Modal impact testing for non-destructive evaluation of wood pole transmission lines

Lay Summary 

Nalcor Energy, Newfoundland and Labrador's largest power generation utility, currently maintains approximately 2400 km of wood pole transmission lines, consisting of approximately 26000 poles of varying ages. Wooden poles lose strength due to a number of factors such as aging, rot, and cyclical wetting or freezing. It is essential to detect "danger poles" early to avoid safety hazards to inspection personnel, and to maximize the opportunity to apply corrective actions such as preservative treatment. Low strength poles can fail during wind and ice loading, leading to cascade failure and extensive power outages. On the other hand, prematurely removing a pole from service wastes energy, materials and money. Existing commercial non-destructive evaluation (NDE) equipment tends to overpredict strength of old poles, creating the risk of leaving danger poles in service for too long.


Nalcor Energy and Memorial University have an ongoing research program to develop new NDE methods based on modal impact testing. Preliminary results show good correlation between damping ratios (as measured with a modal impact hammer under laboratory conditions) and strength in the laboratory. The proposed phase of research will see testing of poles in the field, with the goal of improving the robustness of the method to real-world conditions. Transmission line poles that are to be relocated will be subjected to modal testing, using portable field-test equipment, with and without conductors so that the effect of wires can be determined. The poles will then be removed and transported to the laboratory for testing in a rigid clamp, to quantify and aid in modeling the effect of the foundation. The poles will finally be destructively tested, with the destructive test results used to create prediction models based on vibration data. Given that the number of such poles is approximately 170000 in Atlantic Canada and 2 million in North America, success in the research program will motivate development of versatile and portable test procedures and equipment for the commercial market.


Adapted from:

Mechanical Engineering
Natural Sciences And Engineering Research Council Of Canada
Newfoundland and Labrador
Electric Power
Start date 
1 Jan 2015
End date 
31 Dec 2020
Partner Organization 
Nalcor Energy