central testing circle,dvc, maithon transformer protection by jayanta dutta, superintending engineer...

CENTRAL TESTING CIRCLE,DVC, MAITHON TRANSFORMER PROTECTION BY JAYANTA DUTTA, SUPERINTENDING ENGINEER CRITM, DVC, MAITHON

PHYSICAL ARRANGEMENT OF A THREE PHASE TRANSFORMER

CORE MATERIALS USED FOR CONSTRUCTION OF TRANSFORMER Grain oriented Electrical Steel CRGO is undoubtedly the most important soft magnetic material in use today. Whether in small transformer, distribution transformer or in large transformer & generator, grain oriented electrical steel CRGO is a must for the production of energy saving electrical machines. Grain oriented Electrical Steels are iron-silicon alloys that provide low core loss and high permeability needed for more efficient and economical electrical transformers. CRGO Grain oriented grades of electrical steel are typically used for transformer cores and large generators

CORE MATERIALS USED FOR CONSTRUCTION OF TRANSFORMER Important physical properties of Electrical steels (CRGO) include Resistivity, saturation induction, magneto-crystalline anisotropy, magnetostriction, and Curie temperature. Resistivity, which is quite low in iron, increases markedly with the addition of silicon. Higher Resistivity lessens the core loss by reducing the eddy current component. Raising the silicon content will lower magnetostriction, but processing becomes more difficult. The high Curie temperature of iron will be lowered by alloying elements, but the decrease is of little importance to the user of CRGO Electrical steels.

DERIVATION EQUATION OF TRANSFORMER

STANDARD CONNECTION GROUP 1 (ZERO DEGREE)

STANDARD CONNECTION GROUP 2 (180 DEGREE)

STANDARD CONNECTION GROUP 3 (-30DEGREE)

STANDARD CONNECTION GROUP 4 (+30DEGREE)

PARALLELLING OF TRANSFORMERS The theoretically ideal conditions for paralleling transformers are: Identical turn ratios and voltage ratings. Equal percent impedances required for equal Load sharing. Equal ratios of resistance to reactance. Same polarity. Same phase angle shift. (Vector Group) Same phase rotation.

TYPES OF TRANSFORMER FAULTS TRANSFORMER FAULTS ARE GENERALLY CLASSIFIED INTO FIVE CATEGORIES:- WINDING AND TERMINAL FAULTS. (ABOUT 60%) CORE FAULTS. (ABOUT 12%) TANK AND TRANSFORMER ACCESSORIES FAULT. ( ABOUT10%) ONLOAD TAPCHANGER FAULT.(15%) ABNORMAL OPERATION CONDITIONS.(2%) SUSTAINED AND UNCLEARED EXTERNAL FAULTS.(1%)

FAULTS IN AUXILLIARY EQUIPMENT Transformer oil Oil level low. Moisture absorption Transformer cooling system. Failure of insulation between lamination and core bolt. Badly made joints and connections.

WINDING AND TERMINAL FAULTS Insulation failure between winding and core Between (phase to earth) Between phases (phase to phase) Between HV and LV winding Inter turn faults. Cause may be Excessive over load, Loose connection Improper Installation and Commissioning Constant Over voltage, Aging of winding insulation Consequence of minor faults.

CONSTANT OVER VOLTAGE Over voltage conditions are of two kinds; TRANSIENT OVER VOLTAGE arise from switching and lightning disturbances and are liable to cause interturn faults. POWER FREQUENCY OVER VOLTAGE causes both an increase in stress on the insulation and proportionate increase in working flux. Increase in working Flux will increase the working Flux and thereby increase in the Magnetizing Current.

EXTERNAL FAULTS Sources of abnormal stress in a transformer are:- External overloads Short circuits Over voltage Reduced system frequency (v/f ratio) FAULTS IN OLTC FAULTS IN BUSHINGS

TYPES OF TRANSFORMER FAULTS

CRITERION FOR SELECTION OF PROTECTION SCHEME Kva or Mva rating Voltage ratio Winding connections. Per unit / per cent reactance Neutral point Earthing resistance Value of system Earthing resistance. Whether indoor or outdoor Dry or oil filled. With or without conservator Fault level at the power transformer terminals Network diagram showing the position of transformer in the system network.

