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

Nalcor能源公司是纽芬兰和拉布拉多最大的发电公司，目前维护着大约2400公里的木杆输电线路，由大约26000个不同年龄的电线杆组成。由于许多因素，如老化、腐烂、周期性潮湿或冻结，木杆会失去强度。及早发现“危险极点”，以避免对检查人员造成安全隐患，并最大限度地利用防腐处理等纠正措施的机会。低强度的电线杆可能在风和冰载荷下失效，导致级联故障和大面积停电。另一方面，过早拆除电线杆会浪费能源、材料和金钱。现有的商业无损评估（NDE）设备往往会高估旧电线杆的强度，造成危险电线杆使用时间过长。

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.