Thermoelectricity

OBJECTIVE

PROTECTION OF TRANSFORMERSMini Project Presentation on

submitted byP.KIRANMAYIR.HEMALATHAN.MOHAN SAI KRISHNAK.LAKSHMI THULASIR.N.ADITHYA SHARMA11121A029211121A029311121A028212125A020810121A0281 Under the esteemed guidance ofDEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERINGSREE VIDYANIKETHAN ENGINEERING COLLEGE(AUTONOMOUS)SREE SAINATHNAGAR, A.RANGAMPET-517102 External GuideMr. S.V.KRISHNA ,ADE Chandragiri,33/11kV substation.Internal GuideDr. P.NAGARAJU MANDADI, M.Tech, Ph.D, Professor,SVEC. OBJECTIVE The main objective of this mini project is to study the need for protection of transformer, various schemes employed to provide continuous and reliable power supply.27-10-20142Department of EEE, SVECIntroductionTransformerPower transformersNeed for protection of TransformersFaults in TransformersProtection of TransformersAnalysis of Transformer Protection at substationReferencesConclusion

CONTENTS27-10-20143Department of EEE, SVEC INTRODUCTIONElectrical power system have a dynamic and complex behavior. Different types of faults can interrupt the healthy operation of the power system.Some of the major Electrical faults are phase faults that include phase to phase faults and phase to ground faults and three phase faults.27-10-20144Department of EEE, SVEC TRANSFORMERAtransformeris a static electrical device that transfers power from one side to other side without change in frequency.

It works on the principle of Faradays Laws of Electro Magnetic Induction.

Fig.1: Transformer

27-10-20145Department of EEE, SVEC TYPES OF TRANSFORMERS

Transformers are classified as two categories:Power Transformers Distribution Transformers

Power Transformers Power transformers are used in transmission network of higher voltages

Fig.2: Power TransformerContd.,27-10-20146Department of EEE, SVEC

Contd.,Distribution transformers:

Transformers of rating upto 200kVA, used to step down the distribution voltage to a standard service voltage are known as distribution transformersFig.3: Distribution Transformer27-10-20147Department of EEE, SVEC

NEED FOR PROTECTION OF TRANSFORMERElectricity plays a crucial role in our lives today. The electrical power system has several components and equipments to transform and regulate the current flow.

Transformers are crucial equipment among them. Hence transformer must be protected to:minimise loss of revenue due to outage.Reduce inconvenience to the consumers.

27-10-20148Department of EEE, SVEC FAULTS IN TRANSFORMERExternal FaultsInternal FaultsIncipient FaultsShort CircuitsPhase to EarthShort Circuit in laminationsHigh Voltage, High frequency disturbancePhase to PhaseCore Bolt Insulation FailureOver Load Condition

Inter TurnLocal heating due to clogging of oil27-10-20149Department of EEE, SVECTable No: 1External FaultsInternal FaultsIncipient faultsAtmospheric voltage surgesInsulation breakdown between windings and EarthImproper formation of the coreSwitching operation Insulation breakdown between different phasesInsufficient cooling ducts in the windingOverloadingSudden disconnection of large load Insulation breakdown between adjacent turnsBad quality of raw materialCAUSES FOR THESE FAULTS27-10-201410Department of EEE, SVECTable No: 2 PROTECTION OF TRANSFORMERThe protection of transformer consists of:RelaysCircuit BreakersSurge ArrestorsThermostatPressure Relief Valve27-10-201411Department of EEE, SVECRELAYS

A relay is a device that detects the fault and initiates the operation of the circuit breaker to isolate the defective elements from the rest of the system.

Percentage differential protection relay and Buchholz relay are used in the substation.

27-10-201412Department of EEE, SVEC

Fig.5: Percentage Differential Protection of Transformer27-10-201413Department of EEE, SVECPERCENTAGE DIFFERENTIAL PROTECTIONBUCHHOLZ RELAY:This relay being filled with oil, displaces the oil for the case of gas collection due to internal fault and issues alarm contact and as per the severity of gas collection, tripping results. This is mechanical tripping device.

Fig.6: Buchholz Relay27-10-201414Department of EEE, SVECPOSITIONING OF BUCHHOLZ RELAY: Fig.7: Positioning of Buchholz Relay

27-10-201415Department of EEE, SVECCIRCUIT BREAKERSAn automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

Fig.8: Vacuum circuit breaker Fig.9: SF6 Circuit Breaker

27-10-201416Department of EEE, SVECSURGE ARRESTORSProvides protection from voltage surges such as those caused by lightning.Presence of higher voltage- they provide a path to the ground.

Fig.10: surge arrestors in substation

27-10-201417Department of EEE, SVECTHERMOSTATComponent of a control system which senses the temperature so that the systems temperature is maintained near a desired set point.

