Recommendations for Condition Monitoring Facilities. Tutorial of Cigre WG A2.27 Convener: Paul Jarman, UK

Transcription

1 Recommendations for Condition Monitoring Facilities Tutorial of Cigre WG A2.27 Convener: Paul Jarman, UK

2 Summary The working group Transformer monitoring issues and uses General situations when monitoring is useful Some examples Types of monitoring Inputs and sensors Recommended deployment Condition assessment facilities Transformer generic model for SCS 2

3 Scope Review existing and developing condition monitoring systems to determine the range of sensors and facilities employed. Determine if standardisation could improve the market for systems and sensors. Make recommendations for the provision of sensors, facilities or data from new transformers to facilitate condition monitoring and assessment. 3

4 A2-27 Meetings and Members Members 21 contributing members 14 countries 19 organisations Meetings London 22/6/04 Paris 1/9/04 Glasgow 24-25/2/05 Stuttgart 21-22/9/05 Regensburg 11-12/5/06 4

5 Conclusions of A2-27 Generally thought helpful to have a guide to the appropriate sensors and fittings to allow easy fitting of monitoring systems. Significant commonality of sensors found between systems 5

6 Outline of document Types of monitoring system Review of sensors and data inputs Summary table of recommended facilities Recommendations for condition assessment facilities (off-line tests) Data generic model for transformer/substation interface 6

7 Monitoring system issues How to get real value from continuous on-line monitoring systems? Tend to be expensive to install except on new units Not usually required for new plant (should be reliable) Only required once a problem has initiated Often difficult for a utility to maintain Communications are a problem Don t directly increase reliability! Can provide vital information at a critical time 7

8 The condition assessment process Start Fix problem ok repairable Routine tests Special tests & interpretation yes Normal? no Terminal Indeterminate or marginal Other operational, technical or commercial trigger Scrap & replace Monitor 8

9 When is monitoring useful? As a routine test Detect new problems on a healthy transformer Routine DGA is very effective but: Only periodic Does not cover whole transformer For diagnosis of a problem Determine what the problem is once it has been detected 9

10 What can be monitored Temperatures Currents, system voltages Tap-changer Oil levels Oil - DGA, moisture, breakdown Bushing taps, Leakage current, RF, pressure Radio Frequency Signals Acoustic signals Neutral current Magnetic circuit Cooler operation 10

11 Advantage of continuous measurement - Diagnosis SGT6 Hydrogen Trend Vs Reactor State Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul-06 Date Jul-06 ppm

12 Advantage of continuous measurement accuracy Moisture measurement SGT10A Moisture Activity 13/09/ :52 15/09/ :01 16/09/ :10 18/09/ :18 20/09/ :27 21/09/ :36 23/09/ :44 25/09/ :53 26/09/ :01 28/09/ :09 30/09/ :18 01/10/ :27 03/10/ :35 04/10/ :42 06/10/ :51 08/10/ :00 09/10/ :08 11/10/ :17 13/10/ :26 14/10/ :35 16/10/ :43 17/10/ :52 19/10/ :01 21/10/ :10 22/10/ :18 24/10/ :27 26/10/ :35 27/10/ :44 29/10/ :53 30/10/ :02 01/11/ :11 03/11/ :19 04/11/ :27 06/11/ :36 08/11/ :45 09/11/ :54 11/11/ :02 13/11/ :11 14/11/ :20 Date Time RH% Temp RH%/Temp Linear (RH%) Linear (Temp) 12

13 Comparison Moisture - periodic measurement Moisture Activity SGT 10A 18/04/ /04/ /05/ /05/ /05/ /06/ /06/ /07/ /07/ /08/ /08/ /09/ /09/ /10/ /10/ /10/ /11/ /11/ /12/ /12/ /01/ /01/ /02/ /02/ /03/ /03/2006 Sample Date H2O MT H2O Sel 13 ppm

14 Types of monitoring systems Stand alone Substation based (monitoring several transformers) Remote using SCADA Recommendations do not favour any one approach 14

15 Stand alone Electrical interface Mechanical interface A Transformer B C C Standard sensor Special sensor Monitor Substation system 15

16 Typical system architecture Server Field Bus Monitoring Module Sensors Cabling 16

17 Shared sensor Electrical interface Mechanical interface A Transformer B C Standard sensor Special sensor Monitor Substation system 17

