Research on anti-halation of 600MW steam turbine generator

Anti-halation structure is a very important aspect in the design of motor insulation structure. The anti-halation effect directly affects the preventive test and safe operation of the motor. As the capacity of the motor continues to increase, the rated voltage of the motor is also increased accordingly. The anti-halation at high voltage is more important in the design and manufacture of the insulation structure of the motor. The anti-corona structure, materials and test results of our company's 22kV 600MW turbine generators will be discussed in detail below.

2 The selection of raw materials The anti-corona forming method of motor coils is various. The large-scale motor coils of our company mostly adopt the mold hot-pressing method, that is, the anti-halation layer and the main insulation are simultaneously hot-pressed and then processed twice. Therefore, the anti-corona material includes an anti-halation substrate, a semiconductor anti-corona paint, and an insulating cover paint.

2.1 Glass ribbon For the actual situation of our company, the anti-halation of 600MW steam turbine generator starts from the material. Because the asbestos products are harmful to the human body, foreign countries have been completely eliminated, and they are rarely used in China, and the supply is unstable. Therefore, we decided to use glass ribbons for the anti-corona substrate of the 600MW turbine generator. We use the pre-treated yarn for the webbing, which saves the process of dewaxing after the glass ribbon enters the factory, improves the impregnation of the glass ribbon, and improves the mechanical strength of the glass ribbon.

2.2 Low-resistance anti-corona paint We have improved the original low-resistance anti-corona paint. For example, the problem of the original 134 anti-corona paint is: the resistance is easy to be high, the adhesion is poor. In response to these problems, we changed the conductive material graphite in the original low-resistance paint to acetylene black, which can reduce the content of conductive materials in the paint, and increase the adhesive content to improve the adhesion. In addition, the particle size of acetylene black is smaller than that of graphite. After uniform mixing, the electrical resistance can be stably controlled within the range required by the standard.

2.3 High-resistance anti-corona paint High-resistance anti-corona paint anti-halation principle is to use the nonlinear characteristics of carbonization hanging, and the electric field at the end of the coil is automatically distributed evenly under the action of electric field. Therefore, the most critical raw material in high-resistance anti-corona paint is silicon carbide. In this development, we have prepared different components of abrasive silicon carbide and electrical silicon carbide from several different production plants, and selected 945 high-resistance anti-corona paint and 947 high-resistance anti-corona paint suitable for 22kV anti-halation. .

3 Anti-halo structure design According to the high-voltage motor stator coil at the ventilation slot and the end of the slot at the insulation surface electric field distribution is uneven, when the local field strength reaches a certain value, the gas is locally ionized to produce corona.

3.1 Prevention of crotch corona The generation of corona in the groove is due to the existence of a gap between the insulating surface and the groove wall, and the field strength at the gap exceeds the critical stun field to produce corona. According to the calculation of the distributed parameter circuit, the field strength of the groove is 8.lkV/cm. The method of preventing the corona is to stabilize the grounding of the coil insulation surface and eliminate the air gap voltage. The specific method is to perform anti-corona treatment on the surface of the coil, and the coil groove portion is formed integrally with a semiconductor material. The resistance value of the semiconductor material can also be obtained by the calculation method of the distributed parameter circuit. Considering the loss of the stator core, the resistance value is usually controlled between 102 and 15f. This can not only prevent the occurrence of corona, but also affect the loss of the core and produce unnecessary temperature rise.

3.2 Prevention of end corona The field strength of the insulating surface of the stator coil is increasing in the direction of the core. Therefore, the voltage drop of the insulating surface is the largest at the slot and the axial field strength is also the highest. The ultimate goal of the end anti-halation is to evenly distribute the electric field at the end of the coil and to make the surface field strength lower than the corona starting field strength. A non-linear material carbonization provides this possibility. The test shows that when the field strength reaches the height of the halo field, the antihalation layer will stun. When the value exceeds a certain value, the antihalation layer will be overheated and carbonized. By adjusting the resistivity and nonlinear coefficient of the anti-corona material, the effect of neither the halo nor the heat can be achieved well. The theoretical calculation combined with the test proves that the surface resistivity of the end anti-corona material should be 18~11 ( > The nonlinear coefficient should be between 1 and 2.

3.3 anti-halation treatment length 3.3.1 groove anti-halation treatment length groove anti-halation treatment length need to consider the motor structure to reduce the unevenness of the electric field, no other parts (such as copper shielding, bracket screws, etc.) The discharge is as short as possible from the slot.

3.3.2 End anti-halation treatment The length of the end anti-corona treatment is based on limiting the electric field strength of the coil end surface to the faint field strength. According to the rated voltage of our company's 600MW turbine generator is 22kV, the minimum length of anti-halation at the end of the coil can be obtained by calculation. Considering a certain margin, we finally determined the end anti-halation length of the turbine generator suitable for our company.

