Heat treat furnace element help wanted

Discussion in 'The Projects Forum' started by dt38k, Jul 16, 2012.

  1. dt38k

    Thread Starter New Member

    Jul 16, 2012
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    This is my first post, and I have been through pages of archives and am still searching for an answer.
    If my problem is not allowed for discussion, I won't take it personally.
    Short version, purchased an external quench furnace with element damage with electrical components missing.
    It came with a step down Delta 480v/90 amp to Wye 57.7v/ 180 amp transformer.
    I am powering this transformer with a 75kva Delta to Delta step down transformer in boost form, line side 240v (45amp fused) to 480v load side (15 amp fused) at an estimated 37.5kva.
    My main current is a 400 amp, 3 phase 240v/208v with a wild leg that comes from a 2 wire line through a 15 and 25kva transformer from my local REC.
    I have 3 ribbon elements .750 wide x .067 thick x 25' long, each separately wired to the Wye transformer, phase to neutral.
    I have 57.5 volts phase to phase, drawing 90 amp from room temperature, up to around 750 degrees in 15 minutes and that's as high as it goes.
    These high nickel elements have very low resistance and I have been unable to make any other connection work without blowing fuses or popping breakers.
    I even tried resistors on the neutral end to slow the current, but only gained about 100 degrees.
    I have to get the voltage and current working before I can move on to designing a scr/ssr controlling circuit.
    Does anyone have any idea what I need to do?
    I just can't think of any thing else and no one around here has an answer either.
    Thanks in advance
     
  2. takao21203

    Distinguished Member

    Apr 28, 2012
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    So you mean with increasing temp. the current will increase?
     
  3. takao21203

    Distinguished Member

    Apr 28, 2012
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    It would also be helpful to provide a schematic.

    Isn't Delta configuration giving lower voltage, but higher current?
    You wrote that current the elements are wired in Star configuration (or WYE).
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    you should probably state your primary objective.

    First question, how is a trans with a primary of 480v at 90 amps, giving a secondary of 57.7 at 180amps. Tell us more about this transformer, what is it's KVA.

    second question, why fuse your 480/57.7 volt primary at 15 amps if it's rated for 90?
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    Still would be 10.8 Amps only
     
  6. dt38k

    Thread Starter New Member

    Jul 16, 2012
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    I made a schematic and scanned it.
    Hopefully it will bring some light.
    On the left side, I number the questions as they came in and tried to answer them.
    I also put in a request to have the rec come out and check the phase rotation at my shop, there is some concern that some transformers don't work correctly when the rotation is counter clockwise rotation.
    On the last question, I don't know about the 10.8 amps.
     
    Last edited: Jul 17, 2012
  7. takao21203

    Distinguished Member

    Apr 28, 2012
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    Interesting. Unfortunately I don't have much experience with transformer arrangement to create 3-phase from 2 phase.

    You write the 90A remain the same, but then the elements reach 750 degree, and the fuses trip? The 15A fuses?

    Do you have any means to verify that really 90A flow through all 3 heating elements?
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I don´t think there is such a transformer than can make 3ph out of 2ph. You could theoretically use two more capacitors to get three different phases, but the schematic doesn´t look like it does that.
     
    strantor likes this.
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Looking at your drawing, the only thing that comes to mind is WTF. Either what you're doing is totally wrong, or there's something you know that I've never heard of ( there's a good chance of that ).

    Why bother with all these transformers? All it is heater elements. They shouldn't care about 3phase. Why can't you take the heaters out of wye configuratio, put them all in parallel, and run them straight of the single phase service?
     
    #12 likes this.
  10. dt38k

    Thread Starter New Member

    Jul 16, 2012
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    Hi Takao21203

    The REC. called today, I thought they were on their way to check my phase rotation, but this person wanted to know for sure what I was looking for since he was looking at a service call sheet only.
    I filled him in on everything, not positive he didn't get confused but I think he got the most of it.
    #1. I have no issues with my 3 phase power coming into my shop, except I want to know what direction the rotation, phase to phase is.
    Example is:
    Delta triangle, A at top, B at right, C at left.
    Clockwise rotation: AB,BC,CA / C' clockwise rotation: AC,CB,BA
    I don't know what it does, but there is a difference, and a big difference when there is a lot of power like coming into a sub station.

