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Basic protection and relaying


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Basic protection and relaying

  1. 1. BASIC PROTECTION ANDRELAYING SCHEMES Guided by-Submitted by-  Dr. AbhimanyuSomali ajal Das Mohapatra  Dr. Ranjan Ku. Jena0901106068
  2. 2. Agenda  Why protection is needed  Principles and elements of the protection system  Basic protection schemes  Digital relay advantages and enhancements
  3. 3. Disturbances: Light or Severe The power system must maintain acceptable operation 24 hours a day Voltage and frequency must stay within certain limits Small disturbances The control system can handle these Example: variation in transformer or generator load Severe disturbances require a protection system They can jeopardize the entire power system They cannot be overcome by a control system
  4. 4. Power System ProtectionOperation during severe disturbances: System element protection System protection Automatic reclosing Automatic transfer to alternate power supplies Automatic synchronization
  5. 5. Electric Power System Exposure to ExternalAgents
  6. 6. Damage to Main Equipment
  7. 7. Protection System A series of devices whose main purpose is to protect persons and primary electric power equipment from the effects of faults The “Sentinels”
  8. 8. Blackouts Characteristics Main Causes Loss of service in a  Overreaction of the large area or protection system population region  Bad design of the Hazard to human life protection system May result in enormous economic losses
  9. 9. Short Circuits Produce High Currents Three-Phase Line a b c I Substation Fault Thousands of Amps I Wire
  10. 10. FAULTS ON POWER SYSTEMS RISK :Severe damage to the faulted equipment : Excessive current may flow; Causes burning of conductors or equipment windings; Arcing - energy dissipation; Risk of explosions for oil - filled switchgear, or when in hazardous environments.Damage to adjacent plant : As the fault evolves, if not cleared quickly; Due to the voltage depression / loss of supply.
  11. 11. Mechanical Damage DuringShort Circuits Very destructive in busbars, isolators, supports, transformers, and machines Damage is instantaneous Mechanical Forces f1 f2 i1 i2Rigid Conductors f1(t) = k i1(t) i2(t)
  12. 12. The Fuse Fuse Transformer
  13. 13. Essential qualities of protection: Reliability Selectivity-Absolute or relative Fastness Discrimination
  14. 14. Protection System Elements Protective relays Circuit breakers Current and voltage transducers Communications channels DC supply system Control cables
  15. 15. Protective relays: A device which detect intolerable or unwanted conditions within the assigned area. * A watchman or watchdog for the equipment/area * Silent sentinels to power system.
  16. 16. How relays are differentiated? Can be differentiated based on: * Functional categories * Input quantities *Operating Principles * Performance Characteristics.
  17. 17. What are various designcriteria? * Dependability/Reliability * Security * Selectivity *Speed * Simplicity/flexibility *Stability *Performance Vs. Economy
  18. 18. What are various techniqueused? * Electromechanical *Solid state/Static * Microprocessor/Numerical
  19. 19. Non-Unit, or UnrestrictedProtection :No specific point downstream up to whichprotection will protect Will operate for faults on the protected equipment; May also operate for faults on downstream equipment, which has its own protection; Need for discrimination with downstream protection, usually by means of time grading.
  20. 20. Unit, or RestrictedProtection :Has an accurately defined zone of protection An item of power system plant is protected as a unit; Will not operate for out of zone faults, thus no back-up protection for downstream faults.