BASIC PROTECTIONS OF TRANSFORMERS BIASED DIFFERENTIAL PROTECTION RESTRICTED EARTH FAULT PROTECTION. HV BACK-UP OVERCURRENT AND EARTH FAULT PROTECTION. EARTH FAULT PROTECTION MAY HAVE AN ADDITIONAL DIRECTIONAL ELEMENT. LV BACK-UP OVERCURRENT AND EARTH FAULT PROTECTION. OVERFLUXING PROTECTION

DIFFERENTIAL PROTECTION Protects the transformer against winding faults such as phase-to-phase fault and phase to earth fault. It works on circulating current principle. Balanced three phase through current suffers a phase change (30 degree for Group 3,4) which must be corrected in CT secondary leads by appropriate connection of the CT secondary windings. Elimination of Zero sequence through CT secondary Connections for Star Connected Winding.

DIFFERENTIAL RELAY CURRENT BALANCE CONDITION

Problems / Difficulties, While Incorporating Differential Protection : Different voltage levels at primary and secondary of the transformer. Possible ratio mismatch of the current transformers. 30 phase shift in case of delta / star transformer. Operation of the transformer at different tap position. Ct ratio errors Different CT performance at high fault currents. Inherent difference in the CT characteristic Saturation of CTs cause large ratio errors ip = k*is + im. Presence of d. C. Component in the fault current.

MAGNETISING INRUSH 6 to 10 times the rated current. Present only on the primary side of the transformer. Depends on residual flux of the transformer and voltage wave position at the instant of switching (i.e. Zero or peak).

MAGNETISING INRUSH CURRENT WAVEFORM

BIAS OF DIFFERENTIAL RELAY

DUAL SLOPE OF BIAS OF DIFFERENTIAL RELAY

BIAS OF DIFFERENTIAL RELAY There may be some ratio errors in CTs (upto 5%) and some difference in primary and secondary currents due to tap changing (upto 10%). Biasing is used to avoid false trippings from these effects. The differential protection uses some percentage of through current for biasing (or restraining). say we use tripping slope as 20% and differential & restraining currents in a typical relay are : Differential current = |I1+I2| Restraining current = (|I1|+|I2|)/2 The relay will trip when: Differential current / Restraining current> 0.2

RESTRICTED EARTH FAULT PROTECTION Provides sensitive, instantaneous earth fault protection within the protected zone of the transformer. Operates on circulating current principle. CAG 14 high impedance relay is used with external stabilizing resistor for the stability against through faults. Operating coil of the relay is connected with L. C. Circuit in series to immune harmonic produced by ct saturation. The residual current of 3 CTs is balanced against the output of a CT in neutral conductor.

HIGH IMPEDENCE RESTRICTED EARTH FAULT PROTECTION RATIO AND ACCURRACY CLASS ALONG WITH KNEE POINT VOLTAGE OF ALL THE 4 CTS SHOULD BE IDENTICAL. R R R C B A TRANSFORMERCTs TRANSFORMER A B C LINE CTs RELAY & SR NEUTRAL CTs

RESTRICTED EARTH FAULT PROTECTION CONNECTIONS

CALCULATION OF STABILISING RESISTANCE FOR R/E/F PROTECTION Example:- For a 50MVA 230/36KV transformer, through fault Stability req. up to say 20 Times Full Load Current with Neutral CT assumed completely saturated. Line CT ratio & Neutral CT Ratio considered as 400/1. CT resistance = 5ohms. Relay resistance 4.5 ohms Cable and Lead Resistance - 1 ohm. Relay Pick Up - 0.1 Amps. Calculate the value of Stabilizing Resistance. Full Load current = 50,000/ 3 x 230 = 125.51A Maximum Current Stability = 125.51 x 20 = 2510.218A = 2.5kA Considering the Saturation of the Neutral CT, Voltage developed across the relay = 2510.218 ( 1+5+1 ) = 43.93 Volts Now Volts to operate the relay: - IR = 0.1 x 4.5 = 0.45Volts.