    REC. is going to send me a schematic on my 3 phase system and I will share it with the forum, ( I will need help on how to rotate the page so you don't have to view it by twisting your neck)

    Basically, two primary wires come underground from a higher voltage run that is on a main secondary highway, about 1,000 feet behind my property to 2 outside transformers.
    One wire feeds into a 15kva transformer, the second into a 25kva transformer, and they call this an open bank, (one missing) 3 phase power system.
    These primary wires are not the run of the mill, they are huge and carry some serious voltage.
    The cost was $3,500, 7 years ago when copper prices were down and I could go a lot bigger on the transformers if I ever would need more power, like big cnc machines with 25-50 hp motors.
    When the wires from these two transformers enter my shop, I have 4 separate pairs of wires, 2 black, 2 taped blue, 2 taped orange, 2 taped white.


    #2
    No, I never lost any 15A fuses, it was 30A fuses from the first disconnect that brings power to the Delta/Delta transformer.
    My first three tests:
    First test blew L2, second test blew L3, third test blew L1.( This was before I even connected power to the element coils)
    I changed polarity on two wires like you would do if you wanted to change motor rotation.
    (Theory was that Delta transformer has to run clockwise to perform properly to internal wires/coil configuration and that I had the rotation going C' clockwise)
    Transformer ran idle for 15 minutes, no blown fuses.
    Next two tests with elements energized, blew 30A fuse on L2 both times at around 400 degrees F.
    (L2 is my wild leg, more current on this phase, to ground)
    When I stepped up to 45A, no more fuses blown.

    #3 I'm using a clamp on meter, (old but still works.)
     
  11. dt38k

    Thread Starter New Member

    Jul 16, 2012
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    Well, the schematic is pretty much Dummie type.
    My drawing should show 8 wires coming from the two transformers outside into the 400 amp main inside.
    I don't have enough knowledge to use all the symbols like you guys would be familiar with but as soon as I get it, you will see how it is done.
    Look up "wild leg delta system" and we will compare schematics if you want.
    Don't give up on me yet guys, remember this first.

    #1. I have three coils that I am energizing with 57.5 volts (phase to phase) on a 3 phase WYE grounded circuit, drawing 90 amps for 15 minutes, no changes after 15 minutes in voltage, temperature, or amp draw.
    I don't recall what phase to ground reading was, could be the 33.3 that is on the nameplate.

    #2. I would like to be able to energize these coils with single phase power if possible.
    I had hoped with the information that brought the coils to 750, one might have an idea of conversion from 57.5 volts 3 phase WYE grounded, to 120v or 240v single phase, via filters, capacitors, resisters, thyrister, etc...

    #3 Final projection would be building a zero voltage cross over firing SCR
    power module to control the temperature, or possibly a simple PDI control with SSR's.
     
  12. dt38k

    Thread Starter New Member

    Jul 16, 2012
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    Hello Strantor.

    First thing comes to mind, WTF?
    Well put, you are right on, I've used that phrase in long form over 100 times in the last 6 weeks and 100's more phrases that I'm sure the group is familiar with.
    The reason I've been using the 480v boost transformer into the Delta/WYE is because it allowed me have a voltage lower than 120v to ground for testing.
    This Delta/WYE transformer was designed and built for this furnace to operate three coils that were .247 in diameter, looped in 5" long x 1" wide rungs in an 18" diameter circle.
    Total length of material is approximately 40' long.
    One element was missing and the remaining two are ate up from hot molten bearing babbit dripping onto them.
    All of the electrical wiring is gone and the internal parts from the thermocouple are missing.
    I have tried 120v single, 240v single, and 240v 3 phase both connected in parallel, series, and combination.
    Every test that I have tried, has failed (breakers , fuses) within 5 minutes.
    Research on low resistance heating elements shows that a good share had to be energized with step down transformers.
    Now this is research from back around the 40's and a lot of technology has came to light since then.
    If I need more resistance to hold the electrons inside the element, is there some way to damn up the current flow without blowing the component into a piece of melted gue?
    I need to do some digging for more parts laying around here to try.
    I have parts from two rotating anode x-ray defractometers that had 38 transformers each and a lot of electronics inside them.
    They had water cooled towers that shot the beam and their transformers were oil cooled inside 50 gallon stainless tanks, that also had the water coolant lines ran inside the tanks through a type of radiator.
    I attached 3 pictures of this stuff?
    These machines new were around 1/4 million, came out of Abbott Laboratories, they pull 50,000v to the chamber tower and the power plugs look like big cattle prods.
     