Fig.11: Temperature in thermostat

27-10-201418Department of EEE, SVECPRESSURE RELIEF VALVEOver pressure caused by internal faults can be instantaneously relieved through the valves, thus avoiding greater damages such as the deformation or even the burst of the tank .It is necessary to protect the transformer tank with a suitable equipment capable of almost instantaneously discharging overpressure already at the development, before the structure integrity is damaged and the safety valves has just this function.

27-10-201419Department of EEE, SVECPower Transformer ProtectionAbnormal conditionProtection RemarksEarth FaultsDifferential Protection

For Transformers of above 5MVAOver Loads1.Thermal Overload Relay2.Temparature Relays sound alarmTemperature increase is indicated on control boardThrough FaultsGraded time lag over current RelayProtection of distribution TransformersHigh voltage surges due to lightning, switching1.Horn gaps2.Surge arresters1.Not favoured2.In addition to arresters for incoming lines.Saturation of magnetic circuit1.Over fluxing protection 2.Overvoltage protection.For important generator transformer and feeder transformers.27-10-201420Department of EEE, SVECTable No: 3Abnormal conditionsProtectionRemarksLarge internal faults ph-ph, ph-G, below oil level.Faults in tap-changer1.Buchholz relay trips the CB2.Percentage differential protection1.It is too slow and less sensitive2.It is used for transformers of above 5MVAIncipient faults below oil level resulting in decomposition of oil, faults between phases and phases and groundsBuchholz relay sounds alarmBuchholz relay is used for transformers of rating 500KVA and above Contd.,27-10-201421Department of EEE, SVECTable No: 4ANALYSIS OF TRANSFORMER PROTECTION AT 33/11 kV SUBSTATION LOCATED IN CHANDRAGIRI, TIRUPATI

The substation is an outdoor air insulator switch gear (AIS) type.The input to this substation is a 33kV line from 132/33kV Chandragiri substation.The protection is given to the two 8MVA, 33/11kV transformers on both primary and secondary side.

27-10-201422Department of EEE, SVECON 33kV SIDE:The protection for the input side i.e., H.V side includes isolators, lightning arresters and circuit breakers.For the purpose of metering CTs and PTs are used.27-10-201423Department of EEE, SVECEquipmentRatings & FunctionLightning Arrestors

Metal oxide surge arrestors(3)Rating: 30kV/10AFor protection from over voltages during lightningCircuit BreakersSF6 circuit breakersRating: 36kV, 1600A,31.5kA and 3sec.To connect or remove sections of substation from supplyIsolatorsIsolators with earth switch(2) & without earth switch(3)Rating: 36kV, 1600A, 31.5kA, 1secThe isolators used should be in tune with the circuit breakers.CTs & PTsRatings:CT-33kV,400ARatings:PT-33kV/110VA pair of CT and PT is used for energy metering by the APSPDCL.Another CT with 3 primaries is used for differential protectionOne more CT is used near the transformer.ConductorsACSR zebra conductor.27-10-201424Department of EEE, SVECTable no: 524ON 11kV SIDE:The protection for the output side i.e., LV side includes isolators, lightning arresters and circuit breakers of small ratings.

For the purpose of metering CTs, PTs are used.

27-10-201425Department of EEE, SVECEquipmentRatings & FunctionLightning ArrestorsMetal oxide surge arrestorsRatings:10kV,10kAProtection against voltage surgesCircuit BreakersVacuum Circuit BreakerRatings:12kV, 1600ATo connect or remove sections of substation from supplyIsolatorsIsolators without switchRatings: 12kV, 1250A, 31.5kA, 1sec.The isolators used should be in tune with the circuit breakers.RelaysDifferential RelayBuchholz relay(mechanical relay)

CTs CT Ratings:11kV,20kA27-10-201426Department of EEE, SVECTable no: 6CONCLUSIONThus the transformer protection is studied at 33/11kV in Chandragiri and various schemes of protection are analysed.27-10-201427Department of EEE, SVECREFERENCES[1]. Sunil S Rao, Switchgear and Protection, 11th edition, Khanna Publishers, 2005[2]. Badri Ram, D .N. Viswakarma, Power System and Protection and Switchgear , 18th reprint, Tata McGraw-hill Publications,2005. [3]. Bogdan Kasztenny, Michael Thompson and Normann Fischer, Fundamentals of Short- Circuit Protection for Transformers, Schweitzer Engineering Laboratories, Inc, March 2009.[4]. B. L. Soni, Guptha, Bhatnagar, Chakrabarthy, A Text Book on Power System Enginnering, Dhanpat Rai & Co, 2007.[5]. www.electrical4u.com