CALCULATION OF STABILISING RESISTANCE FOR R/E/F PROTECTION To ensure Stability of Protection Circuit Voltage drop across the S.R = 2510.218 ( 1+5+1 ) = 43.93 Volts Hence resistance required - 43.47/0.1 = 434.7ohms. Now the relay must pick - up at internal faults. For 0.1A pickup requires 0.1( 5+1+434.7+4.5+1) = 44.62 Volts. Now Im at Vk = 800mA Total Mag. Current for 4 CT = 4 x 0.8 = 3.2A Effective Relay setting = Irelay + Im = 0.1 + 3.2 = 3.3A Or in terms of primary the Line Current = 3.3 x 400 = 1320A. Hence for a internal E/F current of 1320A the relay is found to operate.

COMBINED DIFFERENTIAL AND RESTRICTED EARTH FAULT PROTECTION

NUMERICAL DIFFERENTIAL RELAY PROTECTION WITH HIGH IMPEDENCE R/E/F PROTECTION

Connection of transformer differential protection with high impedance REF (I7) and neutral current measurement at I8

OVERFLUXING PROTECTION E = 4.44 * * f * T E / f WHEN THE FLUX DENSITY INCREASES BEYOND SATURATION POINT, A SUBSTANTIAL AMOUNT OF FLUX IS DIVERTED TO STEEL STRUCTURAL PARTS AND INTO THE AIR. AT SATURATION FLUX DENSITY THE CORE STEEL WILL OVER HEAT. STRUCTURAL STEEL PARTS WHICH ARE NU-LAMINATED AND ARE NOT DESIGNED TO CARRY MAGNETIC FLUX WILL HEAT RAPIDLY. FLUX FLOWING IN UNPLANNED AIR PATHS MAY LINK CONDUCING LOOPS IN THE WINDINGS, LOADS, TANK BASE AT THE BOTTOM OF THE CORE AND STRUCTURAL PARTS AND THE RESULTING CIRCULATING CURRENTS IN THESE LOOPS CAN CAUSE DANGEROUS TEMPERATURE INCREASE. IT MAY BE SEEN THAT METALLIC SUPPORT STRUCTURES FOR CORE AND COIL, WINDINGS, LEAD CONDUCTORS, CORE LAMINATION, TANK ETC. MAY ATTAIN SUFFICIENT TEMPERATURE WITH THE EVOLUTION OF COMBUSTIBLE GAS F=(V/F)/(V n /Fn)1.11.21.251.31.4 Duration of withstand time(min.)Continuous210.50

BACK UP O/C AND E/F PROTECTION BACKUP PROTECTION OF TRANSFORMER IS O/C AND E/F PROTECTION APPLIED AGAINST EXTERNAL SHORT CIRCUIT AND EXCESSIVE OVER LOADS. NORMALLY IDMT RELAYS WITH STANDARD INVERSE OR VERY INVERSE CURVES. GENERALLY INSTALLED IN THE HV AND LV SIDE OF THE TRANSFORMER. FOR HV SIDE, THE TRIPPING SHOULD BE OF BOTH SIDES. FOR LV SIDE, THE TRIPPING WILL ONLY BE FOR THE LV SIDE. BACKUP PROTECTION OF TRANSFORMER HAS FOUR ELEMENTS, THREE OVER CURRENT RELAYS CONNECTED EACH IN EACH PHASE AND ONE EARTH FAULT RELAY CONNECTED TO THE COMMON POINT OF THREE OVER CURRENT RELAYS.

INHERENT PROTECTIONS OF TRANSFORMERS BUCHOLZ PROTECTION FOR MAIN TANK. OIL SURGE RELAY PROTECTION FOR DIVERTOR TANK. PRESSURE RELEASE VALVE (PRV). OIL TEMEPRATURE HIGH ALARM AND TRIP. WINDING TEMPERATURE HIGH ALARM AND TRIP. OIL LEVEL LOW ALARM.

