Ampacities for Aluminum Overhead Electrical Conductors 1

[Mbrooke]

I have this PDF on my hard drive which I really like. My question is- is it legit? Are the values conservative or less so? Have they changed since? Can this be used in real world T&D engineering?

https://www.aluminum.org/sites/defa...num & ACSR Overhead Electrical Conductors.pdf

 

[7anoter4]

In my opinion, what we have to do it is to check if the tables are calculated according to IEEE-738/1986.
In my copy of IEEE 738/2007 is a QBasic program for steady-state and transient temperature calculation.
Never the less before 2007 and before Visual Basic 6 I worked in QB4.5, but now I don't remember how to run the application.
Therefore, I have to prepare an Excel file to check it, which means it won't be so soon.

 

[stevenal]

Southwire

 

[waross]

I remember an ampacity chart for cable in the field specs of a utility.
There was a note that using the maximum allowable ampacity from the tables would in most cases result in unacceptable voltage drop and heat losses and the maximum ampacities should only be used for short term temporary repairs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

The Southwire values look very conservative- and list 75*C instead of the minimum 100*C set by most ISOs and POCOs that I know of.

 

[DM61850]

Of course, they are going to be conservative. They want to sell more expensive conductors.

There are composite core conductors now that can be heated up to very high types without worry of permanent sag due to annealing. One utility installs it exclusively but I don't know how its price compares to ACSR and the like.

 

[Mbrooke]

ACCC conductor?

 

[stevenal]

394.5 AAAC Canton Southwire with wind and sun - 532 A.

Aluminum Association says 530, but all the values appear to be rounded to the nearest 5 A. Based on a sample of one, I see no difference.

A former boss of mine once did a loss/cost evaluation, and decided the rule of thumb should be to double the size determined based on ampacity. I don't know if the rule is still valid.

 

[DM61850]

Mbrooke,

Yeah, it is ACCC. Wikipedia says it cost 2.5-3.0 times as much as ACSR. At that price point, I kind of wonder if it makes sense for reconductoring where you don't want to have to put up new poles and towers rather than newly built towers that can been built to handle bundled conductors.

 

[Mbrooke]

I don't trust wiki- see the other thread- but it is certainly cheaper than having to rebuild miles and miles of towers.

 

[cuky2000]

For short OH transmission line (<50 mi) and short runs of cables for substation applications, the conductor thermal ratings should be used. Check if the ampacity data suggested by the PJM Guide for OH Transmission Cables are comparable with the one published the Aluminum Association for ACSR cables.
[sub]NOTE: For conductors such as ACSR, ACAR, and AAC that use hardened aluminum wires (1350-H19) or aluminum-alloy wires (6201-T81), the application of temperatures in excess of 100°C can result in annealing of the wires and loss of strength. [/sub]

Beware that for transmission lines of medium length (>50 mi) and long length(>150 mi), the operating ampacity is much less than the thermal rating that is driving by the allowable voltage drop ~(<5%) & SS stability limits ~(<35%).

 

[Mbrooke]

Thanks Cuky- all true.

 

[Mbrooke]

Maybe I'm wrong- but I thought 100*C was a minimum design operating temp and ACSR could go higher but not above 200*C.

 

[bacon4life]

Some older lines were designed for clearances at 49C or 75C. Operating ACSR at 200C would lead to some very dramatic loss of strength per the PJM guide. Splices and crimps are typically designed to operate at 70C for AAC and ACSR lines. Yes, utilities take hardware designed for 70C and apply it on lines rated much hotter. Luckily, most lines rarely operate at the rated temperature.

ACSS can operate at 200-250C, and always uses specially designed hardware.

 

[Mbrooke]

Thank you for the info. I was probably thinking of ACSS. What is ASCR typically run at?

 

[bacon4life]

I have seen anywhere between 75C and 140C as the specified max operating temperature for transmission ACSR.

I am curious what temperatures distribution utilities use, as we limit distribution lines to 75C. Distribution lines seem to have more risk of thermal failure than transmission lines because distribution lines may have more splices, more conductor damage, and lower quality workmanship.

EPRI has a good report available on high temperature operation of conductor hardware at

https://www.epri.com/#/pages/product/1002094/?lang=en-US.

If anyone has access to IEEE 1283-2013, I would love to hear if it is worth purchasing.

 

[jghrist]

Operating overhead distribution lines at high loading is usually not economical because of the cost of losses.

 

[DM61850]

Usually it is to for a contingency case and not normal operations.

I did a study for a wind farm once that wanted to not have to upgrade their tape with the expansion of their wind farm with the reasoning that the line had a lot of extra capacity due only being able to generate when it is windy. The utility didn't want to do it in the event there wasn't even flow over the line. The losses get to be ridiculous if you start assuming a decent amount of air flow. Capacity goes up by a lot but you end up with a ton of losses.

 

[bacon4life]

I am under the impression high thermal loading under normal conditions is uneconomical for most new build application at either distribution or transmission voltages. Our distribution lines only approach 75C under contingency conditions. The very high losses with using ACSS at 200+C seems to be economical for restring applications where the existing towers can be reused.

 

[DM61850]

At least from what I have seen, a huge chunk of the spare capacity on the transmission system is for contingency. The NERC TPL standards demand N-1-1 contingency design requirements.