CABLE DIAGNOSTICS testing - 15-8-2007.ppt
- 1. DIAGOSTIC TESTING OF POWER CABLES IN SERVICE S.N. MOORCHING, JOINT DIRECTOR (RETD.), CPRI
- 2. INTRODUCTION RELIABILITTY -- GEN/DIST IS INCREASING UNPLANNED SHUTDOWN – TREMONDOUS LOSS OF REVENUE INCONVENIENCE TO CUSTOMER STRATEGY -- CONDITION MONITORING CHECK QUALITY/HEALTH OF CABLE BEFORE SETTING TO OPER/PERIODIC
- 3. NEED FOR CABLE DIAGNOSTICS FAILURES OF CABLES INCREASING FAILURE IN BANGALORE 1998-99 1656 1999-00 1713 2000-01 1611 JAN 01- DEC 01 1880
- 4. AGEING STRESS CABLES -- AGED STRESS DETERIORATION FAILURE ELECTRICAL THERMAL MECHANICAL COMBINATION ENVIORNMENTAL
- 5. MODES OF FAILURE PILC INTERNAL & SURFACE DISCAHRGES TRACKING ALONG LAYER OF PAPER PAPER DRYING - LACK OF IMPR FLUID MOISTURE INGRESS FATIGUE FAILURE DUE TO TEMP DIFF—CRACKS IN LEAD SHEATH PI AND COND ARE FACTORS EVAULATE CABLE CODITION POLYMERIC CABLES XLPE --- PD- VOIDS/CONT, TREEING WATER & ELECTRICAL OVERHEATING/DEFORMATION/TRACKING
- 8. TREEING THREE TYPES-ELEC/WATER/ELE.CHEM ELEC TREE INITIATION-VOIDS/MET IMPURITIES/PROJ IN SC SHLDG/STRESS CONC/BD OF INS WATER TREEING—PRES OF MOIST+ELECT FIELD E C TREEING—MOISTURE+CHEM+ ELEC STRESS
- 15. WATER TREE EVALUATION TECHNIQUE CURRENT MAGNITUDE CURRENT TREND DC CONDUCTIVITY DETERIORATION NON- LINEARITY– DR W R T CHARGING VOLTAGE
- 16. DIAGNOSTIC TESTING TECHNIQUES HELPS IN– STATE CONDITION --REPLACE/REPAIR --EXTEND LIFE SEVERAL TEST METHODS --EACH HAS ITS MERITS/DEMERITS --NO INDUVIDUAL TEST GIVES FULL INFORMATION --LOT OF RESEARCH WORK IS STILL IN PROGRESS TO UNDERSTAND DEGRADATION --FINDING TOOLS FOR INS DIAGNOSIS/RLA
- 17. DIAGNOSTIC TESTS IEEE-400-2001 FIELD TESTING & EVALUATON OF MV CABLES -- AC HIPOT TESTING --DC HIPOT --0.1 HZ HIPOT (VLF) -- DISS FACTOR AT VLF --PD TESTS --OSC WAVE PD / COMPLEX DISCHARGE ANALYSER
- 18. EXCEPT PD – REVEAL STATE & CONDITION PD -- INCIPIENT FAULTS OTHER PRACTICES -- RECOVERY VOLTAGE -- DIELECRIC SPECTROSCOPY, CAP & DF AT FREQ OF 0.001 TO 2HZ -- ISOTHERMAL RELAXATION CURRENT
- 19. AC HIPOT TEST 2-3 TIMES OPERATING VOLTAGE MASSIVE TEST KIT LARGE POWER REQUIREMENT GO-NO GO TEST DEGRADATION OF WEAK SPOT DO NOT IDENTIFY LOCALISED DEFECT REQUIRES RESONANT TEST SET
- 20. DC HIPOT TEST MOST POPULAR SINCE LONG --SMALL SIZE KIT --SMALL POWER REQUIREMENT --IDENTIFY DEFECTS LIKE WATER LAMINATION --INDUCE SPACE CHARGE --SOME DEFECTS GROW IN AGED CABS --DONOT REPLICATE AC CONDITION --DONOT REVEAL HIGH IMP DEFECTS SUCH AS VOIDS, CUTS/NICKS --DURING 97-02, 10% OF DC TESTED FAILED
