Youping Tu

Research of insulation properties of polymer materials using in oil-filled transformers under high temperature

Traditionally, oil-filled transformers have utilized densified cellulose paper as the primary conductor insulation. However, cellulosic insulation is a relatively low temperature material and thermal degradation due to overload conditions and long-term aging can lead to transformer failures. In order to improve the structure and insulation performance of oil-filled transformers, this paper choose 4 insulation materials with special applications to research, electrical properties of polymer before and after aged under 130°C at different times have been examined, the examined dielectric parameters are dielectric constant, dissipation factor and ac electric breakdown strength. The characteristics of dielectric constant and dissipation factor versus temperature before and after aged under 130°C at different times have been analyzed. Preliminary results show that PTFE and Polycarbonate are ideal substitutes of cellulose paper.

Study on hydrophobicity recovery characteristics and mechanism of HTV silicone rubber after corona deterioration

The hydrophobicity recovery characteristics of HTV silicone rubber (SIR) at different corona deterioration stage have been investigated with static contact angle method. The surface microstructure variation with the corona deterioration processing, along with the chemical composition change at the end of corona discharge have been analyzed by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. Experiment results show that the hydrophobicity recovery characteristics vary with corona deterioration processing and the hydrophobicity recovery rate goes through four periods, which are increase-reduction-increase-reduction. Moreover, after corona deterioration a certain time, the hydrophobicity cant recovery back to the initial value, even if the storage time is long enough. On the basis of surface appearance variation of HTV SIR, as well as the SEM, FTIR and XPS analysis results, the hydrophobicity recovery courses are explained in details and it is confirmed that the changes of surface microstructure and chemical composition act as important roles influencing the recovery speed and grade of hydrophobicity of HTV SIR.

A method to detect the deterioration of HTV silicone rubber under corona discharge

This paper has investigated the thermally stimulated current (TSC) characteristics of the deteriorated HTV silicone rubber under varied corona discharge duration, the hydrophobicity, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) of the corresponding test samples have also been measured. The experimental results show that the TSC characteristics of HTV silicone rubber gradually varied with the corona deterioration process, and it has relationship with the change of its hydrophobicity, SEM, and also FTIR. As a result, it could be suggested that the TSC characteristics might be used as an effective index for assessing the corona deterioration of HTV silicone rubber.

Hydrophobicity Loss of HTV Silicone Rubber after Corona Discharge

This paper presented the results of a study on the hydrophobicity loss of HTV silicone rubber under the different corona discharge conditions. The experimental results show that the speed and grade of hydrophobicity loss vary with the corona discharge time and the corona intensity. Moreover, it is noticed that the hydrophobicity would not become worse as long as the corona intensity keeps below a certain level.

Study on DC Breakdown Characteristics of Polyimide at Cryogenic Temperature

With the rapid development of superconducting technology, the electrical characteristics of insulating materials at cryogenic temperature has become an important factor which influences the operating performance and reliability and has attracted extensive attention. This paper mainly deals with a new test system which is used to produce a vacuum cryogenic environment for studying the DC insulation characteristics of polyimide from cryogenic temperature to room temperature. Meanwhile, as the wrap structure is primarily used in superconductive electrical equipment insulation, the DC breakdown characteristics of single-layer and double-layer polyimide films were studied in this paper.

Study of composite insulator leakage current characteristics in contamination and humidity conditions

Formation of contamination flashover arc in composite insulator is closely related to leakage current, which is affected by surface contamination and humidity. In this paper, a composite insulator in service over 6 years was taken as a sample, and leakage current tests were carried out in an artificial climate facility, which can provide experiment conditions with a series of humidity and contamination levels. Based on leakage current information collected from different flashover pattern, reasons of variation in leakage current waveforms were analyzed. The results indicate that, under high humidity conditions, the higher artificial contamination level leads to smaller leakage current phase shift between applied voltage and higher resistive current. The current waveform distortion is considered to be mainly related to harmonic components resulting from arc discharge. Hence, characteristics of leakage current waveforms can be exploited to evaluate surface discharge of the composite insulator.

DC surface flashover characteristics of polyimide under low temperature and low pressure

The insulation system of superconducting power equipment often works under cryogenic vacuum environment. However, due to special cases such as material gas releasing and helium leakage, local low pressure environment is prone to be formed and this will lead to damage the insulation system so as to influence the normal operation of power equipment. Polyimide (PI) has been widely used as insulation material in various superconducting power equipments for its excellent dielectric performance and mechanical properties. In this paper, by using the home-made test system which is developed for testing cryogenic electrical characteristics of dielectrics, a series of tests for studying polyimide films DC surface flashover characteristics have been done at temperature range from 78 K to 300 K under low pressure environment. The test results show that the surface flashover times under low pressure environment have little influence on the DC surface flashover strength of polyimide films. In the pressure range of 10 to 2000 Pa, the flashover strength decreases with the pressure increasing, but the decrement becomes slow gradually. However, the flashover strength increases to a certain extent in the range of 2000 to 3000 Pa.

Effect of Corona on the Hydrophobicity Recovery Characteristics of HTV Silicone Rubber

This paper has investigated the hydrophobicity recovery characteristics of HTV silicone rubber after different corona deterioration time using the static contact angle method. The experimental results show that the hydrophobicity of HTV silicone rubber can get some recovery after the corona deterioration, and the procedure of hydrophibicity recovery would be varied with the corona deterioration condition, moreover, the hydrophobicity would not recover back to the initial value after a certain condition of corona deterioration, even if the storage time is long enough.

Study on the aging characteristics of insulators sheds

As composite insulators have been widely used in power system, the aging of composite insulator has become a threat to safe operation of transmission line. In order to investigate the influence of several aging factors on the sheds of high temperature vulcanized silicone rubber composite insulator, nine pieces of energized sheds on the high voltage end serviced on 500kV transmission lines have been selected as test samples. The salt deposit density (ESDD) and non-soluble deposit density (NSDD) measurements are adopted to measure the contamination accumulation characteristics of composite insulator sheds. In addition, thermally stimulated current (TSC) and hydrophobicity tests are also carried out on the shed samples. It indicates that TSC characteristics have the same tendency with the change of the contamination accumulation characteristics in both sides of one shed, but different from that of hydrophobicity. Combining with the contamination accumulation characteristics, hydrophobicity and TSC characteristics, a conclusion can be drawn that the contamination accumulation and ultraviolet radiation might be the main causes of aging, which are account for the difference of the aging characteristic between the two sides of one shed.

DC Surface Flashover Characteristics of Polyimide at Low Temperature under Vacuum

Polyimide (PI) is widely used as insulation in various superconducting power equipments for its excellent dielectric performance and mechanical properties. The cryogenic vacuum is the actual work environment of the insulation systems of superconducting power equipments. Therefore, the study of polyimide films DC surface flashover characteristics at low temperature in vacuum is of great significance. In this paper, a series of tests for studying polyimide films DC surface flashover characteristics have been done at temperatures from 78K to 300K in vacuum by using the home-made test system which is developed for testing cryogenic electrical characteristics of dielectrics. The test results show that the surface flashover times and temperature both have some influence on the DC surface flashover strength of polyimide films.