IR Detection for Electric Arc Furnace 1

[cjhut]

We have a 7MVA electric arc furnace transformer that uses water cooled jacketed cables to feed our electrodes. Each phase has two paralled conductors connecting from the secondary bus 275v 17,000 amps to our electrode holders. At times we don't get enough water flow to one or both of the conductors and it doesen't take much time to do some damage. I was thinking about a IR sensor or combination to monitor the bus temperature at the secondary side connection. I would like a 4-20ma feedback to go to a PLC and then go from there. Has anyone out there tried this before? Any suggestions on a cost effective unit? Or maybe there is a more simple approach. As far as moniotring the water flow, it's well water and very high n minerals. We haven't had any success going that route. Aside from that it doesn't foretell a bad connection.

 

[Zogzog]

These are perfect for your application

http://www.qhigroup.com/infrared_monitoring.html

 

[Compositepro]

It seems to me the least expensive, most robust, and fastest acting would be to use a voltage sensing wire and relay that would act if the voltage drop between the buss and electrode rose above a certain level. With a meter display you will also have some ability to forecast a failure.

 

[cjhut]

Thanks Zogzog. I'll look into these. My only concern would be the magnetic field caused by the large currents. I will talk th=o the mfr.

 

[Zogzog]

I used to deal with them on a regular basis and recall them doing a similar project for a steel mill.

 

[PHovnanian]

cjhut, I guess I'm not following the problem exactly. Is it a water flow problem or an electrical connection problem?

Each problem may dictate a different sensing approach (V drop,thermal sensing, water flow and/or temperature rise).

 

[cjhut]

phovanian,

A water problem turns into a bad connection in a hurry. If the water stops flowing the buss and connected cabling expands considerably, then when not loaded cools. This causes the connections to come loose. So heat is the enemy, which is the first problem leading to a bad connection.

 

[PetroSynergy]

Im no EE, however, I do know quite a bit on hydraulics and thermo. Wouldn't the simplest solution just be to fix the water issue? Install a small activated carbon filter and water softener to keep the jacketed cables from fouling due to high mineral content in the well water.

William Hammett
Synergetic Engineering Consultants

 

[PHovnanian]

IR sensing will work But coolant flow sensing will give you the earliet indication of trouble.

Perhaps you can enlist the aid of a mechanical engineer with experience in handling your water type. A thought about high mineral content water: It could react with, coat or otherwise plug up your cable cooling system. If the minerals are interfering with flow sensors, they could be plugging lots of stuff up. So filtering might be in order. Then, some sort of flow and or filter back pressure monitoring will be necessary.

 

[cjhut]

Phovnanian/PetroSynergy--I agree with you both. I have left out alot of details about the water cooling system. We have discussed these types of options before. I would love to see a cooling tower sytem, but we don't have enough physical space left to install a unit big enough for the BTU's needed. We are cooling other parts of the sytem with this water system. There is a 10 inch pipe feeding all of the devises on the water train. To properly filter it, it would take some extensive downtime to replumb all of the piping, not to mention shut the well pump off which is critical to other operations. Our facility doesn't do any scheduled shutdown's anymore. So time is a factor. Keep in mind the amount of power flowing through these cables. It only takes seconds for the heat to rise quickly. I am thinking if I can catch it before it reaches a critical expansion point, I can alarm the system and open the vacuum switches feeding the transformer. However, I would like to look into filtering, is there anyone in the US, Pennsylvania area that anyone knows of who could help us size and quote this?

 

[matthewm1965]

When I was involved with electric furnaces years ago, we fitted flow switches in the water return pipes from each electrode. When the flow rate dropped below a predetermined level, it signalled an alarm. Simple and effective.