  13. takao21203

    Distinguished Member

    Apr 28, 2012
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    I think you have to analyze the circuit, means to measure currents/voltages at all points. The fact that the 30 Amp fuses did blow but the 15 Amps one's did not hints that either the currents are unbalanced, or one of the transformer is defective, or not wired correctly.

    You kind of need to estimate the currents in theory, and then verify in reality.
     
  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You may(should) have already done this, but. The first thing since this is used equipment would be to check the transformer coils for shorts and opens. Then check that the controller cont actors are wired correct and not shorted internally. Just because its three phase doesn't mean that normal trouble shooting steps don't apply.

    Have you checked to see if the ribbon heaters have all their separators in place? If they are working to a certain heat then blowing fuses, they could be "moving" as they heat-up and shorting between 'loops' effectively lowering the resistance to the point of placing too much load on the fuses.
     
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  15. strantor

    AAC Fanatic!

    Oct 3, 2010
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    It sounds like your heaters are fail. Sometimes things really do reach a point that they can't be fixed (cost effectively) and you need to take a step back and replace them. Other times they can be cost effectively fixed, by someone with all the right equipment. I service a plant full of extruders, each one having at least a dozen high dollar heaters on them. So I see a lot of bum heaters. I send them off to a local company called as askco heater who fixes them or replaces them and sends me a (big) bill.
    I've never seen tranformers used to reduce the voltage to a heater. It seems like a waste to me. If you had 3 good heaters, you could put them in series and 1/3 the applied voltage would be dropped across each one. So 120VAC would drop 40V across each. This is already less than your 57V output so it should draw less than whatever amps that's drawing. The fact that it doesn't, seems to be some confirmation that your heaters are no good. Heaters often short as shortbus detailed, as well as shorting to ground. I've seen heaters fail shorted to ground somewhere in the center, which effectively cuts their resistance in half and draws double amps.
    Yes, put more good heaters in series.
     
  16. strantor

    AAC Fanatic!

    Oct 3, 2010
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    what's the resistance of each of your elements, end to end, with nothing connected to them?
     
  17. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Are the heater elements marked anywhere with the intended applied voltage, 'cause 57 volts just sounds like a unusual number. And if the number is some low oddbal number, I second strantor about putting them in series. Using your clamp on meter, what is the current draw and at what voltage did you measure it?
     
  18. wayneh

    Expert

    Sep 9, 2010
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    You overestimate us. I can't make heads or tails out of this thread and lose interest quickly when there's a lot of words and few pictures. And by picture I mean schematic, or at least a block diagram. Scan a hand drawing if you have to. A photo of a box full of junk (no offense) doesn't count. It looks pretty much like my boxes of junk.
     
  19. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    @strantor, if they are the heat treat furnace heaters I'm familiar with, they are nothing like a extruder heater. Instead of a band or cartridge that is enclosed in a metal "jacket", they are similar to a heater in a toaster. But instead of a nichrome wire they are a "ribbon" that is looped back and forth, more like a kind of a squiggle. They are supposed to have spacers between the loops. No other insulation on them because of the high heat they produce.
     
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  20. strantor

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    Oct 3, 2010
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    I'm trying to take the mental image of a toaster and wrap it around something that I'm assuming is round (is it round? I don't know why I'm assuming it's round...) OP: Is there a wafer of high temp material that keeps the ribbon separated from itself and from surrounding material? If so, is this wafer a screwed up? is there any possibility of the ribbon touching anything?
     
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