Graeme Robertson, Sulzer Downing and Mills: Generator repair and rewind
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Graeme Robertson, Sulzer Downing and Mills: Generator repair and rewind



Graeme Robertson, Head of Operations – UK, Sulzer Dowding & Mills delivered this presentation at the 2013 Gas Turbines conference. The event is designed as a platform for discussion on the latest ...

Graeme Robertson, Head of Operations – UK, Sulzer Dowding & Mills delivered this presentation at the 2013 Gas Turbines conference. The event is designed as a platform for discussion on the latest technologies & developments in gas power generation. For more information on the annual event, please visit the conference website:



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Graeme Robertson, Sulzer Downing and Mills: Generator repair and rewind Graeme Robertson, Sulzer Downing and Mills: Generator repair and rewind Presentation Transcript

  • Sulzer Dowding & Mills GasTurbine Conference , Brisbane, October 2013 Graeme Robertson – Head of Operations UK Sulzer Turbo Services
  • LARGE HV MACHINE REPAIR OPTIONS Sulzer Turbo Services  Repair to coil lead  Cutting coils out of circuit  Splicing in a coil side  Replace a failed coil [s] / bars  Complete rewind | slide 2
  • FACTORS TO BE CONSIDERED  Machine Specific  Secondary damage, core loss or impact  Impregnation system  Type of winding Sulzer Turbo Services  General Factors  Physical size & access  Impact on other operations  Production loss and outage cost / Budget Availability  Age of winding | slide 3
  • REPAIR TO COIL LEAD OR CONNECTIONS - 1 Sulzer Turbo Services  Simplest repair option if only one coil leg or connection is affected  Damage to adjacent coils increases the risk of repair escalating  Likely that secondary arc flash damage will be evident  Global VPI makes this process more difficult | slide 4
  • 2.5MVA, 2 MW, 8 Pole, 11KV Sulzer Turbo Services Global VPI Impregnation Lead Arc Flash Damage | slide 5
  • CUTTING COILS OUT OF CIRCUIT - 2 Sulzer Turbo Services  Will affect machine performance  Likelihood of reduced output  Excitation current will change  Out of circuit coils need to be isolated and insulated to prevent circulating currents  Minimise air gap harmonics to minimise, noise, vibration, increased losses  In all cases Stator core requires to be fit for service as a result of failure | slide 6
  • 12 MW 4 Pole 11KV Compressor Motor Sulzer Turbo Services Failed with multiple failed coils and earths Stator Winding Earth Fault Damage to sidewall insulation | slide 7
  • ORIGINAL COIL CIRCUIT Sulzer Turbo Services | slide 8
  • CUTTING COILS OUT OF CIRCUIT Sulzer Turbo Services  Coils reduced from 72 to 66  1 coil splice repair  STAR connected with 2 parallel circuits.  Coils / Phase parallel path 12 to 11  10% increase in gap density  Rating reduced from 12MW to 9MW  Minimal outage time available, required for production | slide 9
  • REDESIGNED COIL CIRCUIT Sulzer Turbo Services | slide 10
  • REDESIGN MODIFICATIONS TO CONNECTION RING New Coil to Coil Connections @ Conn Ring Sulzer Turbo Services Connections of coils taken out of circuit | slide 11
  • MODIFICATION TO NON CONNECTION END COIL Sulzer Turbo Services Cut Coil Knuckle @ Non Conn End Cut Coil Isolated & Insulated | slide 12
  • SPLICE IN COIL SIDE - 3 Sulzer Turbo Services  Straight forward with top coil side, can be achieved on bottoms legs  Must maintain strand continuity  Must maintain strand, turn & ground insulation levels  Must maintain coil bracing, coil to coil, coil to support arm  Must not restrict airflow – staggered scarfing | slide 13
  • SPLICE IN COIL SIDE Sulzer Turbo Services  Slot Cleaning is critical  Care taken to avoid damage to adjacent coils  Lift Centre strip packing  Vacuum to remove all debris before, repacking and wedging | slide 14
  • STAGES OF SPLICING IN COIL Sulzer Turbo Services | slide 15
  • REPLACE A FAILED COIL / BARS - 4 Sulzer Turbo Services  No change in performance  Easier with half bars, diamond coil requires care / process  Must lift all coils in coil pitch [Diamond]  More coils lifted for WAVE winding  Depends upon condition of original winding, evolute / nose stress  Very difficult for global VPI windings, hard coil cells, prone to cracking during removal | slide 16
  • 120 MW 2 Pole 13.8KV Gen Sulzer Turbo Services  Connections un-brazed to allow bar testing and subsequent removal  Stator bar being jacked out of slot | slide 17
  • 120 MW 2 Pole 13.8KV Gen Sulzer Turbo Services | slide 18
