Simulation Study on the Transient Characteristics of HVDC Voltage Divider and Their Effects on undervoltage sensing protection

In order to analyze the transient characteristic of voltage dividers in HVDC systems, the transfer function of DC voltage divider is derived. Analysis results show that the characteristics of DC voltage divider are determined by both two-stage resistor-capacitor voltage bleeder circuit and isolation amplifier circuit. Especially, if the parameters of the resistors and capacitors in two-stage bleeder circuits are all match well, cutoff frequency of the isolation amplifier will become the most key parameter, which determines the transmission characteristics of divider. When the cutoff frequency of isolation amplifier decreases, the rise time of the step response of DC voltage divider increases significantly. Furthermore, the effects of the transient characteristics of DC voltage divider on undervoltage sensing protection are also analyzed by simulation. Simulation results indicate that the fault component of the voltage at the secondary side of divider is much smaller than that in the first side, when the short fault occurs. Therefore, the sensitivity and the anti-resistant capacity of the protection are also decreased. Increasing the cut-off frequency may be an effective way to increase the sensitivity of such protection.