BUCHOLZ RELAY

TRANSFORMER PROTECTIONS PROTECTIONTRANSFORMER RATED BELOW 500KVA TRANSFORMER RATED BETWEEN 500KVA AND 5MVA TRANSFORMER RATED ABOVE 5MVA DIFFERENTIALXX R.E.F.XX BACK UP O/CX BACK UP E/FX TRANSFORMER OVERFLUXING XX BUCHOLZX P.R.V.X O.T.I AND W.T.I.X OIL LEVEL MONITORING X FUSES XX

EARTHING SYSTEM FOR UNGROUNDED DELTA

POWER TRANSFORMER PROTECTION IN DVC

PRESENT DAY POWER TRANSFORMER PROTECTION IN 132KV FOR DVC

PRESENT DAY POWER TRANSFORMER PROTECTION IN 220KV FOR DVC

PRESENT DAY ICT PROTECTION IN 400KV INSTALLATION FOR DVC (6 CT SCHEME)

STANDARD A.C. SCHEMATIC OF TRANSFORMER PROTECTION.

MAINATAINANCE PRACTICES REQUIRED FOR TRANSFORMER The general cleaning of bushings and transformer top on main tank. The small oil leakage attending. The tightness checking of control wire and terminal blocks. The cleaning of contactor coils at marshalling box. The test of Buch. relay by loss of oil method. The OTI & WTI checking by both hot oil bath method and dial rotating method. The cooling system also are checked.

MAINTAINANCE PRACTICES REQUIRED FOR TRANSFORMER The OTI & WTI pocket oil are checked. The alarm for Main tank & diverter tank low oil level. The trip test by PRV and diver tank OSR. The Phase marking of bushings. The IR Value of Transformer are measured by 5.0KV Megger. The power factor test. The main tank oil BDV and moisture content test. The DGA test of both main tank and diverter tank oil at CRITL

MAINATAINANCE PRACTICES REQUIRED FOR TRANSFORMER Without shut down activities. Checking of bushing oil level :- M/D2 Checking of oil level in conservator :- M/D3. Checking of oil level in OLTC conservator :-M/D4. Manual actuation of cooler oil pumps and fans :- M/D5. Checking of oil leaks :-M/D6. Checking condition of silica gel in breather :- M/D7. Checking of oil level in oil seal of breather :-M/D8. Testing of oil for DGA and other oil parameters :-HY

CHANGE OF DIFERENTIAL CIRCUIT WITH CHANGE OF VECTOR GROUP THROUGH PRIMARY CONNECTIONS.

Monitoring test on a Transformer There are certain tests, which after rectifying the value nearer to permissible limit, minimizes the failure of transformers due to internal fault. DGA test: DGA will indicate heating, burning, sparking/arcing, loose joint, etc. inside the xmer. Capacitance Tan Delta / P.I. & A.I. tests: Capacitance Tan Delta and P.I. & A.I. values will indicate insulation condition of transformer. Oil sample test: As per IS - 1866. Also, the trend of change in the oil gives useful information (can be known from its colour and odor) Oil sample test will indicate oil quality, which is directly affecting transformer health and life both.

MONITORING OF TRANSFORMER BY INSULATING OIL EVALUATION MINERAL OILS USED IN TRANSFORMERS AS COOLANTS AND INSULANT SHOULD HAVE THE FOLLOWING PROPERTIES:- HIGH DIELECTRIC STRENGTH TO WITHSTAND ELECTRICAL STRESS IMPOSED IN SERVICE. SUFFICIENTLY LOW VISCOCITY SO THAT ITS ABILITY TO CIRCULATE AND TRANSFER HEAT IS NOT IMPAIRED. ADEQUATE LOW TEMPERATURE PROPERTIES DOWN TO THE LOWEST TEMPERATURE EXPECTED AT THE INSTALLATION SITE. RESISTANCE TO OXIDATION TO MAXIMISE SERVICE LIFE.

TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE ACTION TESTS RECOMMENDED BRIEF EXPLANATION BREAKDOWN VOLTAGE (IEC60156) MEASURES THE OILS ABILITY TO WITHSTAND ELECTRICAL STRESS WATER CONTENT (IEC 60814) WATER ACCELERATES THE DETERIORATION OF BOTH THE INSULATING OIL AND THE PAPER INSULATION, LIBERATING MORE WATER IN THE PROCESS. ACIDITY (NEUTRALIZATION FACTOR) (IEC 62021-1) ORIGINATES FROM OIL DECOMPOSITION. SOMETIMES ALSO FROM ATMOSHPHERIC CONTAMINATION.

TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE ACTION TESTS RECOMMENDED BRIEF EXPLANATION INTERFACIAL TENSION (ASTMD971-99A) THE INTERFACIAL TENSION (IFT) MEASURES THE TENSION AT THE INTERFACE BETWEEN TWO LIQUID (OIL AND WATER) WHICH DO NOT MIX AND IS EXPRESSED IN DYNE/CM OR mN/m. DEFINITE RELATIONSHIP WITH IFT AND ACIDITY. INCREASE IN ACIDITY CAUSES DROP IN IFT. RATIO OF IFT/ACIDITY GIVES QUALITY INDEX SYSTEM. AND A NEW OIL CAN HAVE A QI OF >1500(45/.03) DIELECTRIC DISSIPATION FACTOR OR RESISTIVITY (IEC60247) THE DISSIPATION TEST MEASURES THE LEAKAGE CURRENT THROUGH AN OIL. REVEALS PRESENCE OF CONTAMINATION AND PRESENCE OF MOISTURE RESIN, VARNISH, FOREIGN CONTAMINANTS.ETC

TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE ACTION TESTS RECOMMENDED BRIEF EXPLANATION DISSOLVED GAS ANALYSIS (DGA) IEC60567 GASES ANALYSED :- HYDROGEN - H 2 METHANE CH 4 ETHANE C 2 H 6 ETHYLENE C 2 H 4 ACETYLENE C 2 H 2 CARBON MONOXIDE CO CARBON DIOXIDE CO 2 NITROGEN N 2 OXYGEN O 2 ADVANCE WARNING OF DEVELOPING FAULTS. A MEANS FOR CONVENIENTLY SCHEDULING REPAIRS. MONITOR THE RATE OF FAULT DEVELOPMENT ORIGIN OF GASES PARTIAL DISCHARGE MAJOR GAS HYDROGEN AND MINOR GAS IS METHANE THERMAL FAULTS - 300 DEG :- ETHYLENE MORE THE TEMP. MORE IS THE PRODUCTION OF ETHYLENE. ARCHING HIGH ENERGY DISCHARGE. MAJOR GAS ACETYLENE.

DISSOLVED GAS ANALYSIS Transformer Chemistry Services method of interpretation is based upon : Key gases : CSUS values (Age compensated) BS 5800/IEC 599 ratios (providing the Total Combustible Gases present are above 300 ppm) Rogers Ratios Trend (Production rates of gases) Morgan-Schaffer Tables Total Combustible Gas Production Rates TDCG(c57.104-1991) Total Combustible Gas Westinghouse Guidelines Age of transformer. History of transformer (Repaired, degasses, etc).

GAS CONCENTRATION LIMITS OF TRANSFORMER (IEEE) GASNORMALCAUTIONWARNINGINTERPRETATION HYDROGEN - H 2 700PPMARCHING CORONA METHANE CH 4 400PPMSPARKING ETHANE C 2 H 6 100PPMLOCAL OVERHEATING ETHYLENE C 2 H 4 100PPMSEVERE OVERHEATING ACETYLENE C 2 H 2 5 PPMARCHING CARBON MONOXIDE CO 570PPM SEVERE OVERLOADING CARBON DIOXIDE CO 2 10000PPM SEVERE OVERLOADING TCG1900PPM

TOTAL DISSOLVABLE COMBUSTABLE GAS. Total Combustible Gases Recommended Action 0-500 PPM NORMAL AGING ANALYZE AGAIN IN 6-12 MONTHS 501 to 1200 PPM DECOMPOSITION MAYBE IN EXCESS OF NORMAL AGING 1201 to 2500 PPM MORE THAN NORMAL DECOMPOSITION ANALYZE IN 1 MONTH 2500 PPM and above MAKE WEEKLY ANALYSIS TO DETERMINE GAS PRODUCTION RATES CONTACT MANUFACTURER

TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE ACTION TESTS RECOMMENDED BRIEF EXPLANATION FURAN ANALYSIS (IEC61619) ANALYSIS OF THE CONDITION OF PAPER INSULATION. DIRECT TEST OF PAPER IS THE TENSILE STRENGTH OR DEGREE OF POLIMERISATION (DP). INDIRECT METHOD IS FURAN ANLYSIS WHICH MEASURES THE QUANTITY OF 2- FURALDEHYDE (IN PPM) IN OIL IS DIRECTLY RELATED TO THE DP OF THE PAPER INSIDE THE TRANSFORMER.

ANALYSIS OF THE DP VALUES DP RANGE REMARKS

ANALYSIS OF THE DP VALUES DP RANGE REMARKS 360- 450 THE PAPER IS STARTING TO APPROACH THE CRITICAL CONDITION. SUGGEST A RE-SAMPLE IN 1-2 YEARS TIME. 460- 600 SIGNIFICANT PAPER DETERIORATION BUT STILL WELL AWAY FROM THE CRITICAL POINT 610- 900 MILD TO MINIMAL PAPER AGEING. >900NO DETECTABLE PAPER DEGRADATION

RECOMMENDED LIMITS OF INSULATING OILS (OLD) AS PER IS1866 - 2000 TESTSTRANSFORMER VOLTAGE RATING LIMITS INTERFACIAL TENSION (N/m) FOR ALL VOLTAGE LEVELS 0.015(Min) NEUTRALIZATION VALUE MG OF KOH/G FOR ALL VOLTAGE LEVELS 0.3 (MAX) BREAKDOWN VOLTAGE ABOVE 170KV BETWEEN 72.5 170KV BELOW 72.5KV 50(MIN) 40(MIN) 30(MIN) DIELECTRIC DISSIPATION FACTOR @90C ABOVE 170KV BELOW 170KV 0.2(MAX) 1.0(MAX)

RECOMMENDED LIMITS OF INSULATING OILS (OLD) AS PER IS1866 - 2000 TESTSTRANSFORMER VOLTAGE RATING LIMITS RESISTIVITY X 10 12, OHM-CM@ @90C FOR ALL VOLTAGES0.1(MIN) WATER CONTENT PPM ABOVE 170KV BETWEEN 72.5 170KV BELOW 72.5KV 20(MAX) 40(MAX) NO FREE MOISTURE SEDIMENT AND SLUDGE FOR ALL VOLTAGESNIL

RECOMMENDED LIMITS OF UNUSED INSULATING OILS AS PER IS1866 - 2000 PROPERTIESHIGHEST VOLTAGE OF EQUIPMENT (KV) 170KV APPEARANCECLEAR FREE FROM SEDIMENT AND SUSPENDED MATTER DENSITY @29.5C(G/C M) MAX 0.89 VISCOSITY @27C(CST) MAX 27 FLASH POINT C (MIN) 140 POUR POINT C (MAX) -6

RECOMMENDED LIMITS OF UNUSED INSULATING OILS AS PER IS1866 - 2000 PROPERTIESHIGHEST VOLTAGE OF EQUIPMENT (KV) 170KV NEUTRALIZAT ION VALUE MG OF KOH/G (MAX) 0.03 WATER CONTENT PPM (MAX) 201510 INTERFACIAL TENSION (N/m) Min.035

RECOMMENDED LIMITS OF UNUSED INSULATING OILS AS PER IS1866 - 2000 PROPERTIESHIGHEST VOLTAGE OF EQUIPMENT (KV) 170KV DIELECTRIC DISSIPATION FACTOR @90C (MAX) 0.015 0.010 RESISTIVITY X 10 12, OHM- CM@ @90C (MIN) 666 BREAKDOWN VOLTAGE (Min) 405060

MEASUREMENTS MODES FOR TAN DELTA GST MODE :- GROUNDED SPECIMEN TEST IS REFFERED TO AS MEASUREMENT OF AN INSULATION SAMPLE THAT HAS ONE OF ITS TERMINAL GROUNDED. GSTg- MODE :- GSTg MODE MEANS GROUNDED SPECIMEN TEST WITH GUARDING UST MODE :- THE UNGROUNDED SPECIMEN TEST IS REFERRED TO AS THE TEST OF AN INSULATION SAMPLE THAT IS NOT GROUNDED.

