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Nidec asi service partial discharge basic diagnostic

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SERVICE PARTIAL DISCHARGE BASIC DIAGNOSTIC

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Nidec asi service partial discharge basic diagnostic

  1. 1. Service PARTIAL DISCHARGE BASIC DIAGNOSTIC Basics, Sensors & Instruments, Experience PPT2013.01.01.20EN www.nidec-asi.com
  2. 2. BASICS  “Partial discharges” are fast flows of electrons (discharge) due to a local concentration of the electric field which occurs across two insulated bodies at different potential, that does not breakdown the whole insulation.  They normally occurs within gases (air or other).  PD’s normally occur within electric machines and other apparatus due to the technology utilized in the insulation systems (termosetting materials). There are different kinds of discharges, some are harmful some are not.  It is not true that the most dangerous PD phenomena exhibits the larger amplitude  PD quantities and PD intensity must be associated with the defect typology to properly assess harmfullness  Different insulation systems exhibits different characteristics as to PD patterns and PD levels, therefore experience is the Key-factor PPT2013.01.01.20EN www.nidec-asi.com 2
  3. 3. BASICS  PDs are slow degrading phenomena, therefore they can be used for early detection of potential cause failure, and normally they allow for proper planning of corrective actions.  PD are at the same time both a symptom of a defect and a new degradation process that can lead to the final breakdown.  PDs measurement allow for local defect identification and monitoring, improving CBM efficacy . PPT2013.01.01.20EN www.nidec-asi.com 3
  4. 4. BASICS International Standards on PDs measurements: IEC 60270 – High-voltage test techniques – Partial discarge measurements IEC 60034-27 – Rotating electrical machines – Partial discharge off-line measurements on the stator winding insulation of rotating machinery  STANDARDS do not give acceptance criteria for new machines or machine in service  At the moment, there are not end-of-life criteria based on PD  Diagnostic is based on trending and experience PPT2013.01.01.20EN www.nidec-asi.com 4
  5. 5. BASICS Rotating Machines PD Sources Stator core Pressure finger Slot PD Surface PD (stress grading) B2B Tracking Sparking Tracking Internal PD PPT2013.01.01.20EN www.nidec-asi.com 5
  6. 6. BASICS Internal Conductor Delamination PPT2013.01.01.20EN www.nidec-asi.com 6
  7. 7. BASICS Surface Discharge PPT2013.01.01.20EN www.nidec-asi.com 7
  8. 8. PD Detection And Measurement Discharges result in a electric charge displacement that generates current pulses, which are detected as voltage pulse (Vm) at the sensor terminals. Capacitive sensor Ck Cx Va Zm Vm Measurement principle PD pulse detected by the instrument PPT2013.01.01.20EN www.nidec-asi.com 8
  9. 9. PD Detection And Measurement NIDEC ASI’s instruments, differently from others, are not simple PD peak detectors, but they acquire and process the complete pulse shape. signal UWB Digitizer Trigger level time Pre trigger Recording time RAM Bank Personal Computer Insulation system 50 W HF resistor PPT2013.01.01.20EN fiber optic IEEE-488 bus High Pass (HP) Filter Digitizer Permanent storage dev. www.nidec-asi.com 9
  10. 10. PD Detection And Measurement  Signals coming from different PD sources and/or locations present differents waveshapes.  The whole shape of signals is digitally detected at the fastest sampling rate, to avoid the frequency aliasing.  Pulse signals are synthesized considering both their amplitude and phase of occurrence and reported on a standardized cycle of the applied voltage to obtain a 3D plot (or 2D plot).  Pulse signals are recorded in a number high enough to perform statistical analysis.  Different PD sources are separated through TF mapping.  Noise by different sources (power electronics switches, broadcast signals, arcing, AC/DC rectifiers, random noise, PD cross-talk, etc.) is rejected by identification throught TF mapping.  PD sources are identified by comparison PPT2013.01.01.20EN www.nidec-asi.com 10
  11. 11. Synthesization Pulse signals are synthesized considering both their amplitude and phase of occurrence and reported on a standardized cycle of the applied voltage to obtain a 3D plot (or 2D plot): PPT2013.01.01.20EN www.nidec-asi.com 11
  12. 12. TF Mapping F Fast pulses: Short duration, High frequency content Each Pulse is processed individually and represented by a point on the TF map. Slow pulses: Long duration, Small frequency content PD pulses are separated into subseries each one homogeneous in terms of shape (time-frequency mapping). T PPT2013.01.01.20EN www.nidec-asi.com 12
  13. 13. Separation Signals Having Different Shape are grouped din different classes TF Map End-winding stress grading deterioration, due to thermal stress, is the defect typology associated to pattern F1 PPT2013.01.01.20EN F2: Internal PD www.nidec-asi.com 13
  14. 14. Identification  Visual comparison between the given 3D PD plot and a collection of known patterns (databases).  Automatic pattern matching by means of Neural Net., distance classifiers, statistical classifiers (expert system).  3D shape analysis by means of identification markers derived by both standard and PD pulse height and phase distribution analysis. PPT2013.01.01.20EN www.nidec-asi.com 14
  15. 15. Diagnostic-Risk Assessment Different defects can affect differently the insulation system reliability: it is not true that the most dangerous PD phenomenon exhibits the larger amplitude PD quantities relevant to PD intensity must be associated with the defect typology At the moment, there are not end-of-life criteria based on PD A complete collection of 3D PD plots and the relevant defect typologies is essential for reliable diagnostics Design and manufacturing greatly affect PD patterns and levels: OEM experience is essential for reliable diagnostics PPT2013.01.01.20EN www.nidec-asi.com 15
