Protection basic

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Protection of power system

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Protection basic

  1. 1. Protective relay -Bhagawan Prasad Chartered Engineer amieclub@gmail.com
  2. 2. What Components (Equipment) Do We Protect?
  3. 3. content 1. Introduction to Protective Relay 2. Working Principle of Protective Scheme 3. What is Relay? 4. Functions of Protective Relay 5. Desirable qualities of protective relaying 6. Terminology of protective relay 7. History of Protective Relay 8. Types of Relays 9. Types of Relay based on Relay Operation Mechanism 10. Protective relay testing: Test relays of all
  4. 4. 1.introduction to Protective relay  Protectiverelay works in the way of sensing and control devices to accomplish its function. Under normal power system operation, a protective relay remains idleand serves no active function.  whe n fault o r unde sirable co nditio n arrive s Pro te ctive Re lay m ust be o pe rate d and functio n co rre ctly.  Failure o f a pro te ctive re lay can re sult in de vastating e q uipm e nt dam ag e and pro lo ng e d do wntim e .
  5. 5. 2.Working Principle of Protective Scheme
  6. 6. 3.What is Relay? A relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. Thus the fault is se nse d and the trip circuit is actuate d by the re lay and the faulty part is iso late d.
  7. 7. 4.Functions oF Protective relay  To sound an alarm or to close the trip circuit  To disconnect the abnormally operating part so as to prevent subsequent faults  To isolateor disconnect faulted circuits or equipment  To localizetheeffect of fault to improve system stability, service continuity and system performance.  To minimize hazards to personnel.
  8. 8. 5. Desirable Qualities of Protective Relaying  Selectivity,  Discrimination  Stability  Sensitivity,  Power consumption  System Security  Reliability  Adequateness  Speed & Time
  9. 9. 6.Terminology of protective relay  Pickuplevel of actuatingsignal: value of actuating quantity voltage or current  Reset level: relay opens its contacts and comes in original position.  OperatingTimeof Relay: The time which elapses between the instant  Reset timeof Relay: relay contacts returns to its normal position.  Reachof Relay: This impedance or corresponding distance is called reach of the relay.
  10. 10. 7.History of Protective Relay 1900 to 1963 1963 to 1972 1972 to 1980 1980 to 1990 Electromechanical Relay Static Relay Digital Relay Numerical Relay 1925=Single Disc Type Relay (Single Input) 1963=Static Relay (All Purpose) 1980=Digital Type Relay (All Purpose) 1990=Numerical Type Relay (All Purpose) 1961=Single Cup Type Relay (Impedance Relay) 1972=Static Relay with self checking (All Purpose)
  11. 11. A. Types of Relays: Based on Characteristic:  Definite time Relays.  Inverse definite minimum time Relays (IDMT)  Instantaneous Relays  IDMT with Instantaneous.  Stepped Characteristic  Programmed Switches  Voltage restraint over current relay
  12. 12. B. Based on logic:  Differential  Unbalance  Neutral Displacement  Directional  Restricted Earth Fault  Over Fluxing  Distance Schemes  Bus bar Protection  Reverse Power Relays  Loss of excitation  Negative Phase Sequence Relays etc.
  13. 13. C. Based on Actuating parameter: Current Relays Voltage Relays Frequency Relays Power Relays etc.
  14. 14. D. Based on Operation Mechanism:  1. Electro Magnetic Relay 2. Static Relay ……• Analog Relay ……• Digital Relay ……• Numerical /Microprocessor Relay 3. Mechanical relay  Thermal • OT Trip (O ilTe m pe rature Trip ) • WT Trip (Winding Te m pe rature Trip ) • Bearing Temp Trip etc.
  15. 15. Based on Operation Mechanism  Float Type • Buchholz • OSR (oil surge relay) • PRV(Pressure Relief Valve ) • Water level Controls etc.  Pressure Switches  Mechanical Interlocks  Pole discrepancy Relay
  16. 16. E. Based on Applications Primary Relays Backup Relays
  17. 17. Electromagnetic AttractionRelay  1.1Electromagnetic AttractionRelay This Relay works on Electromagnetic Attraction Principle
  18. 18. Electromagnetic Induction Relay  1.2 Electromagnetic InductionRelay This Relay works on Electromagnetic Induction Principle
  19. 19. IDMT =inverse definite minimum time
  20. 20. Limitations of Electromagnetic relays  Low speedof operation.  Change in characteristics over a period due to ageing effect.  Component failure leading to relay failure.  Relay is Bulky  Imposes high burden on CT  No fault data available except phase indication.  Inherent in its design,  When an electromechanical Relay is activated, bounce occurs at the contact site.
  21. 21. 2.Solid State (Static) Relay  2.1 Analog Relay: measured quantities are converted into lower voltage but similar signals, which are then combined or compared directly to reference values  2.2 Digital Relay: measured ac quantities are manipulated in analogue form and subsequently converted into square-wave (binary) voltages.  2.3 Numerical Relay: measured ac quantities are sequentially sampled and converted into numeric data form. A microprocessor performs mathematical and/or logical operations on the
  22. 22. Standard lead No. Sr. Alphabet Series Purpose Example 1 J Series D.C Incoming J1, J2, etc. 2 K Series Control – Closing, Tripping, etc. K1, K2, K3 etc. 3 L Series Alarms, indications and annunciations L1, L2, L3, etc. 4 M Series Motor Circuit M1, M2, etc. 5 E Series Potential transformer secondary E1, E2, E3, etc. 6 H Series LT A.C Supply H1, H2, H3, etc.. 7 A Series C.T secondary for special protection A1, A2, A3, etc. 8 B Series Bus bar protection B1, B2, B3, etc.. 9 C Series Protection Circuits C1, C2, C3, etc. 10 D Series Metering Circuit D1, D2, D3, etc
  23. 23. Ferrule on CT/PT  Metering CT secondary’s – D11, D31, D51, D71 etc.  Protection CT secondary – C11, C31, C51, C71 etc.  Special Protection CT secondary – A11, A31, A51, A71 etc.  PT secondary – E11, E31, E51, E71 etc.
  24. 24. ANSI(American National Standards Institute), numbering EXAMPLE  - Lockout Relay  87 - Differential Protective Relay  88 - Auxiliary Motor or Motor Generator  89 - Line Switch  90 - Regulating Device  91 - Voltage Directional Relay  92 - Voltage and Power Directional Relay  93 - Field Changing Contactor
  25. 25. Company  AREVA (ALSTHOM)  ABB  SIEMENS  L&T
  26. 26. CT COPNNECTION  STAR -STAR
  27. 27. CT CONNECTION  DELTA- STAR
  28. 28. CT CONNECTION  CT WITH 3 NOS. O/L
  29. 29. 2 O/C +1 E/F  OVER CURRENT AND EARTH FAULT COMBINED
  30. 30. Core balance CT
  31. 31. THANK YOU

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