1. POWER SYSTEM PROTECTION

2. Power system Generators Transformers Transmission lines »Underground cables »Overhead lines Distribution systems

3. Sri Lanka Transmission system

4. PROBLEMS Abnormal situations »Over loading »Over and under voltages »Under frequency »Over speeding Faults »Three phase faults »Phase-phase faults »Earth faults »Open circuits

5. FAULTS Excess current Liberates heat Damage at the point of fault Overheats the upstream system Creates voltage drops Hence faults and abnormal operations have to be detected and cleared as quickly as possible.

7. SITUATIONS HAVE CHANGED….. Expansion of power systems Need for an automatic device to detect faulty/abnormal situations First automatic protection

8. FUSE Very effective Still being used in distribution systems Complexity of power systems Development of protective gear based on automatic devices - RELAYS

9. PROTECTIVE RELAYS Protective relays monitor the state and operating conditions of all elements of a power system and responds to the occurrence of faults and disturbance

10. GENERAL REQUIREMENTS OF PROTECTIVE RELAYING Selectivity Speed of Operation Sensitivity Dependability and Reliability Primary and Backup Protection Unit and Non Unit Protection