2023年水轮发电机定子绝缘缺陷现场修复工艺.doc

水轮发电机定子绝缘缺陷现场修复工艺（On site repair technology of stator insulation fault of Hydrogenerator）
水轮发电机定子绝缘缺陷现场修复工艺(On site repair technology
of stator insulation fault of Hydrogenerator)
Northwest power plant installed 3 * 6300kW, generator rated voltage 6.3kV. The first phase of 2 x 6300kW was put into operation in 1992, and the second phase of the project was installed with 1 x 6300kW in . The 3 units are vertical shaft mixed flow turbine generator sets. The first phase of the project installation and commissioning is very smooth, the second phase of the project found in the installation and commissioning of the generator stator has a major quality defects, after the site repair qualified before commissioning power generation.
First, the phenomenon of failure
The generator stator in March 26, by the factory car to power plants, in which the frame welded by steel plate, diameter 3400mm, high 1710mm, high silicon steel sheet by 0.5mm thick core laminations of fan-shaped punching pressure, axial length is divided into 14 sections, section between the radial ventilation channel 10mm high 13. A total of 144 stator coils, each of which is 2 sections of 5 * 2mm flat copper bars, is wound and formed, the main lead line and the neutral lead line each have 3, for the double stack winding, the 6 branch, the Y type connection, the insulation class is B class.
In May 19th, the stator was installed in the pit. In May 21st, the substation was installed and tested by the power bureau, and the stator transfer test was carried out according to the preventive test procedure for electrical equipment
(DL/T596-1996):
DC withstand voltage, DC withstand voltage
AX-BYCZ (ground) 5000/10000 5000/10000
BY-AZCZ (ground) 5000/10000 3000/
CZ-AXBY (ground) 5000/10000 5000/10000
1. stator DC resistance (m):AX:24.74; BY:24.72; CZ:24.72.
2. stator insulation resistance (M)
3. DC withstand voltage test voltage should be 3Ue=18.9kV, the actual pressure 18kV.
A continues for a minute with a leakage current of 51 mu A;
B phase lasts less than 1 minutes, breakdown;
C stalemate for 1 minutes, leakage current 31 mu A.
Preliminary conclusions: 3 generator stator coil B phase DC voltage failure, there is breakdown phenomenon.
Do B phase DC voltage test, when the first time pressure to 18kV, the leakage current is larger, not to the duration of the provisions of the breakdown discharge, all test instruments all back to zero, and hear the sound of the discharge, the general direction of discharge recording sound, preliminary
determination for B DC breakdown. To prevent further expansion of the accident, the next test project AC voltage test suspended, comprehensive inspection of test equipment, test instruments, test wiring, carefully check whether the stator coil metal foreign body. After confirming that no one is in error, repeat the B phase DC withstand voltage test. The result has not been tested until the test voltage has been reached. It is confirmed that there is a major quality defect in the stator B phase coil, that is, the insulation is not qualified.
Two, confirm the fault
In May 23rd, the manufacturers and technicians came to the scene to test the stator B phase coil with DC voltage withstand test again, together with the test staff at the test station:
1. DC withstand voltage test:
B phase insulation: 15 seconds, M, 60 seconds, 6000M
2. DC withstand voltage test, test voltage 1.0kV to 1.3kV, leakage current of 300 A to 1000 mu A, and then breakdown.
3. DC voltage withstand test: B phase insulation: 15 seconds 20M, less 30M.
Conclusion: the B phase coil has DC breakdown and the insulation is not up to standard.
Three, find fault points
Once again confirm that the stator B phase coil insulation is not qualified, start looking for the fault point. We will discharge along the direction of sound B phase coil branch electric soldering iron to burn the head and tail connector, insulating shake table test, carefully recorded the insulating shake meter readings, the coil readings unqualified is coil fault. After testing, the first winding of the branch insulation is normal. When the second time is hot to open another branch, the meter reading shows that the insulation is not qualified, and the fault coil is in the 8 coil of the branch. The 8 coils are boiled and connected in series for 2 groups, each group has 4 coils, and a group is removed by the insulation elimination method, and the test is repeated repeatedly, and finally the fault coil is B phase ninety-sixth slot coil.