- 22. DC HIPOT TEST IN USE IN CASE OF PILC CABLE SINCE LONG. TEST VOLT LEVEL=4 TO 5 Uo AS PER AEIC AND IEEE COULD ISOLATE DEFECT WITHOUT DAMAGE TO CABLE XLPE REQD. 5 TO 8Uo TO BREAK RCOMM. OF IEEE 400-2001/IEC/VDE FURNISHED
- 23. Testing according to IEEE 400-2001 Guide for Field Testing and Evaluation of insulation of service aged cable system recommends the following voltages for 5kV to 500kV cables. System Voltage KV Accepted Voltage DC KV Phase to Ground Maintenance Voltage DCKV Phase to Ground 5 28 23 15 56 46 25 75 61 69 175 130 115 275 205
- 24. Test voltages according to IEC & VDE System Voltage KV Standard After laying test KVDC Phase to Ground 1 to 30 IEC 502 VDE 0276 4 Uo/15 min No DC 45 to 150 IEC 840 VDE 0263 3Uo/15 min 150 to 500 No DC Not defined
- 25. DC HIPOT TEST PREMATURE FAILURES OF DC TESTED SERVICE AGED CABLES==ALTERNATE TESTIND TECHN.. VLF/OSC WAVE EFFCT OF DC ON PILC CABLE --DEGRADATION HASTENS TO AN EXTENT --NO PREMATURE FAILRES REPORTED --CERTAIN FAULTS-WATER ENTRY-CAN BE DETECTED
- 26. EFFECT OF DC ON XLPE SEVERAL FAILURES AFTER RETURNING TO SERVICE REDUCES LIFE/INCREASES WATER TREE GROWTH/NO EFFECT ON NEW CABLE BEFORE ENERGISING LONG LIFE SPACE CHARGES PRODUCED AROUND DEFECTS– INCREASES LOCALISED FIELD STRENTH DURING POSITIVE HALF CYCLE OF AC
- 27. VERY LOW FREQ HIPOT TEST POPULARITY ON INCREASE PORTABLE KIT CONUMES LESS POWER (1/500OF AC) GOOD TEST FOR CONDUCTING AND HIGH IMPEDANCE DEFECTS DONOT INDUCE SPACE CHARGE SOME DEFCTS GROW IN AGED CABLE DO NOT REPLICATE AC CONDITIONS
- 28. VLF TEST SET
- 29. VERY LOW FREQUENCY VLF CHARGING CURRENT : I= V C @ 50 Hz LARGE TESTING TRANSFORMERS EXORBITANT COST VLF : LOWER COST 0.1 Hz SOURCE < 500 TIMES @ 50 Hz 0.1,0.005,0.02 or 0.01 Hz (AC) D.C SOURCE XLPE D.C POLARIZATION VLF SOURCE CAP 50 F
- 30. DIELECTRIC LOSS ANGLE GIVES INFORMATION REG WEAK SPOTS PORTABLE COSUMES LESS POWER EVALUATE WATER TREES – FREQ DOMAIN IDENTIFY BAD JOINTS/TERMINATIONS Premature failure - HV & EHV
- 31. Dielectric Loss Angle Measurements at 0.1 Hz
- 32. DIELECTRIC LOSS ANGLE IMPERFECTION IN THE DIELECTRIC D.L : V 2 ω C TAN D.L : TAN LIMITING VALUES : XLPE SOME COUNTRIES HEALTHY CABLES TAN @ 2 Uo < 1.2 % Δ TAN 2 Uo & Uo < 0.6 % AGED CABLES: TAN @ 2 Uo > 2.2 % Δ TAN 2 Uo & Uo 1.0 %
- 34. DIELECTRIC LOSS ANGLE Cx R3 Cn C4 R4 Rx Rx Cx I1 VR = I1 Rx Vc = I1 / w Cx I V V1 VR VC Tan = VR / VC = w Rx Cx Rx = (C4 / C3) R3 Cx = ( R4 / R3) Cn Tan = w R4C4 Cx = Winding capacitance Cn = Loss-free standard capacitor R3 = Variable resistance R4 = Fixed standard resistance C4 = Variable capacitance D = Oscilloscopic Null indicator D Schematic diagram of measuring circuit of High Voltage Schering bridge
