Protection Philosophy and Guidelines

1. Protection Philosophy and Guidelines Group Member: Mr. Jayant D Shrotri Ms. Deepa Joshi Mr. Girish T Jawale Mr. Sanjay K Prasad

2. Topics to be covered • CT Cores used for different protection • PT Cores used for different protection • Protection General Theory • Protections of • Lines – 220 kV & 110 kV Lines • Transformers • MV feeders, capacitor banks • Generators • Motors • Consumer s/s • System Protection • Specification for Numerical Relays

3. Basic Requirements of Protection system • Sensitivity • Speed • Selectivity • Security

4. Need for Protection system • To Minimise damage • To Minimise down time • To Minimise system disturbance

5. Components of Protection system • Instrument Transformers (CT AND PT) • Relays • Circuit Breakers • Control Battery • Communication • Monitoring System (Supervision and Alarm)

6. Instrument Transformers FOR 220 KV SYSTEMS: 5-CORES CT Core 1: Main – I Protection Core 2: Main – II Protection Core 3: Back-up Protection + LBBU Core 4: Metering Core 5: Bus-fault

7. Instrument Transformers FOR II0 KV SYSTEMS: 4-CORES CT Core 1: Main Protection Core 2: Back – up Protection + LBBU Core 3: Metering Core 4: Bus-faults

8. Instrument Transformers Potential Transformers for 110 / 220 kV Core 1: Main - I Protection Core 2: Main – II + Back-up Protection Core 3: Metering Core 4: Open-Delta for Directional E/F

9. Protective Relays for Lines 220 kV Lines: Main – I Main – II Back-up O/C Protection 110 kV Lines: Main Back-up O/C Protection

10. Power Transformer Protection Requirement • Main Protection: Current differential relay with PS class CT • One non directional O/C and E/F on HV and LV side each, with 5P20 class CT

11. 33 / 22 / 11 kV Feeder Protection Main: Non directional 3 Phase O/C and E / F relay

12. Line Differential Protection • A Line Differential (current based) Numerical Relay at both the end line. communication: optical fiber link • Required features • Phase Segregated line Differential Protection • Suitable filtering ensuring correct performance during transient conditions. • Communication Channel Supervision. • Three or single pole auto-reclosing with synchrocheck. • Emergency O/C Protection in case of failure of Communication Media. • Inter-tripping

13. Line Distance Protection Numerical Distance relay features • Non-switched relay with Quadrilateral Characteristics • Four Distance Zones • Suitable filtering ensuring correct performance during transient conditions. • Internal function supervision check (Int. relay failure protection). • Three or single pole auto-reclosing with synchrocheck. • Emergency O/C Protection in case of PT Failure • Fuse Failure Protection • Power Swing Blocking

14. Line Over current Protection A numerical directional 3 phase O/C and E / F protection relay having features • Directional O/C and E/F • IDMTL Char. • 2 / 3 high DT settings

15. Back-up Dir E/F relay for Line • Electromechanical Directional Earth Fault Protection shall be provided as a final b / u protection • It shall be connected in series with the numerical Back-up Protection.

16. Main Protection of Power Transformer Biased Current differential Numerical relay with features • Vector group compensation . • CT ratio correction. • Biased differential protection. • Differential Highset. • 2nd and 5th Harmonic restraint. • Non-Directional O/C • Ckt bkr failure • Different Group Settings • Fault Disturbance Recorder • Transformer trouble alarm/ Trip e.g. Bucholz / PRD / Winding Temp / Oil Temp

17. O/C Protection of Power Transformer Non directional Numerical 3 Phase O/C and E / F Protection on HV & LV side Required Feature • Non directional O/C and E/F for HT side. • LT Side O/C as a part of Differential Relay.

18. LT Neutral E/F Relay for Power Transformer An electromechanical E/F relay as backup protection for faults between transformer terminals and the LT breaker • Connected with the Transformer neutral CT.

19. 33 / 22 / 11 kV Feeder Protection Main: Non directional numerical 3 Phase O/C and E / F relay Feature required • Non directional 3 phase O/C and E/F (each element shall have one IDMTL and 2/ 3 DT stage) • CB Failure protection relay. • Trip ckt supervision • Summation I2t • Different Group setting • Fault Disturbance Recorder

20. Bus-bar Protection Numerical bus bar protection scheme • Dedicated PS Class CT core with same turns Ratio on all HV Bays

21. Capacitor Bank Protection Require feature • Non directional 3 phase O/C and E/F with • IDMTL and 2 DT stages • In-built Ckt bkr failure protection • Trip ckt. Supervision • Thermal Overload • Neutral current unbalance relay • Over voltage relay • Under voltage relay • Residual O/V Relays

22. Requirement for Numerical Relays • serial interface on the front for local comm. through PC and at least one on rear with RS485 serial port, working on an open protocol like IEC60870-5-103 for remote communication, data transfer etc. • Time Synchronism with IRIG-B port or via BI • Configurable LEDs • Self-diagnostic features to reduce the down time of the relay and provide useful diagnostic information on detection of an internal fault. • Multiple settings group feature. • Galvanic isolation between the field connection and the relay hardware. • No. of Output contacts

23. Requirement for Numerical Relays • Record Analog as well as Digital signals • Triggering of DFR through an external input. • FDR Scan rate of sampling > 1000Hz • Transfer of data stored in the FDR to PC in IEEE / COMTRADE format. Data format compatible for dynamic protection relay testing on Relay test kit. • Selection of Prefault memory / Post fault memory