# The Power System and Microgrid Protection--A Review
## 4 Future Trends of Protection Systems
### Wide Area Protection (WAP)  
Wide area protection (WAP) is a protection and control system that can meet the future challenges of protection. This system is a new concept that has been proposed with the complexity of the power system and the high penetration of distributed generations in recent years [126; 127; 128]. The WAP system improves reliability and stability performance and coordinates protective relays. Moreover, the performance of WAP is based on power system data through network communication. It can detect and clear the fault selectively and quickly. Then, it analyzes the effect of power system stability after fault components disconnection and uses appropriate control measures [126]. The performance time of a WAP system has significant importance during the fault. The WAP should collect data from different locations of the protected areas and analyze data collecting to respond to the disturbances in a somewhat longer time frame. The processing time of the WAP system operation is long due to the communication delays during the information transmission process. The speed of the operation leads to the use of wide-area information to enhance the reliability of backup protection. It is imagined that improved communication and measurements will provide enhanced solutions to protect against instability in the future [127]. The research works in References [128; 129; 130] have introduced wide-area protection algorithms. Reference [131] proposed a WAP algorithm based on the composite impedance directional principle that can realize fault detection. The authors of Reference [132] presented a wide-area backup protection algorithm using distance protection fitting factor because of time delay and potential information loss problem in wide-area data acquisition. Reference [129] mainly focused on three aspects of the WAP-based methods:  
1. Online adaptive computing and verification of protection settings;
2. Preventing chain trips of backup protections by recognizing large-scale flow transfer and faults with the help of a regional stability control system;
3. Wide-area backup protection centering on the identification of fault equipment, which also takes advantage of PMU/WAMS. RTUs are data acquisition and digital measurements. SCADA systems use RTUs to collect data from remote sites and send them to the energy management system (EMS) every two to ten seconds. Computer-based devices can record and store massive amounts of data aperiodicity depending upon the intended purpose of the device [133; 134]. The SCADA's sampling speed is very slow and needs to be improved. Furthermore, the technology of conventional SCADAs does not have a phase angle as an analog measurement. Hence, the synchronized phasor measurement technology is required [130; 135]. The phasor measurement unit (PMU) can measure the voltage phasor of the installed bus and the current phasors of all the lines connected to that bus [136]. The PMU technologies have a high-speed power system device that can provide synchronized measurements of real-time phasors of voltages and currents, respectively. These technologies are also used for the calculation of voltage and current magnitudes, phase angles, real/reactive power flows, etc. The synchronization is usually achieved by simultaneous sampling of voltage and current waveforms using timing signals from GPS satellites [137; 138; 139]. Generally, PMU takes 30 measurements per second, thereby presenting the possibility of a much limelier view of the power system dynamics comparing to conventionalmeasurements. Basically, PMUs measurements are based on synchronizing, as they are time stamped by the GPS's universal clock [140]. Some of the advantages of using PMUs are summarized as follows [137]:  
1. Improving real-time monitoring and control of power system;
2. Enhancing congestion management;
3. State estimation of the power system;
4. Post disturbance analysis of the power system;
5. Overload monitoring and dynamic rating;
6. Restoration of the power system;
7.