On the east edge of Mishawaka, Ind., there is a large electrical substation that remains where the Twin Branch coal-fired generating plant once stood. The plant was built in the 1920s next to the St. Joseph River hydroelectric plant. The power from the hydro plant could be used to bring the coal-fired plant online after a cold shutdown. The river also furnished water for the steam condensers. The environmentalists convinced the power company to switch from coal to oil. When the oil embargo hit, they were told to switch back to coal. Lacking a sense of humor, the owners had the plant dismantled in the late 1970s.
A few years ago, there was an explosion and fire in a transformer. It was one of those fires that they just let burn until all the oil used to cool the transformer had been consumed. Not every firefighter wants to rush into an area where 138,000V is the norm and start spraying water from a fire hose. Oil and water are not a good combination, even without the high voltage. I don’t remember if they tried foam. If they did, it didn’t work.
After watching the fire for a while, I wondered if removing the oil from the transformer would help. You need fuel, heat, and air to keep a fire going. I’m wondering if it would be feasible to have an underground tank connected to a drain on the transformer. Something as simple as a ball valve could be connected to a long linkage. This would allow the valve to be opened from a safe distance. It could also be motorized. Gravity would allow the oil to flow into the underground tank. The tank might need to be kept purged with an inert gas just to be safe.
I’ve heard about aircraft in trouble dumping their excess fuel before landing. You have to wonder where that fuel goes after being jettisoned. Jet fuel does not evaporate like gasoline. My hunch is that the fuel is jettisoned to aid firefighters in the event of a fire. If it works for aircraft, it might work for transformers. If the oil could be contained in the underground tank, that might aid in the cleanup. The less oil there is leaking out on to the ground, the better. Murphy says that if you are ready for the fire, it won’t happen.
I don't know if this system has ever been put into service, but it was apparently not at the Twin Branch fire.
This entry was submitted by Pete Ostapchuk and edited by Rob Spiegel.
Pete Ostapchuk was a radar operator on a Nike Hercules site in the Army, where he studied electronics through correspondence courses. He ended up in the electronics engineering department at CTS for eight years, where he worked on industrial automation projects. He also worked at Bayer for eight years in medical diagnostics R&D.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
I would like to know a bit more about the tranformer failure modes and then design safety features around the most common issues. Removing the fuel from the fire and keeping it away and safely held after an incident is a good idea.
My guess is that the incidence of this kind of failure are low enough that the insurance companies are willing to put up with it.
Recall that in the early part of the last century steam boilers were routinely used for heating apartment buildings. teh insurance companies eventually enforced the adoption of what would become ASME standards for boiler inspections and safety operations.
The same thing applies to the blowout preventers on oil drilling rigs like the one that failed on the BP rig in the gulf. the oil companies should have to obtain unsubsidized insurance on their operations and be held liable for uncapped (by the Feds) liabilities if they screw up. the blowout preventer manufacturers should have good designs, well tested and thorough inspection standards to insure their systems perform adequately.
Insurance costs can be a pretty effective way to force environmental responsibility.
Gee, the idea of an underground tank connected to the drain on the transformer seems obvious. Could there must be some good reason why it hasn't been done?
I don't know enough about the electric industry to say that it has not been done or proposed. If it has not been done, it might just be one of those things like surfing the internet while walking the dog. We never realized we just had to have the capability.
Even the pole transformers that feed your house have oil in them but it's not a big deal when one of them catches on fire. As the size increases, the scope of the issue goes from a nusance to a catostrophe.
If it hasn't been done, it could be an economic issue. How much would such an installation cost? How much would the property tax on such an installation cost each year? How often do the really big transformers catch on fire? Would there be any savings on insurance?
Maybe someone with the answers will respond. Pete O.
The oil in these transformers is there as an insulator and coolant. The incidence of these transformers exploding is very small, and I'd guess the possibility of something opening the drain and emptying the oil by mistake is greater than the possibility of an internal short-circuit igniting the oil. As a firefighter, our protocols for high-voltage electrical fires is quite clear; protect your exposures, evacuate as necessary, enjoy the show. As far as aircraft dumping fuel; most aircraft taking-off with a sufficient load of fuel for the trip and reserve are too heavy to land without overstressing landing gear and other parts of the aircraft. When fuel is dumped, the aircraft are typically advised to either move to a loiteriing area and begin dumping, or dump as they travel to the nearest airport. The fuel becomes a mist which is quite diffuse and is considered non-hazardous. As opposed to keeping it in the aircraft and converting the entire load to heat immediately after landing.
I would not be too concerned about the oil being dumped accidently. These monster transformers do or should have their vital signs monitored at all times. We're not talking about a $5,000 pickup truck running low on oil.
I looked at the oil evacuation system in the supplied link. Two problems that I saw were the secondary tank in close proximity to the transformer and the theory of operation requiring the integrity of the transformer case to not be compromised so the transformer can be pressurized. At least someone has given it some thought. Pete O.
Adding to Bob's aircraft comment- Long range aircraft carry about 1/3 of their takeoff weight in fuel (e.g. 300,000 pounds of fuel on a 747 with 900,000 pound max gross takeoff weight). The max landing weight is lower, so fuel is dumped if a problem happens on or after takeoff. If the emergency requires an immediate landing, an overweight landing inspection is performed.
Shorter range aircraft such as 737 and A320 can land with max fuel and don't have a fuel jettison system. If a situation requries minimium fuel it has to be burned off. Usually by circling around for a few hours at low altitude where jets are inefficient.
We recently had an oil filled pad mounted transformer 'explode'. At least the earth moved for me in my office, about half a block away. Although the transformer case was severly deformed from the internal pressure, there was neither fire, nor appreciable leakage. These are typically out in the open, no longer contain dangerous pollutants, and fairly rarely ignite. I can imagine that it would not be cost effective to add all these components being discussed, or the utilities would be all over it.
Now if it's and underground transformer, downtown...
I agree, Chuck. It is surprising this safety featue has not be imagined earlier. While it would involve costs, the costs would be nothing compared to the value of ending a fire quickly.
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