transformer room construction

[dilbert318]

Our client has a old transformer that is powering an electric arc furnace. They want to replace the existing transformer with a larger one (over 100 MVA). The field generated by the existing unit induced currents in the elevated concrete floor slab reinforcing bars that raised the floor temperature to a little over 100 degrees F. We are replacing the floor with cast in place concrete and non-magnetic rebar. A question came up about also possibly using steel beams to support the floor. Will currents be generated in the beams and cause them to heat up as well (assuming the floor is about 12" to 18" thick)?

 

[EdStainless]

Using non-magnetic rebar will do little to reduce heating. It is still electrically conductive and will heat by the induced current.
And yes, the beams would heat also. How much depends.

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P.E. Metallurgy, Plymouth Tube

 

[SlideRuleEra]

Fiberglass rebar is non-magnetic and non-conductive. Here is a typical product: Link
I agree the beams will heat. Ground them with dedicated ground rods.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dik]

FRP reinforcing may not do well with the heat. I'll check with one of the electrical engineers tomorrow and see what can be done. May just be an issue of grounding reinforcing steel.

Dik

 

[dilbert318]

I am planning on using fiberglass rebar (GFRP) because of the electromagnetic fields. They should not heat up so the only heat in the room should be from the transformer itself. The unit is water cooled and the room is ventilated (natural not forced air) so I would not expect it to get too hot (will ask client about current room temperature). If we do use steel beams to support the floor, is there anyway to determine how far they would have to be from the transformer (how thick the floor would have to be) to keep them from being affected?

 

[EdStainless]

FRP rebar makes sense. Good call.
The beams will not be damaged, even common structural steel will take 800F without a problem.
The issues are things like thermal expansion and does a hot beam become a safety hazard.

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P.E. Metallurgy, Plymouth Tube

 

[wannabeSE]

I suggest contacting the project's electrical engineer or the transformer manufacture for recommendations. They should know more than structural engineers about inductive (?) heating of nearby steel. If FRP reinforcing won't work, stainless steel may be an alternative.

 

[Tmoose]

Magnet fields and conductive metal, like aluminum = Lenz effect.

https://www.youtube.com/watch?v=yk4ACjzDFRY

I like the demo at the end, after 4:00, with a steel ball dropped into an aluminum tube and descending slowly.

 

[dilbert318]

The electrical engineer has been looking into it and contacted the transformer supplier without and luck. We will just keep digging, thanks for all the input.

 

[dik]

checked with an electrical engineer in the office and he wasn't sure, except that grounding the rebar won't help.

Dik

 

[BUGGAR]

The Navy builds degaussing wharves for their submarines. Stainless and fiberglass rebar, aluminum superstructure, plastic piling. The in-haul machinery was some exotic material like titanium? They circle the sub with cables and pump in huge amps to de-magnify the sub. See one at Google Earth at Beckoning Point, HI; it looks like a sea monster cage*. Heat is not a problem but consider the exposure. And money is no object.

*After its completion, we spread rumors about the Navy secretly discovering and chasing a sea monster all around Hawaii for three years before they finally built a cage to hold it. And it took all that electricity to keep the beast restrained. This rumor was quickly squelched. Have you ever heard it?