MEC&F Expert Engineers : UNDERGROUND TRANSFORMER EXPLOSION IN INDIANAPOLIS SENDS MANHOLE COVERS FLYING, RESULTS IN POWER OUTAGES; 2ND IN A WEEK

Thursday, March 19, 2015

UNDERGROUND TRANSFORMER EXPLOSION IN INDIANAPOLIS SENDS MANHOLE COVERS FLYING, RESULTS IN POWER OUTAGES; 2ND IN A WEEK






MARCH 19, 2015

INDIANAPOLIS, INDIANA

Crews are responding after a reported explosion in downtown Indianapolis.
It happened at the intersection of Capitol Avenue and North Street. Smoke was seen pouring from manhole covers. At least two manhole covers were sent flying. The explosion was first reported around 6:45 a.m.

Crews from Indianapolis Power and Light, the Indianapolis Fire Department and the Indianapolis Metropolitan Police Department have been dispatched. IPL said some customers will experience power outages. Several traffic lights were out in the area, and IFD said power was out in a 4-6 block radius from Capitol and North.

One person was trapped in an elevator and later rescued after the explosion. Several buildings in the area were evacuated as a precaution.

The explosion follows an incident on Mass Ave earlier this week attributed to faulty equipment.

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IPL provided the following statement for the Mass. Avenue explosion:

At 8:42 PM IPL received a report of a possible underground network event in the 300 block of Massachusetts Avenue.  IPL crews are on-scene and have reported that a primary oil chamber failed. The chamber is located within a vault. There was a report of a flash and loud bang when the event occurred. The area has been secured and IPL crews will continue to investigate the reason for the failure.


Portion of Mass Ave closed. IFD says preliminary investigation indications underground transformer blew.

The company is trying to determine what caused the piece of equipment to blow.


"We've brought a second-party group in to help with that investigation to make sure that it's a thorough, complete investigation. We don't anticipate results from that for probably two or three months," Riley said.

"We've isolated the piece of equipment, so we'll be able to do the investigation, and when the time comes to replace or restore that piece of equipment, we'll be able to do that without any interruption of service."

Aaron Hutchinson, general manager/operating partner of Oceanaire Seafood Room, said the restaurant did not attempt to reopen for dinner Wednesday night, after power was restored.

Oceanaire, Napolese Pizzeria, Kite Realty and Carson's department store were evacuated and without power after the incident. A building at 30 S. Meridian with state court and administrative offices also was evacuated and closed after the incident.

"I was in the office when it happened ... it kind of sounded like somebody dropping a keg or something," Hutchinson said. "But we were back open again this morning. Today it has been business as usual."

Riley said it is too early to lay out plans to prevent these kinds of equipment failures in the future. Officials will know how to proceed once the investigation is complete.

"I think the results of the investigation will either reinforce that we're doing everything that we could and should be doing, or if something else comes up that informs us that we need to be doing something different in the future, we will certainly take that into consideration," Riley said. "We want to make sure that people still feel safe and comfortable coming Downtown and enjoying all that it has to offer."

IPL was investigated by state utility regulators, after underground explosions in 2010 and 2011 damaged cars and buildings and hurled manhole covers into the air.

Riley said residents shouldn't worry about these kinds of explosions happening on a regular basis.

"This is really just a unique and isolated incident. I know there have been some other situations with manholes in the past, but this is a different situation," he said. "We've not seen anything like this in 20 or 25 years. ... We've not had a network protector fail like this."

The fact that these explosions happened back to back within a week means that the transformers have reached their useful life and they will have to be replaced before they cause any more damage.  The operational life of transformers is 30 to 40 years.  Since many of them were placed in the 1950s and 1960s, their useful life has expired by quite a bit.  Time to replace them folks.


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HOW DO UNDERGROUND  AND ABOVEGROUND ELECTRIC TRANSFORMERS EXPLODE

Electrical transformers transfer energy between circuits, switching energy from one voltage to another. But when flooded with too much electricity, the sudden surge can cause a transformer explosion. As transformers detect an energy spike, they're programmed to turn off, but it can take up to 60 milliseconds for the shutdown. However fast those milliseconds may seem, they still may be too slow to stop the electrical overload.

A chamber full of several gallons of mineral oil keeps the circuits cool, but given too much electricity, the circuits fry and melt, failing in a shower of sparks and setting the mineral oil aflame. Mineral oil, in turn, combusts explosively and rockets transformer scything into the air.

All it takes is a trigger, a corroded or faulty wire, and the circuits surge will get ahead of the breaker--and in New York City, the previous day's snowstorm could have done the trick. Underground electric systems often suffer problems after heavy snowfall, says Bob McGee, a spokesperson for Con Ed. While salting streets may make vehicles and pedestrians safer, the salt can create hazardous conditions for underground electrical systems--salt that slips through manholes can corrode wires. 

If any arcing failure occurs within an oil-impregnated-paper (OIP) bushing, it frequently results in an explosive failure, causing arcing in the air, an oil spill and a major oil fire. This is not the case with resin-impregnated polymer insulator bushings.

Manhattan houses 35,000 underground and 47,000 overhead transformers for its 10 million residents, and of those 82,000, about 35 fail every year, McGee says. A failure doesn't always equate to a fire or explosion either; in fact, in the steadily decreasing number of failures per year, such an explosion is rare. 

Cable terminations failures in air- or oil-filled cable boxes also result in a high percentage of transformer fires. The typical scenario with oil-filled cable boxes is the initiation of an arcing fault in or at the cable termination. The pressure buildup from the arc ruptures the cable box explosively, ignites oil in or from the cable box, which continues and escalates as it gets fueled by oil spilling from the conservator or the main tank.

Mechanical forces on the cables from the explosive pressure forces and the fault current will often cause breakage of the bushings, and the oil spilling from the broken bushings will then be ignited by the arc.

Though the snowstorms may have had something to do with the incident, it will take time to analyze just what went wrong. If it turns out the salt from the snowstorm wasn't to blame, it may have been an older transformer. These can explode when their insulating materials begin to fail. This happens as cellulose and oil absorb water over time and degrade cellulose's ability to insulate, triggering an explosion.

The U.S. expanded its electrical infrastructure in the 1950s and '60s, and now, most older transformers have met or are nearing the end of their operational lives of between thirty to forty years.