Sulfur hexafluoride (sulfur hexafluoride) is a colorless, odorless, non-toxic, non-flammable and stable gas with chemical formula SF₆ its molecular weight is 146.07 and its density is 6.1 kg/m3 at 20°C and 0.1 MPa, which is about 5 times of the density of air. Sulfur hexafluoride is gaseous at room temperature and pressure, its critical temperature is 45.6°C, the temperature of the triple-phase point is -50.8°C, and the temperature of the sublimation point at atmospheric pressure is -63.8°C. The molecular structure of sulfur hexafluoride is octahedrally arranged, with small bonding distance and high bonding energy, so its stability is high, and its compatibility with electrical structure materials is similar to that of nitrogen when the temperature does not exceed 180°C.

SF6 is a strong electronegative gas, its molecules are very easy to adsorb free electrons and form a large mass of negative ions, weakening the collision ionization process in the gas, so its electrical insulation strength is very high, in a uniform electric field is about 2.5 times the insulation strength of air. SF6 gas in t ≈ 2000K thermal decomposition peak, so in the AC arc current over zero, SF6 on the arc of the cooling effect is much stronger than air Therefore, its arc extinguishing ability is about 100 times that of air. Because of its excellent arc extinguishing and insulating properties and good chemical stability, SF6 gas has been used as an arc extinguishing medium for high-voltage circuit breakers since the late 1950s. In the ultra-high voltage and extra-high voltage circuit breakers, SF6 as an interrupting medium has replaced oil, and has replaced compressed air in large quantities.

Sulfur hexafluoride is an asphyxiant that causes breathing difficulties, wheezing, blue skin and mucous membranes, and generalized cramps at high concentrations. After inhaling a mixture of 80% sulfur hexafluoride + 20% oxygen for a few minutes, the human body will experience numbness of the limbs and even death by asphyxiation. China stipulates that the allowable concentration of sulfur hexafluoride gas in the air between operations should not be greater than 6g/m3 or the oxygen content in the air should be greater than 18%; for short-term exposure, the allowable concentration of sulfur hexafluoride gas in the air should not be greater than 7.5g/m3. sulfur hexafluoride is pharmacologically inert gas, low toxicity but has asphyxiating effect on human body.

System Composition:

1.1Collection device

It includes sulfur hexafluoride gas collector, sulfur hexafluoride gas concentration transmitter, oxygen transmitter, temperature transmitter, humidity transmitter, and infrared sensor to detect whether there are people entering the distribution room.

1.2Monitoring of host devices

Complete data display, alarm data storage, sending control commands, alarm control, alarm query, etc. When an alarm signal occurs, the system should be able to automatically start the fan exhaust, and the exhaust time can be set flexibly.

 1.3Alarm devices

When the concentration of sulfur hexafluoride gas and humidity data in the distribution room environment are higher than the set alarm value or the oxygen content is lower than the set alarm value, the equipment outputs an alarm signal and can issue an audible and visual alarm to alert relevant personnel and take further measures.

Technical Requirements:

1.Ambient temperature:-5℃~+70℃;Relative humidity:≤85%;Input voltage:220×(1±10%)VAC

2.Appearance system shell paint film should be complete and uniform, no defects, no rust, no cracks. The connection of each part is free of looseness, the plating layer of the plating parts should be smooth, no leakage of plating, spots and rust.

3.Monitoring sampling points

3.1The sampling point of sulfur hexafluoride gas in the distribution room; set a sensor below the connection of each interval, because the density of sulfur hexafluoride gas is about 5 times of air density, the sampling point must be in the lowest place below the tank containing sulfur hexafluoride gas.

3.2Oxygen sampling point in the distribution room: an oxygen transmitter is placed below the coupling of each interval

3.3Sampling points of temperature and humidity inside the distribution room: one temperature and humidity sensor is placed in each room

Function：

1.Sampling detection function

1.1Sulfur hexafluoride gas concentration

Measurement range:0~1500×10 Accuracy:±5%FS,±10%FS,±15%FS

Note: Due to the different detection theory and methods: such as semiconductor method, electrochemical method, laser method, etc., so there will be different accuracy.

1.2Oxygen content

Detection range:5%~25%;Accuracy:±1%

1.3Temperature display

Range:-50℃~+100℃Accuracy:±1%S

1.4Relative Humidity Humidity

Range:1%~99% Accuracy:±5%

2.Alarm function

2.1Sulfur hexafluoride gas concentration alarm

When the concentration of sulfur hexafluoride gas in the environment at the gas collection point is higher than the set alarm value, the system shall issue an alarm signal and output a control signal to start the fan.

2.2Oxygen level alarm

When the oxygen content in the environment of the distribution room is lower than the set alarm value, the system should issue an alarm signal and output the control signal to start the fan.

2.3Humidity Alarm

When the humidity in the distribution room is higher than the set alarm value, the system should issue an alarm signal and output the control signal to start the fan

2.4Personnel entry alarm

The distribution room is equipped with infrared sensors with a sensing range of more than 3 m. When a person enters, the system should issue an alarm signal and output the control signal to start the fan.

2.5Alarm parameter setting

The alarm value of sulfur hexafluoride gas concentration, oxygen content and humidity can be set by the authorized person (or the responsible person) as needed. Automatic exhaust, forced exhaust and manual exhaust mode can be set, and the time of automatic exhaust and forced exhaust can be set flexibly.

3.Display memory function

It can display the status of the monitored object in real time, with operation interface and man-machine communication function, and memory function for the occurred alarm indicator, and the memory time can be saved for 5 years.

4.Remote transmission function

It can realize wired or wireless data transmission function to transmit the real-time monitoring data and alarm information of the system to the relevant equipment far away, and can connect with the existing communication equipment on site such as power plants, substations and high-voltage switchgear manufacturers to transmit real-time data and alarm information to the field equipment.