# Sensor Technologies for Transmission and Distribution Systems: A Review of the Latest Developments
## 3 Key Transmission and Distribution System Components
### Summary  
Table 2 attempts to provide a summary of some of the major developments in sensor technology and their unique applications in transmission and distribution systems. The latest developments in sensor technologies have substantial influences in the monitoring and control of some of the key components of the power grids that can be summarized in the following manner. The modern-day power transformer is equipped with low cost and contactless optical sensors to enable online dissolved gas monitoring DGA analysis [14]. Furthermore, uniquely fabricated gas, chemical and humidity sensors have been used for more accurate detection of target specific analytes in transformer oil. Detection of partial discharges is not just limited to current and vibration sensors. Various unique sensors such as acoustic sensors, ultrasonic sensors, piezoelectric sensors, and optical sensors have been used for this purpose for better fault detection as well as fault location. Finally, complete monitoring of the transformer body is now being realized with smart IED-based sensors as explained in Table 2. In transmission line and distribution line power conductors, the detection of power conductor vibrations along with the sagging and  
galloping of transmission lines are being more accurately detected with newly developed MR sensors, surface acoustic wave SAW sensors, and ultra-high frequency UHF based vibration sensors [18]. In transmission line insulators, the latest sensor technologies such as infrared thermography and fiber optics-based sensors have been deployed for the efficient detection of faults arising from insulation deterioration and partial discharges [87; 93]. Efficient fault detection in transmission line towers through structural health monitoring is currently being realized with MEMS-based acceleration sensors [107]. Furthermore, remote and on-line monitoring of underground power conductors are now possible with Wi-Fi, LoRa, ZigBee, and other wireless-based sensor networks [120]. Arc control and the efficient temperature monitoring of circuit breakers are currently being realized with the help of emission spectroscopy-based optical sensors [101]. The deployment of infrared position sensors with cameras as well as newly developed magnetic and fiber optic sensors have made it possible to locate the position and frequency of high voltage lightning strikes through lightning current monitoring systems [132]. Thus, it can be inferred that sensors have become significant components of the transmission and distribution systems since it has become a prime area of research among researchers and engineers who are continuously upgrading and improving these sensors by integrating them with newer technologies. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Component** & **Sensors** & **Application** \\ \hline \multirow{8}{*}{**Power Transformers**} & 1. MIS/Fiber optic gas sensors & 1. Contactess, fabricated \& \\  [14; 46] & optical sensors for DGA & \\  & monitoring & \\ \cline{2-3}  & 2. FBG based humidity sensor [14] & 2. Fabrication of moisture \\  & 3. Piezoelectric/FBG/ultrasonic transducer based acoustic/ vibration sensor [50; 52; 53; 54; 55] & 4. Various methods of \\  & 5. Special Hall effect & 5. Monitor brushing insulation, \\  & sensors/smart IEDs [56] & aging, of body \\ \hline \multirow{8}{*}{**Overhead Line Power**} & 1. Piezoelectric/FBG/Hall \& MR \\  & sensors [71; 72] & 1. Magnetic field and current \\ \cline{2-3}  & sensors [71; 72] & sensing for detection of aging, \\ \cline{2-3}  & 2. MR sensors/ Optical sensors/UHF-based vibration sensors [18; 70] & 2. Detection of sagging, galloping, etc. \\ \cline{2-3}  & 3. SAW temperature sensor/ & \\  & Optical sensors [20; 74] & 3. Temperature monitoring \\ \hline \multirow{8}{*}{**Overhead Line**} & 1. IR thermography/X-Ray spectroscopy/ ultrasonic/MR sensors [87; 88; 89; 90] & 1. Detection of aging, defects like \\ \cline{2-3}  & 2. Optical sensors [91; 92; 93] & 2. Monitoring of leakage currents \\ \hline \multirow{8}{*}{**Transmission Line**} & 1.