High voltage wire pull

Status
Not open for further replies.
M

Mporter4

Member
I have a question on a high voltage wire pull. And the specifics are:
1- 500 kcmil al. wire 15kv.
2- 2500' long.
3- 2- 90.'s
4- 6" pvc conduit
5- splice to be made in manway.


The question is can i just serve the al. wire on to the pull rope with conventional method of stipping back the ins. and cutting several of the strands. or use a pulling eye? if pulling eye( for al).does anyone have a link?
My concern is with the al. wire breaking during the pulling. also i would like some sort of calculator to determine the pull tension on this run.
:-? :-? :grin:
 
Mporter4 said:
I have a question on a high voltage wire pull. And the specifics are:
1- 500 kcmil al. wire 15kv.
2- 2500' long.
3- 2- 90.'s
4- 6" pvc conduit
5- splice to be made in manway.


The question is can i just serve the al. wire on to the pull rope with conventional method of stipping back the ins. and cutting several of the strands. or use a pulling eye? if pulling eye( for al).does anyone have a link?
My concern is with the al. wire breaking during the pulling. also i would like some sort of calculator to determine the pull tension on this run.
:-? :-? :grin:
Click to expand...

After doing a preliminary calc, (using copper not Al) and assuming there is a 90 on each end, with approx. 2500ft in between, IMO the cable will be damaged if this pull is attempted. It will require a pulling tension of over 18,000lbs and so your equipment would need to be quite beefy just to get it pulled in.

Redesign the run by using some small MH's, start with 2, and work your way toward an acceptable solution. You might want to put 1 MH where the splice will be, and put the other one at the longer pulling end. Oh, and you don't really need 6", 5" should work just fine.
 
Last edited:
kingpb said:
After doing a preliminary calc, (using copper not Al) and assuming there is a 90 on each end, with approx. 2500ft in between, IMO the cable will be damaged if this pull is attempted. It will require a pulling tension of over 18,000lbs and so your equipment would need to be quite beefy just to get it pulled in.
...
Click to expand...
The OP specifies using AL not CU. Not sure how this information is of any help.:-?
I did like the link to the calculator though...I will definitely have to save that one.:)
 
My concern is with the al. wire breaking during the pulling.
Click to expand...
Most times the pulling tension is not the limiting factor in a pull. The sidewall pressure (crushing force on the insulation when the conductors are pulled around bends) is often the limiting factor. Make sure you look at that in addition to the pulling tension.
Don
 
Last edited:
bstoin said:
The OP specifies using AL not CU. Not sure how this information is of any help.:-?
I did like the link to the calculator though...I will definitely have to save that one.:)
Click to expand...

The point being is that if it can't be done with copper, then why would anyone think it can be done with Al. Cu has almost 3 times the strength of Al.

I think this point alone is a good illustration of the general lack of understanding of what is involved with cable pulling.

I would be more then happy to do a check of the actual pull, if the proper conduit design and cable information is provided.
 
Mporter4 said:
I have a question on a high voltage wire pull. And the specifics are:
1- 500 kcmil al. wire 15kv.
2- 2500' long.
3- 2- 90.'s
4- 6" pvc conduit
5- splice to be made in manway.


The question is can i just serve the al. wire on to the pull rope with conventional method of stipping back the ins. and cutting several of the strands. or use a pulling eye? if pulling eye( for al).does anyone have a link?
My concern is with the al. wire breaking during the pulling. also i would like some sort of calculator to determine the pull tension on this run.
:-? :-? :grin:
Click to expand...

It makes me a little nervous that someone would ask such a question. I am not sure I want someone doing such a pull that does not already know the answer to this question.
 
Okonite lists 15kv calbe as follows
500 cu 2.25 lbs/ft OD = 1.40 in
500 AL 1.18 lbs/ft OD = 1.40 in

2500 ft 4" conduit with 90 on each end
Cable pull for copper T= 666 lbs and SWP = 166 lbs

Cable pull for AL = T= 119 lbs and SWP = 88 lbs

Why do you need 6" conduit? Future?
 
Bob,
What did you use for a coefficient of friction? I used 0.4 and get a pulling tension of ~11,500 pounds and a side wall pressure of 1760 pounds using a 3' radius bend. The maximum permitted sidewall pressure is usually 500 pounds or less.
Don
 
don_resqcapt19 said:
Bob,
What did you use for a coefficient of friction? I used 0.4 and get a pulling tension of ~11,500 pounds and a side wall pressure of 1760 pounds using a 3' radius bend. The maximum permitted sidewall pressure is usually 500 pounds or less.
Don
Click to expand...
Don
I used the Polywater program. They give a 0.10 cof using one of their products. The cof for unlubed PVC varied from 0.8 to 0.10. Using a .40 for copper the results at the last 90 were T=4235 and SWP = 1412.
I had T = 0 going into the first 90.
Come Back.
 