- 35. DIELECTRIC LOSS ANGLE Tan Gaseous loss Material loss Voltage Typical tan delta voltage characteristics Tan Voltage Degraded insulation Sound insulation Curves depicting Sound & Degraded Insulation
- 36. PARTIAL DISCHARGE --XIVE LOCAL ELECTRIC FIELD IN INS --DUE TO STRESS ENHANCEMENT--- VOIDS/CONTAMINATIONS/CUTS/NICK WEAKENING OF STRESS—THIN SPOT --POWERFUL TOOL/LOCATION POSSIBLE/MAPPING OF SITES/MAGNITU =CANNOT LOCATE MOISTURE
- 37. PARTIAL DISCHARGE CONCEPT Partial Discharge Test * Concept of Partial discharges - Discharge process in which the gap between two electrodes is only partially bridged. HV Void Conductor Insulation * Occur in voids & other inhomogenities in the insulation. * Cause chemical & mechanical destruction of the surrounding medium & hence premature failure.
- 38. PARTIAL DISCHARGE TEST • AIR GAPS BETWEEN CONDUCTOR AND INSULATION,SHARP PROJECTIONS FROM CONDUCTORS PROTRUDING TO INSULATION,MICRO VOIDS,FOREIGN IMPURITIES • STRAIGHT DETECTION METHOD Z-Detection impedance DETECTOR T CX CB
- 39. PARTIAL DISCHARGE PATTERN RECOGNIZE & LOCATE ON SITE REALISTIC RESULTS HIGH POWER SOURCE VLF OR RESONANCE SOURCE
- 40. PARTIAL DISCHARGE VLF PD Detection Set up VLF PD Detection Set up
- 41. TIME DOMAIN REFLECTROMETRY METHOD ( TDR ) OFF LINE STEP –I : LV TDR MAPPING STEP –II :SENSITIVITY STEP -III:DIAGNOSTIC TEST FOLLOWED BY DATA ANALYSIS- INTERPRETATION PULSE—4 & 8 V WIDTH :20 seconds to 650 seconds MATCHING IMPEDANDE 12-35 PULSE TRAVELLING –LENGTH CABLE CHARCTERISTIC SPEED 480 TO 500 ft / secs IMPEDANCE CHANGES - PULSE REFLECTED ESTIMATOR—ORIGINAL & REFLEDTED PULSE DIGITALLY PROCESSED
- 42. CALIBRATION CORRECT SIGNAL MAGNITUDE @ FACTORY REFERENCE TDR MAPPING CABLE – SYSTEM-EXCITATION VOLTAGE APPLIED OPERATING VOLTAGE VOLTAGE RAMPED MAX DECREASED OPERATING VOLTAGE -- ZERO EACH CABLE- LV TDR- DIAGNOSTIC ANALYSIS -- INFORMATION -- LOCATION OF DEFECTS --SITES EACH SITE – GRAPH – PHASE ANGLE – MAGNITUDE—pC
- 43. STEP-1
- 44. STEP - 2
- 47. OSCILLATING TEST VOLTAGE METHOD PD –SYSTEM -- HUGE SOURCE VLF OR RESONANCE ALTERNATIVE -- OSCILLATING TEST VOLTAGE RISE TIME :10 Secs TAIL TIME : 10 m Secs PD DURING TAIL TIME NON-CONVENTIONAL TRASIENT VOLTAGE STRESS CDA – COMPLEX DISCHARGE ANALYSIS
- 48. OSCILLATING WAVE METHOD EVALUATE PD CABLES ACCESSORIES
