This paper introduces arc extinguishing and overvoltage protection device (XHG). When arc grounding occurs, the device can make fault phase grounding through a group of vacuum contactors which can be controlled separately, so as to eliminate arc completely. The controller detects the fault phase through PT transformer, and then sends out control signal to the fault grounding switch, so that arc grounding becomes metal grounding. Most of the 3-35KV power supply systems in China are neutral ungrounded systems. When single-phase grounding occurs, the power grid can still operate with faults, which greatly reduces the operation cost and improves the reliability of the power supply system. When removing a reactor or a transformer with inductive load, there will be a high overvoltage between the reactor and transformer. Without inter-phase protection, the overvoltage may exceed the inter-phase withstand voltage of the reactor or transformer. During the operation of vacuum circuit breaker, the overvoltage caused by interception, reburning and bouncing will also occur between phases, which will threaten the phase insulation of electrical equipment.
Previous solutions were to install arc suppression coils at neutral points to compensate capacitive currents to suppress the probability of arcing at fault points. Obviously, the purpose of this method is to eliminate arc light, thermostatic element but because of the characteristics of arc suppression coil, it is difficult to compensate capacitive current effectively, especially the harm of high frequency component to power supply equipment can not be overcome. The controller has compact structure and advanced technology. The core of the controller is a signal acquisition and data processing system composed of PIC MCU produced by Microchip Company and some peripheral devices. According to the results of signal acquisition and data processing, corresponding signals are sent out. Pt break line and metal grounding, only alarm but not grounding; when arc grounding occurs in the system, the MCU integrated controller makes judgment and sends out action signal, so that the contactor acts, so that the corresponding phase of the system is transformed into gold grounding. The controller has 485 (or 232) communication port, through which the host computer can access the PC integrated controller. The MCU integrated controller gives the response signal to tell the computer the operation status of arc suppression and over-voltage protection device at the moment.
The host computer can also send instructions to the microcontroller through this interface under windows. The MCU integrated controller is based on the voltage signal of [MSOffice 1] provided by PT. It is based on the neutral point to ground insulation power supply system will appear zero-sequence voltage when the line fault occurs. The zero-sequence voltage will be calculated as the starting signal.
Then, according to the situation of each phase voltage when the fault occurs, the logical analysis and calculation will be carried out to determine the phase difference and grounding attributes of the grounding fault, and then the corresponding treatment will be made according to the results of the determination.
The shunt resistance of the gap is divided into two categories: non-linear resistance and linear resistance. The linear shunt resistance gap is mainly used in the combined overvoltage protector. By using the principle of voltage divider under parallel voltage and high voltage under the power frequency voltage, the impact coefficient of gap is less than 1 under the condition of high impact voltage (high equivalent frequency). Under suitable irradiation conditions, the impact coefficient can reach 0.7, and the clearance structure is simple. At present, the main product of the combined overvoltage protector in power grid is that the inner series gap does not have parallel resistance. Similarly, due to the existence of neutral points in the “four-star” connection, the insulation matching of the protector is more difficult than the gap with parallel resistance. For the need of insulation coordination, most manufacturers assume that the impact coefficient of such clearance is 1 in parameter design. This premise is obviously not valid. The gap impact coefficient without parallel resistance is greater than 1.1. The specific number is related to the material and structure used in the gap of each manufacturer.
At this time, the protection level of the protector depends on the discharge characteristics of the gap rather than the residual voltage of the resistor. Even when the impulse coefficient is 1, the protection level of the combined overvoltage protector is still an ideal coordination value.
Because of the large dispersion of gap discharge, the safe operation of the product leaves a great hidden danger in the design. Therefore, the introduction of gap is mainly to consider the long-term stability of resistor materials, to reduce the resistor withstand voltage, or to achieve a lower level of protection.
However, the introduction of gap can not solve the problems caused by the “four-star” structure of the combined overvoltage protector. It is difficult to achieve insulation coordination, and the structure becomes complex. It also brings about the disadvantages of gap, which is not the future direction of development. When the knife closes, the auxiliary switch is pulled by a small tie rod on the handle to close the normally open node on the auxiliary switch.
When the knife closes, the display screen will display “put into operation”. In this case, when the drive of the contactor is debugged again, the contactor will no longer act, because at this time the knife-gate signal has shielded the debugging action signal software, thus preventing the misoperation of the contactor after operation from causing the contactor to act and lead to grounding. When the fuse is fused, one end of the fuse will pop up a bumper and impact the micro switch. When the fuse signal is detected, the controller will send out an alarm signal and display the corresponding fault phase. When the knife gate is disconnected, the contactor can be detected, which can be detected by several keys on the controller panel.
When we electrify the controller, it can check itself. If the controller itself has problems, the “running” indicator will not be on and the display screen will not be displayed. This device can not be put into operation. If the display screen of the controller only shows the outage (the knife gate is separated) and the time, indicating that the knife gate is separated, then it can be put into operation. Under the time setting function, the system time can be set. The adjusted time display sequence is first year, month and day, then time and minutes.
When fuse fusing, PT breaking, metal grounding and arc grounding occur in the system, the controller will record the nature and time of the fault. Through testing, if everything is normal, the device can be put into operation.
When arc grounding occurs in the system, the MCU integrated controller makes a judgment and sends out action signal to make the contactor act, so that the corresponding phase of the system can be transformed into gold grounding. At this time, the grounding phase is displayed on the controller panel, and an alarm signal is sent out at the same time. When the system undergoes metal grounding, the controller will only send an alarm signal to the central control room, but will not make the contactor move. The panel shows the difference of metal grounding.
Similarly, when the system breaks, the controller will only send an alarm signal to the central control room, but will not make the contactor act. The panel shows different broken lines. When the fuse breaks, the controller displays as shown in the test. Lu Xianqiang, graduated from the Department of electrical engineering and automation, is currently an assistant engineer in the heavy and heavy plate business department of Laigang Group.