What Is the Main Function of the SF6 Gas Density Micro-Water Online Monitoring Device?

SF6 Gas Density Micro Water Online Monitoring Device is mainly used for online monitoring of SF6 gas's micro water content, temperature, and their changing trend in circuit breakers. When there is a fluctuation in the related indicators of SF6 gas, it provides a change curve. When the indicators exceed the standard and reach a dangerous condition, it alarms or automatically starts the alarm device, and uploads the monitoring data to the upper monitoring host and management center in real time to ensure the safe operation of the equipment and the whole system of the substation.

Why do we need to use the SF6 Gas Density Micro Water Online Monitoring Device?

During the operation of SF6 electrical equipment, SF6 gas leakage from the internal electrical equipment and the penetration of external moisture into the high-voltage electrical equipment will inevitably occur, resulting in a decrease in the SF6 gas density and the presence of excessive micro water content in the SF6 gas, posing a safety hazard to the high-voltage electrical equipment.

The leakage of SF6 gas and the penetration of external moisture into the electrical equipment occur simultaneously. Leakage causes a decrease in the SF6 gas density, which reduces the insulation performance and arc extinguishing performance inside the equipment. An increased water content in the SF6 gas leads to condensation, and under the impact of the arc, a trace amount of H2O reacts with SF6 and metal, producing toxic and corrosive gases, damaging the insulation and threatening safety operation. The leakage of SF6 gas and toxic corrosive gases from the equipment poses a risk to human health and increases the greenhouse gas effect in the environment.

SF6 Gas Density Micro Water Monitoring Principle and Implementation Method

When the gas chamber of high-voltage equipment is filled with SF6 gas, its insulation or arc extinguishing requirements are often determined by the concept of SF6 gas density. This is because the insulation strength inside the SF6 gas chamber depends on the size of the SF6 gas density, which is the number of molecules of SF6 gas per unit volume and is independent of temperature. The size of the density value is reflected by the inflation pressure at 20℃. In order to ensure the safe and reliable operation of SF6 gas insulation equipment, it is necessary to monitor the SF6 gas density value instead of the gas pressure.

•  When the gas density is constant, the breakdown strength of SF6 gas is independent of temperature;

  
  

•  When the pressure is constant, the breakdown strength of SF6 gas decreases as the temperature rises (as the temperature rises, the SF6 gas density gradually decreases).

Because the pressure changes with temperature under constant density, different density curves correspond to different changes in pressure. Therefore, in order to correctly reflect whether the change in pressure is caused by leakage or by temperature, it is necessary to use temperature compensation or correction methods to make the reading of the pressure indicator always be the standard pressure value at 20℃, which is equivalent to the density value of the gas chamber. When a leak occurs, the density relay can immediately indicate the density change caused by the leakage. When the density indication value of SF6 gas is lower than the preset alarm value, the density relay gives a signal for alarm refilling, indicating that the leak is not significant and should be refilled so that the equipment can continue to operate to prevent a decrease in insulation performance. In the case of severe leakage, it gives a pair of interlocking contact signals, locking the switch operation, indicating that the equipment cannot operate normally at this time, and any operation may cause accidents.

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