Dampen Core Bars at Turbine Side
Core compression bolts
Core compression bolts has been inspected by visual, no red oxide deposit on its head or no loose indicate was found.
D. Winding measurements
Generator was storage at open air area since December 2009, termination was exposure without any shield or roofing.
Based on first inspection on November 2009, when generator still on foundation, winding insulation resistance is indicate no solid grounded but found very low insulation on phase “T” and winding resistance still in balance and in tolerance range when comparing to the factory measurements, (see previous pages report).
Following is the Insulation measurements by using 500 VDC and 5000 VDC dated : 30 June 2010
Phase R – Ground = 1.8 MΩ at 5000 VDC
Phase S – Ground = 0.1 MΩ at 500 VDC
Phase T – Ground = 0.2 MΩ at 500 VDC
Comparison to first inspection on November 18-19, 2009
Phase R – Ground = 2.24 GΩ at 5000 VDC
Phase S – Ground = 1.98 GΩ at 5000 VDC
Phase T – Ground = 0.6 MΩ at 5000 VDC
Winding DC Resistance
Winding resistance was measured at 300C, dated : 30 June 2010
Phase U – x = 1.32 mΩ
Phase V – y = 1.32 mΩ
Phase W – z = 1.33 mΩ
Comparison , inspection dated: 18 November 2009,
Phase U – x = 1.4 mΩ
Phase V – y = 1.4 mΩ
Phase W – z = 1.4 mΩ
After inspection was complete done, all of mechanical parts including, inner shields, bearings, oil deflectors, H2 shield, excluding rotor, to be re assembled on dated 1-2 July, 2010. Cover shaft was covered by temporary cover plate, while the rotor to be kept at workshop.
Based on these inspection here we can be summarized as the following items.
Frame : as visual inspections, no anomalies was found on the external frame
Dampen vibration bars and core support: found overheating on the bars dampen and support, but no welding crack was found
Core: found damaged at both TE / EE side endcore +/- 50 – 90 cm from each end due to copper melt and metal touching when rotor still moving, disc grinding and pencil grinding were involved to removed copper and metal melting before ELCID test, some of thot-spot was successfully removed but some of them still remain
HV bushings: no anomalies (crack or chips) were found at frame inside and outside
Stator winding: found overheating and resin melt at endwinding and connections end, almost of winding at the slot region was found overheating.
Stator wedges, almost of stator wedges at 1m long from end core at both side TE/EE were found burnt due to overheating
Stator winding: based on the first inspection dated November 2009, no solid grounded was found and winding DC resistance still in factory measurements tolerance. Measurement has been re inspect on June 30, 2010, Winding DC resistance at each phase still in balance.
Insulation resistance phases S - to Ground, T – Ground, are found zero using 500 VDC, and over than 1 MΩ on phase R – to Ground with 5000 VDC.
ELCID, Stator core was inspected and analysis using ELCID, almost of stator core still remain hot-spot, even copper melted was removed from core surface, random correction was try to identified and analysis for repairing programs.
Hot spot was found only at surface area. No hotspot was found in the slot areas or back core side areas.
Significant hotspot was successfully removed and come down when re grinding were involved to made a correction.
Slot No. 1, first test ELCID was measured at 740 mA, after correction, hot spot was comedown to 102 mA and slot No.2 was come down from 148 mA from 844 mA.
1. Frame, supports and HV Bushings
- Stator frame, no anomalies was found
- Core vibration dampen bars, found overheating at top side close to the stator outgoing leads but no crack on the welding areas was found
- HV bushings, No anomalies (crack, chips) are found on these parts, rust were found on the top cover due to generator was storage at open air for long time since December 2009.
2. Stator winding, surge rings, connections lead, and stator wedges
- Insulation Resistance Stator winding for phase S and T were measured zero MΩ using 500 VDC and 1.6 MΩ at phase R by using 5000 VDC, no solid grounded, very low insulation resistance are causing moisture absorption in the winding, due to stator was storage at open air for long time without any heaters are energized during in storage
- Winding insulation as physical inspections, found brittle, brownish and too dry due to overheating especially insulation winding at top side close to HV bushing.
- Winding insulation at endcore region, whole of insulation was found delamination due to overheating and copper melti touching to this areas when rotor still moving.
- Connection leads. Found brownish color due to overheating
- Stator wedges, whole of stator wedges at end core areas (+/- 1 m) found burnt and all of wedges at middle area was found moved due to loose.
3. Stator Core
Whole of stator core at end region (1m) at both end side TE/ EE found damaged due to metal touching when rotor still moving, copper and steel wedge was found meletd and deposit at this areas, overheating was also found in the middle region.
ELCID test indicate that, almost of the stator region identified hot-spot, random correction and re –test was carried out, some of the hotspot was successfully removed but some of them still remain, especially at end region.
Stator core is still possible to be repaired for rewinding, after total re-stacked and replace of end core region at least 1m long at each end core TE and EE side by new core.
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