# Sensor Technologies for Transmission and Distribution Systems: A Review of the Latest Developments
## 3 Key Transmission and Distribution System Components
### Transmission Line Towers
Fiber Briggs grating is fast becoming popular due to its immunity to electromagnetic interference, the lack of a requirement for a power supply on site, and the immunity to harsh chemical environments with a longer lifespan than other sensors. Optical fiber composite ground wires and FBG load cells are most popularly used for tower monitoring. An all-optical fiber sensing system is developed in [12], where an optical sensing probe is made by coaxially splicing a thin core fiber with tilt fiber gratings inscribed into its core. The sensing probe is mounted on the transmission tower and provides the measurement of two wavelength-separated spectral signatures, one from the core-guided mode and the other from the cladding mode. The optical power of the cladding modes provides real time amplitude and frequency of vibration of the transmission tower. The power of the core mode provides in situ measurement of temperature and inherent self-calibration to remove the fluctuations of light source intensity and loss in optical transmission. In ref [109], measurement of on-line strain, generally caused by transmission line galloping is conducted by using fiber reinforced plastic packaged fiber Bragg grating sensors. The strain coupling is between the angle braces and sensors at a different position on the transmission tower. In certain cases, design flaws in the tower structure can stem from irregular force fitting or wielding defects during the construction of the transmission tower. Over time, these defects could lead to the buildup of residual stress, resulting in mechanical deformationsand occasionally causing tower collapse. Various non-destructive testing methods such as radiation testing, ultrasonic testing, eddy current testing and leakage flux testing have been employed recently by installing current sensors, ultrasonic sensors, or magnetic sensors such as MR sensors, fluxgate sensors, and Hall sensors on the transmission towers. An example of this is the deployment of [110] an array of 64 GMR sensors that are used to detect the changes in magnetic flux density due to mechanical deformations in tubular type transmission towers [110]. Currently, the remote and real-time, on-line monitoring of transmission towers has gained a lot of interest. In [111], transmission tower tilt angle prognosis is conducted with the help of a solar-powered LoRa sensor node which consists of a solar panel, a LoRa radio frequency chip, super-capacitors, accelerometer, and gyroscope to measure the initial tilt angle and the angular rate of the transmission tower which is wirelessly transmitted to control center through LoRa gateway. In [106], multiple inclinometers that can measure the transmission tower tilt with respect to the force of gravity are used to detect the tilt and broken materials of the transmission tower with low powered NB-IoT technology. However, the installation of these sensors is limited due to the requirement of power supply for data sensing, data transmission, etc. A new generation of remote sensing technology employs unmanned aerial vehicle UAV with LiDAR or laser scanning sensors [112] that have high density and high penetration ability. They take laser pulse as a measurement medium to obtain high-precision 3D coordinates of target areas in the transmission tower to accurately measure the tilt rate of the transmission towers.