- 50. OSCILLATING WAVE METHOD SEQUENCE: CABLE- DC VOLTAGE –FEW SECONDS DISCH ACROSS CABLE -L (AIR) 1S USING ELEC HV SWITCH CREATES AN OSCILLATING VOLTAGE RESONANCE FREQUENCY OF DECAY VOLTAGE IS: F= 1 / 2 LC 50 TO 1 K Hz TAN LOW- Q FACTOR : 30 to > 100 SLOW DECAYING OSCILLATING WAVEFORM , T :0.3 to 1.0 SEC PD SIGNALS SIMILLAR TO 50 Hz REALISTIC RESULTS HIGH POWER SOURCE VLF OR RESONANCE SOURCE
- 51. EVALUATION STEP I : PD PULSES ANALYSED REFLECTION TRAVELLING WAVE ANALYSIS PD LOCATION : STATISTICAL EVALUATION STEP II : CAP & TAN OSCILLATING TRUE AND FREQUENCY CHARACTERISTICS STEP III :PHASE RESOLVED PD PATTERN PATTERNS SIMILLAR TO PF CONDITIONS
- 53. LIMITING VALUES OF PD MAGNITUDE
- 54. Damped AC Circuit & PD Detecting System Damped AC Circuit & PD Detecting System
- 55. FREQUENCY TUNED RESONANT TEST ON SITE TEST SYSTEM: FREQUENCY CONVERTER EXCITER TRANSFORMER RESONANT REACTOR ( FIXED L ) HV FILTER Cm ,Cc & Zm PD NOISE LEVEL –SITE LENGTH - CABLE
- 56. COMPLEX DISCHARGE ANALYSER ON SITE MEASUREMENTS PD HV CABLE ATTENUATION—HIGH NOISE ACCESSORIES - PROBLEM OVER COME –TWO DIRECTIONAL COUPLER SENSORS —ONE ON EACH SIDE OF THE JOINT LOCATION – ABOVE SEMICON ACTUAL DISCHARGE- PD- NOISE PD-ON SITE-AFTER LAYING-PERMANENT MONITORING VALUES
- 58. CDA Method Front Time : 10 seconds Tail time : 10 milli seconds PD measurement during the tail time More realistic Low voltage stress Low Power Demand
- 59. Voltage Shape of CDA Test Voltage Voltage Shape of CDA Test Voltage
- 60. COMPARISON OF PD TEST METHOD PD results identical to Power demand System design demands Operating conditions and complexity AC TEST SET Yes Very high High VLF TEST SET Partially Low High OSCILLATING WAVE No Low Moderate CDA TEST SET Yes Low Low
- 61. RECOVERY VOLTAGE / RETURN VOLTAGE TEST OFF LINE TEST NON- DESTRUCTIVE PILC: AGEING EFFECTS AND MOISTURE CONTENT – BULK INSULATION RETURN VOLTAGE CURVE DETECT DEFECTS TEMPERATURE DEPENDENT CABLE LENGTH
- 62. DIELECTRIC CIRCUIT COMBINATION –IR—PARALLEL CAPACITANCES POLAR COMPONENTS SERIES R-C CIRCUIT WATER INGRESS -BULK OF INSULATION DISCHARGE PATTERN DIFFERS PILC, XLPE DAMAGE – PILC LOSS OF OIL WATER HIGHER CONDUCTIVITY HIGHER PERMITTIVITY
- 63. RVM –TEST SEQUENCE CABLE EARTH ISOLATED CHARGE @ 1 Kv : 30 minutes QUICK DISCHARGE 2-5 seconds MEASURE & RECORD RETURN VOLTAGE FOR 30 minutes CHARGE @ 2 Kv : 30 minutes QUICK DISCHARGE 2- 5 seconds MEASURE & RECORD RETURN VOLTAGE FOR 30 minutes ANALYSE - PC
- 64. POLARIZATION SPECTRUM & DIAGNOSTICS METHOD •Principle – Determination of Polarization spectrum by applying DC Charging & Discharging of insulation •Steps 1 thru 5 Plot Ur against time constant tc; Plot gives Polarization spectrum
