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

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

Basic Requirements of Protection system Sensitivity Speed Selectivity Security

Need for Protection system To Minimise damage To Minimise down time To Minimise system disturbance

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

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

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

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

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

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

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

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

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

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

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.

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

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.

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.

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

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

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

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

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