Failure and treatment of the hottest bulb tubular

Bulb tubular generator failure and treatment

1 overview of Gaosha hydropower plant

located on the main stream of Shaxi River, Fujian Gaosha hydropower plant is the sixth level power plant of cascade development in Shaxi River Basin. It was started construction in September 1992. It is a medium-sized hub project with comprehensive utilization of power generation, flood control, shipping and so on. The power station is of low head runoff type, and the hub is composed of overflow dam, riverbed power generation 5, dynamometer main bearing, no refueling plant, 110 kV indoor switch station, ship lock, etc. With a total installed capacity of 50 MW, four domestic bulb tubular generator units with a single unit capacity of 12.5 MW were installed, which were successively put into operation in 1995 and 1996

2 generator parameters and structure

2.1 generator parameters

model: sfwg12/4950

rated speed: 125r/min

rated capacity: 12 500kw/13 889kva

rated voltage: 6 300V

rated current: 1 272A

stator overall dimension: *5 100 × 2 350mm

insulation grade: grade F

2.2 generator structure

the stator base adopts a full circle structure, the stator core is a wall attached structure, which is made of fan-shaped laminations punched with low loss and high silicon steel sheets. 54 dovetail bars are positioned in a full circle, and pressed with pressing rings and bolts. The outer diameter of the iron core is 4950 mm, the inner diameter is 4500 mm, the length of the iron core is 970 mm, and the general requirements for no radial ventilation are 0.2 ~ 0.4 grooves, There is a gap of about 0.4 mm between the outer circle of the iron core and the inner wall of the base in cold state, and close to the base wall in hot state for heat dissipation and cooling. A total of 24 temperature measuring elements are set between the layers of the circle and the bottom of the iron core groove, 12 upstream and downstream, 8 for each phase, 4 interlayer and 4 groove bottom. The rotor adopts "t" structure

3 brief description of typical accidents

(1) in March 1996, the generator differential and voltage memory overcurrent protection acted during the operation of unit 1, and the unit shut down in an accident. After inspection, it was found that the stator core toothed pressing strip fell off due to the upper direction of the downstream side of the stator, causing the stator phase A and C bars to be sheared and short circuited. The manufacturer sent experts to the site to guide the emergency repair, and took the temporary measure of "opening and short circuiting" to throw away the burnt wire rod. We are very interested in deep cooperation with innovative enterprises, which took 25 days to repair

(2) in July 1997, the stator of unit 1 suddenly smoked during operation. During the smoking process, the generator protection resource potential was huge and no signal was sent. After inspection, it is found that the iron core of the 5th ~ 26th slots of the stator is overheated and discolored, the slot wedge is charred and carbonized, and there is a serious short circuit in the iron core. After lifting out the stator, a total of 26 rotor poles were found to have obvious scratch marks corresponding to the burned parts of the stator core. During the removal of the iron core, it was found that a total of 9 locating bars were obviously loose around the burned part of the iron core, and 4 of them fell down after the iron core was removed. The manufacturer takes measures such as strengthening and replacing part of the locating ribs, and strengthening repair welding of the stator core tooth pressing strip

(3) in June, 1999, during the operation of unit 3, a large amount of black smoke was emitted from the manhole of the generator, accompanied by a strong burning smell, abnormal operation sound, and the unit was shut down. After inspection, it was found that the stator and rotor were rubbing, some iron cores on the downstream side of the stator were worn, spanning 9 teeth, about 25 cm wide (0.225 m2), and there were obvious signs of heating. The slot wedge plate changed color, turned yellow and fell out. The inner circle of the iron core was measured, and it was found that the stator became bell shaped, that is, the inner diameter of the upstream side was large, and the inner diameter of the downstream side was small. The reason was that the dove tail bar fixing screw and plug welding point were broken, resulting in the stator and rotor sweeping accident

(4) in October 2000, the stator of unit 2 was grounded at one point during parallel operation, and the shutdown inspection found that the iron core toothed pressing strip between slots 161 ~ 162 on the upstream side of the stator was stuck between the stator and rotor after being desoldered, causing the upper coil bar of slot 162 and the lower coil bar of slot 161 to be sheared, resulting in a short circuit. After a comprehensive inspection of the stator, it was found that there was no looseness in other parts except the iron core at the place where the toothed strip fell off. It was decided to replace the damaged wire rod on site, drive epoxy toothed strip into the place where the toothed strip fell off to compress the iron core and treat it with epoxy glue

(5) in July 2001, the differential protection and voltage memory overcurrent protection of No. 2 generator tripped and shut down. The inspection found that the jumper wire at the B-phase end of stator slot 108 of No. 2 generator was blown, causing local insulation damage of stator and forming phase AB short circuit accident. After that, it was decided to replace the damaged bar locally

4 accident cause analysis

4.1 defects in stator manufacturing process

from the maintenance after the accident, it is found that most of the gap between the stator core and the inner wall of the base