# A Review on Distribution System State Estimation Algorithms
## 5 Technical Requirements and Applications
### Technical Requirements  
It is evident that the most important requirement for a DSSE algorithm is the availability of measurements. Installing metering devices on a system is a necessary step for monitoring its performance and achieve the desired observability [119]. For having an accurate and up to date representation of the network, DSSE needs to be applied at least once for every hour of the day, so new measurements are needed for every new application of the algorithm. For example, the authors of [120] apply the DSSE in 10 min intervals, and in [121] the algorithm is performed every 30 min. The most common measuring components found in distribution systems are Phasor Measurement Units (PMUs) and  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Method** & **Description** & **Advantages and Disadvantages** \\ \hline Rule-based [21] & Set of rules for meter placement with low cost. & Easy and fast algorithms, but not optimal. \\ \hline Metaheuristic [114; 115; 116; 117] & GA [114], PSO [115], fruit fly [116], TS [117], etc. for: (i) maximization of accuracy or, (ii) minimization of units while sustaining observability, etc. & Efficient bio-inspired algorithms which do not guarantee global optimal solutions. \\ \hline Optimization [19; 25; 118] & MISDP, etc., usually for the maximization of accuracy. & Optimal, advanced algorithms, more demanding than the others. \\ \hline \hline \end{tabular}
\end{table}
Table 5: Meter placement strategies [19; 21; 25; 114; 115; 116; 117].  
Smart Meters (SM) [122; 123; 124]. PMUs offer synchronous power, voltage, and current measurements, as well as phase angles. SMs, on the other hand, record information such as energy consumption, voltage levels, current, and power factor. In specific distribution systems where only SMs exist and, consequently, no information concerning the phase angles, DSSE algorithms have to make assumptions about phase angle computation [125; 126; 127]. In addition, PMUs produce measurement samples in a higher frequency (reaching 30 kHz) than SMs (0.277 mHz-16.7 mHz) [13]. One can conclude that PMUs provide more sophisticated information than SMs. However, PMUs are not vastly used in distribution systems because of the high per unit costs. This demonstrates the need for developing algorithms for optimal PMU number and placement while lowering the costs [128].  
The metering devices send measurement information to the Supervisory Control and Data Acquisition (SCADA) system under the IEC 60,870 communication protocol [129]. The SCADA is a control system architecture that contains computing devices, databases, and various interfaces that enable the real time monitoring and control of a distribution system [130]. Data-driven approaches of DSSE as well as algorithms associated with DSSE, such as forecasting models for pseudo-measurement creation and bad data detection, need large amounts of historical data to be trained and function properly. Thus, databases of SCADA, capable to perform DSSE, must be able to hold years of hourly or sub-hourly power, voltage, and current data [131].  
In conclusion, a lot of resources are needed to perform DSSE successfully. Performing DSSE and evaluating the distribution system's state is paramount as RES penetration and the use of electrical cars is on the rise [132; 133].