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Welcome. Significance of protection systems . T.ANIL KUMAR Sr.Asst.Engineer Regional Lab Power Grid Corporation of India Ltd. Ph.No-94906111092. What is protection?. The process of keeping something or someone safe and Secure Electrical equipment need protection from abnormal conditions.

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  1. Welcome...

  2. Significance of protection systems T.ANIL KUMAR Sr.Asst.Engineer Regional Lab Power Grid Corporation of India Ltd. Ph.No-94906111092

  3. What is protection? • The process of keeping something or someone safe and Secure • Electrical equipment need protection from abnormal conditions.

  4. WHAT IS A PROTECTION ?Why it is required? Humans need protection from external disease , sun and whether. All the internal parts of the human beings are protected naturally. Heart and lungs are protected by ribs bones from external impact. Brain is protected by skull.Eyes are protected by eyelids and by closing eyes. We need cloths to protect us from external environment conditions. Similarly electrical equipment needs protection from any external or internal faults which may produce a detrimental effect on it.

  5. Objective of Protection • Protect persons and equipment in the surrounding of the power system • Protect apparatus in the power system • Separate faulty parts from the rest of the power system to facilitate the operation of the healthy part of the system

  6. Electrical faults in the power system • Transmission lines 85% • Busbar 12% • Transformer/ Generator 3%

  7. Fault statistics • Single phase to earth 80% • Two phases to earth 10% • Phase to phase faults 5% • Three phase faults 5% The probability of line faults caused by lightnings are 0 - 2.3 faults/ 100 km and year

  8. Primary Relaying Generator Protection Circuit Breaker Low voltage Protection Power Trans. Protection High voltage Protection Transmission line Prot. High voltage Protection

  9. What is a Relay? • A device which has an electrical / non-electrical quantity as input • Output is in form of a switch called “Contacts”, which either close or open depending on the input quantity

  10. A Simple Relay Solenoid Input Armature Normally Open Contact Normally Close Contact

  11. ELEMENTS OF PROTECTION Bus Trip Ckt CB CT Current DC SOURCE Voltage CVT Relay Feeder

  12. FUNCTIONALCHARACTERISTICS OF PROTECTIVE RELAYING • SENSITIVITY • SELECTIVITY • SPEED • REPEATABILITY • ECONOMY Any relaying equipment must be sufficiently sensitive so that it will operate reliably when required under actual condition that produce the least operating tendency.

  13. REQUIREMENTS OF PROTECTIVE RELAYS SENSITIVITY : The relay shall be sensitive to operate for minimum quantity of operating parameter. SELECTIVITY: The relay/scheme should be able to select the faulty section and isolate. SPEED : The relay should operate faster so that fault is isolated as fast as possible. RELIABILITY : The relay/scheme should operate for all types of faults with repeatability and reliability. COST :The relay/scheme should be economical .

  14. Basis of Classifications • Quantity of response: Voltage, current, frequency, power etc. • Function: Detection, time-delay, tripping, alarm, signaling, flag, contact multiplication etc • Construction: Electromagnetic, Static or Numerical

  15. Basic Types Based on Operating Principle • Attracted Armature • Moving Coil • Induction • Thermal • Motor-Operated • Mechanical • Static • Numerical

  16. Induction Type Relays • Work only with ac quantities, working principle same as that of induction motor • For use with single quantity, phase splitting arrangement is needed • Relay comprises of: • A set of two or more ac magnetic fluxes, which are displaced in space as well as time, • An induction disc (or cup) which acts as rotor of an induction motor • A restraining force usually provided by spring

  17. Thermal Relays • Thermal overload relays based on bi-metallic strips • A bimetal strip when heated, changes shape due to unequal expansion. This phenomenon is used to close or open contacts

  18. Motor – Operated Relays • A small electric motor drives a contact-making arrangement through reduction gears. • Typical applications include control of complex sequence of operations, introduction of delay, repeated auto-reclose of CB or matching of speed of generator to the network before energization

  19. Mechanical relays Various relays responding to: • Pressure • Liquid levels • Fluid flow etc..

  20. Static Relays Relays making use of various electronic devices / phenomena such as: • Electronic Relays • Transductor (magnetic amplifier) relays • Rectifier bridge relays • Transistor Relays • Hall effect relays • Gause effect relays

  21. Static Relays…(Contd) • Basic measurement using various static circuitry using analog / digital techniques • Use of gates and microprocessor etc for logical decisions • Some basic building blocks are level detectors, phase comparators etc

  22. Numerical Relays • All input signals are converted to digital quantities after conditioning using ADCs • All measurements are performed by DSPs numerically • Relays are highly accurate and immune to drift and calibration problems.

  23. Application based classifications • Directional O/C & E/F relays • Distance relays • Differential relays • Over-flux relays • Pilot-wire relays • Phase comparison relays etc..