OVERALL POWER FACTOR AND CAPACITANCE

OVERALL POWER FACTOR AND CAPACITANCE GST MODE ICH + ICHL

OVERALL POWER FACTOR AND CAPACITANCE GSTG-A MODE. ( CAPACITANCE CH)

OVERALL POWER FACTOR AND CAPACITANCE UST-A (CAPACITANCE CHL)

OVERALL POWER FACTOR AND CAPACITANCE MEASUREMENTS OF HV SIDE MEASUREME NT TEST MODE SWEEP V TEST FREQ. WATT LOSSE S CAP MEAS PF MEAS. ICH+ICH L GSTNONE50 HZ ICH GST g - A NONE50 HZ ICH(f) GST g - A FREQUEN CY 50 HZ TO 400 HZ ICHL UST-A50 HZ ICHL(f) UST-A 50 HZ TO 400 HZ

MEASUREMENTS FOR TAN DELTA AT DIFFERENT FREQUENCY

OVERALL POWER FACTOR AND CAPACITANCE LV SIDE (CALCULATION OF CL)

OVERALL POWER FACTOR AND CAPACITANCE GST MODE ICL + ICHL

OVERALL POWER FACTOR AND CAPACITANCE GSTG-A MODE. ( CAPACITANCE CL)

OVERALL POWER FACTOR AND CAPACITANCE UST-A (CAPACITANCE CL)

OVERALL POWER FACTOR AND CAPACITANCE MEASUREMENTS OF LV SIDE MEASUREME NT TEST MODE SWEEP V TEST FREQ. WATT LOSSE S CAP MEAS PF MEAS. ICL+ICL H GSTNONE 50 HZ ICLGST g - A NONE 50 HZ ICL(f)GST g - A FREQU ENCY 50 HZ TO 400 HZ ICLHUST- A 50 HZ ICLH(f)UST- A 50 HZ TO 400 HZ

CONDENSER TYPE BUSHINGS

MERITS OF CONDENSER BUSHING

MEASUREMENT OF TANDELTA OF BUSHING C1

MEASUREMENT OF TANDELTA OF BUSHING C2

RANGE OF DISSIPATION FACTOR ITEMS TYPICAL POWER FACTOR VALUES @ 20C OF 400KV GRADE NEWOLDWARNING/ALA RM LIMIT POWER TRANSFORMERS, OIL INSULATED 0.2- 0.4% 0.3- 0.5% >0.5% BUSHING0.2- 0.3% 0.3- 0.5% >0.5%

REACTOR PROTECTION SINGLE LINE DIAGRAM

REACTOR PROTECTION LEGENDS ELEMENTSDESCRIPTION 49Reactor Thermal Overload Protection 63PRV 71GGas Accumulator Protection Buchholz 71QLow Oil Level 80QOil Flow Low Indicator 87PPhase Differential Protection REFRestricted Earth Fault Protection 50PPhase Instantaneous O/C Protection 51PPhase Time O/C Protection 50NNeutral Instantaneous O/C Protection 51NNeutral Time O/C Protection 67G Zero Sequence Voltage Polarized ground directional O/C

SHUNT REACTOR PROTECTION SCHEME CT AND VT PHASE CT PROVIDES INFORMATION FROM PHASE SIDE, NCT PROVIDES INFORMATION FROM NEUTRAL SIDE AND GROUND CT IS SINGLE PHASE CONNECTED BETWEEN NEUTRAL AND GROUND. GROUND CT MEASURES 3i0 ACCURATELY AND HELPS IN DETECTING LOW CURRENT FAULTS LIKE TURN TO TURN ETC.

TRANSFORMER PROTECTION

central testing circle,dvc, maithon transformer protection by jayanta dutta, superintending engineer...

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