  21. 21. Types of relaysAs per function: Main Auxiliary SignalAs per actuating quantity Overrelays Underrelays
  22. 22. Types…As per connection Primary Secondary(common)As per action on CB Direct acting Indirect actingAs per construction Electromagnetic
  23. 23. Types.. Static NumericalAs per comparator types Single input comparator Two input comparator Multiple input comparator
  24. 24. Methods of disciminations: To locate fault by time by current grading by time and direction by distance by time, current and distance by current balance by power direction comparison Type of fault
  25. 25. Three-Phase Diagram of the Protection Team
  26. 26. DC Tripping Circuit
  27. 27. Circuit Breakers
  28. 28. Current Transformers Very High Voltage CT Medium-Voltage CT
  29. 29. Voltage Transformers Medium Voltage Note: Voltage transformers are also known as potential High Voltage transformers
  30. 30. Protective Relays
  31. 31. Examples of Relay Panels Microprocessor- Based Relay Old Electromechanical
  32. 32. How Dofault takes place, the current, When a Relays Detect Faults? voltage, frequency, and other electrical variables behave in a peculiar way. For example: Current suddenly increases Voltage suddenly decreases Relays can measure the currents and the voltages and detect that there is an overcurrent, or an undervoltage, or a combination of both Many other detection principles determine the design of protective relays
  33. 33. Primary Protection
  34. 34. Primary Protection Zone Overlapping Protection Zone A 52 Protection Zone B To Zone A Relays To Zone B Relays Protection Zone A 52 Protection Zone B To Zone A Relays To Zone B Relays
  35. 35. Backup Protection Breaker 5 Fails C D A E 1 2 5 6 11 12 T B F 3 4 7 8 9 10
  36. 36. Typical Short-Circuit Type DistributionSingle-Phase-Ground: 70–80%Phase-Phase-Ground: 17–10%Phase-Phase: 10–8%Three-Phase: 3–2%
  37. 37. Balanced vs.Unbalanced Conditions Ia Ic Ic Ia Ib Ib Balanced System Unbalanced System
  38. 38. Decomposition of an UnbalancedSystem
  39. 39. Power Line Protection Principles Overcurrent (50, 51, 50N, 51N) Directional Overcurrent (67, 67N) Distance (21, 21N) Differential (87)
  40. 40. Characteristics of overcurrent relays: Definite time IDMT- inverse definite minimum time Very inverse Extremely inverse
  41. 41. Application of Inverse-Type Relays Relay t Operation Time I Radial Line Fault Load
  42. 42. Inverse-Time Relay Coordination I Distance t } ∆T } ∆T } ∆T Distance
  43. 43. 50/51 Relay Coordination I Distance t } ∆T } ∆T } ∆T Distance
  44. 44. Directional Overcurrent ProtectionBasic Applications K L
  45. 45. Distance Relay Principle L d I a , Ib , Ic Radial 21 Three-Phase Va ,Vb ,Vc Line Solid Fault Suppose Relay Is Designed to Operate When: | Va |≤ (0.8) | Z L1 || I a |
  46. 46. The Impedance RelayCharacteristic R 2 + X 2 ≤ Z r21 X Plain Impedance Relay Operation Zone Z ≤ Z r1 Radius Zr1 Zr1 R
  47. 47. Need for Directionality F2 F1 1 2 3 4 5 6 RELAY 3 X Operation Zone F1 F2 R Nonselective Relay Operation
  48. 48. Three-Zone Distance ProtectionTime Zone 3 Zone 2 Zone 1 1 2 3 4 5 6 Time Zone 1 Is Instantaneous
  50. 50. Differential Protection Principle Balanced CT Ratio CT CT Protected Equipment External Fault 50 IDIF = 0 No Relay Operation if CTs Are Considered Ideal
  51. 51. Differential Protection Principle CTR CTR Protected Equipment Internal Fault 50 IDIF > ISETTING Relay Operates
  52. 52. Problem of Unequal CTPerformance CT CT Protected Equipment External Fault 50 IDIF ≠ 0 False differential current can occur if a CT saturates during a through-fault Use some measure of through-current to desensitize the relay when high currents are present
  53. 53. Possible Scheme – PercentageDifferential Protection Principle ĪSP ĪRP CTR Protected CTR Equipment ĪS ĪR Relay (87) Compares: I OP = I S + I R | IS | + | IR | k ×I RT =k× 2
  54. 54. Differential ProtectionApplications Bus protection Transformer protection Generator protection Line protection Large motor protection Reactor protection Capacitor bank protection Compound equipment protection
  55. 55. Differential ProtectionSummary The overcurrent differential scheme is simple and economical, but it does not respond well to unequal current transformer performance The percentage differential scheme responds better to CT saturation Percentage differential protection can be analyzed in the relay and the alpha plane Differential protection is the best alternative selectivity/speed with present technology
  56. 56. Advantages of Digital Relays Compatibility with Low maintenance Multifunctional digital integrated (self-supervision) systems Highly sensitive, Highly reliable secure, and Adaptive (self-supervision) selective Reduced burden Programmable on Low Cost Versatile CTs and VTs
  57. 57. Why study this protectionscheme?? Protection scheme plays a vital & important role for the normal operation or the steady state operation of different components of power system network, which must be reliable, fast and efficient. In order to achieve all these features, it is essential that these should be proper care in designing and choosing an appropriate and efficient protection scheme. The protective relays functions as the brain behind the whole schemes…
  58. 58. THANK YOU