I am working to design a circuit to heat up a punch and die mould for plastic. I want to use 3 phase power in order to heat up fast. The plan currently is to build three seperate delta configured 3 phase heaters and run them in parallel. I will draw 3 phase power from the building mains and I plan to use Arduino to control the 3 phase heaters using 2 x 3phase SSRs. All three 3 phase heaters are planned to be the same, balanced, taking 3x 1000W cartridge heaters wiring them in delta configuration. Please see the pictures attached below of the schematic for each heater and complete system.
My first question might seem dumb but I figure it is worth checking, when I run all three of these heaters in parallel I have assumed 3 phase circuits have the same electric properties as with single phase. Furthermore that the Power and Current of each heater is summed to a total and the 400 V is the same over all. Is this correct?
Second question is regarding the neutral wire in a 3 phase power cable. From what I have researched about 3 phase circuits I know that the neutral wire comes from the centre of a Y connected system and is not necessary in a delta system. Does this mean when I wire my circuit I can just have this wire completely disconnected?
Finally if you see any other red flags or something that does not make sense or work in this circuit design please let me know!
Wiring regulations vary according to which territory you are in.
Because this is an international website, and contributors have varying degrees of expertise, you may receive information that is inaccurate and / or in conflict with local regulations,
JohnLincoln:
Wiring regulations vary according to which territory you are in.
Because this is an international website, and contributors have varying degrees of expertise, you may receive information that is inaccurate and / or in conflict with local regulations,
Right, thanks, I will continue searching for the regulations but I am in Germany if anyone knows about that.
My first question might seem dumb but I figure it is worth checking, when I run all three of these heaters in parallel I have assumed 3 phase circuits have the same electric properties as with single phase. Furthermore that the Power and Current of each heater is summed to a total and the 400 V is the same over all. Is this correct?
If your mains is 230V, then the interphase voltage is 400V, yes. Each 1000W element takes 2.5A, but
each mains phase takes 4.3A, not 5A, due to the 60 deg phase difference between elements. So you
have to be careful summing currents and voltages where there are phase differences - often its easier just
to work in terms of power which always sums.
Second question is regarding the neutral wire in a 3 phase power cable. From what I have researched about 3 phase circuits I know that the neutral wire comes from the centre of a Y connected system and is not necessary in a delta system. Does this mean when I wire my circuit I can just have this wire completely disconnected?
Neutral isn't used in a delta load, yes.
Finally if you see any other red flags or something that does not make sense or work in this circuit design please let me know!
Seems reasonable apart from the lack of contactor/fuses...
You clearly have no idea of what working with power systems involves.
You need to speak to a properly certified power design engineer to develop your requirements in order that your system is not only functional, but both safe and legal.
ccomparey:
Right, thanks, I will continue searching for the regulations but I am in Germany if anyone knows about that.
I have worked in Austria, Germany, Switzerland & the UK.
3-Phase requirements are strict in all those countries.
I personnel would not touch a 3 Phase Power Project.
There are just too many places to make an error and those can kill people or cause serious damage to property.
I can tell you that in your heater project TUV would require Current limiters to shutdown the entire heater is one heater were to become shorted.
They would also require a sensor circuit to look for an open heater or an open leg.
My first question might seem dumb but I figure it is worth checking, when I run all three of these heaters in parallel I have assumed 3 phase circuits have the same electric properties as with single phase. Furthermore that the Power and Current of each heater is summed to a total and the 400 V is the same over all. Is this correct?
I'm not sure what you're asking here. When wired delta, yes, each element sees 400V. Your calculations are correct, for each group of three heaters wired delta, you'll have 4.3 amps of phase current. For three sets of heaters, the total phase current will be 12.99 amps. The sanity check for that is that 12.994001.732=9000 which is the wattage expected.
Second question is regarding the neutral wire in a 3 phase power cable. From what I have researched about 3 phase circuits I know that the neutral wire comes from the centre of a Y connected system and is not necessary in a delta system. Does this mean when I wire my circuit I can just have this wire completely disconnected?
Yes, you could do that but then where would you get 230V to provide power to the Arduino? Since your project could be powered with a standard 16 amp circuit, you'd want to power it from a standard 5 wire cable.
In general, for SSR's, uR type fusing would provide the best protection. This will all need to be in an enclosure and it will need some form of isolation from mains, a pistol handle disconnect is the most common method and you should consider a small enclosure fan and louver to remove the heat from the SSR's.
avr_fred:
I'm not sure what you're asking here. When wired delta, yes, each element sees 400V. Your calculations are correct, for each group of three heaters wired delta, you'll have 4.3 amps of phase current. For three sets of heaters, the total phase current will be 12.99 amps. The sanity check for that is that 12.994001.732=9000 which is the wattage expected.
Yes, you could do that but then where would you get 230V to provide power to the Arduino? Since your project could be powered with a standard 16 amp circuit, you'd want to power it from a standard 5 wire cable.
In general, for SSR's, uR type fusing would provide the best protection. This will all need to be in an enclosure and it will need some form of isolation from mains, a pistol handle disconnect is the most common method and you should consider a small enclosure fan and louver to remove the heat from the SSR's.
Thanks, I plan to use a standard 5 wire cable, the question is meant to be, with that 5 wire cable is it alright to have the neutral wire disconnected, as it is unneeded in the delta configuration. Arduino is planned to be powered separately from a DC source.
I am looking into pistol handle disconnects and appropriate SSR heatsinks and cooling methods now
TomGeorge:
Hi,
Yes you can leave the neutral disconnected.
But make sure Earth is used.
Do you have an Electrician to help you with the 3phase wiring?
Will this be wired in to a switchboard or plug into a 5 pin 3phase outlet.
Do you plan to phase control the heater supply or just switch it ON and OFF around a setpoint?
Thanks.. Tom...
Yes I will have a certified electrician for wiring. plugged into a 5 pin 3phase outlet. planning for only on and off around set point as that has worked well with the single phase system so far.
Watch out for that "A" prefix, it means AC (90 - 280V) control input.
Also, the control input current is about 20 mA at 5V, you may want to consider a buffer transistor.
