Duct Bank Reliability Assessment

[kingpb]

I need to put together a proposal to do a duct bank reliability and condition assessment, whereby a Contractor will do the physical work and engineer observes and writes a report.

The tasks I have thought of:
1. Open manholes and look for obvious damage and rusting of supports. Take pictures.
2. Run a mandrel through each open conduit to verify integrity of each spare, and possibly determine any significant internal damage or deflection.
3. Megger each cable, although I don't think there is historically data to use.
4. Thermal scan any cable which splices in the manholes.
5. Provide updated as left conditions of conduits used and indicate usable and any unusable spares.
6. Check cable insulation types and gather cable manufacturer data on potential damage to cable insulation that has been submersed for 25+ years.

Anything else that would make sense?

Thanks

 

[nollij]

3. Megger each cable, although I don't think there is historically data to use.

I would recommend a VLF per manufacturer's recommendations if this is Medium Voltage Cable. It will give a more accurate assessment of cable integrity.

6. Check cable insulation types and gather cable manufacturer data on potential damage to cable insulation that has been submersed for 25+ years.

Sometimes you will get helpful information as in: "look for this this and this" and you may also get "you need to replace EVERYTHING."

Regardless, it would be best to talk to the cable manufacturer about the integrity of the cables and what testing would give useful information.

"Just because *you're paranoid, doesn't mean they're not out to get you"

 

[wireguru]

dont forget to include a copy of the report on the Bellagio incident

 

[BJ Conner]

Check Bends

Check Bends

Observe and record the static bends ( training ) in the valuts.
Note wheather they exceed the manufacturers minimum bending radius.
The cables that have been left in tight bend are the ones that let the blue smoke out when they are moved.

 

[Mike01]

??

??

dont forget to include a copy of the report on the Bellagio incident

sorry for my ignorance but what is the "Bellagio incident"?

 

[nakulak]

apparently the primary and backup power systems were run in the same pipes, causing some problems when the power went down, and an inability to work on one power system safely (deenergized). I don't know the whole story, but you can probably find it on the web.

 

[wireguru]

sorry for my ignorance but what is the "Bellagio incident"?

bad stress cone caused a whole bunch of stuff to burn up. generator feeders were in the same duct bank and vaults as the utility feeders, couldnt run generators during repair -down for 3 days at a cost of several million. they had every MV splicer they could find working there around the clock and had to get cable from a utility in los angeles as they couldnt find enough cable to replace the damaged runs.

 

[don_resqcapt19]

I would want to know about the cable loading. There was a lot of discussion about thermal damge to duct bank conductors when they are loaded any where near their Table 310.16 ampacity for the 93 or 96 code. At one point, the ampacity tables in Annex B were acutal code ampacity tables and the reason was the heating in duct banks.

 

[jghrist]

You might also want to check the condition of the manhole concrete. Note any cracks, deterioration such as spalls, scaling, peeling, delamination, and drummy areas, exposed reinforcement or other embedments and the amount of corrosion.

In fact, you might want to check this first so that if there are any major problems, you can get the #%*!@ out of there and not do the rest of the work without structural reinforcement.

Also note the presence of water. Also integrity of ground wires. Also integrity of fireproofing tape if used.

 

[BJ Conner]

Belligo Fire

Belligo Fire

http://www.reviewjournal.com/lvrj_home/2004/Apr-15-Thu-2004/news/23660454.html

This is the LAs Vegas newspaper story on the fire.
When I first heard about the fire my thought was "Why didn't they go nuclear?"

They had two utility feeds, at least one from Emergency Generators all in the same vault. Everything went down. I would bet money the high heat in the duct bankfrom the desert and from the amperage made a fine oven.

The figure I read was $28 million a week down time. At that cash flow you can build a "trained" duct bank system with what falls out of the wheel barrows on the way to the vault ( money vault, not cable vault).

 

[kingpb]

Thanks everyone.

Has anybody got experience with IEEE 400 Type 2 testing?