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<FONT COLOR = "000000" face="Arial">Havard Engineering Inc. - Structural Testing
Havard Engineering Inc.
Structural Testing
E-mail:dhavard@rogers.com
To determine the strength and remaining life of aged conductors and worn fittings, it is necessary to carry out mechanical tests of sample components removed from the overhead lines. Frequently, aged conductors are found to be capable of continued safe use because the load applied is significantly less than the rated capacity of the new conductor or hardware.
The photo at the left shows a sample strand from a thirty year old ACSR conductor undergoing tension testing. This test was part of a program to determine the capability of the aged conductor to carry additional loads due to an upgrading of the transmission line. The test data confirmed the integrity of the conductor and saved the cost of restringing the line.
Stockbridge dampers, spacer-dampers, conductor support hardware and other line items need to be qualified to meet utility specifications. These devices can be tested for static and dynamic mechanical performance using standard methods.
The photo on the right shows a disassembled aged conductor, with the corroded steel core reduced to a pile of rust, along with the replacement trapezoidal strand "compact" conductor.
Analytical methods are used to assess unusual configurations, and to permit alternative designs to be compared. Examples include:
- Determining clearances for galloping between adjacent conductors or skywires and plotting clearance ellipses.
- Checking sags of individual suspension spans of a line section after adding detuning pendulums.
- Finding optimum dimensions for Stockbridge damper wave traps to control aeolian vibration of a long inlet crossing.
The photographic sequence below shows the final stages of the in situ mechanical test of a sixty year old lattice tower which was part of a major transmission system assessment program.
The photo on the right shows a wooden structure with hinged horizontal vee arms during testing for structural stiffness. The stiffness of such flexible structures is an important factor in the stability of the line during high winds.
Steel lattice structures can vibrate due to direct wind action on the members if they are sufficiently long and thin. In the photo on the left, the right hand tower has fewer braces in the arms than that on the left, and some towers of this design experienced failure due to fatigue of the hangers. An add-on damping solution was developed to mitigate the vibrations at much lower cost than conventional solutions, such as adding stiffeners to brace the hangers.
If you have need for mechanical testing of new or aged components, or require assistance with analysis of unusual configurations of spans of conductors, we are prepared to assist you. Just send us an e-mail and we will contact you promptly to discuss your problem.
To contact us please send an E-mail to:
dhavard@rogers.com
Updated October 9, 2006