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

纳尔科能源是纽芬兰和拉布拉多最大的发电公司，目前维护着大约2,400公里的木杆传输线，由大约26000根不同年限的杆组成。木杆由于老化、腐烂和周期性潮湿或冻结等一系列因素而失去强度。必须及早发现“危险极”，以避免对检查人员的安全危害，并最大限度地利用纠正措施的机会，如防腐处理。低强度的电杆在风和冰的负载过程中可能会失效，导致级联故障和大范围的停电。另一方面，过早地将杆子从服务中移除是浪费精力、物质和金钱的。现有的商用无损评估(NDE)设备往往高估了旧电杆的强度，造成了危险电杆长时间使用的风险。纳尔科能源和纪念大学正在进行一项研究计划，以开发基于模式冲击测试的新的无损评估方法。初步结果表明，阻尼比(在实验室条件下用模式冲击锤测量)与实验室强度之间具有良好的相关性。在拟议的研究阶段，将在实地测试电杆，目的是提高该方法对现实世界条件的稳健性。要重新安置的输电线杆将使用便携式现场测试设备进行模式测试，包括带导线和不带导线，以便确定导线的影响。然后，电线杆将被移除，并被运送到实验室，在刚性夹子中进行测试，以量化和帮助模拟基础的效果。最后将对电杆进行破坏性测试，破坏性测试结果将用于基于振动数据建立预测模型。鉴于这样的电杆数量在大西洋加拿大约有170000个，在北美约有200万个，研究计划的成功将推动商业市场多功能和便携式测试程序和设备的开发。

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.