# Sensor Technologies for Transmission and Distribution Systems: A Review of the Latest Developments
## 3 Key Transmission and Distribution System Components
### Power Transformers
Here, a highly selective and sensitive molecularly imprinted polymer has been used as an artificial receptor with surface plasmon resonance transduction in the plastic optical fiber for the detection of molecules of furan-2-carbaldehyde in the insulating oil that  
Figure 2: Key sensing areas in a power distribution transformer. indicates dielectric breakdown and power transformer failure. Resistive, optical palladium or platinum-based thin film-based sensors and Pt-GaN based Schottky diodes are often used for hydrogen gas sensing that is an essential indicator of the incipient occurrence of faults in power transformers [14]. Methane gas [48] associated with the presence of both thermal and electrical faults are detected with the help of metal oxides-based sensors at high temperatures. For room temperature measurements, resistive, optical and quartz crystal- based thin film and nano wire structure sensors with cryptophane and silica based-electrochemical fabrications are used. Insulation deterioration in power transformers can be detected by sensing the emission of carbon monoxide gas. A combination of electrical and resistive thin film and nanotubes structure-based sensors are used for carbon monoxide detection. Acetylene can be emitted from either overheating due to high temperature and circulating currents, partial discharge or high intensity arching in the transformers. Thin film structure-based resistive and optical sensors with Ag, ZnO, Fe and graphene oxide-based fabrications and fiber Bragg gratings are commonly used for the detection of acetylene. Various wireless sensing network methodologies have also been developed in theory with transmission and distribution networks for remote system monitoring and data processing of gases emerging from a transformer. One such system is the wireless ultrasonic gas sensor nodes system with a microcontroller and a ZigBee transceiver that is used for binary gas concentration detection such as hydrogen and SF6 in a high voltage substation [49]. There has also been works on fabricating nanomaterials and nanotechnology using semiconductor technology to develop high precision, low power gas detection chemical sensors. With the change in temperature owing to the dielectric breakdown or circulating fault currents in the transformer, the relative humidity around the transformer tends to change. This change is captured by the humidity sensors to detect fault conditions. High moisture content in the transformer oil also leads to insulation breakdown. Thus, the online moisture content monitoring and humidity monitoring in transformer oil are important aspects. Humidity sensors were previously known to be fabricated with chemically inert polyimides and were immersed in the transformer oil to sense the level of moisture that, when it increases above the threshold, leads to the dielectric breakdown of the oil. Later, capacitive humidity sensors based on polyimide films were incorporated with temperature sensors for the online monitoring of moisture content, relative saturation, and temperature in the oil. Fiber Bragg grating humidity sensors with poly methyl methacrylate are developed with lower detection limits of water content and hence are more effective. Porous ceramics of the ionic and electric types are also used as moisture sensitive materials on humidity sensors. Thin film polyimide and alumina fabricated capacitive and optical humidity sensors [14], as well as poly methyl methacrylate-based fiber Bragg grating humidity sensors, have also been deployed in power transformers. The latest technology uses the platinum nanostructures indium tin oxide substrate to detect moisture in the transformer oil since it has the best sensitivity for detection. Acoustic emissions are fault indicators produced by the partial discharge in the on-tap load changers as they are employed in the fast switching of load currents between circuits. The operation and technical condition of the on-load tap changers can be diagnosed by analyzing these acoustic emissions.