## 3 Development of Thermal Condition Monitoring System
### Overview of the Communication Link  
Most existing network thermal conditions monitoring are models of the medium and high voltage grid systems. It is essential to note that those networks have different compositions from the renewable distributed power generation network. Therefore, it is unique to have a suitable communication assisted link for thermal condition monitoring with functions relating to the dynamics of renewable power generation network. The ability to manage thermal behavior efficiently in the distributed network depends on the prompt nature of the grid communication network and configuration strategies, as the operation of the communication link promptly impacts system performance. The communication link composes the channel conveying the signal and the terminal hardware components transmitting or receiving signal. Communication channels used for monitoring thermal conditions of existing power networks have their functions attached to the established infrastructures. Such communication links use network configuration channel involving power line carrier, microwave, and fiber optics. With the increasing concern for the reliability of the DERs network, thermal condition monitoring scheme demands communication links to have advancement in characteristics. The DERs integrated grid differs from the conventional power network, usually having distance within short ranges with more connecting loads, which are subject to greater load variance and congestions. The distributed network requires a communication link to have the characteristics giving an assurance of reliable performance with low cost and low power consumption [22; 54]. Review of available related works presents the strengths and weaknesses of communication links such as direct pilot wire, leased digital phone line, fiber optic cable, licensed radio, and spread-spectrum radio (in which ZigBee belongs). The consideration for the choice of a specific communication link includes the bandwidth and speed of signal transmission with security robustness [22; 54; 55]. However, priority begets the ZigBee link capabilities regarding the systems vast array of potentials for WSNs monitoring and controlling. The economical synthesis of the project targets in rural and remote areas focuses on the low cost of components and low power consumption. In appraising the communication link characteristics, it was an undeniable fact, the spread-spectrum radio and licensed radio channels share essential advantages with fiber optic channel as unique links. They have the lowest latency, dilation of signal, and are unaffected by the electrical transients or ground potential rise (GPR) associated with power system faults. They have good speed of communication channels, which depends on the channel's data rate, the size of the message, and the existence of dominancy in both ends terminal equipment. The same cannot be said of a leased phone line or a direct pilot wire, which may be out of service during a fault condition [21; 56]. Routing the communication signal directly from the terminal equipment of the transmitter to the receiver avoids delay and this applies to the frequency of unlicensed radio bands of 900 MHz and 2.4 GHz, including others from point-to-point spread radios which ZigBee WSNs affirms. The advancement in ZigBee application embraces an acceptable line of sight range depending on the configuration supports applicable [55]. Although the radio signal may experience interferences of co-existence of spectrum from Wi-Fi, spread-spectrum radio sets reasonable classification of signal protections across a wide frequency band. As a result, the link signal has security features to overcome interference when applied properly. Link signals on spread-spectrum have special characteristics of disallowing narrowband interference from intruding [55]. Invariably, fiber optic has the best attributes regarding communication links with numerous advantages and operational easiness. However, some drawbacks cause fiber optics to suffer beyond the technical performance.