4 test to verify the final completion of the motor anti-halation, only through the theoretical design is not enough, because raw materials and high voltage often bring great dispersion, so anti-corona structure and materials must be verified by a large number of tests to finalize .

4.1 Verification of raw materials 4.1.1 Glass fiber belt 600MW steam turbine generator anti-corona glass fiber belt is customized to the glass fiber production plant according to special requirements, changed to the original wax glass weaving for pre-treatment glass wool weaving, after entering the factory There is no need to remove the wax, and the warp and weft density and the twist of the original yarn are changed to improve the impregnation of the glass fiber ribbon. In addition to the degree of twist in the domestic glass fiber belt, the other indicators have reached and exceeded the technical requirements of Hitachi. It can fully meet the needs of anti-halation of 600MW steam turbine generator.

4.1.2 Low-resistance anti-corona paint For low-resistance anti-corona paint for one-time anti-halation belt and brush, change graphite to acetylene black, and change the formula for multiple tests to obtain the desired low-resistance anti-corona paint. .

Its performance fully meets the domestic standards and the technical requirements of Hitachi.

4.1.3 High-resistance anti-corona paint High-resistance anti-corona paint is made from domestic and foreign countries using silicon carbide as the main raw material. Therefore, its performance mainly depends on the performance and content of carbonized laurel in anti-corona paint. We have applied the carbonized laurel produced by different manufacturers and changed the previously used graphite conductive group to acetylene black. Through a large number of tests and summaries, a high-resistance anti-corona paint suitable for 600MW steam turbine generators was selected. Through experiments, it is proved that this high-resistance anti-corona paint is also the same (down to page 110). However, due to the small specific speed of the super-high head pump turbine, the water thrust generated by the small pressure difference between the outer back pressure of the runner and the side pressure portion of the runner changes the total water thrust.

Due to the transient operating conditions, it is difficult to accurately estimate the pressure distribution around the runner. Therefore, Mitsubishi Corporation has tried to maintain the water thrust balance in the design of the pump structure considering the structure of the pump turbine. The characteristics are as follows: the gap between the outer back pressure chamber and the side pressure chamber of the runner is made as equal as possible.

An inner balance pipe (2nd balance pipe) and an outer communication pipe (1st balance pipe) are provided to balance the water pressure of the runner back pressure portion and the side pressure portion.

When the man is interrupted, the guide vanes adopt a closed mode with a small influence on the counterflow zone.

The water thrust changes before and after the load shedding and the interruption of the force are as shown. The results of the site test show that under all operating conditions, including normal operation and transient operation, no excessive water thrust is generated and the operation is very stable.

Power Thrust Characteristics of Generator Output (MW) Pumping Operation 4 Conclusion This paper introduces the design and test overview of the ultra-high head water pump turbine of the world's highest head in the Geyechuan Pumped Storage Power Station in Japan. The site test results are basically consistent with the pre-validation and predicted values ​​studied on the microcomputer to meet the design requirements.

From the viewpoint of further pursuing economics, the technical problems of high-head and high-speed pump turbines are not all solved, and research on improving analytical techniques must be continued in the future.

Lin Xiuzi and Fu Zhiyue School (on page 98) can fully meet the requirements of 22kV motor anti-halation. 4.1.4 Cover paint 600MW turbine generator anti-corona cover paint is basically the same as Hitachi, in line with technical requirements.

5 Structural tests Through the screening and testing of raw materials, all anti-corona materials used in 600MW steam turbine generators can meet and exceed Hitachi's requirements in main performance. The aluminum row anti-halation treatment sample test and the real machine coil anti-halation treatment test results show that the anti-corona performance meets and exceeds the requirements of the company.

6 Conclusions 6.1 Motor anti-halation structure process is simple, reliable, anti-corona performance is stable.

Anti-corona requirements for the machine.

In comparison, our company's 600MW steam turbine generator is more resistant to anti-halation performance due to the secondary treatment after one molding.

6.4 The shortening of the length of the low-resistance anti-halation layer has obvious advantages in improving the reliability of the motor operation and smoothly passing the process withstand voltage test.

Functional features:

1. With adoption of gear mechanical transmission systems, the machine is featured with high efficiency and low noise.

2. With braking function, the spindle is flexible and reliable.

3. With adoption of frequency control in electrical system, the machine controls braking using a frequency converter, so start and brake slopes can be preset for optimal winding.

4. The scope of frequency control is wide. Sped regulation is accurate and stable. The insulation level of the motor is level F.

5. Automatic winding displacement, auto-displacement inter layer trapezoid insulation.

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