  16. 16. PD Sources & 3D PD Patterns Surface Discharge Surface PD Tape delamination PD PPT2013.01.01.20EN Surface PD with tracking Slot PD www.nidec-asi.com Bar-to-bar PD Distributed microvoids PD 16
  17. 17. The Strength of Our Analysis Surface Discharge S I D Separation Identification Diagnosis • Potential defect ..harmfulness ..(one source at a .. .. time) • Risk assessment • Noise rejection •Source separation • Maintenance program • Life extension (trend of ..the weakest spots, ..time to end point) PPT2013.01.01.20EN www.nidec-asi.com 17
  18. 18. Off-Line Measurements PROS CONS  The whole winding is tested  Voltage distribution across the winding is different from that in service.  Applied voltage can vary to determine inceptions and fading voltage  Reduced noise Easier analysis of the data collected PPT2013.01.01.20EN  Operating load and temp. of the winding cannot vary  Interphase PD cannot be detected www.nidec-asi.com 18
  19. 19. Off-Line Measurements PROS CONS  Actual PD are measured while the machine is operating  Applied Voltage cannot varies  Change of load and temperature to check the influence on PD  Interphase PDs are measured PPT2013.01.01.20EN  Pulsating noise is higher than in off-line measurements  Analysis and diagnostic is more difficult than off-line www.nidec-asi.com 19
  20. 20. Sensors and Accessories A large range of sensors and filters are available to cover any possible PD acquisition need and optimise the metering circuit. Sensors are: capacitive, inductive, antenna Capacitive sensors family Inductive sensors family Antenna sensors family PPT2013.01.01.20EN www.nidec-asi.com 20
  21. 21. Sensors Installation On Rotating Machines Capacitive couplers Generators/critical motors Coupler HFCT on surge capacitors Large/critical motors provided with surge capacitors HFCT HFCT on MV cables ground leads Large/critical motors not provided with surge capacitors Clamp HFCT HFCT on ground leads Large/critical motors not provided with surge capacitors PPT2013.01.01.20EN www.nidec-asi.com 21
  22. 22. PDBase Innovative Digital PD Diagnostics System • Ultra wide band acquisition unit • IEC60270 standard feature • Pulse shape analysis • Fuzzy logic tools and statistical processing • Noise Rejection • PD Source Identification • Database application • Location of defects • Fiber optic transmission • External or line synchronization • Fully remote controlled • SMART gating options • Spectrum Analyzer • Quality control test management • Immediate diagnosis and alert • Preprocessing-Post Processing 250x250x100 mm, 7 kg PPT2013.01.01.20EN www.nidec-asi.com 22
  23. 23. PDCheck The Ultimate Solution for on-line PD Monitoring • Ultra wide band acquisition unit 203x135x55 mm, 1 kg! • Pulse shape analysis • Fuzzy logic tools and statistical processing • Noise Rejection • PD Source Identification • Waveform Analyser • Spectrum Analyser • Database application • Location of defects • Ethernet interface • Fully remote controllable (internet/intranet) • Stand alone or part of centralized complex monitoring system • Possibility of connecting several instruments to the same network • Large data storage capability (with memory cards) • Ideal for permanent on-line monitoring of PD and other quantities i.e. temperature, humidity, currents, voltages, etc. PPT2013.01.01.20EN www.nidec-asi.com 23
  24. 24. Coupling capacitors Installation G 3~ C1 B1 A1 R R R HP Filter PD HP Filter PD HP Filter PD Ph.C In Ph.B In Ph.A In LP Filter Sync Sync In Capacitive coupler installed in a Generator Busbar Derivation Box PD Acquisition/ Monitoring System Derivation Box PPT2013.01.01.20EN www.nidec-asi.com 24
  25. 25. HFCT Installation Sync PD HFCT HP Filter PD HFCT HP Filter HP Filter PD HFCT LP Filter Ph.C In Ph.B In Ph.A In PFCT Sync In M 3~ Derivation Box HFCTs installed on a motor cable terminal box PD Acquisition/ Monitoring System Derivation Box PPT2013.01.01.20EN www.nidec-asi.com 25
  26. 26. Case Study: Power Generator On-line PD monitoring was performed on a Generator in a Power plant, in order to collect data to assess the whole machine conditions PD measurements evidenced that the machine was affected by:  Distributed micro-voids (all three phases) Typical of modern thermosetting insulation systems  Bar to bar (ground) discharges (phase U) the high frequency currents may degrade, in the course of time, both the stress grading system and the slot coating protection in the region where the bars leave the iron core  Slot Discharges (phase V) Dangerous phenomenon: inspection and maintenance required ! PPT2013.01.01.20EN www.nidec-asi.com 26
  27. 27. Case Study: Power Generator Phase V Entire Pattern acquisition Classification map cross talk of bar to ground discharges in overhang of phase U Exciter noise cross talk of distributed micro voids discharges in phase U PPT2013.01.01.20EN www.nidec-asi.com Distrib. Microvoids: 20% Slot discharge 80% 27
  28. 28. Case Study: Power Generator Phase V Results confirmed by endoscopic inspection on generator !  PD traces found in 12 of the 60 slots  (7 white traces and 8 suspecious traces) Slot discharges: Potential danger PPT2013.01.01.20EN www.nidec-asi.com 28
  29. 29. Services  Off-line and on-line PD testing for on-site diagnostics on rotating machines.  Off-line and on-line PD testing for the commissioning and condition assessment of other electrical apparatus.  Sensors and instruments sales and installations.  Training on PD measurements  Remote data analysis of PD data acquired by customers. PPT2013.01.01.20EN www.nidec-asi.com 29

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