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

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 IEC 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