The insulating gas circulation system of the gas insulated switchgear breaks the static distribution of gas in the closed cavity through the synergy of active flow and structural guidance, ensures that the insulating gas (such as SF6) is evenly distributed inside the equipment, and provides a basis for stable insulation performance. This system is not a simple gas flow device, but a precise control system designed for the complex structure inside the gas insulated switchgear, so that the gas density and pressure are consistent in each area to avoid the occurrence of local insulation weaknesses.
The directional drive of the circulation fan is the core power of gas flow. The system has a built-in low-noise, high-reliability circulation fan, which pumps the gas at the bottom or corner of the equipment to key areas such as high-voltage conductors and insulating sleeves through a preset airflow path. The operating parameters of the fan have been optimized to generate sufficient airflow speed to promote gas circulation without causing local turbulence due to excessive airflow (turbulence may cause local electric field distortion). The continuous directional airflow allows the gas that may have been trapped to be "driven" and forms a repetitive cycle in the closed metal shell, ensuring that there is no "dead corner" where the gas is static for a long time, fundamentally avoiding the problem of low local gas density.
The internal flow guide structure guides the gas flow to the key insulation area. The equipment cavity is designed with arc-shaped flow guide plates, grille-type air ducts and other structures. These flow guide components plan the airflow path according to the law of electric field distribution (high field strength areas such as conductor connections and insulation surfaces require higher density gas). For example, at the connection between the busbar barrel and the circuit breaker, the flow guide plate will guide the airflow to the surrounding of the conductor docking surface, allowing the insulating gas to preferentially cover these areas prone to partial discharge; at the corners of the cavity, the arc-shaped flow guide plate can reduce the airflow resistance and prevent the gas from accumulating here. This "on-demand distribution" guidance method allows the gas to form a higher circulation efficiency in key areas and ensure that the gas density at the weak insulation point always meets the standard.
The pressure balance mechanism eliminates the density difference between regions. The different functional modules of the gas insulated switchgear (such as circuit breakers, disconnectors, and busbars) form an overall closed system through connecting pipes, and the circulation system uses these pipes to achieve gas intercommunication between modules. The built-in pressure sensor of the system monitors the gas pressure of each module in real time. When the pressure in a certain area is slightly higher, the circulating fan adjusts the direction or speed to "push" the gas to the area with lower pressure; if the pressure difference is large, the fine-tuning valve on the connecting pipe will assist in the adjustment until the pressure in each area tends to be consistent. The uniformity of pressure directly guarantees the uniformity of gas density, because at the same temperature, the same pressure means the same number of gas molecules per unit volume, and the insulation performance is naturally stable.
The temperature compensation design reduces thermal density fluctuations. The gas density will change with temperature - when the temperature rises, the gas expands and the density decreases, and when the temperature drops, it shrinks and the density increases. The circulation system balances the temperature distribution inside the gas insulated switchgear through the linkage between the temperature sensor and the heating/cooling device: in winter or low temperature environment, the heating belt outside the cavity will moderately heat the lower temperature area (such as the bottom of the equipment and the shady side) to prevent the gas from being too dense and gathering due to low temperature; in summer or high load operation, the heat sink and the fan cooperate to accelerate the heat dissipation in the high temperature area (such as near the current transformer) to prevent the gas from decreasing in density due to high temperature. The uniformity of temperature is further diffused through the circulating airflow, so that the density distribution of the gas inside the equipment is not significantly affected by temperature fluctuations.
Closed-loop control with real-time monitoring and dynamic adjustment improves stability. The system installs gas density sensors and trace moisture sensors at key nodes of the equipment (such as both sides of the insulation basin and near the conductor shield) to continuously monitor the gas status in these areas. When the sensor detects that the gas density in a certain area is lower than the threshold (which may cause the insulation strength to decrease), the control system will immediately increase the power of the circulation fan to enhance the airflow supply in the area; if it is found that there is a trace amount of moisture exceeding the standard in a local area (moisture will reduce the insulation performance), the circulation system will drive the gas to flow through the drying device, remove the moisture and then send it back to the area. This closed-loop mechanism of "monitoring-feedback-adjustment" can correct it in time when the gas distribution is slightly uneven to avoid the problem from expanding.
Redundant design ensures long-term circulation reliability. The circulation system adopts a dual-fan redundant configuration. When the main fan is running, the backup fan is on standby. Once the main fan fails, the backup fan can be started within milliseconds to ensure that the gas circulation is not interrupted. At the same time, the guide structure adopts corrosion-resistant and aging-resistant metal materials to avoid structural deformation caused by long-term airflow scouring (deformation may change the airflow path and affect the distribution uniformity). This redundant design allows the circulation system to maintain stable performance in long-term operation. Even if a single point failure occurs, the backup mechanism can maintain the uniform distribution of gas, providing lasting protection for the insulation reliability of gas insulated switchgear.
Through the coordination of active drive, structural guidance, pressure and temperature control, real-time monitoring and redundant design, the insulating gas circulation system builds a comprehensive and evenly distributed protection system, allowing the gas insulated switchgear to maintain stable insulation performance under various working conditions, laying the foundation for the safe operation of the high-voltage power grid.
