Study Of Fast Switch Type Arc-suppression Technology In Urban Distribution Network

The probability of arc grounding fault is high in distribution system and its harm is large.With many cable lines are adopted in urban distribution network,the traditional neutral resonant grounding method has been difficult to meet the requirements of arc suppression.With arc-suppression completely,easy operation and other advantages,switch type arc-suppression device can be applied to a variety of line conditions of distribution network,but there are still some problems in the application,such as the long response time of the device lead to expanding of cable failure,and the device action easily lead to PT ferromagnetic resonance and other issues.Fast switch type arc-suppression technology is based on this device,and the fast switch is used to improve the response speed,and harmonic eliminator is installed to solve the problem of ferromagnetic resonance of PT.The purpose of this thesis is to study the problem of coordinating the operation of fast switch with module of single phase earth fault discrimination,phase selection and line selection,and put forward reasonable and effective technical scheme and process.Firstly,the type and mechanism of fault in neutral point ungrounded distribution network which may cause the change of the zero sequence parameters are studied because the change of the fault feature quantity is the theoretical basis for the discrimination of single phase grounding fault,the phase selection and the line selection.Voltage type arc-suppression principle and the action principle of fast switch based on electromagnetic repulsion mechanism are also studied,which is the key to realize arc-suppression rapidly and completly.Then,the scheme and process of the fast switch type arc-suppression technology are studied.It is proposed to use the neutral point voltage to judge the single phase grounding fault in the system;as for the high-resistance grounding fault,the rise of neutral point voltage is not obvious,so sudden change of the line zero sequence current is applied to judge the fault;through installing thermistor harmonic eliminator on the neutral point in primary side of PT to achieve rapid harmonic elimination,and avoid the impact of resonance on the fault discrimination.The fault phase selection is based on the change of the three-phase voltage amplitude after the fault.Therefore,different selection criteria should be used when transition resistance is different.The zero sequence current of the faulty line is in the opposite direction to the non-faulty line,and the amplitude is larger;the zero sequence current direction of the faulty line is changed after the fast switch close,and the non-faulty line is unchanged.So,the combination of feature of zero sequence current before and after the switch close can complete the fault line selection with high accuracy.Through matching the above process with operation of fast switch,the switch is controlled to quickly close to transfer failure when single phase grounding fault happen,and then disconnect after the arc grounding fault removed,therefore the system will be able to resume normal operation;if the fault occurs in the cable line or a permanent grounding fault happen,targeted operation strategy should be made to ensure minimize the harm of the grounding fault on the system.Finally,EMTP/ATP is used to simulate the principle and process of fast switch type arc-suppression technology.The rationality of the thachnical scheme and process is verified by analyzing the change of the relevant feature quantity.At the same time,operation performance test has been did on the fast switch arc-suppression device.The results show that the device can operate reliably in the conditions of metal,arc and small resistance grounding fault,and the action time is controlled at about 20ms.The insulation damage of arc grounding overvoltage on equipment and line can be eliminated through installing the device,while the hazards of other type grounding fault on the system can be reduced.So the fast switch type arc-suppression device has greater advantages in the urban distribution network.