ELCID test on Generator 400 MW
Generators to be assembled at site, the stator core was stacked with overlapping method and there is NO splitting core inside.
Core stacking process assembly
Stator core are clamping by compression bolts and providing with the insulation tube at top and bottom side
TESTING
During the ELCID test we identify high fault current at several slot and distributed from the bottom core to top, the fault currents is much higher than other slot. Following are the screenshot of the ELCID single trace intersection.
Single Trace with Combine slots were shown that the peak current are identified at both slot from the beginning to end core (from bottom to top).
Tracing the problems.
Inspection to be done at that slots, there are NO physical damaged or abnormalities were found, a Mega-ohm meter was used to measure the insulation of the compression bolts, that identified “zero” ohm.
Repair action.
The compression bolts to be removed from the core clamping and found rust on the bolts, we suspect that the rust is cause the problems..
To improve the bolts, we try to cleaning and adding 0.1mm thickness of KAPTON® insulation and tapping onto the bolts, and then reinstalled and re testing with a Mega-Ohm meter and ELCID.
After reinstall we measure the Insulation Resistance at 500 VDC, and the value was improved from 0 M-Ohm up to round 500 – 600’s Mega Ohm.
Re Testing with ELCID
After all bolts finished repair, re test with ELCID performing on that slots, and the maximum peak current is 17mA
Conclusion:
- The rusting on the compression bolts is causing stator interlamination short.
Tubing insulation for the compression bolts is too short, it is not sufficient to cover contact free between compression bolts and the core
ELCID TEST ON THE HYDRO GENERATOR 35 MW WITH SPLIT CORE
The units are constructing with two splitting core. with splitting gap round 1.5mm, the manufacturer tolerance is 2.0mm, located at slot 61 and 181.
EL CID test.
During ELCID test high peak current occurred at the splitter areas, following is the screenshot the single trace intersection at slot 61, the peak current is 161 up to 270mA (from the bottom to the top side), with the max peak current 270mA with distance 0.694m from the bottom (turbine side).
Single Trace Intersection Slot 181, the peak current is 135 up to 262mA (from the bottom to the top side), with the max peak current 262mA with distance 0.669m from the bottom (turbine side).
Single Trace Intersection at non Splitter area
The split core is potential to causing hotspot, to remove the hotspot at this area is need better cooling system than others.
