# Heterogeneous Wireless Networks for Smart Grid Distribution Systems: Advantages and Limitations
## 3 Smart Grid Distribution System  
Smart grids aim at realizing efficiency and reliability during different system operation modes. They allow advanced distribution management systems with remote controllability, whereas conventional distribution systems utilize local control algorithms [23]. Admittedly, data sharing among different elements in distribution systems is vital for smart decision-making. This requires transferring large amounts of data for real-time or non-real-time analysis according to the system operation mode and targeted function. However, the available communication infrastructures for distribution systems are not up to this challenge [24]. For instance, the SCADA systems of most utility companies do not monitor medium/low-voltage distribution substations. Figure 1 shows the main block diagrams of local/remote wide-area networks required for upgrading conventional distribution systems towards a smart grid. As illustrated in Figure 1a, the local monitoring and control units aim at continuous metering, control, and protection of main distribution system components. Several local monitoring and control units share information over a wide area network for remote controllability and implementation of different smart grid functions. The lower layer presents the typical physical components of a distribution system and the upper layer presents the centralized control system. The wide area and local communication networks are supposed to provide complete system integration that satisfies smart operation functions as shown in Figure 1a. Figure 1: Future distribution system. (**a**) integrating local monitoring/control for future distribution functions; (**b**) a conventional distribution system upgraded towards a smart grid. An example realization of the envisioned distribution system illustrated in Figure 1a is demonstrated in Figure 1b. The figure shows a part of an underground conventional 30/11 kV distribution system. The network configuration of conventional systems is typically radial in suburban and rural areas but looped in urban centers with high population density [1]. Compared with higher voltage level systems, there is a much lower level of network monitoring and automatic control that supports real-time operation. Intelligent electronic devices (IEDs) are located in the primary substations for monitoring, metering, control, and protection of outgoing feeders and primary substation transformers. Distribution substation automation can be enhanced by the deployment of smart meters/sensors that support large data set collection and metering functions. In this paper, the conventional system is upgraded using monitoring and control units (MCUs) with integrated sensors for enhancing the operation monitoring and control. These MCUs are capable of communicating with one another over a hybrid communication network, which operates using two different wireless technologies. The upgraded distribution system model shown in Figure 1b is employed as a case study for investigating the advantages and challenges of HWNs in handling large data sets for real-time analysis. In future smart grids, different levels of message classes (in terms of criticality and priority) should be analyzed and reported, in real-time or on-demand in order to realize different system functions. The required message delivery performance varies between a very high-speed (to develop a protection command) or a low-priority on-demand (for monitoring a quality of service). For example, a protection \"Trip\" command shall be delivered to other local IEDs within a total time of 4 ms or 5 ms for 50 Hz substations. However, fault recorders and power quality monitors, which are reported on demand, can deliver 64 to 256 samples/power system cycle with low priority within several seconds [9].