As a new and efficient cooling technology, rumor evaporative cooling has been successfully applied to the stator winding internal cooling of Lijiaxia 400MY hydro-generator; 50MY stator evaporative cooling turbine generator has been safely operated for nearly ten years, larger The unit is in the pre-development. This cooling has proven to be not only feasible, but also safer, more reliable and easier to maintain than other cooling methods. In the process of developing high voltage and large capacity, the steam turbine generator adopting evaporative cooling can improve the stator insulation structure, and further break through the structure and operation and maintenance of the cooling system.
Evaporative cooling is divided into pipeline internal cooling and immersion cooling. Compared with hydro-generators, there are two major disadvantages of using internal cooling evaporative cooling on steam turbine generators: one is that the stator bars of turbo generators are concentrated heating elements, and the thermal load is higher than the equivalent when using conventional insulation structures. The capacity of the hydro-generator, the cooling effect is far less than the hydro-generator, and it is applied to the evaporative cooling of the steam turbine generator, and the high insulation performance and evaporative cooling effect of the evaporative cooling medium cannot be fully exerted. The other is that the steam turbine generator is mostly horizontal structure, the stator bar is placed horizontally in the trough, and the vapor and liquid two-phase flow resistance of the evaporating flow in the pipe is much larger than the flow of the pipe in the stator bar of the vertically placed hydrogenerator. resistance, so that pump power is required, and increasing the pressure equalization facility the flowing liquid, with the result that the motor stator cooling system complicated. Immersion cooling does not have the above drawbacks, and at the same time makes full use of the advantages of evaporative cooling, but the use of immersion cooling with conventional insulation thickness bars limits the development of turbo generators to large capacity, for which a new insulation system must be developed. , breaking its bottlenecks. It can be said that if the insulation problem of the evaporative cooling turbine generator is completely solved, the motor will be in the world leading level.
The Evaporative Cooling Group of the Institute of Electrical Engineering of the Chinese Academy of Sciences has carried out a large number of them. Two or three of them are stator simulation guides made of epoxy phenolic board wrapped with aluminum skin, which are placed in the slot simulation device item 1. The slot simulation device is composed of two walls, an upper cover and a bottom plate. For the convenience of observation, the copper mesh is pressed into the two walls to simulate the stator slot, the upper cover is made of plexiglass, the bottom plate is aluminum plate, and the copper mesh is connected with the bottom plate and then passed through the screw. Ground. The guide rod 2 is connected to the high-voltage end of the step-up transformer through the spring piece item 8, that is, the high-pressure porcelain bottle item), the guide rod 3 is grounded through the spring piece, and the other side is connected to an internal heating device, and then the entire groove simulation device is placed. In the plexiglass cylinder item 6, both ends are sealed with a rubber ring by a phenolic plate item 5. Item 7 is an exhaust valve, and gauge item 4 is used to measure the pressure inside the Plexum.
The first group consists of a semi-layered guide cloth with a layer of silk cloth and an epoxy board for the position; the second group is a plexiglass frame with a semi-folded polyester film in the frame; the third group is a plexiglass frame. In the position, a polyimide film is half-packed in the rack.
During the test, the pressure in the test model was first adjusted to 760 mmP+, and then the filtered F113 had a breakdown voltage of 45 kV/2.5 mm or more) and poured into the model. External heating was started to keep the pressure inside the cylinder constant, that is, the entire chamber was heated, and then to improve the test environment and speed up, the resistance wire was wound on the guide 3 for internal heating. The test equipment uses a corrected 50kV and 65kV booster, an external heating internal resistance wire, an internal heating regulator and a step-down transformer, and the pressure gauge is 2.5. During the whole process, the pressure of the medium in the model increases continuously, and the value of the breakdown or halo voltage is recorded. The distance between the guide rod and the groove wall is changed to change the thickness of the main insulation. The breakdown and the halo voltage are obtained at different distances. The relationship of distance.
"Test results and analysis According to the state of the cooling medium in the test process, it is divided into gaseous, liquid, gas-liquid mixed state to collate and analyze the test data, and the relationship between the halo voltage and the medium pressure and the main insulation distance is obtained. And breakdown voltage versus medium pressure, main insulation distance. Series 1 is a combination of silk tape and epoxy board, Series 2 is a combination of plexiglass and polyester film, Series 3 is plexiglass and polyimide Combination. The fixing of the guide rod and the insulation in the simulation tank is as shown. The selection of the insulation of the three sets of guide rods and the position of the fixed guide rod are tested successively, and the breakdown voltage and the main insulation distance in the series of 30 gas-liquid mixed state are tested. The relationship 10 relationship curve yields the following facts: 1) The gaseous corona voltage and the breakdown voltage increase with the increase of the medium gas pressure, which is in accordance with Basing's law, that is, the pressure rises, the gas density is large, and the ionization is possible. As the main insulation distance increases, the electric field strength E in the tank decreases, causing the gas halo voltage to rise. For every 1 mm increase in distance, the halo voltage increases by about 2~3kV. The gas breakdown voltage follows the main The edge distance increases and increases.!) The liquid medium only corona appears under negative pressure, and the halo voltage is very high (greater than !405), but no corona is seen under positive pressure, and the flashover along the surface of the rack occurs directly. Breakdown. Because the corona is generated with a certain temperature and electric field non-uniform conditions, the boiling point of F113 is very low (47.69) distributed in the place where the inside and outside of the tank can flow, resulting in the overall temperature of the insulation structure is not high and uniform, and the insulation of F113 is higher. The characteristics improve the electric field distribution condition. As long as it is not the extreme non-uniform electric field of the tip electrode, it is difficult to generate corona in F113. The breakdown voltage of the liquid medium increases with the pressure increase to a nearly linear relationship, and increases with the increase of the distance.
Under the same external conditions, the dielectric gas and liquid mixed state are not far from the breakdown voltage in pure liquid state, which is about 1! 2kV lower, which is beneficial to ensure the insulation strength when the temperature rises.
F113 media generally has good self-recovery ability after breakdown, and the insulation strength decreases only after 2:3 consecutive breakdowns.
Three sets of insulating material, a third set of bits plexiglass frame, with the optimum packet polyimide insulation.
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