Development Of Capacitor Resonant Overvoltage Protection Device

With the rapid economic development, the use of power electronic device and nonlinearloads has increased year by year, harmonic pollution in the power grid also has become moreand more severe. At the same time, the power company increase using of the capacitor bank alot in order to compensate for reactive power and improve power factor. Harmonic hasadversely affected when it run for reactive power compensated capacitors. On the one hand,the capacitor may not work good because overvoltage or overcurrent or even destruct under acombined action of a harmonic and the system combine under a specific condition, on theother hand capacitors may enlarge harmonics so that harmonic pollution will become moresevere.This research starting from the basic principles of harmonic and resonance, analysis theconditions of the generation of harmonic and the calculation of the resonant frequency, alsodo the resonance analysis and simulation with the actual power grid equivalent model. Thisresearch also analyze the hazards of harmonic for capacitor from the three aspects: amplifiedharmonic current from the capacitor, the capacitor impedance amplifier, the influence of theharmonics on the capacitor operating parameters. This research also analyze the protection ofthe capacitor harmonic, According to national standard (GB/T11024.1-2001), from the capacitorharmonic limit value, capacitor harmonic overload capacity capacitor and harmonicover-voltage and overcurrent protection setting, and propose formula for harmonicover-voltage, overcurrent protection under a single capacitor harmonics or total harmonic.This research discussed the suppression of capacitor with the harmonic current and harmonicvoltage: First from the harmonic source in the power system, reduce the harmonic content ofthe system, thereby reducing the influence which from harmonic to capacitor; Second, to thecharacteristics of the capacitor, allocate a reasonable capacitor parameters (including theseries reactor), reduce capacitors harmonic current injection, thus improve the reliability ofrunning capacitors.DSP is selected as calculated core for the capacitor protection devices and using FPGAfor data acquisition and control. For the outer, the designs are a harmonic acquisition,conditioning circuitry, the FPGA unit circuit and communications interface circuits.DSP module uses eZdsp TMS320F2812as minimum system, and developed the calculation andcommunication program. And developed a human-computer interaction program based onAltai ARM8019industrial grade embedded board,thus the device can able to facilitate theentry of the power grid device parameters,set the limit value for protection,and also canquery the current line, capacitor operating parameters, historical data, historic preservationand so on, and can choose different devices running pattern: At offline conditions, equipmentadjustment information to be manually determined not directly issued; At online condition,the device regulating information directly issued without manual confirmation.Finally, compare the measurement data of the device with standard power qualityanalyzer, and analysis accuracy when device work properly. Comparing the harmonic voltage,harmonic currents the device calculates and the value of theoretical analysis, to obtain theresonance analysis and voltage prediction accuracy.