18 Shared data Data Standard sensor Transformer Special sensor Monitor Substation system 18

19 Integrated Data Standard sensor Transformer Special sensor IED Substation system EMS Monitor 19

20 Review of available sensors and measurements Temperature Currents and voltage Tap-changer Bushings Oil Partial discharge Other 20

21 Temperature measurements Thermometer pocket, PT100, 4-20mA Tank Cooler inlet Top oil Bottom oil TC selector TC diverter Cooler outlet Cooling medium (air) 21

22 Temperature measurement outputs Thermal rating Cooler efficiency Tap-changer condition (differential temperature) Lifetime use 22

23 Tap-changer monitoring Tap position Motor drive real power/torque Diverter position switch Selector angular position Diverter oil quality Acoustic sensor 23

24 Diverter position switch 24

25 Tap-changer motor active power measurement 25

26 Outputs from tap-changer monitoring Indications for maintenance Slow operation Change in motor drive power characteristic Trip of motor drive Selector operates bur diverter does not Abnormal motor current Trip of transformer Diverter stuck 26

27 Load current and voltage Load and temperature MVA Deg C MVA Temperature May May May May May May May May June 2007 Time 02 June June

28 Current and voltage outputs Current With temperature gives winding hotspot and real time load capability Contact wear on TC Cooler efficiency Short circuit stress Voltage TC control Over-fluxing Ferroresonance 28

29 Bushings Not included in transformer DGA Failure can have safety consequences 29

30 Bushing pressure sensor 30

31 Bushing tap electrical sensor 31

32 Bushing monitoring outputs Bushing condition (oil level, pressure) Bushing capacitance and power factor Transient recording PD in bushing and main transformer Frequency response of windings 32

33 Continuous oil monitoring Hydrogen moisture full DGA 33

34 Continuous DGA data Gas ppm in Oil for NGC - Neilston Partial Discharge Experiment TrueGas Data for All Detected Gases and Experimental Applied Voltage vs. Date/Time Hydrogen (H2) Methane (CH4) ppm (gas-in-oil) % of Applied Voltage Carbon Monoxide (CO) Carbon Dioxide (CO2) Ethane (C2H6) Ethylene (C2H4) 0 0 Acetylene (C2H2) 23/06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/ /06/ % Voltage Date/Time 34

35 Sensors measuring dissolved gas in oil Rapidly developing area Many systems on the market or in development Facility for fitting is easy to provide Sensors tend to require care/attention Very effective at detecting and diagnosing faults 35

36 Buchholz gas sensor Measures rate of collection of gas evolved from transformer. DGA + Moisture Sensor Could be useful for operators but potential safety risk unless gas is air 36

37 Other Sensors and measurements Oil levels Detecting and monitoring leak DC neutral current Geomagnetic currents DC terminals Traction and industrial applications Magnetic circuit earth current Monitors for core and frame insulation failure Cooler operation Fan and pump failure 37

38 Partial Discharge detection and monitoring Usually PD is detected using DGA Need to study behaviour and location to determine if it is damaging Monitoring techniques developing in this area 38

39 Acoustic technique Methods fixed to tank (adhesive or magnetic) array moved over tank inside tank via valve Results Good for sources outside the windings Problems with multiple sources Problems with sources within insulation Safety issues for mobile sensors 39

40 Acoustic sensor array 40

41 Electrical techniques Methods CT on bushing tap earth Direct on bushing tap with fibre optic isolation CT on neutral Results Problems in interpretation for multiple sources Can be calibrated but calibration may not be valid Interference from air corona needs to be considered Φ-q-N analysis can be effective 41

42 Example phase-magnitude-number plot Surface discharge from C- phase bushing merged with some internal discharge activity Corona from C-phase bus Surface dischar ge from A-phase bushing Internal discharge C- phase Corona from A-phase bus Corona from B- phase bus Surface discharge from B-phase bushing 42

43 Electrical location of PD 43

44 Radio frequency techniques Methods Results Sensors in tank via valve Sensor on dielectric window External aerials very good sensitivity good potential for location external aerials signal less sensitive but still useful 44