After finding the fault coil, the next step is to find the fault point. By analysis, the DC voltage is unqualified creepage phenomenon, generally end coil, obviating the fault point in the groove, without dismantling the whole coil, only to find fault point in two near the end.
In the end of visual inspection of insulation surface, the upper end of the lower side found a slight crack, the eradication of two layers of insulation skin, with the shaking table tests, the readings showed no abnormalities, continue to check for obvious fault point not found.
In the dark night with the lamp method for boost leak, when DC voltage to about 10kV, the above frame in the stator coil middle test station staff observed about blue corona phenomenon in around the crack, but not breakdown. When the test voltage
continues to rise, corona phenomenon intensifies, and finally hear "pa" a sound of the breakdown discharge, confirm the fault point around the end of the crack.
The end of the insulation epidermal peel, insulated with self-made probe, shake table pole fault coil joints, the other pole with a movable probe, which will continue to lower the data to the depths of the direction of peeling search, but each peel a layer, the fault point in moving, until the shaking table is close to zero, reading with a multimeter direct measurements have been conducted, this point is the point of failure, specifically for the B phase coil slot ninety-sixth lower side upper iron core 4cm left.
Four, fault point treatment, repair
Confirm the fault coil breakdown point, with a self-made special slender blade will be around the breakdown point about 7cm to eradicate a portion of the insulating wrapping, around the fault point circle online with 0# emery cloth polishing, blowing with compressed air pressure. Because the distance between the coil and the coil is very small, the lower side of the working face is narrow, the hand can not extend into work, bring some difficulties to the repair work, be very careful not to damage the non fault coil, so had to unlock the upper coil fixed bandage, exit wedge outward traction about 5mm, work to expose more the lower side surface, with polyamide resin and epoxy resin with the ratio of 1:1 into colloidal and adding mica powder mix into colloidal state, a block insulation breakdown point is coated with a layer of colloid and then paste a layer of mica tape will sag filled with smooth, sticky total of four
layers of mica tape. The surface coated with a layer of polyamide mica colloid around on the system with a half stack package winding eight ring mica tape wrapped around each layer is coated with a layer of polyamide mica colloid, which is slightly convex to the other normal skin insulation, and is consistent with other normal insulator. Then the upper coil is reset, bound and fixed and impregnated with insulating paint,
Finally, the coil is energized with a DC welder for 15 hours, heating, drying, curing, and re coating the paint on the repair site.
All open joints, with the special head will fight the two joint overlap compaction of tin foil after the first winding of two layers of glass ribbon, winding eight layer half stack package mica tape and finally winding two layers of glass ribbon, brush dry insulating paint, then brush the gray surface of insulating paint, to restore to the original shape of stator coil.
In May 26th, the repaired stator coils were tested again:
1. stator DC resistance (m)
AX:24.88 BY:24.97 CZ:24.91
2. stator insulation (Mn)
AX-BYCZ (ground) /6000
BY-AXCZ (ground) /5500
CZ-AXBY (ground) 2500/7000
3. DC withstand voltage test, the test voltage is 3Ue=18.9kV
A continues for one minute with a leakage current of 4 mu A;
The B phase lasts one minute with a leakage current of 8 mu A;
C continues for one minute with a leakage current of 6 mu A;
4. AC withstand voltage test, the test voltage is
2Ue+1.0=13.6kV
Each phase is pressed by the test voltage for one minute without breakdown.
Conclusion: the stator winding defect is completed and the stator transfer test is qualified.

After the stator fault was repaired, it was put into operation in June 20, . After 1 years' operation, the operation has been running smoothly and normally.
Five, suggestions
Manufacturers of stator coils appear DC voltage breakdown phenomenon is explained: stator coil insulation factory test specifications for the CS86750-91, only do AC voltage withstand test, DC voltage test, so the test process, no major defects of unqualified stator coil DC voltage test found.
The stator coil of No. 3 unit of the northwest power plant has such a serious defect. If we only put it into operation with the experimental report of the factory, it will lead to an accident, and the consequences will be unimaginable.
I remind colleagues here, as manufacturers and the power bureau, according to the standards of the test there are differences, the owners in signing the purchase contract, should be made clear by the Power Bureau test standards.