Analysis Of Voltage Sag Characteristic Under Main Network Fault In Dongguan Power Grid

Electric energy is a kind of secondary energy with economy,cleanliness,practicability and easy conversion,transportation and control.As a special commodity,power quality directly affects the operation characteristics of electrical equipment and the safe operation of power grid.Therefore,power quality is of great significance to the operation of social production and people's life.Voltage sags,as a common problem of power quality,exist in power system for a long time.Voltage sags lasting only a few cycles may have a significant impact on electrical equipment,resulting in irreversible economic losses.Therefore,exploring the basic characteristics of voltage sag and predicting the risk of voltage sag are of great significance to improve the reliability of power grid operation.Firstly,the basic concept of voltage sag is introduced.The main causes of voltage sag and the characteristics of voltage sag caused by different disturbance sources are analyzed.The characteristics of voltage sag caused by no-load operation of transformer,start-up of large induction motor and short-circuit fault are emphatically explored.The propagation mechanism of voltage sag is analyzed in terms of the amplitude variation characteristics of voltage sag at PCC nodes and the distance profile between critical distance and sag.The phasor diagram of phase voltage and line voltage characteristics under single-phase grounding fault,two-phase inter-phase fault,two-phase grounding fault and three-phase short-circuit fault and the voltage calculation formula are given.Then,taking the typical accident of voltage sag caused by main network fault as an example,the influence characteristics of voltage sag on the operation of power network are analyzed,the characteristics of voltage sag caused by multiple line faults of different voltage levels causing large-scale voltage sag on the AC bus voltage of each side of substation are explored,and the effect of voltage sag on the main network and distribution network is analyzed.The user load sensitivity is analyzed and classified according to the impact of voltage sag on the main industrial sensitive equipment.Finally,the calculation of the load tripping amount in the case of voltage sags in the grid is carried out,and the calculation model of the load tripping amount is established.The corresponding load tripping amount is calculated when the voltage of each node is sagged,The example shows that the method is small in workload,has good operability and has good practicability.