Development Of Power Frequency Flat-Topped Sinusoidal Wave Power Supply

Through investigation of several domestic series compensation projects, it is found that malfunction in the spark gap occurred many times for each of the series compensation integrators and the reasons remain unknown.Presently, the spark gap discharge test is carried out under power frequency sinusoidal wave. However, the practical waveform applied on spark gaps is similar to power frequency flat-topped sinusoidal wave due to action of the voltage limiter (MOV) in the actual projects. There is no relevant research about spark gap discharge characteristic differences between power frequency sinusoidal wave and power frequency flat-topped sinusoidal wave up to now, although it attracts more and more attentions of the power industry. Therefore, a proposal of spark gap recovery voltage test requiring the use of power frequency flat-topped sinesoidal wave voltage was added to the latest version of IEC60143-2SERIES CAPACITORS FOR POWER SYSTEMS-Part2:Protective equipment for series capacitor banks. In order to carry out the research of spark gap self-discharge characteristics under power frequency flat-topped sinusoidal wave, it is needed to develop a high voltage test power supply which can produce power frequency flat-topped sinusoidal wave. The power supply will be used in spark gap self-discharge test to get more practical discharge characteristic for spark gap distance setting.The traditional flat-topped sinusoidal wave generator is realized by using linear and non-linear resistors connected in series. This realization has disadvantages of poor flexibility, and the resistors produce a lot of heat which makes the testing time being difficult to control. For many shortcomings of the traditional realization, this paper designs a new type of power frequency flat-topped sinusoidal wave power supply which is based on microprocessor and high-power op-amp chip, and through a step-up transformer generates a high-voltage power frequency flat-topped sinusoidal wave voltage for spark gap discharge testing.The design of signal generator, power amplifier and test transformer are core parts of this paper, and the working status of these devices will directly affect the quality of output waveform. Signal generator uses a microprocessor to achieve overall control, and uses D/A converters to realize dynamic regulation of the waveform and its amplitude, and output it after filtering and isolation. Proteus software has been used to perform simulation of the signal generator, and proved the feasibility. The inherent stray parameters of test transformer may cause the waveform distortion. In order to determine the extent of the impact, theoretical analysis is given first. It is found that the output waveform is affected greatly by the transformer damping ratio. Then the equivalent parameters of the cascaded transformer are measured by using high-low frequency method, and an equivalent circuit is built up and simulated in the Matlab/Simulink environment. The simulation result shows clearly that oscillations do exist in the transformer output waveform, and therefore proves the validity of theoretical analyses. Finally, both increasing of the transformer damping ratio and modifying of the waveform data code are proved by using Simulink simulation to be effective ways to obtain a high precision waveform, and the key design parameters of power amplifier circuit are determined. According to the design parameters of the power amplifier chips, APEX’s high current power amplifier chip PA52is selected as the core of the power amplifier circuit. While by adding the feedback, voltage boost and protection circuits, a basic circuit framework is formed to ensure the reliability, availability, and operability. Pspice simulation software is used to confirm the feasibility of the design. Ultimately the basic hardware circuit is determined, a prototype is developed through several experiment and debugging in the laboratory, and related experiments are carried out. The test results show that the performance can meet the design requirements.Although the initial purpose of the subject is to provide a technical measure for testing the self discharge voltage of spark gaps with a more practical waveform as being applied in real series compensation, this test power supply, by programming, is suitable for generating arbitrary voltage waveform to meet a variety of electrical equipment testing requirements. Therefore, the study of this issue is of universal significance.