Big Electricity

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Working with industrial electricity is a lot different than household wiring. One of the people who work with this also blogs as Mostly Cajun and he related a wonderful story of one state government at work: bq. Just about twenty or so miles to the north of where I�m sitting is a medium security facility owned by the State of Louisiana. Several years ago, one of the local electrical contractors called us. They�d been called to the prison because of a �transformer blow-up.� We do work on transformers way past the scope normally done by electrical contractors, so off I went. The problem wasn�t actually IN the transformer, but rather the switch which determined which of two high voltage sources fed the transformer. bq. The transformer itself was installed in a little utility room in the prison�s maximum security cellblock, and there was an open window next to the utility room door. That window was heavily barred, but it was in the guard�s office. When he saw me first walk up, the called to me and I asked what he�d heard. He said it was a loud blast, like a big shotgun, then the lights went out. He and I laughed about the idea of a shotgun blast in a prison. I imagine his laughing was a relief, because I�d bet when that transformer went off, he had other ideas in mind. bq. Anyway, I tested the transformer just to make sure it was okay, then discussed with the electricians what they needed to do to repair the blown-up switch. After everything was repaired, I was on my way. Of course, being a good steward of my company�s business, I left business cards with the maintenance people at the prison. bq. Fast forward a few months. The story is a long one so I have put it below. Click on the Continue Reading "Big Electricity" link for the rest.
bq. About ten at night. I get a phone call. Could I please hurry over to the prison. All the lights are out. ALL THE LIGHTS. So I do indeed hurry. And when I get there, I find I have been told the absolute truth. The prison is in the dark. Not a single light on, except for the headlights of the prison guards who are now sitting OUTSIDE the fence in their pickup trucks, shining their headlights through the double security fences into the prison compound. bq. I drive around to the prison powerhouse, which is (fortunately) outside the security fence. When I get there, I am met by the maintenance manager, the �electrician� and two prison trustees. I ask what they know, and they don�t know much. They did determine that the fuses had blown on the pole where the utility company feeds the prison. We�re waiting on the utility company to come replace the fuses. bq. By flashlight, we go into the powerhouse and I start looking at the big line-up of 13,800-volt circuit breakers. One of these should have tripped for sure unless the electrical fault was between the utility pole and the powerhouse. If there was a fault between the pole and the powerhouse, we were out of luck. But that wasnt the case. My flashlight was shining on the indicators showing me that the fault was on one of the two high voltage cables that circle the prison, powering up several different transformers. None of the breakers had opened. I had them all opened at this time so we could investigate the problem. bq. The arrangement was what we very descriptively call a �double ring bus". Two cables make a loop around the facility, hitting each of the transformers. Each transformer has a big selector switch which lets it take power from either of the two feeds. This is normally a very good system. Here�s why. One of the cables had failed. Normally, this means that the circuit breaker for that cable and that cable only would open. Of course, the transformers feeding off that cable would become deenergized, and they�d lose whatever loads were on those transformers, but not the transformers feeding off the other cable. And as soon as a determination was made that it was a bad cable, all they had to do was switch the affected transformers to the other feed and all the lights would be back on. That�s the way it�s meant to work. bq. What happened, though, is at some time prior to this problem, they had trouble with a battery charger. The �electrician� didn�t know what that big bank of batteries was for, so they just killed the battery charger and let the batteries run down. And nobody knew there was any sort of problem, because the batteries had only ONE function in life, to trip those big circuit breakers in case of a fault. bq. In the electrical power business, there are a couple of terms I want to briefly explain. The first is �selectivity� as it pertains to protective device operation. Selectivity basically means that you don�t want to trip off as little equipment as possible in the event of a fault. In our case, ONLY the circuit breaker supplying that one feeder cable should have tripped. The rest of the equipment should have stayed on line. bq. That�s the second term, coordination. Simply, that means that an upstream device like the main breaker that feeds the line-up of branch breakers will trip slower than the branch breakers, if both see the same level of current. What should have happened was that the main breaker and the branch breaker both saw the fault current but the branch breaker was set to trip much faster. bq. But without the battery bank to supply the trip ower, NONE of the breakers tripped. And the next protective device up the line was the pole-mounted fuses. These too saw the fault current and blew after the appropriate time lapse. And ALL the lights went out. bq. The guy from the electric company showed up and put in a new set of fuses. We went back into the powerhouse to close the main breaker. But there was a hitch in this plan. The same batteries that provided trip power also provided power to close the breakers. I asked how they�d been closing breakers. The �electrician� said they just stuck a bar in that hole in the front of the breaker and pulled up. I sort of shuddered. The �hole� and the �bar� were tools meant for use in manual operation for maintenance, not for closing under load. But he knew his equipment, right? I soon found out differently. bq. He maotioned for one of the prison trusties, a young black fellow, to come over and close the breaker. This was successful. Then he closed a breaker that fed the station power for the powerhouse. Lights came in in the powerhouse. Me and a platoon of prison guards and the �electrician� then went into the prison and switched all the transformers off the failed �B� feeder onto the presumably good �A� feeder. I was thinking that this should get the lights back on inside the prison. bq. So while we were standing around talking about the next step, the trusty went over and closed� the wrong breaker! The one connected to to the failed feeder. And the brand new set of fuses on the pole outside blew. And all the lights went out again. I reached in my back pocket for my flashlight. I illuminated the phone for the maintenance supervisor to call the utility company, and they turned their guy around before he got home. Luckily for us, he had just one more set of fuse links, and in a bit we had the lights back on. bq. This time we got the RIGHT breaker closed, and the prison lighting returned to normal. So I told them that night, and I wrote in my official written report: �Fix the battery charger. Get the old feeder replaced. You�re running on your ONLY feeder now.