| Lightning strikes can seriously affect the normal operation of the power system.When the substation is struck by lightning,the substation grounding grid can quickly discharge the lightning current into the ground,make the potential of the ground grid conductors tend to be balanced,and ensure the safety of equipment and operators in the substation,the grounding performance is directly related to the safe and normal operation of the substation.Existing grounding systems are often designed to evaluate the safety performance of the grounding grid from the perspective of the power frequency response of the grounding grid.However,compared with the power frequency current,the frequency and amplitude of the lightning current are much larger.After it flows into the substation grounding system,it will lead to the rise of impact ground potential far greater than the situation of power frequency fault,and the distribution of ground grid potential is uneven.Only evaluating the power frequency characteristics of grounding grid has certain limitations.The ground potential rise will be coupled to the wire through the grounded cable shielding layer,causing great harm to the secondary equipment,and with the improvement of the substation automation,microelectronic equipment made of highprecision integrated modules is widely used in secondary protection and the control system makes the secondary system extremely susceptible to the interference of the ground potential rise.At the same time,there is no unified standard for lightning and surge protection of the secondary system of the substation.Therefore,it is of great significance to carry out the research on the impact characteristics of the grounding grid and the protective measures of the secondary system.Firstly,this paper uses PSCAD software to establish the overall transient circuit model of the grounding grid under the action of lightning current.The distribution law of transient voltage at each node of the ground network is analyzed.The effects of different lightning current injection points,lightning current waveforms,soil resistivity,ground grid area and mesh size on the impact characteristics of grounding grids are analyzed,and the impacts of transient ground potential rise on the safety of secondary equipment and personnel are calculated.The simulation results show that the calculation method in this paper meets the requirements of engineering practice calculation accuracy and greatly shortens the calculation time.Secondly,use simulation and test methods to study surge protectors used in lowvoltage power supply systems.On the basis of the traditional surge protector,an improved circuit structure was designed.Through a large number of simulation calculations for different combinations and different decoupling inductance values,reasonable internal component parameters were determined,and the simulation proves the effectiveness of the improved circuit.Assemble the actual surge protector and conduct an impact test.The simulation and experimental results are good agreement.Using the built overall simulation model,it is verified that the improved surge protector has a good suppression effect on the transient overvoltage generated by the transient ground potential rise on the low-voltage power supply line.Finally,through theoretical analysis and simulation calculation,the coordination between the multi-level surge protectors and between the protectors and the load is studied.Simulate the three coordination methods when the front and rear varistor voltages are different and the SPD coordination when the cable length is used to obtain the voltage,current,power and energy on the front and rear protectors,select the most reasonable coordination method,and the best range of cable length under this coordination mode.In addition,the software is used to calculate and analyze the oscillation of the RC and RC load voltages under different cable lengths,and obtain the protection range of the surge protector under different types of loads. |
