Power System Protection国外电力系统保护课件.pptVIP

Power System Protection Dr. Ibrahim El-Amin Protective Device Coordination Definition Overcurrent Coordination A systematic study of current responsive devices in an electrical power system. Objective To determine the ratings and settings of fuses, breakers, relay, etc. To isolate the fault or overloads. Criteria Economics Available Measures of Fault Operating Practices Previous Experience Design Open only PD upstream of the fault or overload Provide satisfactory protection for overloads Interrupt SC as rapidly (instantaneously) as possible Comply with all applicable standards and codes Plot the Time Current Characteristics of different PDs Analysis When: New electrical systems Plant electrical system expansion/retrofits Coordination failure in an existing plant Protection vs. Coordination Coordination is not an exact science Compromise between protection and coordination Reliability Speed Performance Economics Simplicity Protection Prevent injury to personnel Minimize damage to components Quickly isolate the affected portion of the system Minimize the magnitude of available short-circuit Spectrum Of Currents Load Current Up to 100% of full-load 115-125% (mild overload) Overcurrent Abnormal loading condition (Locked-Rotor) Fault Current Fault condition Ten times the full-load current and higher Coordination Limit the extend and duration of service interruption Selective fault isolation Provide alternate circuits Coordination Equipment Motor Transformer Generator Cable Busway Capability / Damage Curves Transformer CategoryANSI/IEEE C-57.109 Transformer Transformer Protection Protective Devices Fuse Relay (50/51 P, N, G, SG, 51V, 67, 46, 79, 21, …) Thermal Magnetic Low Voltage Solid State Trip Electro-Mechanical MCP Overload Heater Fuse Non Adjustable Device Continuous and Interrupting Rating Voltage Levels Characteristic Curves Min. Melting Total Clearing Application Current Limiting Fuse(CLF) Limits the peak current of short-circuit Reduces magne