� bq. But this was a part of Louisiana government, where competence is but a word in that big book on the shelf that doesnt� have a lot of pictures so nobody reads it. bq. Fast forward a year. Near midnight, the phone rings. �We�re in the dark again.� bq. So off I go. I get there, driving past all the guards in their pickup trucks, straight to the powerhouse. The utility company guy is right behind me. I met a contractor electrician there. And the prison maintenance manager and his �electrician". bq. First get the lights on in the powerhouse. Okay! They�re on! bq. Now, I ask the maintenance manager and the �electrician� why ALL the transformers are still on the �A� feeder. bq. �Let�s put them on the �B� feeder. Ya�ll got that fixed a year ago, didn�t you?� bq. The hanging heads and silence spoke volumes to me. bq. �You mean the other feeder never got fixed?� bq. �No.� bq. �Well,� I said. �Maybe I can isolate the bad section of the �A� feeder and we can get part of the lights back on.� bq. They okayed that idea. So I set up the equipment to start testing. And while I was testing, the maintenance manager was telling me how these cables were thirty years old and needed to be replaced anyway, so he hoped they�d all fail. The cables failed. The music I�d been hearing changed from �I hope this old crap fails� to �Omigod! What�re we gonna do now?!� bq. I gave him the number to Aggreko, a major supplier of portable generators. �You�re gonna need at least three big ones, here, here and here.� I pointed to locations on the prison�s electrical plan. �I think these guys (pointing to the electrical contractor) will get things connected for you. And they can change the cable out. If you want me to test it when they�re done, call me.� And I took my signed timesheet and left. bq. A week later I got the call to come test the new cables. Approaching, I saw three big Aggreko diesel generators and their fuel tanks sitting around the prison. My tax dollars at work. bq. I expected that the contractor would be waiting for me with the cables finished when I got there. Nope. I found upon arrival that the electrical contractor doing the installation was not the same company that I�d been working with before. THAT company was a highly competent bunch, supplying trained workers capable of doing any task in a heavy industrial environment. High voltage cables were an everyday job for these folks. bq. What was out there installing cables was small-town electrical contractor, apparently some sort of �brother-in-law� deal having been made. And while these guys might be fine installing the 277-volt feeders for a Burger King restaurant, they were over their heads in dealing with the 15,000-volt cable they were installing here. First thing I did was give a quick class on high voltage cable splicing and terminations. My words were eagerly received by smiling, bobbing heads. And off they went. Their foreman confided that they had a real high-voltage cable guy, but he was off sick with the flu. By mid-afternoon, they were ready to test the cable. So I hooked up my test set and began the application of test voltage. This was a 15kV cable, and I was headed for 65,000 volts, the standard test for new cables of this type. But I got to 8,000 volts and < > the set tripped off. It had failed! bq. The audience I�d acquired to watch my test was crestfallen. I wasn�t. It wasn�t totally unheard-of for a poorly made splice or termination to fail. Even brand new cable could fail, especially if it had been improperly handled during installation, like beeing pulled too hard or pulled around to sharp a bend. Competent contractors knew this and took the necessary measures. bq. All I had to do was locate the failure point so we could fix it. For this we had a little bit of magic called an impulse fault locator. We referred to it as a �thumper". The idea was that you hook this thing up to the failed cable and a high voltage source, fill the thing (capacitor) up with electricity, and when it gets full the voltage causes it to jump a spark gap and dump into the cable. Then wherever the cable is faulty, the electricity jumps that spot with a loud �thump". You can locate the fault spot with your ear. Except the sound is more like a pistol shot. And it was heard resoundingly in the middle of a yard full of prisoners in the midst of their afternoon stroll. To say that the sound drew more than passing attention is an understatement. You should have seen the heads turn! bq. We had our fault location. Down in a manhole where the electrical contractor had just spent several hours making up a complex splice. I descended into the hole and checked the splice myself. The top, the easy to reach part, was beautifully done. Buthe underneath, harder to reach, well, it had a hole in the tape that I could stick my finger into. I climbed out of the hole and called all the contractors together for another little training session. bq. This time I emphasized the salient points to successful high voltage splices: Clean. Dry. Proper sequence of taping. No voids. Proper thickness. I told them to make the guy in the hole doing the splicing as comfortable as you can get in Louisiana in August: Shade. A fan. Dry rags to keep his sweat off the splices. And we tried it again. Several hours later, we were ready to try it all again. And this time the cable passed. We disconnected generators and put the power system back right, except they still didn�t have the battery charger hooked up. I couldn�t convince anybody at the place that it was important. bq. That did not surprise me. They had a half-million dollar standby diesel generator in their powerhouse that had NEVER (according to them) run right since it was installed. They (and I) doubted that it would even start. And the maintenance manager and the �electrician� both regaled me of tales of their many faithful years of state service, but neirther knew as much about their power system as a good hoe handyman. The fact that the place ran at all was an amazement to me. Had any of my industrial clients found their equipment in similar condition, heads would have rolled. But then, industrial clients had to show a profit. State facilities just have to exist�

1 Comment

Major engineering college, where the campus 'computer room' has both a mainframe and a supercomputer along with the standard piles of other lesser servers/phone switches/etc.

Outside is a major diesel generator - when running it provides not only power for everything inside that 4 story computer building, but full power for several other nearby buildings and lights-only power for most of the campus. But it takes 3 full minutes for the output to stabilize.

There was a year or two where the battery backup could handle the load for 3:07.

Watching the guys responsible for starting the diesel blast out of the room running for the diesel and powering off everything (other than the mainframe and the sc) is... amusing. (They have more than 7 seconds once they start dropping other load, but jeeeze.)

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This page contains a single entry by DaveH published on October 17, 2004 11:53 AM.

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