  • Replace Failed Coil Sulzer Turbo Services Secondary Epoxy Injected  | slide 19
  • 120 MW 2 Pole 13.8KV Gen Sulzer Turbo Services  Significant number of top bars [25] which had to be removed  Finished stator with bracing and blocking all restored, new connection caps fitted | slide 20
  • REPLACE FAILED COIL Sulzer Turbo Services  Stator bar being jacked out of slot, note the use of multi point jacking, the fit of coil and VPI system meant that the coil had to be drilled and tapped to facilitate removal without damage to core | slide 21
  • FULL STATOR REWIND - 5 Sulzer Turbo Services  Performance maintained or Increased  If possible engineer out the previous failure mechanism – [ increase interturn or sidewall insulation]  Restores Winding & Bracing system to new condition  Winding is a ‘consumable’ of a Motor or Generator, has a life span, which is determined by loading / cycling / starts /environmental conditions / maintenance procedures  New Windings will obviously extend the machine expected lifespan | slide 22
  • Production Platform – Generation Problems Sulzer Dowding & Mills Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 23
  • Overview Sulzer Dowding & Mills  Total generation capacity of 35MW  GT 4 was to be returned to Service after period of inactivity, this was a 15MW, 6.6kv, 4 pole Generator driven by an Avon Engine  Provided critical power for Sea Water Injection Pump motors  Platform required SWI Pump Motors running to support production  Module Roof was not watertight !  Generator Anti-Condensation Heaters were defective ! Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 24
  • Bringing back to service… Sulzer Dowding & Mills  Pre-commission checks identified very low IR and no PI.  1000v DC Test IR value 0.2MΩ & breaking down after 4 minutes  As our engineers were being mobilised to site, platform staff spun the turbine generator for a period of 4 hours unexcited to determine if dampness / condensation was the issue.  Retest did not show any difference in the IR or PI levels  Complete winding was wet with an earth fault present Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 25
  • Investigating the problem Sulzer Dowding & Mills  Our Service Engineers then carried out a methodical check:   opened alternator for internal inspection of rotor / stator for any evidence of ingress of contamination cables and all connections from the cubicle to the alternator terminal box, removed all clamps / post connections  disconnected the star point / split phase connections  split low reading phase coils to form 2 halves for inspection & test  continue to split until defective coil or coils were located  identify the defective area / coil section Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 26
  • The Defective Coil Sulzer Dowding & Mills  The defective coil was identified by a process of elimination, and located at 4 o'clock position when viewed from DE, fault was specific to one diamond coil.  The stator winding had 66 coils connected in 2 parallel circuits  The winding had 5 & 6 coil groups  We proposed an in-situ repair potentially saving 16 weeks on time scale and circa £700k on rewind costs  A primary objective was to minimise outage time to get SWI pumps operating ASAP. Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 27
  • The Turbo Generator Sulzer Dowding & Mills Generator with end covers partially removed to expose Stator Winding Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 28
  • Source of the Problem Sulzer Dowding & Mills Generator Stator Coils ready for splitting to locate defective coil Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 29
  • Winding Modification Sulzer Dowding & Mills 4 pole 3 Phase Generator 66 Slots & 66 Coils 2 Parallel Circuit Star 12 Coil Groups 5 coils & 6 Coils 2 Coil Groups in each parallel path 1 with 5 coils the other with 6 coils Failed coil 2nd in 6 coil group Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 30
  • Winding Modification Sulzer Dowding & Mills 4 pole 3 Phase Generator 66 Slots & 60 Coils 2 Parallel Circuit Star 12 Coil Groups all 5 coils Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 31
  • Our Solution.. Sulzer Dowding & Mills  We calculated what would be the effect of cutting out 6 coils, 2 per phase, on the performance of the Generator  It was necessary to take 2 coils from each phase, to prevent circulating currents and kept the winding balanced  We assessed that a maximum 10 % loss of output would result in changes  Results were relayed to Client who approved the process and methodology of repair. Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 32