45 Permanent UHF coupler 45

46 Location using two UHF couplers 46

47 KEMA RF probe 47

48 Frequency spectrum from RF probe Background signal Transformer energised 48

49 Recommend additional valves for monitoring, Not all existing valves suitable! Recommend 4 x 50mm valves Not co-planar 25mm clearance 250mm away from corners 49

50 RF detection aerials 50

51 Combined techniques Methods Results Acoustic + RF Acoustic + Electrical Helps to discriminate discharges especially from multiple sources 51

52 Monitoring tailored to the application Many sensors a complete set would be very expensive Target simple and effective sensors on new units Sensor set depends on cost an criticality Target more specific sensors on transformer with problems Examples Top oil temperature and load current (from new) Tap-changer monitor (from new?) Simple DGA (from new on important units?) Electrical transients (when needed) PD location (when needed) Full DGA in oil (when needed) 52

53 Monitoring applications Level 1 Minimum set to give basic operating information and facilities for some further monitoring Level 2 Sensors and facilities appropriate to an important new transformer Level 3 Sensors and facilities provided from new when comprehensive monitoring is desired for critical applications 53

54 Summary of recommendations table (1) Sensor Level Level 2 Level 3 1 Active Part Top Oil Temperature Fit fit fit Bottom oil temperature facility fit Gas-in-Oil Content (single facility facility fit output) Moisture in Oil facility fit Oil Level in Conservator alarm fit fit Oil Level in Conservator fit fit indication Multiple gas monitor facility facility Partial discharge sensor facility facility DC Neutral current facility Magnetic circuit facility facility 54

55 Summary of recommendations table (2) Cooling unit Sensor Level 1 Level 2 Level 3 Cooling medium Temperature facility fit Cooler operation fit fit Cooler inlet oil temperature fit Cooler outlet oil temperature fit Bushing Voltage at bushing tap facility Facility fit Load current Fit Fit fit Oil pressure fit 55

56 Summary of recommendations table (3) Tapchanger Sensor Level 1 Level 2 Level 3 Tap-position facility fit fit Active power of motor facility fit Diverter oil temperature facility fit Selector oil temperature facility facility Main tank temp near TC fit Diverter oil level indication fit Diverter oil level alarm fit fit Diverter oil condition facility fit Diverter switching supervision facility fit 56

57 Condition assessment test facilities There are many condition assessment tests that provide information that is critical for good asset management DGA of transformer tap-changer and bushings Winding resistance Insulation resistance Frequency response analysis Dielectric response measurement Cap and tan delta of windings and bushings Core earth resistance Internal inspection of tap-changer and transformer The ability to do these tests should be considered at the design stage 57

58 Condition assessment facilities Helpful features for of-line tests. External core earth External connection to test and stabilising windings Separate neutrals (costly) Separate tap-changer (costly) Disconnection facility Direct cable or SF6 connection Internal inspection Benchmark testing 58

59 Benchmark tests Frequency response Capacitance and tan-delta Dielectric response Magnetisation current Short circuit impedance (phase by phase) Tap-changer motor power or torque fingerprint measurement 59

60 Data outputs for SCS Generic transformer model Direct outputs from transformer For remote monitoring these outputs should be accepted by the substation system Top oil temperature Derived winding hotspot temperature (WTI) Tap-position Oil level Moisture in oil Dissolved gas in oil Cooling medium temperature Direct measurement of hotspot temperature (optional) 60

61 Monitoring system alarm outputs Monitoring system abnormal (fail) Tap-changer blocked Tap-changer abnormal Gas in oil abnormal Cooling abnormal Bushing abnormal Transformer abnormal 61

62 Normal alarms and trips For completeness a list of other transformer outputs is included (basic monitoring) Main tank buchholz alarm and trip Top oil temperature high alarm and trip Winding temperature high alarm and trip Main conservator oil level low Main tank pressure relief operated Tap-changer diverter sudden pressure or oil surge trip Tap-changer motor tripped Cooler supply fail TC supply fail Breather fail 62

63 Conclusion Technology developing rapidly but parameters and basic sensors not likely to change much Facilities can be provided for future sensors (for example valves) Standardisation should be helpful Monitoring can be beneficial 63

64 Some personal observations Simple sensors provide good information for normal operation Complex sensors are useful but not as reliable as the transformer Need to be able to retrofit complex sensors easily Communication is often a problem Need to integrate condition monitoring 64

65 For more information consult Cigre Brochure