Abstract: The conventional overcurrent protection is ineffective in isolating faults in microgrids due to the low

fault current level contributed by distributed generations（DGs）. Because of its high agility and adaptability，the

measured impedance-based protection schemes are considered as common alternatives to detect faults. However，the fault ride-through（FRT）requirements are not considered in the exiting schemes，and action performance is

susceptible to transition resistance. To solve the problem，a new inverse-time distance（ITD）protection scheme for

AC microgrids was proposed. The proposed scheme used the inverse-time characteristics to set the operating time，

which can meet the FRT requirements of inverter interfaced DGs（IIDGs）as well as the selectivity of feeder

protection system. In response to the influence of transition resistance and branch feed-in，a method was developed to improve the performance of ITD protection，which was based on transmitting signals between adjacent relays. Time domain simulations were conducted in Matlab/Simulink and the effectiveness of the proposed protection scheme was verified by the results.

      Key words: microgrid；inverse-time distance（ITD）protection；feeder protection scheme；fault ride-through

（FRT）