Distributed differential protection can achieve accurate location and rapid isolation of faulty sections of distribution lines，Is the best choice to solve the current distribution network relay protection problem。However, differential protection requires real-time exchange of data between protection devices，Previously only Fiber Channel met such high requirements，But there are many distribution points、Difficult to lay、Big investment、Long cycle and many other difficulties。5G communication has high bandwidth、Low latency、High reliability and other features，Provides a new opportunity to solve the problem of differential protection channel in distribution network。Professor Gao Houlei’s team from the School of Electrical Engineering unites power grid companies and manufacturers，Being the first in the country to carry out research on the application of 5G communications in distribution network protection；After more than two years of hard work，Developed a new distribution network differential protection device based on 5G slicing network and fault time self-synchronization technology，Obtained national invention patent authorization，And will be connected to the Internet for pilot operation in June 2020。
To further evaluate the ability of 5G differential protection to detect real power grid faults，March 19，State Grid Qingdao Power Supply Company、State Grid Shandong Electric Power Research Institute、Shandong University jointly organized and implemented the first domestic 10kV line artificial short circuit test and achieved success。This is after the team successfully implemented the first cross-base station 5G communication differential protection test in China in October 2019，Major breakthrough in engineering applications，Indicates that this achievement is ready for engineering application。
The test was conducted on the 10kV Kangda Line of Gujia Substation, Huangdao Military-Civil Integration Zone, Qingdao。This line is the location of Qingdao Power Supply Company’s 5G differential protection pilot project，Two sets of 5G communication differential protection devices developed by the team were put into operation in T1 and T1-01 ring main unit，Communication between devices via 5G dedicated slicing network。By implementing artificial single-phase grounding short circuit in the busbar lead of T1-01 ring main unit，Make the fault point inside one set of protection and outside another set of protection，Assess the differential protection performance of two sets of protection devices at the same time，Including communication delay and reliability、Data synchronization error、Segment internal and external fault identification capability、Protection action time、Technical indicators such as fault isolation time。
According to the test plan，The single-phase metallic grounding short circuit in the neutral point ungrounded mode and the small resistance grounding mode were respectively conducted through 0Ω、100Ω、500Ω、Single-phase grounding short circuit test with 900Ω transition resistance。Of all short circuit faults implemented，The responses of both sets of protection devices are all correct；The fault protection action time in the zone is 33-51ms，Average 39.8ms；Fault clearing time is 71-90ms,average 79ms；The average end-to-end delay of 5G communication is 10.35ms,The average end-to-end communication delay of the protection device is 12.3ms；Data transmission packet loss rate 0，100% reliability；Under low resistance conditions, the phasor synchronization measurement error at both ends is less than one sampling interval (3º），In the case of high resistance fault, the synchronization error at both ends is not greater than two sampling intervals (6º）。
Test data shows，The various performance indicators of the developed 5G communication differential protection have reached the expected goals；Innovative designs in three aspects have been fully verified。One is to use adaptive current differential criterion，Can correctly determine various phase-to-phase short circuits and sensitively respond to single-phase ground faults under small resistance grounding methods，Allows transition resistance capability up to 1000Ω；The second is to adopt the self-synchronization method at the fault time，The accuracy of synchronous detection of actual fault current is within 2 sample points，Meet engineering application requirements；The third is to use 5G uRLLC slicing network as the data channel，Make differential protection action faster、Reliable，Achieved tripping exit within 60ms and fault isolation within 100ms。The test results further confirmed，The application and promotion of 5G differential protection in distribution network is helpful in eliminating protection overlevel tripping、Shorten power outage time、Reduce the risk of personal electric shock、Improving power supply reliability plays an important supporting role，Will produce huge economic and social benefits。
State Grid Qingdao Power Supply Company、State Grid Shandong Electric Power Research Institute、Shandong University、State Grid Huangdao District Power Supply Company、Shandong Kehui Company、More than 40 people from China University of Petroleum (East China) and other units participated in and witnessed the test process。
1. Test personnel in place 2. Set up short-circuited ring main unit T1-01
3. On-site grounding control switch and grounding phase cable 4. Ground point and transition resistance 
5. T1-01 ring main unit protection device monitoring site 6. T1 ring main unit protection device monitoring site
7. Metallic single-phase ground fault wave recording diagram in the ungrounded neutral point system area
8. Single phase 500 in small resistance grounding system areaΩTransition resistor ground fault wave recording chart
