Analysis and treatment of generator corona phenomenon Zhong Weitang, Cong Xibin (Department of Electrical Engineering, Liaoning University of Engineering and Technology, Liaoning Fuxin, the reason for this phenomenon, find out the solution to the corona phenomenon, and through the experimental and operational proof, the analysis is correct, Properly handled, accumulated valuable experience for dealing with similar issues in the future. The parameters are in compliance with the regulations. However, in December 2001, when the generator was in normal operation, the temperature measuring component of the line showed an induced voltage of about 200V. When the voltage was increased to 4000V during the experience, the steam core slot was found. Corona sparks between the lines were examined in detail, and it was found that there was a white powder substance between the core of the sixth slot and the wire rod. This substance was generated by the corona phenomenon. The temperature measuring element in which the induced voltage appears is also between the upper and lower bars of the sixth slot. Therefore, it shows that the stator wire has corona phenomenon during operation. 1 Corona phenomenon analysis 1.1 Coil insulation structure 1 The generator is a rated voltage of 6.3kV rated capacity of 12MW in Shanghai Electric Machinery Factory. The main insulation of the wire is a thermosetting ring. The arrangement of the oxygen powder mica with the stator core groove is as follows. It can be calculated that the gap between the insulation and the groove wall is (19.5-18.7)/2=0.4mm. 1.2 Anti-corona structure In order to prevent the corona phenomenon during the operation of the generator, the manufacturer has done the equipment at the factory. Anti-halation treatment, spraying a layer of A38-4 semiconductor lacquer in the stator core slot, padding 0.5mm thick semiconductor glass cloth board at the bottom of the groove, and the line is also treated with anti-halation treatment, that is, the insulating part of the straight part of the wire rod is painted low. Resistive semiconductor electrocoating, the end insulation surface is coated with a high-resistance semiconductor electrocoat. After the straight line of the rod is used for anti-halation treatment, the coating should be sufficiently in contact with the groove wall to short the gas gap and reduce the groove. After the voltage on the air gap (slot voltage) but after the wedge is removed, it is found that the sides of the lower bar of all the grooves are in good contact with the groove wall, between 0.0b and Q05mm, and the distance between the two consecutive contact points is only 10-15cm, and the upper rod, especially the upper trough rod of 1 trough to 7 trough, the gap between the rod and the trough wall is about 0.4 to 0.5mm, and the longest distance between two consecutive contact points is 2/3 iron. Core length, therefore, the voltage of the bar slot on the 1 slot-7 slot must be greater than 200V. In addition, due to the improper anti-corona treatment of the upper and lower layers of the 1 trough-7 trough, the corrugated rod sometimes still produces corona in the trough, especially for the thermal insulation of the main rod, which will generate a large amount of energy. Capacitive discharge (slot discharge), the anti-halation layer is seriously damaged. As the running time increases, the halo voltage gradually decreases, so that under the condition of the phase voltage, a corona phenomenon is generated for a long-term corona discharge. Forming electrical corrosion, reducing insulation strength and causing insulation breakdown. Furthermore, during the winter operation last year, due to a sudden change in generator load (a sudden change from 12MWf to 14-wire rod under the action of electrodynamic force, the semiconductor coating on the surface was damaged, which is one of the reasons for the corona phenomenon of the generator. 2 treatment method In the past operation of the generator, the operation is stable, there is no analysis of any difference, the main insulation will not be too much damage, so only the straight line part of the bar is treated with anti-halation treatment. The processing steps are as follows: First, All the wedges are withdrawn, the wire rod is dusted and the gap between the two sides of the wire rod and the groove wall is measured. Secondly, according to the measured gap, different thicknesses of the semiconductor glass cloth board are inserted into the gap, in order to make the sides of the semiconductor glass cloth board fully contact with the groove wall and the wire rod, before the insertion, a low layer is brushed on both sides Resistance semiconductor paint, semiconductor paint resistivity is calculated as follows: It can be known that the main insulation thickness of the linear part of the generator bar is d=from the actual measurement, the most unfavorable bar, the distance between two consecutive contact points of the groove It is a 2/3 stator core length, so the distance between the middle portion of the air gap and the two contact points is such that the surface resistivity of the grooved semiconductor layer is on the order of 104. The preparation method is as follows: the toluene liquid is slowly poured into the low-resistance semiconductor lacquer and stirred uniformly, and a little evenly coated on both sides of the white cloth belt, and the resistance value of 1 cm long is measured by a multimeter, and the value is 10 orders of magnitude. The resistivity should not be too large or too low. If it is too large, it will cause corona corrosion in the groove. If it is too low, it will cause loss of induced current on the surface of the semiconducting layer. Third, a 0.5mm thick semiconducting layer is placed on the upper part of the wire rod. The glass cloth board is then inserted into the wedge. The semi-conductive glass cloth board is slightly wider than the width of the iron core groove, so that after the wedge is driven, the two sides of the glass cloth board form a line contact with the groove wall. 3 After the wedge is driven, the three phases of the generator stator ABC are carried out. The tank voltage test and the 1.5 times AC withstand voltage test, the tank voltage test results are shown in Table 1. As can be seen from Table 1, the effect is very obvious. The AC withstand voltage test results are shown in Table 2. The constant %-sheng corona phenomenon only starts from the C200 Sheng c12 month id time! For the shorter liblishhgHouse.Allrightsreserved., the domestically produced diatomaceous earth with the appropriate thickness is divided into two types, which can be used alone or in combination with different particle sizes, which can achieve extremely high filtration precision. The bulk density of diatomaceous earth has a great influence on the filtration effect. The smaller the bulk density, the larger the pore volume of the filter aid particles, the better the permeability and the adsorptivity, so it is generally preferred to have a lower bulk density. The filter parameters of the diatomaceous earth 2.4 filter element pore size depends on the filtration accuracy and the particle size distribution of the filter aid. During the precoating operation, the concentration of the diatomaceous earth in the precoat liquid and the circulating flow rate of the precoat liquid should be controlled. The diatomaceous earth particles are bridged to form a uniform precoat. The diatomite concentration is generally taken as 0.3-06%, and the circulation flow rate can be taken as -2 times the normal flow rate, and the pre-coating pressure is generally about 0.1 MPa. For the filtration operation of the grinding fluid with low viscosity and near water solubility, there are Table 1 data: Table 1 Filtration Accuracy (μm) Filtration Aid Particle Size (μm) Filtration Rate (mhr) Filtration Area According to Required Flow Rate And filter flow rate, namely: filtration area = flow filtration flow rate 3 Conclusion diatomaceous earth pre-coating filtration, high filtration precision, convenient operation and maintenance, suitable for purification and filtration of oily grinding fluid used for precision grinding, The diatomite pre-coating filtration technology needs to be further studied in detail in different applications. This article has only been discussed in general. Ningbo Cijie Chemical Equipment Co., Ltd. , https://www.shengjie-tower.com
April 20, 2023