- 67. RVM –TEST – ANALYSIS RATIO : RETURN VOLTAEE 1kV/2kV -- PERIOD 30 minutes DECREASE OF IR INTEGRITY OF INSULATION NON-DESTRUCTIVE TEST POLARIZATION OF DIELECTRIC CURVE:CHARACTERISTIC INFORMATION AGEING & MOISTURE CONTENT FEEDBACK :INGRESS OF MOISTURE
- 68. ISOTHERMAL RELAXATION CURRENT TEST IRC USES 1 KV DC 1000 SECS TO POLARISE CABLE INSULATION INS POLARISATION TRAPS CHARGE AT DISCRETE ENERGY LEVELS DISCHARGE INS. FOR 5 SECS DURING THIS PROCESS ELS GIVES RAISE TO DIFF TIME CONSTANTS IN DISCHARGE CURRENT IRC TEST LOOKS FOR TIME CONSTANTS FOR WATER TREES IN DEGRADED CABLE REL CURRENT OCCURING AFTER INS DISCHARGE IS DIGITISED & PROCSSED
- 69. IRC PC CONVERTS CURRENT INTO CHARGE AND PLOTS AGAINST TIME AGEING IS IDENTIFIED BY REL VALUES OF TIME CONSTANTS AUTOMATED CABLE DIGNOSIS IS IN 2 PARTS -- DESTRUCTIVE FREE DETERN. OF AGEING STATUS --REIDUAL STRENGTH PROGNASIS IN THE FORM Kuo=AVAILABLE BY DESTRUCTIVE STEP TEST
- 72. IRC-measurement ABC-1 ABC-2 ABC-3 DEF-1 IRC-ageing class old mid-life mid-life critical typical RSP 65 kV 80 kV 80 kV 36 kV calculated RSP 63 kV 62 kV 53 kV 24 kV comparable RSP 72 kV 82 kV 96 kV 24 kV Prognosis (mU0 ) 5 U0 7 U0 6 U0 3 U0 Step test result (kU0 ) 5 U0 8 U0 7 U0 2 U0 IRC PROGNOSIS TABLE
- 73. DIELECTRIC RESPONSE IN FREQUECY DOMAIN MAJOR PROBLEM—DETERIRATION DUE TO WATER TREES ONSITE MEAS. USING DIELECTRIC SPECTROSCOPY DETECT WATER TREES APPLN OF DIEL FIELD ON MATERIAL-- MECHANISM OF POARISATION & CONDUCTION ARE ACTUATED PRESENCE OF WATER TREES LEADS SUCH INCREASES. IN TURN LEADS TO INC IN DF FREQ DOMAIN DIELEC SPECTROSCPY-MEAS OF CAP & DFAS A FN OF FREQAROUND 0.1HZ
- 75. FREQ DOMAIN DIELECTRIC SPECTROSCOPY SWEPT FREQ—DIFF STAGES OF WATER TREE AGEING, ALSO OF ACCESSORIES TYPPICALLY TECHNIQUE MEASURES== ==DF, CAPACITANCE, PERMITTIVITY ==FREQ DOMAIN0.01mHZ TO 1 KHZ ==VOLTAGES UPTO 30 KV VARIATION OF DP, CAP—REVEALS CONDITION DR IS CAPABLE OF DISTINGUISHING INFLUENCE OF JOINTS, TERMIN AND INS DEGRADATION DUE TO WATER TREEING
- 76. METHODOLOGY OF TESTING SUBJECT CABLE == 5 FREQ SWEEPS ==AT 0.25U, 0.5U, 0.75U, U& BACK 0.5U ==FREQ 0.01 HZ TO 1 KHZ DR IS ANALYSED
- 86. RESIDUAL CHARGE MEASUREMENT DC VOLTAGE FOR PRESTRESSING CHARGES ACCUMULATED IN WATER TREEING SHORT CKT FOR 1 MT. AC VOLTAGE IS APPLIED CHARGES ACCUMULATED IN WATER TREERELEASED DURING AC, PRODUCES DC COMPONENT
- 87. CURRENT FLOWING =AC+ DC COMP DC COMPONENT IS DETECTED USING LOW PASS FILTER RES CHARGE IS OBTAINED BY INTEGRATION OF CURRENT SIGNAL
- 88. Residual charge Method- Measurement Circuit Residual charge Method- Measurement Circuit