A novel principle dispensing with data synchronization for distributed bus protection

This paper presents a novel algorithm of distributed bus-bar protection based on admittance to solve the data out-synchronization problem of distributed differential current bus-bar protection. With the introduction of voltage, the relationship between the differential admittance and the braking admittance can be used to realize the distributed busbar protection without data synchronization. When an internal fault occurs, the differential admittance is larger than the braking admittance. When an external fault occurs, the differential admittance is far smaller than the braking admittance. According to such characteristics, the internal and external fault can be distinguished. Reflecting the grid structure, the admittance which is time-invariant, should be a constant value. Even though electrical quantity sampling of each Bay Unit (BU) are out-synchronous, the calculated results are not affected. The EMTP simulation results have proved that the calculated differential admittance and braking admittance of this algorithm are not affected by the data out-synchronization whenever an internal or external fault occurs. In addition, comparative simulation between novel principle and conventional distributed bus-bar protection are also made to analyse the data out-synchronization and other properties. Results show that this algorithm is not affected by system operation mode, less affected by transmission delay and has a high capacity against fault impedance.