I worked on a project that received agency approval that used a water cooled copper RF coil for inductive heating. Not exactly the same but it had some of the same issues.
Jeff wrote- >(1) Is it considered necessary to completely isolate the water-cooled >live component from circuitry by locating it in a separate chamber? We did not isolate the live component by placing it in a seperate chamber. >(2) Single-fault safety when circuitry is in the same enclosure as the >coil if the tube ruptures and the box fills up with water, this is a hazard >as water is rightly considered a conductive element. Drains are >sometimes used to avoid this, but there is still the problem of water >spraying. Splash guards and the like may be used but this involves >some expense. Is copper tubing considered inherently unsafe, i.e. >something that is expected to rupture? We solved this problem by ensuring that any shorts caused by leaking water would open the circuits involved very quickly. We also used a drain in the floor of the enclosure. We used no splash gaurds. Copper tubing was not considered unsafe, but welded connections and water connections were considered unsafe. In these areas we had some additional covers over other exposed components (sealed plexiglass covers). >(3) If we use de-ionized water (and stainless steel tubing to avoid the >copper corrosion problem), can we assume the water acts as a >protective impedance? Could we prove this by filling the chamber >with de-ionized water, applying RF, and measuring the leakage >current? How much RF leakagecurrent is permissible? We also used DI water, but this issue never came up. >(4) Are water fittings considered inherently unsafe? We have been >unable to find any agency-approved fittings. You won't find any either. Water fittings are considered inherently leaky. You will have to address leaking water wherever they are located. >(5) Has anyone considered (or accepted) putting a ferrite around the >water tubing to form an inductor, thus limiting the RF current in the >water? Or coiling the tubing to create an air-core inductor? This issue also did not come up. >(6) I once received an RF burn from an experimental system with a >water-cooled cathode. This was in a crude garage shop >atmosphere (not our company). The cathode was immersed in >water that was sourced from a faucet, so it was ordinary tap water. >The supply was 400kHz, 5kW. The water supply >hose was ordinary garden hose. Between the faucet and the >cathode were two lengths of garden hose with brass fittings. I >inadvertently touched the >fitting that connected the two hoses together, about ten feet from the >cathode. The only grounding at the time was whatever was achieved >at the faucet. We later provided some grounding at the fittings and >supplementary grounding at the faucet. All this prompts the question: >Is it considered sufficient protection if the bulkhead fittings are fitted >to a grounded enclosure? Are starwashers or the like required? We used discrete grounding straps everywhere, secured with star washers. >(7) Is it necessary to provide a SUPPLEMENTARY ground for the >enclosurecontaining the water-cooled coil/electrode? We had a supplementary ground for the enclosure. I think that you could not have enough grounding in this situation. >(8) What if, instead of running water THROUGH the coil, the entire >coil is IMMERSED in water in a metal enclosure? Would double >ground connections be sufficient, assuming the leakage current is >within allowablelimits? No experiance with this issue. >(9) Is it allowable to connect neoprene hose to the coil? I have some >doubts about neoprene's capacity to withstand RF fields. What hose >materials would be considered safe/reliable? No experience with this issue either. >(10) Is a drain required? If so, must it be large enough to drain the >water at the maximum rate at which it could accumulate, or is the >pressure relief provided by the drain sufficient? Then there's the >question of equipment orientation . . . must a drain be provided to >serve each potential physical >orientation of the installed equipment? We had a drain, large enough to remove the water that could accumulate from a worst case leak (meaning no water accumulation). I hope this helps. Frank West Regulatory Engineer TUV Essen Of course, these are my opinions, not those of TUV Essen. --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
