When You Need It
- · A route has been set and the joint positions have not been proven installable
- · An installer or manufacturer has issued a pulling study and it needs checking
- · The route has tight bends, level changes or long straight sections and the tension is in question
- · You want the number of joints reduced, because every joint is a cost and a failure point
Standards Applied
The report states the clause and the edition it works to, so the calculation can be reproduced by whoever reviews it.
What You Get
That last point is not padding. On a 132 kV review we found a pulling study that had applied a copper allowable stress of 60 N/mm² to a 1000 mm² aluminium conductor, against a datasheet limit of 40 kN and a CIGRE TB 889 default for aluminium of 30 N/mm². Half again over the manufacturer’s own limit. The material the number belongs to matters more than the number.
Frequently Asked Questions
Can you reduce the number of joints on our route?
Often, yes. On a 6.1 km 33 kV route we took the pulling sections from 23 down to 13 by iterating the section lengths and pull directions, which took a large amount of work out of the installation.
What do you need to run a pulling calculation?
The route with its bends and level changes, the cable weight and diameter, the duct or trench arrangement, and the manufacturer’s allowable tension and sidewall pressure. If the allowable stress is not stated we will use the CIGRE TB 889 default for the conductor material and say so.
Will you check somebody else’s pulling study?
Yes, and it is worth doing. The inputs are where these go wrong, particularly the allowable stress and the assumed coefficient of friction.
The Rest of the Cable Chain
Review, calculation, drawings, testing and fault location, from one place. See the whole picture.