Induction Heaters

[Ravyn355]

I'm seeing excessive heating on my line wires feeding large induction heaters. Looing for cause and remedy. Anything would help.

 

[zbang]

How big are the heaters?
What is "excessive heating"? How did you measure it?
Are the wires undersized for the load?
Is the load drawing more or running longer than expected?
Ambient temperature is higher than expected?

As always, more detail about a problem is better than less.

 

[augie47]

Induction heating is a different breed of animal. Be sure to check NEC Art 665 especially 665.6. Often times grounding is unusual and standard grounding methods can cause excessive heating in raceways. You might also discuss the problem with the manufacturer as they often have solutuions.

 

[Ravyn355]

How big are the heaters?
What is "excessive heating"? How did you measure it?
Are the wires undersized for the load?
Is the load drawing more or running longer than expected?
Ambient temperature is higher than expected?

As always, more detail about a problem is better than less.

to induction heaters, 1500 kw and a 200 kw...wiring size is good... supplied with 6000A to gear. Seeing heating from heaters to transformer. wire by transformer at 100F by heater reading 130f. unit runs 24/7 temp measured with a flir infrared. some of the parts, like the bus way has hit 174f.

 

[Ravyn355]

Induction heating is a different breed of animal. Be sure to check NEC Art 665 especially 665.6. Often times grounding is unusual and standard grounding methods can cause excessive heating in raceways. You might also discuss the problem with the manufacturer as they often have solutuions.

currently there are (4) 500kcmil conductors to structure.

 

[augie47]

IT's been a while since I was involved but if I recall correctly we had to accomplish grounding via separate grounding conductors external to our conduit runs and insert non-metallic nipples to prevent the conduit from being a return path.

Lots of Code questions such as 300.3 and lots of discussions with a mfg rep who was also on CMP 12 which covers induction heating before it was all over with.
There are some strange current flows when dealing with this animal.
Who is the equipment manufacturer ?

 

[Ravyn355]

IT's been a while since I was involved but if I recall correctly we had to accomplish grounding via separate grounding conductors external to our conduit runs and insert non-metallic nipples to prevent the conduit from being a return path.

Lots of Code questions such as 300.3 and lots of discussions with a mfg rep who was also on CMP 12 which covers induction heating before it was all over with.
There are some strange current flows when dealing with this animal.
Who is the equipment manufacturer ?

It is 2 old pillar units....

 

[zbang]

174 degrees Fahrenheit is only 79 degrees Celsius, which may be acceptable for the busway. Certainly 130F (55C) would be in-spec for most all wiring and terminals, heck, in some parts of the country, that's ambient . That said, it's certainly worth examining the grounding/bonding and talking with the manufacturer.

 

[mpoulton]

Have you measured current (at all frequencies - true RMS, not a cheap meter) on those conductors during operation? Depending on the type of induction heating system and how it is fed, you can end up with high harmonic currents (or even excessive 60Hz current) due to resonant behavior with power factor correction capacitors upstream of the load. The temperatures you noted seem generally OK but if you're sure there's a problem to be solved then I'd start by checking the current with a meter that will show you what's really going on.

 

[Ravyn355]

Have you measured current (at all frequencies - true RMS, not a cheap meter) on those conductors during operation? Depending on the type of induction heating system and how it is fed, you can end up with high harmonic currents (or even excessive 60Hz current) due to resonant behavior with power factor correction capacitors upstream of the load. The temperatures you noted seem generally OK but if you're sure there's a problem to be solved then I'd start by checking the current with a meter that will show you what's really going on.

at 70% power both units combined pulling 3500 amps @ 480v

 

[junkhound]

Have you put a scope on the line for both voltage and current?

Surprising what the true waveforms will tell you vs rms readings !

 

[mpoulton]

at 70% power both units combined pulling 3500 amps @ 480v

Unless my math is wrong, that number is way too high. The total rated power for both units combined is 1700kW, right? So at 70% power you should be running around 1190kW which would be 1432A. Your measured current is over twice that. The power factor is apparently around 0.4, which is pretty awful. If these are high frequency units and those ratings are thermal power rather than input power then the efficiency of the unit would account for some of the missing power - but not all of it. I'd suspect resonance with upstream PFC capacitors or something. I think you need to use a power quality analyzer or oscilloscope to take a look at what's going on.

 

[Besoeker]

Unless my math is wrong, that number is way too high. The total rated power for both units combined is 1700kW, right? So at 70% power you should be running around 1190kW which would be 1432A.

I made it about 3600A if the PF really is 0.4.
Perhaps you missed that from your calculations? That would account for your 1432A figure.

 

[mpoulton]

I made it about 3600A if the PF really is 0.4.
Perhaps you missed that from your calculations? That would account for your 1432A figure.

I calculated that PF of 0.4 based on the reported power and current numbers. That power factor can't be normal or acceptable for this equipment, can it?

 

[GoldDigger]

I calculated that PF of 0.4 based on the reported power and current numbers. That power factor can't be normal or acceptable for this equipment, can it?

Induction heating is a strange beast.
What does the heating is the "losses" of the inductors. There is a limit as to how bad (i.e. high PF) you can make them and still have them work properly.

 

[Tony S]

I calculated that PF of 0.4 based on the reported power and current numbers. That power factor can't be normal or acceptable for this equipment, can it?

Induction furnaces can give some terrible PF values. Trying to get our plant operators to use the PF trimmers was fighting an up hill battle.

 

[Besoeker]

I calculated that PF of 0.4 based on the reported power and current numbers. That power factor can't be normal or acceptable for this equipment, can it?

Ah, I see now. You did the calculation in reverse as it were. I did wonder about that.

It isn't my area of expertise. If the measurement taken by Ravyn is correct then 0.4PF it is.
Whether that's plausible or not I can't say.

 

[mpoulton]

For a line-frequency induction furnace (operating at 60Hz) a terrible power factor would not be unusual, but can be corrected with PFC capacitors near the unit or built into it (that's essentially how they are supposed to work: the induction coil resonates with parallel capacitors to cancel its reactance). The units this guy is referring to are not line-frequency though. He said they are Pillar units, 200kW and 1500kW. Pillar makes high frequency induction furnaces with solid state power supplies, and those power ratings would be too small for line-frequency furnaces anyway I think. Pillar's systems are supposed to have pretty darn good power factor - 95% for their current lineup and the older ones weren't terrible either. I really don't think these current measurements make sense for a properly operating system. We'd need the nameplate ratings from the power supplies themselves to know for sure though.