Like most Americans, I watched the Big Bowl Game from New Orleans last Sunday night. And, light most, I witnessed the black-out that caused a fairly significant delay in the game. But, unlike most, I’m familiar with the operation of large electrical systems, and thus began fielding questions about the electrical outage from my fellow game watchers shortly after it occurred. It was a tough transition to get my brain from chicken wings and pig-skins to electrons and circuits, but after a few false starts (and accompanying five yard penalties) I was able to start explaining what was going.
So, the Big Bowl Game party I attended may have been one of the few which did not spawn its own conspiracy theory about what occurred on that fateful night. I’ve heard a number of different conspiracies, some more plausible than others, so here are some of my favorites:
- NFL commissioner Roger Goddell ordered a breaker to be thrown so he would have enough time to orchestrate the 49er comeback, and thus boost TV ratings.
- A Vegas bookie that was going to be wiped out if the Ravens won by that much, “made a few calls”, got the lights turned off, and slipped some drugs into the 49ers water in the ensuing confusing.
- Jim and John Harbaugh’s father was asked point blank if he had wanted John to win all along, and he had the lights killed to avoid answering the question.
- Jimmy Hoffa did it!
As much fun as these wild and fanciful ideas are, the truth is much simpler and much more mundane.
You down with OCP… Yeah you know me!
The way electrical circuitry is built in the U.S. is based on the guidelines from the National Electric Code (NEC), which is put out by the National Fire Protection Association (NFPA) every 3 years. The birth of the NEC came out of a number of electrical fires in factories and other buildings that caused a large number of deaths around the 1900s. The NEC is specifically designed to codify the guidelines for the safe installation and operation of an electrical system. (Though not technically law, the NEC is enforced by most municipalities. Certain larger cities, like Chicago, have their own electrical codes.)
Let’s discuss the basic anatomy of a circuit:
The lamps are the ones that went out in the stadium, the “Battery” is the source of electricity, in our case the utility, and the switch is where the lights are controlled. In our case, let’s assume that the lights are controlled directly from the electrical panel. For this type of circuit, the NEC requires over-current protection to be installed on the circuit. (Yeah…, that’s right…, OCP!). The over-current protection device makes sure that current in excess of what the circuit wiring can handle ever goes down the wire. Current in excess of the value for which the wire is rated would cause excess heat on the wire, which would in turn damage the wire’s insulation, leading to a fire hazard. The over-current protection device will “trip” if it sensed currents in excess of its rating trying to pass through the device. The over-current protection device “trips” in order to protect the wire and avoid a fire. Here’s the picture of an over-current protection device you may be familiar with:
The one that tripped during the Big Bowl Game was much bigger than this one, but operates essentially the same way. (Why can we point to it being an OCP trip of some sort? The overall speed of recovery of the lights and other electrical equipment is a major indication. If there was a different fault with the electrical system of the stadium, it would have taken much longer to resolve.)
What a long, strange trip it’s been!
So, now that we know that the issue was most likely caused by an OCP trip, can we determine what caused that trip?
There are multiple points at which circuits are protected with some kind of OCP device. OCP devices are located in each electrical panel. For large commercial electrical systems, like the Superdome, there can be dozens of electrical panels, with some of those electrical panels housing the OCP for other electric panels (sub-panels). Think of all these electrical panels like a tree, where the trunk is a single electrical panel called a main distribution panel, which feeds larger branches called sub-panels, which further feed smaller branches.
So that’s what’s going on inside the building, but what happens to the wiring outside the build, on the utility side of the meter. The utility also has its own OCP on the circuits that go to the individual feeder circuits. These devices are much larger than the breakers you have in your house. But, you might be familiar with what one of these devices looks like:
Though, these are commonly referred to as transformers, they actually serve double duty. They are transformers that transform the voltage on the electrical lines from one voltage to another, but they also provide OCP for the circuit. (These are typically large fuses instead of breakers, but the principal and the operation of the device is the same.)
So, without additional information, you potentially have to walk the circuit all the way from the lights that went out back to the power plant to figure out exactly where the fault occurred. Because the current electrical grid is a “dumb grid” as opposed to a “smart grid”, the utility has very few sensors that will allow it to quickly pinpoint where the issue is, or even that there is an issue at all.
(I’m guessing the way the local utility found out about the electricity failure was that someone called them to let them know the electricity was out. That’s how they currently find out about power outages, so why would this be any different? This is my plug to get people to support the smart grid. It just makes sense!)
Here’s the official statement from Entergy, the utility that provides electricity to the Superdome:
Shortly after the beginning of the second half of the Super Bowl in the Mercedes Benz Superdome, a piece of equipment that is designed to monitor electrical load sensed an abnormality in the system. Once the issue was detected, the sensing equipment operated as designed and opened a breaker, causing power to be partially cut to the Superdome in order to isolate the issue.
Backup generators kicked in immediately as designed. Entergy and SMG subsequently coordinated start up procedures, ensuring that full power was safely restored to the Superdome.
The fault-sensing equipment activated where the Superdome equipment intersects with Entergy’s feed into the facility.
There were no additional issues detected.
Luckily, the fault occurred at the Superdome, where most of the electrical circuitry has sensors. The sensors let the building engineers know very quickly where the problem was so they could begin to fix it. So, now we know what happened, and why it happened. So, if it was an easy thing to correct, why did it take so long to get the lights back on? The answer lies within the lights themselves.
Ballast, and Lumens, and Metal Halides… Oh My!
The lights at the Superdome are called metal halides, which fall into the category of high intensity discharge (HID) lights. They provide much more light, or lumens, that a normal light. As a comparison, a 60-watt incandescent produces 800 lumens of light per lamp. HID lights can produce more than 15,000 lumens per light. But, let’s face it; you already knew that stadium lights were brighter than regular lights.
The downside to HID lights is in the properties of the materials used for lighting. These lights take 2 to 15 minutes to “warm-up”, and can take 5 to 20 minutes to “re-strike” if they are already warm. (This “re-strike” scenario is the situation we were in with the lights at the Big Bowl at the Superdome.) These time delays are to get the lamps to 90% of their full light output. I’m guessing they waited a few extra minutes to get closer to 100%.
(For more details, check out this article from the Energy Information Administration (EIA) – http://www.eia.gov/todayinenergy/detail.cfm?id=9871&src=email)
Based on what we’ve discussed, here’s a rough timeline of the power outage:
0min OCP tripped
+1 min back-up generation kicked on
+5 min power restoration procedures begun
+25 min lights back to 90%
+30 min players being their re-warm-up
+34 min Game on!
Given what happened and the technology involved, I think everyone involved did a pretty good job, and restored power in a good amount of time. That didn’t stop me from getting antsy for the game to start-up again.
Mr. Goddell – How about next year you make sure the stadium for the Big Bowl game has a smart meter installed? Just in case.
Then again, it’s possible that the extraterrestrials that are slowly taking over the underground nutria fur trade in New Orleans needed a few minutes of distraction to get their latest shipment out of town.