Bob,
I am using the same program and I am not comming up with values that low. You can't really use the low COF shown in the program because you only get that with perfect conditions. That is not likely. I never use T = 0 because in most cases the feeder guy it soaping and can't really keep the incomming tension at zero. I think I used 50 pounds for that value.
Don
 
Using the Okonite cable Installation Practices book, and evaluating the formulas using Mathcad I came up with just over 12,000 lbs, total.

The cable info was from the Okonite Al cable to be consistent with everyone else. I assumed that the friction in the straight sections was 0.35, and in the bends 0.5. I also used the weight correction factor and said that the install was for Cradled install going into conduit.

The conduit cannot be 4" as it comes out with a 2.9 Jam ratio. So staying with the general rule, 5" is required. Albeit 6" works as proposed by the OP, but is not required for technical reasons.

For clarification, sidewall pressure is 1000lbs or less for 2 or more cables larger then 8AWG. The 1st 90 starting the run will need to be the standard 30inch for 5" conduit. Because the tension is so high, the 90 coming out of the pull would need to be 8.3ft radius sweep to meet SWP, but still the total tension exceeds the maximum of 8000 lbs and therefore cable would be damaged, and SWP becomes a mute point.
 
kingpb said:
I also used the weight correction factor and said that the install was for Cradled install going into conduit.

The conduit cannot be 4" as it comes out with a 2.9 Jam ratio. So staying with the general rule, 5" is required. Albeit 6" works as proposed by the OP, but is not required for technical reasons.
Click to expand...
Your post says only 1-500 kcm cable and that is what I used.

Don
For Copper 2.25 lbs/ft
using 3 cables, cof = 0.4, input T = 50
T = 13830 and SWP = 1567

For AL 1.18 lbs/ft
T = 8237 and SWP = 1245
Is your input information the same?
come back
 
Each 90 produces a drag that is proportional to the tension of the cable feeding into it. This is because the tension of the cable is what creates the side wall pressure, and the side wall pressure is what pushes the cable against the conduit and creates friction between the two.

This multiplying effect can be enormous.

If there is some way that one could _guarantee_ that T=0 going into the first 90 (say by having some mechanical rig feeding the cable in as it is being lubed), then the pulling forces coming out the other end will be greatly reduced.

In practise, I do not know if there is any way to guarantee that T=0 going into the first bend :)

-Jon
 
radius of bend

radius of bend

Just curious what is the radius of the two 90 degree bends. I was attempting to do my tension calcs but require the radius of the bend. thanks...
 
Mike01 said:
Just curious what is the radius of the two 90 degree bends. I was attempting to do my tension calcs but require the radius of the bend. thanks...
Click to expand...
I used 36" to match what Don used. SOme use 48".
 
Bob,
I didn't do the numbers for aluminum and I just used the standard 500 kcmil that is in the program. I set the input for not "triplexed".
Don
 
don_resqcapt19 said:
Bob,
I didn't do the numbers for aluminum and I just used the standard 500 kcmil that is in the program. I set the input for not "triplexed".
Don
Click to expand...
Don
The program uses 1.67 lbs/ft and OD = .945 for 500 kcm. The 15kv cable I used was from the mfg catalog. 15kv 175 mils the wt = 2.25 lbs/ft and OD = 1.40 and I used PVC conduit. Cable was entered as not triplexed. That increases the tension more that I thought it would.
 
bob said:
The program uses 1.67 lbs/ft and OD = .945 for 500 kcm. The 15kv cable I used was from the mfg catalog. 15kv 175 mils the wt = 2.25 lbs/ft and OD = 1.40 and I used PVC conduit. Cable was entered as not triplexed. That increases the tension more that I thought it would.
Click to expand...


I think we need to establish what cable everyone is using. This is what I thought was under consideration, please correct me if I am wrong:

Okoguard?-Okoseal? Type MV-105
15kV Shielded Power Cable
One Okopact? (Compact Stranded) Aluminum Conductor/105?C Rating
100% Insulation Level

View attachment 479

Here is the printout of the input and results:

View attachment 480
View attachment 481
 
kingpb said:
I think we need to establish what cable everyone is using. This is what I thought was under consideration, please correct me if I am wrong:

Okoguard?-Okoseal? Type MV-105
15kV Shielded Power Cable
One Okopact? (Compact Stranded) Aluminum Conductor/105?C Rating
100% Insulation Level
Click to expand...

King
I used the same cable as you and data seem to be the same.

Al Cable D = 1.4 in 5"C wt = 1.18 lbs/ft
using 3 cables, cof = 0.4, input T = 50
T = 8237 and SWP = 1245
Is your input information the same?
 
Status
Not open for further replies.
Top