# Sensor Technologies for Transmission and Distribution Systems: A Review of the Latest Developments
## 3 Key Transmission and Distribution System Components
### Transmission Line Towers  
Transmission towers are an important part of the electrical grid since they reinforce the continuity of transmission line power conductors and host an array of power conversion, protection, and insulation devices along with providing ground resistance. Transmission towers are bulky and complex structures and are prone to displacement, inclination, cracking, vibrations, and subsidence. The resulting effects of these issues can cause severe problems such as interruption of the transmission lines and communication networks, transmission line galloping, settlement tilt of the transmission tower and even the collapse of transmission line conductors or transmission tower collapse [104]. These effects are mostly caused by natural phenomena such as heavy rain and snow and high wind speeds. However, in certain cases, these effects can be a result of design or force-fitting flaws during erection or material defects. Depending on the pattern of the failure, there are two major transmission line tower faults [105]. A local failure in the transmission tower occurs due to the failure in the primary or secondary bracings. This does not lead to the complete collapse of the tower structure and is often detected through manual inspections. The second type of failure occurs because of failure in the tower leg or legs causing the failure or collapse of the foundation of the tower. This is called structural failure. Due to its severity in nature, various sensors have been deployed to monitor the structural failures in the transmission line towers such as transmission tower tilt, transmission tower vibrations, the loading effects of ice and wind, and structural and wielding defects. Structural health monitoring technology [19] has been widely used in assessing the damage in the power tower structure. The most common method of measuring tower tilt is conducted with an inclination sensor [106] fitted to the transmission towers. However, inclination sensors can only indirectly reflect the state parameters of stress and load balance when the whole deformation of the tower is large. To detect small deformations on the tower or the yield failure of the local power conductors, pressure and strain sensors are used on the transmission towers. These sensors have a lower measurement range and can successfully sense damages of smaller magnitudes. Currently, fiber Briggs grating-based strain sensors have been developed that have improved range and accuracy for sensing [12]. The vibration response of the tower changes with the change in load and environmental conditions and the formation of mechanical defects, thereby reflecting the structural status of the transmission line tower. Acceleration sensors mounted on the crossarm of the tower are used to measure the vibration response of the system as a part of structural health assessment. An excitation device is used to generate impulse excitation which causes forced vibrations in the tower and the corresponding signals are sensed by the acceleration sensor. Ref. [107] uses a MEMS-based three-axis acceleration sensor that calculates the difference between the acceleration due to a combination of gravity and other stresses and the acceleration due to gravity alone, thereby detecting vibration responses from faults on the transmission line towers. Optical fiber sensors are known to have larger bandwidths and lower frequency ranges for sensing. Hence, fiber Briggs grating sensors have been used to measure vibrations caused by surface displacements as well as the deep displacements of the transmission line tower. The loading effects of ice and wind can cause various structural displacements to the transmission tower structure, and thus their monitoring is essential. Optical sensing-based fiber Briggs grating sensors [108] are used to monitor the ice load effect of inundated ice on the transmission towers. These sensors work on the principle that the wavelength of optical fiber varies with the change in strain and temperature due to the loading effect of ice, etc.