1.Research On Insulator Icing
1) The insulator is naturally covered with ice
In order to improve the technology of insulator icing, it is necessary to investigate the causes of the current situation of insulator icing, and formulate different solutions according to different conditions of icing, so as to fundamentally solve this situation. The natural icing of insulators is based on the construction of stations in locations with serious icing in cold regions as the operation basis of the experiment, and the ice-covered area experiment circuit is used for relevant experiments. From the perspective of natural icing method, this situation is consistent with the reality. Influenced by environmental factors outside the test area, such as harsh climatic conditions, extremely low temperature environment and relatively complex land, the construction will be greatly affected, which makes it difficult to carry out the natural icing method test and ultimately leads to the extension of the test time. Under the influence of these factors, it is easy to bring unpredictable risks to the experiment, resulting in certain dispersion and uncertainty in the test. Therefore, the application of this natural icing test method is relatively small and is not suitable for most experiments. But the method of natural icing is beneficial to the study of the icing process and observe its inherent characteristics and changing rules. To study the special performance of insulators, other methods are generally used for experiments, such as artificial icing, to promote the development and innovation of technology.
(2) Artificial icing of the insulator
Artificial icing of insulators needs to be carried out in the weather laboratory. Experimental operation is carried out according to the simulated climate temperature in the laboratory. This method is a common way to study the icing condition of insulators. This method can obtain more experimental data in a certain period of time and has the characteristics of high repetition performance and easy control. There are two kinds of artificial icing experiments, artificial icing with electricity and artificial icing without current passing through. In the process of power transmission, there is a lot of current passing through insulator icing phenomenon. The power in the wire has a certain influence on the icing speed, density, ice size and overall quality of insulator icing phenomenon. During experimental operation, samples with current passing through should be preferred, but the instability and uncertainty of electric power are likely to pose a threat to the human body during the experiment. Therefore, in general, low current is selected for artificial icing experiment, which will be continuously increased according to the progress of the experiment. This method is less dangerous. Although it is only a miniature experiment of artificial icing, it can better control the leakage of power during the experiment.
The artificial way is used to simulate the natural climate. At the present stage, this experimental way does not reach the unity of ideas. After summarizing many experiments, the following suggestions are made: In the experiment of artificial icing, the simulated climate, wind speed, fog and other influencing factors were adjusted to a stable state, and the spray volume was set as (60±2) L/ (h·m2). The wind speed of < 100m water was < 3m/s during the experiment, and the instability of the experiment was < 10%. The larger volume of water could increase the wind speed. Make the temperature of the cooled water contact with the surface of the experimental body < 0℃, where the deflection Angle of the wind should be 45°.
2. Research on insulator icing and electrical test methods
(I) Relevant preparations before the experiment
Before conducting experiments related to artificial icing of insulators and power generation, strict preparation should be carried out. Rigorous preparation can reduce problems in the process of experiments to a certain extent and improve the accuracy of experimental results. During the freezing period, the simulated insulator showed characteristics such as power tolerance and flashover during the freezing period. Before the experiment, no changes were made to its temperature, freezing rain and other conditions. The experiment in melting period simulates the electrical properties of the melting process of the insulator's surface ice. Flashover faults occur frequently in this process, and its electrical properties are an important basis for the design of the experiment. Before the experiment, the insulators covered with ice were dry frozen for 15 minutes. The insulators were kept at the same temperature as the outer ice sheet, and the water on the outer ice sheet was completely solidified. It is not necessary to consider the speed of temperature rise before the temperature of water solidification rises to -2℃. After the temperature is stabilized, it should be controlled at 2 ~ 3℃/h. Here, it should be careful not to let the temperature rise too fast so as to avoid the phenomenon of ice falling off the surface.
(2) Ice coating on insulators and electrical test methods
Insulator's electrical properties have the characteristics of tolerance and flashover during the ice coating and ice melting stage, but there is no clear regulation on it at this stage. The dirty insulator method is selected for experiment based on the experience of multiple tests. There are several test methods in the experiment process. First, the maximum withstand voltage U2 is the maximum voltage of the insulator under the ice-covered state. The test content of the ice-covered insulator under this voltage is as follows: when the withstand voltage U1 = 0.95U2, the first, second and third test results are all withstand; When the tolerance voltage is U2, the first test result is tolerance, the second test result is flashover, the third test result is tolerance, and the fourth test result is tolerance. When the withstand voltage U3 = 1.05U2, the first test result is flashover, and the second test result is flashover. It can be seen from this test that the voltage U2 of the insulator is tolerated in three of the four tests when the insulator is covered with ice. When the voltage U3 is higher than U2%5, the number of flashover times in the experiment is 2, so it can be judged that U2 voltage is the most tolerated in the test. The second is the experiment with U50 voltage, the tolerance degree of which is 50%. Under the condition that other factors of icing do not change, 10 effective experiments are carried out, U1 is set as the applied voltage, n1 is set as the number of experiments to test U1, and when the value of N is equal to 10, it is the statistical number of effective experiments. So U50 is equal to 1 over N sigma n1 u1. When the indoor temperature is less than 15℃, the insulator sample tested for 15 minutes is gradually covered with ice, and the spray stops after 5s at 25 seconds. Third, the average flashover method is used to apply voltage. In this method, voltage is applied to insulator samples until flashover occurs during the ice-covering and ice-melting stages, and power transmission is stopped. After a while, voltage is raised again until flashover occurs, and the average voltage is obtained several times. U = (1/n) ∑ (Uf1+Uf2+... +Ufn1).
(3) Comparison of several electrical tests on insulator icing
In the pressure resistance experiment, flashover frequency is less, so it is not easy to cause insulator burns and other damage. The final result of the experiment in this way is relatively accurate, but the experiment time of this method is longer and it cannot test the flashover voltage of the insulator in the stage of ice covering and ice melting. The average flashover test method is relatively simple and can get the test result quickly. However, the test times of this method are usually 4-6 times, and the error rate of experimental results is high. The U-shaped curve method can be used to deal with the experimental results according to the law of flashover in the melting stage of the insulator, but this test method can only be used in the melting stage of the insulator. Average flashover and U-curve tests require multiple flashover phenomena to be tested, first method > 4 times, second method > 4 times.
3. Conclusion
In a word, there are many test methods for insulator icing and its electricity, but there is no clear relevant standard at the present stage. After many tests, it is found that the most cost-effective method is the U-shaped curve method, which can simplify the experimental process and display the experimental results more clearly. Insulators have certain pollution during the ice-covered period, which is related to the appearance of flashover. Therefore, power supply should be selected uniformly.