  • The Completion.. Sulzer Dowding & Mills  Work was completed in 14 Days utilising 24 hr working :      The generator was part dismantled, rotor remained in position An environmental habitat was erected around the stator Stator winding configuration was changed and reconnected, the defective coil and 5 other coils removed from circuit. Stoving heaters were applied to dry the rest of winding The stator winding was cleaned, dried, and spray varnished The machine was fully built and prepared for test  Generator returned to service with slow increase of load from 2 MW to 7MW over a shift and then up to 13.8MW  Machine was handed back to client after successful commissioning test, with some alterations to protection relays and AVR settings. Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 33
  • Conclusion Sulzer Dowding & Mills  Drilling Program was at risk due to lack of generation capacity  Failure to complete the ‘well work-over’ in time put the complete well at risk, including future oil revenues  Failure to provide power for the SWI Motors would result in loss of oil production  Generator Repair saved 16 Weeks of down time and circa £700k  Generator operating satisfactorily 15months later  Sister 15MW generator rewound this year  Scheduled to return 2014 to rewind this generator Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 34
  • BEST PRACTICES – SITE WORKING Sulzer Turbo Services  LOCAL SITE CONDITIONS REQUIRE  MITIGATING FACTORS  Simple enclosure to create clean room  Remote Locations  Controlled environment with some or all of:-  Temperature & Humidity          Air Conditioning De-humidifiers Heaters Work platforms Positive pressure Air Filtration Lighting Power outlets Tool storage  Effects of high altitude  Hazardous Atmospheres  Noxious fumes  Political Situation (Risk) | slide 35
  • BEST PRACTICES - STATOR WORKS Sulzer Turbo Services  Stator core fit for 20-30 years  Fit of coil in slot  Resistance between coil & stator core  Tightness of wedging / size and position of ripple springs  Stress grading tape in correct position  Blocking & bracing of coil in endwinding  Continuity of sub-conductors  Insulation integrity / quality of coil / bar | slide 36
  • BEST PRACTICES – STATOR SLOT FILL Sulzer Turbo Services Wedge Top Packing Top Coil Side Conducting Vetronite Conducting Middle Strip Bottom Coil Side | slide 37
  • BEST PRACTICES - STATOR CORE Sulzer Turbo Services  Test by power flux test or El-Cid method  Ensure tightness of lamination packs and cleanliness  Condition of air vents and security of duct spacers | slide 38
  • BEST PRACTICES – STATOR WEDGING Sulzer Turbo Services  For tight fitting wedges max length 8”  Staggered under wedge packing | slide 39
  • BEST PRACTICES – STATOR SCARFING Sulzer Turbo Services  Good scarfing of joints and staggering of scarfs  Avoid local build ups of insulation which would restrict air flow paths Insulation Scarf Joint | slide 40
  • BEST PRACTICES – STATOR BRACING / BLOCKING Sulzer Turbo Services  Maintain end winding blocking & bracing, maintain coil spacing  Ensure adequate clearances;   between connections   between coils and to earth Ensure adequate separation between phase coils 6.6kV 5.5mm 0.22” 11.0kV 8.0mm 0.32” 13.8kV 10.0mm 0.40” | slide 41
  • BEST PRACTICES – STATOR TESTING Sulzer Turbo Services  Winding Tests  DC resistance  Insulation resistance  Polarisation Index  Voltage withstand AC or DC  Tan Delta  Partial Discharge | slide 42
  • BEST PRACTICES – ROTOR REWINDING ON SITE Sulzer Turbo Services Two Options  New Rotor Copper  Utilising Original Copper         Removal of old insulation Validate forging Renew all slot, end-winding and under retaining ring insulation Reinsulate and rewind Maintain all symmetry of blocking & bracing Refit all fan blades and auxiliaries in original position Balance weights all accurately recorded and refitted Minor trim balancing may be required | slide 43
  • BEST PRACTICES – ROTOR REWINDING ON SITE Sulzer Turbo Services  When rewinding Rotor >100MW we would recommend high speed balancing which usually cannot be achieved on site.  Similarly when fitting new retaining rings, we would also recommend high speed balancing to ensure the correct balance condition at speed and also to ensure settlement of the rings | slide 44
  • HIGH SPEED BALANCING FACILITY Sulzer Turbo Services | slide 45
  • Questions ? Sulzer Dowding & Mills Thank you for your attention, Sulzer Dowding & Mills 2013 <Copyright © Sulzer> | slide 46