Distributed bus protection principle based on admittance parameter identification

As the existing distributed bus current differential protection is affected by the asynchronous sampling and transmission delay of bay data, a protection principle based on the admittance parameter identification is proposed. The voltage variable is introduced to calculate the admittance, the differential admittance is defined as the absolute summation of all bay admittances, and the braking admittance is defined as the summation of all absolute bay admittances. When an in-zone bus fault occurs, the braking admittance equals to the differential admittance; when an out-zone bus fault occurs, the differential admittance, reflecting the bus-ground stray capacitance, is much less than the braking admittance. The relationship between differential and braking admittances can be used to reliably distinguish an in-zone bus fault from an out-zone bus fault. EMTP simulation and actual fault-wave records show: being less affected by the transmission delay and better tolerant of the transition resistance, the proposed principle does not need the synchronous sampling of bay data and can identify the in-zone and out-zone bus faults in different operating conditions.