  24. Directional O/C & E/F relays • Direction sensing is achieved by giving voltage input from PT / CVT • Widely used as back-up protection for power transformers

  25. Distance relays Basically measure impedance with voltage and current inputs • Most widely used as primary / back-up protection for transmission lines as well as back up protection for shunt reactors

  26. Phase comparison relay • Makes use of carrier (PLCC or others) • Sends phase information of current to other end • At each end phase information of both the ends is compared. • If both ends indicate current flow to the line, an in-zone fault is inferred

  27. Phase Comparison Relay(Through fault) A B A B B A No Trip A+B A+B No Trip

  28. Phase Comparison Relay (In-Zone fault) A B A B B A Trip A+B A+B Trip

  29. NORMAL PROTECTIONS FOR TRANSFORMER • Differential Protection : DTH31,RADSB,RADHA • Ground Fault Protection : CAG14, RADHD • Over Current Protection : CDD,RXIG • Over Load Protection : VTU,RXEG • Over Fluxing Protection : GTT,RATUB • Buchholz Relay (OLTC & Main Tank) • Pressure Relief Device • Oil and Winding temp alarms and trips • Oil Level Monitoring (MOLG)

  30. Differential Relays I1 I2 i1 i2 id=(i1-i2)

  31. TRANSFORMER DIFFERENTIAL RELAY • For protecting a transformer, we can compare the currents on High Voltage Side and Low Voltage side. It should match as per the transformer ratio. This comparison is used in Differential Protection. • In a shunt reactor, the currents on the HV side and Neutral ends are Compared. • E.g. RADSB

  32. DIFFERENTIAL RELAY FOR BUS BAR • The Differential Current protection is also used to protect the Bus Bars. Here the current entering the bus and leaving the bus are summed up. The sum should be zero. The summation can be done in the relay (ABB scheme) or after paralleling all CT’s, a Voltage Relay can be connected across (EE – (Areva) scheme). • E.g. RADSS

  33. Restricted earth fault protection 64

  34. RESTRICTED EARTH FAULT RELAY • To protect a transformer or reactor, another important protection is “Restricted Earth Fault” (REF). The sum of current entering and leaving a transformer or reactor is zero. After paralleling all CT’s, the relay is connected across to monitor the spill current which occurs if there is earth fault within the protected area.

  35. DIRECTIONAL OVER CURRENT RELAY • Transformer is also protected with Directional Over Current Relays where the power flow direction is also measured by monitoring current and voltage. • Reactor is also protected with Impedance Relay (Backup Impedance) where the winding impedance is monitored like a Line Distance Protection.

  36. OVER FLUX RELAY • Another protection of transformer is Over Fluxing: Here the V/f ratio is monitored from the Bus Voltage. • In addition to these, transformer and reactors are having mechanical protections like : Pressure Release Device, Winding Temperature Indicator, Oil Temperature Indicator, Oil Surge Relay, Gas Operated Relay (Buchholz). A contact from these mechanical relays operate the trip relay to trip the circuit breaker.

  37. OTHER TRANSFORMER PROTECTION • Transformers are also having Alarms for Buchholz, WTI, OTI, Magnetic Oil Gauge. If the transformer is provided with “OF” (Oil Forced) ie., pumps, and “AF” (Air Forced) ie., fans, they are automatically switched ON and OFF through WTI contacts. The WTI is also wired for control room indication.

  38. LOCAL BREAKER BACK UP RELAY • Still if a breaker fails to operate due to any problem like mechanical etc., the Local Breaker Backup (LBB) or Breaker Failure Relay (BFR) will operate to trip other related breakers to clear the fault. The LBB monitors the circuit current for 200 milli second after a trip command to the breaker, and if the circuit current is persisting, LBB trips all connected breakers. This can lead to tripping of Bus Bar, other end of line etc.

  39. OVER VOLTAGE RELAY • STAGE I ( 110% OF THE VOLTAGE ) OPERATE AFTER 5 SEC • STAGE II ( 140% OF THE VOLTAGE) OPERATE INSTANTLY

  40. AUTORECLOSE –PHILOSOPHY • NEED FOR AUTO RECLOSE • REDUCING OUTAGE TIME • IMPROVED RELIABILITY • RESTORATION OF NETWORK STABILITY AND • SYNCHRONISM • 4. REDUCTION OF OPERATING COST BECAUSE • OF ABOVE FACTORS • ANALYSIS OF FAULTS • TRANSIENT FAULTS • SEMI PERMANENT FAULTS • PERMANENT FAULTS

  41. Power Swing Blocking (PSB) function • A power swing can be started by sudden load change due to a fault somewhere in the network. • Close to the centre of the power swing, low voltage and thus low impedance will occur. • A distance protection relay must then be blocked during the power swing. • This can be done by measuring the transit time of the impedance locus passing two dedicated impedance zones. • Normally the time used is 35-40 ms.

  42. Switch on to Fault (SOTF) The protection is provided with switch onto fault feature to cater to breaker closing onto forgotten earthing device. This also takes care of auto reclosing on to a permanent fault. Automatic switch onto fault takes care of configurations where Line PT is used as voltage input to the distance terminal.

  43. FUSE FAIL SUPERVISION AND TRIP SUPERVISION RELAY • THIS FUCTION IS BASED ON CONDITION 3UO > 20 % OF Un / Ö 3 AND 3IO < 20 % OF In • IT CAN BE SELECTED TO BLOCK PROTECTION AND GIVE ALARM OR JUST TO GIVE ALARM. • FUSE FAIL SUPERVISION IS BLOCKED FOR 200ms FOLLOWING: LINE ENERGISATION IN ORDER NOT TO OPERATE FOR UNEQUAL POLE CLOSING AND ALSO DURING AUTORECLOSING.

  44. SYSTEM SUPERVISION.

  45. Thank You

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