Protection engineers dealing with protective relay and communication product manufacturers, strive to achieve fast tripping for all transmission line faults through communication assisted protective relaying. Directional distance and over current schemes, interfaced with communication equipment transceive logic-based information between relay terminals to determine if the external-internal faults to protected line section. Same information can be shared between relay and Personal Computer. For communication purpose microprocessor based digital relays are used. These relays contribute to improved reliability and reduced costs on electric power systems. Microprocessor based relaying scheme can report the events taking place in the system, verify the faults, analyze the voltage dip and identify the fault location. They impose little burden on CTs & PTs enabling relays to be set up for higher sensitivity. So capability of programming and faster response of digital relay helps achieving faster communication between relay and PC. Now a day many software tools are available for communication between master-PC and slaves-Relays. I.E. CAP 501, CAP 505, LIB 510/ Micro SCADA. CAP 501, Relay Setting Tools software, is a Computer Aided Programming system for medium voltage relays in the RED 500 and SPACOM series. CAP 501 is mainly used as local system near the relay. Microprocessor based digital logic communication development for relay operation using six bus sample power system was done. Balanced and unbalanced faults were created at each bus and then fault current values and bus voltages were found out. Using these values of fault currents the fault level is decided and based on this using Time-Current Characteristics for relay the operation time is decided. This paper highlights capability, functions of CAP 501 like online and offline parameterization uploading, downloading, project management, framework for relay tools. We present CAP 501 process to establish communication between microprocessor based relay and personal computer. It also investigates the fault events and event logs together with disturbance recorder tool. An attempt to decide the fault level and operation time of relay is made to establish communication between personal computer and relay.
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