# Sensor Technologies for Transmission and Distribution Systems: A Review of the Latest Developments
## 1 Introduction  
Sensor technology is arguably one of the most significant inventions in the past couple of decades. With the ever-evolving engineering behind the sensor, its role in the power system landscape is dynamic and vital in nature. In recent years, the transmission and distribution systems have relied heavily on sensor technology. Knowledge about the fluctuating nature of the system parameters such as the range of currents, operating voltages, working temperatures, dynamic electric, and magnetic fields to even the moisture content, and the acoustics emanating from various transmission and distribution line equipment are essential for efficient monitoring and control purposes of the electrical power grid [1, 2]. To meet this need, sensors that are faster to be commissioned, installed, and restored are rapidly replacing the voluminous measuring instruments traditionally used on the transmission and distribution systems. These sensors have certain distinctive features such as non-invasive and contactless properties [3] that not only increase their life span and efficiency but also reduce the need for insulation, wear and losses in most sensors. These issues were otherwise evident in the traditional measuring instruments due to their exposure to high levels of voltages or currents in the transmission and distribution lines. Thus, the use of sensors makes fault detection and its remediation faster and helps with the dynamic configuration of the power grid [4, 5]. Modern sensor technology is evolving now more than ever. There have been rapid advancements in the type of sensor materials and their properties such as the fabricationof micro electro-mechanical systems (MEMS) sensors, optical sensors made up of semiconductors, piezoelectric materials, advanced nanotechnology, and spectroscopy. Novel algorithms and approaches have been incorporated to discern the sensor data and deduce system parameters using complex concepts of electromagnetism, spectroscopy, optics, etc., together with machine learning, genetic algorithms, metaheuristic solutions, etc. [1; 6]. A detailed study of the existing sensor technology is essential for its further development and efficient functioning in the forthcoming expansion of the power grid as well as in its transformation into microgrids and smart grids. The existing literature mainly focusses on a particular type of sensor and its function in the power grid. Ref. [7] provides an elaborated review on the construction and functioning of electric current sensors, [8] explains a novel compact voltage sensor with data acquisition and data transmission systems for medium and high voltage power conductors, while [9; 10; 11; 12] provide an extensive review on the recent developments in optical sensors and their fault detection techniques in power systems. However, the focus is only on a single type of sensor, which will not be of much help while building wireless sensing networks that employ multiple sensors for the complete health monitoring of power system equipment. The existing literature also focuses on fault detection of particular power grid equipment and various sensors used for its monitoring. Refs. [13; 14; 15; 16; 17] provide detailed reviews and surveys on different sensors used for power transformer monitoring and health assessment, while [18; 19; 20; 21; 22] provide in depth analysis for fault detection and condition monitoring of power conductors. However, the scope of these studies is limited to the monitoring of specific power system equipment. The overall health monitoring for efficient asset utilization of the transmission and distribution systems requires knowledge of all the power system equipment and the faults associated with it. Furthermore, monitoring systems for smart grids require the status of multiple power system components to account for the faults that occur due to their dynamic interactions and the bidirectional flow of current.