# Communication Technologies for Smart Grid: A Comprehensive Survey
## 2 Overview of Smart Grid
### Grid monitoring  
Grid monitoring is necessary to ensure that the power quality is maintained throughout the power grid. Frequency, voltage, and waveform must stay within defined limits, and consequences for low power quality are reduced lifetime of sensors, devices, and appliances connected to the power grid. Grid monitoring is performed by smart sensors placed throughout the grid, AMI, and integration of SCADA [33]. The SCADA functions are enhanced from the traditional grid due to fast two-way communication and implementation of large numbers of sensors. For transmission line monitoring, wireless smart sensor nodes are distributed along the transmission line, exchanging measurements to the neighboring nodes. The nodes forward the measurements to a central collection site over NAN or WAN. The central is connected to a base station with low latency, high bandwidth, and low cost links [34]. To ensure uninterrupted power delivery continuous monitoring is required. Fast outage identification, management, and restoration systems can be achieved by interfacing the outage management systems with SCADA, AMI, and geographical information systems. Integration of AMI and smart meters can give notifications or the last gap reports to outage management systems before the customer notices the outage, thus helping in reducing trouble-shooting time and restoration time [34]. These systems for status monitoring of the SG infrastructure down to individual components help to detect, predict, and respond to faults faster. The result is better management, more accurate  
Figure 2: Smart metering architecture. optimization of resources, better and faster identification of faults in the grid, reduction in troubleshooting-time, and improved reliability [29; 30]. **Distributed Energy Resources (DER)**  
Distributed energy resources have a substantial potential at generating electricity at the load end. DER include solar photovoltaic panels, windpower and biomass. Two-way communication in the AMI enable the end user to sell surplus energy, and feeding it back to the power grid [35; 36]. Due to the intermittent characteristics of renewable energy sources (RES), the increasing utilization of renewable energy sources in the power grid, will result in more frequency and voltage fluctuations [4; 37]. Thus, fast acting smart sensing and protection equipment, as well as fast reliable communication become more important to maintain system balance and to monitor and coordinate DERs in the grid [4; 37; 38; 39; 40]. **Distributed Storage**  
Distributed storage is an integral part of the SG infrastructure. Energy storage systems should be located near RES or end user to mitigate problems related to variations in energy production from RES [41]. Fast response to stability issues in the grid are dependent on fast and reliable communication links in the SG. Distributed storage in combination with DER can improve the utilization RES and demand response [42; 40]. **Vehicle to Grid (V2G)**  
It is clear that the electrification of vehicles is becoming an ongoing trend around the globe now, which implies the frequent interaction between power grid and vehicles in the future. Electric vehicles (EVs) and chargers connecting a vehicle to a grid network can utilize the stored energy in the vehicle batteries and feed it back to the grid when necessary. EVs in the power grid can be used for power balancing by providing fast response high power. EVs can reduce the energy demand in peak load hours by consuming, storing, and returning energy when needed. EVs can also be used as back up power or in islanded operation if connection to the grid is not possible [43; 44]. These applications require bidirectional communication between the utilities and the EVs. **Demand Response (DR)**  
AMI and communication between end-user and the utilities companies give ability for demand response (DR) from the consumer side, or the utility side in predefined cases. From the consumer side, demand response gives the end-user the ability to monitor its energy consumption and production.