as the kW ratting is the same!

The new elements are rated at 380 Volts, the Old Elements are rated at 220 Volts, the new elements have a higher voltage ratting, do not try to mix the old and new elements together, or there will be problems.

"My question is what is the different about the new elements?. Thicker wiring for the elements to make more resistance?. I thought if you changed from a star to a delta configuration then you would draw three times more power and the elements would melt".

The new elements have a larger cross-section area and the resistance of the elements has changed.

Kvsridhar, "YES YOU ARE RIGHT" and you will get a GA from me, I hang my head in shame.

Best Regards, Kvsridhar

I Remain in Shame

Joe

Why would the remaining elements burnout? Not because the voltage across each remaining element has changed, because it has not. Not because the current in each remaining element has changed, because it has not. The only effect will be a reduction in the power output of the heater. To think otherwise would mean that every system that serves single phase loads off of a three phase transformer has got it wrong. Of course if you are referring to a poorly regulated, weak or isolated system that serves only the heater then things might be different.

Stoaty, I won't answer the question, but I will advise you of a solution to get things going again. If you orignal elements were rated at 380 volts and the Line voltage is 380 volts, then you were operating the elements well below their current ratting. The elements would have been drawing far less than their optimun operating current.

Now if you want quicker heat recovery and the line voltage is 380 volts connect the elements in the delta config, and if you also want to monitor the condition of the elements to ensure that they are all operating ok, there is a simple way to do this, insert a thermal overload of the correct size to the contactor and use the N/O contacts of the overload to operate an indicator "Heating Element Fault", or you could use the N/C contacts to operate an indicator that the "Heating OK"

All of this is dependant on the Line voltage being 380 volts, but you indicator would probally have to be connected to a phase voltage circuit

Line Voltage is the voltage between any 2 Phases

Phase Voltage is the voltage between any Phase and Earth

Hope this is of help and you can sort out the answer to your question from here.

Cheers

Joe

Thanks everyone for your help. I have one of the companys engineers coming out soon. So I will let him connect it up. Then he can melt this set of elements.

i would appreciate it if you could ask him about the resistance values... 72Ω or 24Ω.

To settle a bet

Sure no problem. This has been very interesting for me. Again thank you everyone that has posted.

I don't believe doing a resistance test would show 72 ohms. I think it would be less. I believe the resistance will change with temperature. If the manufacturer says delta at 380 volts, thats the way to hook them up.

i expect the heater wire is Nichrome, whose temperature coefficient is 0.0004 per ºC. If it is operating at 400ºC for example, the cold resistance could be 16% less. Good point.

However, here we are looking at ballpark figures, 72 / 24 / 41 ...???

This has been, (surprisingly to me), a good thread which made me redo my fundamentals. (Not to mention getting a couple deserved-or-not GAs )

Do you realise that the material content in the older, star-configured, heaters and that in the new delta-configured heaters are the same ? Check it out.

If the heater is designed for delta connection then you can connect it in star connection, the only thing that happen is heating time will increased. Or if it is designed for star connection and you connect it in delta, your heater will meltout.

Hey Guys i have somehow the similar problem, The factory has replaced 3 phase configuration with just single phase. can any body help me what is the disadvantage of this system? i mean the life time of elements and energy consumption.