Sunday, December 26, 2010

 

Redundancy, power grids, and trains up in the air


by Larry Geller

The Star-Advertiser this morning printed a comment from their website in the Insight section that I thought was, well, insightful:

"Fourth blackout strikes Ala Moana" Star-Advertiser, Dec. 23: Hawaiian Electric Co.: That's the company that will supply the "juice" to the rail, right? Ha ha! Good luck, all you rail-riders. 1 can just see the news headlines now: "Rail riders stranded mid-air for 7 hours; HECO stumped." You don't build rail on a crumbling infrastructure, and that includes HECO's infrastructure.

This is only slightly unfair to HECO. We’ll never know (unless someone investigates) whether the cause of the repeated Ala Moana power failures was due to “crumbling infrastructure” or not. Actually, an independent investigation would be useful, but given HECO’s power at the Legislature, likely their report will be accepted as the last word.

The writer’s point that impressed me most was that rail riders would be stranded high up in the air should power to that portion of the system fail. Other riders would be able to get to a station and disembark, but they would not be able to complete their trip. That could mean spending hours in town waiting to go home, or taking the much more reliable bus system.

Of course, we could build a grade-level system. Riders would not be stranded up in the air.

Another solution is “redundancy” in the power supply. Regional power grids may be designed with redundancy. The ultimate redundancy is a mesh network, where every node is connected to others, so that if one part fails power still flows from another. Mesh networks are most often prohibitively expensive.

Still, one can have power come in from two directions. Even to a shopping center like Ala Moana.

I’ll cite a memorable example from personal experience. Back in the days of time-sharing computers, GE built a “supercenter” in Ohio. Uptime was critical to the company’s success. Banks were doing deals around the world, and any downtime at all was a catastrophe for them, just as an example. So the power to the huge supercenter was made redundant, right down to the local level. In fact, one set of cables went into the center underground and another was outside on the electrical poles.

One reason this sticks in my mind falls into the “best laid plans” department.  Of course, it pays to maintain equipment and test it from time to time. One day GE planned to test the switchgear for the power line that came in underground. The risk was small, the test would take only a few minutes. They did this periodically to be sure they could survive an emergency.

So they tested the switchgear. Just at that moment, a truck hit the outside power pole, and the commercial power was out.

No computer went down, though, because the internal UPS and generators kicked in.

Still, go figure.

Now, GE was willing to pay for that level of redundancy. Always, redundancy comes at a cost. Given the infrequency of power failures at Ala Moana, it would likely not pay for them to have a fully redundant system.

For a rail system, it would be different. Whether redundancy is in the plans or not, I do not know. It probably should be. Someone might check on this.  In other words, if power to a section of rail fails from the East, it would be supplied from the West, as an example. The cutover need not be instantaneous.

Now, backing off to the power grid itself, it is natural for utilities to eliminate redundancy as much as possible because of the cost. An independent grid operator might make different decisions. Redundancy cuts into the bottom line. Also, we have some geographic considerations, at least on Oahu.

There will always be a tradeoff between reliability and cost. A utility may not balance that equation the same way an independent operator would. How much reliability is built into the system should be a public policy decision, not ruled by shareholder interests.

If done right, a train, even up in the air, should not find itself at the mercy of “crumbling infrastructure.”

Or build the thing at grade level, which makes sense to this writer, anyway, for a number of reasons I’ve expounded on in this blog. Add to my argument the power question raised by the commenter. Power fails? Open the doors of a tram and get out.

Grade level transportation is inherently redundant. Cars  can drive a different route (usually if a street is closed. You can take a bus or taxi if the tram isn’t running. You can call your friend to pick you up.

If power is off and you are up in the air, there’s no backup for you, no redundancy. You’re just stuck. Probably with no air conditioning. Hope that the windows can be opened and it’s not raining.

The commenter is correct. Unless redundancy is already designed in, and unless the whole island goes out again, as it has (sigh).




Comments:

Post a Comment

Requiring those Captcha codes at least temporarily, in the hopes that it quells the flood of comment spam I've been receiving.



Links to this post:

Create a Link



<< Home

This 

page is powered by Blogger. Isn't yours?

Newer›  ‹Older