FG-XHG arc suppression, harmonic suppression and overvoltage protection device

Product Introduction

For a long time, most of China's 3-66KV power grids have adopted a neutral point ungrounded operation mode. This type of power grid has a simple structureThe advantages of low investment and high power supply reliability. When a stable single-phase grounding fault occurs in the power grid, the system line voltage remains unchanged, but the ground voltage of the non fault phase rises to the line voltage. Due to the insulation of the electrical equipment in the system, it can withstand the strength of the long-term line voltage and operate for two hours with the fault. However, if the unidirectional grounding fault that occurs in the system is intermittent arc grounding, it will generate an overvoltage of up to 3.5 times the peak phase voltage in the system. If such a high overvoltage is applied to the power grid for several hours, it will damage the insulation of electrical equipment and even cause normal relative to ground insulation breakdown, which will develop into a phase to phase short circuit accident. During the intermittent arc grounding process, a multi frequency oscillation circuit will also be formed, which not only generates high amplitude relative to ground overvoltage, but also may cause high amplitude phase to phase overvoltage, causing insulation flashover between phases and resulting in phase to phase short circuit accidents.

With the large-scale technological transformation of urban and rural power grids in our country, the distribution networks in urban and rural areas must be developed towards cableization. The system's ground capacitance current is gradually increasing, and the problem of arc grounding overvoltage is becoming increasingly serious. Operating experience has shown that when this type of power grid develops to a certain scale, internal overvoltage, especially the isolated light grounding overvoltage generated when the grid experiences single-phase intermittent isolated light grounding, and the ferromagnetic resonance overvoltage generated under special conditions, have become a major threat to the safe operation of such power grid equipment, among which single-phase arc grounding overvoltage is the most serious. In order to solve the above problems, many power grids install arc suppression coils at the neutral point of the grid. When a single-phase arc is grounded in the system, the inductive current generated by the arc suppression coil is used to compensate for the capacitive current at the fault point, reducing the flow of fault current and achieving the goal of natural arc extinguishing. Operating experience has shown that although arc suppression coils have a certain effect on suppressing intermittent arc grounding overvoltage, some problems have also been found in the use of arc suppression coils.

Due to the diversity of power grid operation modes and the randomness of arc grounding points, it is difficult for arc suppression coils to effectively compensate for capacitive current. Moreover, arc suppression coils only compensate for power frequency capacitive current, while the actual current passing through the grounding point not only includes power frequency capacitive current, but also contains a large amount of high-frequency current and resistive current. In severe cases, only high-frequency current and resistive current can maintain the continuous combustion of the arc.

When the power grid experiences non grounding faults such as disconnection, non omnidirectional, and capacitive coupling of the same pole lines, the asymmetric voltage of the power grid increases, which may cause the automatic adjustment controller of the arc suppression coil to misjudge the grounding of the power grid and act. At this time, a high neutral point displacement voltage will be generated in the power grid, causing a significant increase in one or two phase voltages in the system, resulting in damage to other equipment in the power grid.

The arc suppression coil has a large volume, multiple components, high cost, occupies a large installation site, and is complex to operate and maintain. Moreover, as the power grid expands, the arc suppression coil also needs to be replaced, which is not conducive to the long-term planning of the power grid.

At present, the domestic power grid adopts the method of grounding through small resistors. Although it suppresses the overvoltage caused by arc grounding and overcomes the problems of arc suppression coils, it sacrifices the reliability of power supply to users. All faulty lines are cut off and the types of metallic or arc grounding faults cannot be distinguished; The metallic grounding fault lines that do not pose a risk of arc grounding overvoltage have also been cut off, expanding the scope and duration of power outages. Due to the increased fault current, the arc grounding exacerbates the burning of the fault point.

To this end, our company has developed the FG-XHG arc suppression, harmonic suppression, and overvoltage protection device, which can limit the phase to phase and phase to ground overvoltage of neutral point non effective grounding systems within the safe range of the power grid, completely solving various overvoltage threats to the power grid and improving the reliability of power supply safety.

Working principle

1. When the system experiences arc grounding, the microcomputer controller determines the grounding phase and arc grounding type based on the transmitted voltage signal, and issues instructions to close the vacuum contactor of the faulty phase, changing the system from an unstable arc grounding fault to a stable metallic grounding fault. The ground voltage of the faulty phase drops to zero, the arc light at the original grounding fault point disappears, and the ground voltage of the other two phases rises to the line voltage.

After the vacuum switch is activated for a few seconds (depending on the grounding performance), the microcomputer ZK disconnects the faulty phase's vacuum switch. If there is no arc grounding fault after the vacuum switch is disconnected, it indicates that the grounding fault is temporary and the system resumes normal operation; If the arc grounding fault occurs again after the vacuum switch is disconnected, the microcomputer controller ZK will recognize this fault as permanent arc grounding. At this time, it will issue another command to close the vacuum switch of the faulty phase. ZK will send an alarm signal according to the pre-set program to inform the duty personnel of the phase of the fault. The brief overvoltage that occurs during the grounding process of the vacuum switch is limited by TBP.

After the fault phase vacuum switch is grounded for the second time, it will no longer separate. Only when the fault line is automatically or manually cut off, the central control room or local will issue a reset command to ZK. After ZK receives the reset command, the fault phase vacuum switch will be disconnected and the system will resume normal operation.

2When the system resonates, the microcomputer controller ZK instantly connects a high-power resonant resistor to the open delta winding of the PT, using the resonant resistor to destroy the resonance parameters of the system, consume the resonant power, and eliminate the resonance fault of the system

3. This device is equipped with a dedicated low current grounding option module, which can be used in conjunction with the arc suppression device.

Device features

1. The device has a fast operating speed, which can quickly eliminate intermittent arc light and stable arc light grounding faults, suppress isolated light grounding overvoltage, prevent accidents from further expanding, and reduce the accident tripping rate of the line.

2. It can limit the atmospheric overvoltage and operational overvoltage of the system to a lower voltage level, ensuring the insulation safety of the power grid and equipment.

3. It can quickly and effectively eliminate the resonance overvoltage of the system, prevent long-term resonance overvoltage from damaging the system insulation, and prevent resonance overvoltage from damaging the lightning arresters and small inductive loads installed in the power grid.

4. After the device is activated, a capacitor current of 200A is allowed to pass continuously for at least 2 hours. Users can complete the load transfer switching operation before handling the faulty line.

5. Accurately locating single-phase grounding fault lines is of great significance in preventing the further expansion of accidents and reducing the workload of operation and maintenance personnel.

6. Due to its mechanism of limiting overvoltage being independent of the magnitude of grid current, its protection performance is not affected by changes in grid operation mode or grid expansion.

7. The voltage transformer in this device can provide system voltage signals to measuring instruments and relay protection devices, and can replace conventional PT cabinets.

8. Capable of measuring the single-phase grounding capacitance current of the system.

9. Simple structure, small size, easy installation and debugging, and wide applicability.

10. Compared to the arc suppression coil system, it has a higher cost-effectiveness.

11. The line selection function can accurately select the grounding line regardless of the type of grounding fault that occurs in the system.

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