Paggabas sa gas HV CB

Detalyadong Pagsulay sa Proseso sa Pagpatay sa Arc sa Puffer-Type SF6 Circuit Breaker

Sa puffer-type SF6 circuit breaker, ang proseso sa pagpatay sa arc usa ka kritikal nga mekanismo nga nagtubag sa reliable nga pagputli sa mataas nga current, lalo na sa panahon sa short-circuit conditions. Ang proseso nagsangkot sa interaksiyon tali sa main contacts, arcing contacts, ug usa ka PTFE (Polytetrafluoroethylene) nozzle, nga nagdumala sa flow sa compressed SF6 gas aron mapatay ang arc. Sumala ang detalyadong pagsulay sa proseso sa pagpatay sa arc, step by step:

1. Unang Estado: Main Contacts Open, Current Commutated to Arcing Contacts 

• Main Contacts: Ang main contacts, nga mas dako ug gihimo para sa normal nga load current, gitukod sa labaw sa arcing contacts. Sa unang estado, ang main contacts nagsugod na og open, ug ang current nagi-transfer (commutated) sa arcing contacts.

• Arcing Contacts: Ang arcing contacts mas gamay ug gisudlan para makahandle sa mataas nga temperatura ug presyon nga giproduce sa panahon sa arcing. Sila nagsugod na og open, ug isip sila mabuka, magignite ang arc tali nila.

2. Ignition sa Arc: Ang Arcing Contacts Nagsugod sa Pag-separate 

• Isip nagsugod sa pag-separate ang arcing contacts, ang current magpadayon sa pag-flow sa small gap tali nila, forming an arc. Sa punto niini, ang arc kasagaran stable pa, ug ang PTFE nozzle, nga gipirmahan sa moving contact, nagsugod sa pag-guide sa compressed SF6 gas gikan sa puffer volume patungod sa arc.

• Ang flow sa gas limitado sa unang bahin tungod kay ang cross-section sa arc mahimong dako, lalo na sa high short-circuit currents. Kini nga phenomenon, diin ang cross-section sa arc mas dako kaysa sa diameter sa nozzle throat, gitawag og current clogging. Sa panahon sa current clogging, ang flow sa gas partially blocked sa arc, preventing it from effectively cooling the arc.

3. Build-Up sa Gas Pressure ug Constriction sa Arc 

• Mechanical Movement ug Heat Transfer: Isip nagsugod sa pag-separate ang arcing contacts, ang mechanical movement sa contacts nagsugod sa pag-compress sa SF6 gas sa puffer volume. Giila, ang heat gikan sa arc transfer sa gas, causing its temperature to rise rapidly. Kini nga combination sa mechanical compression ug heat transfer leads to a significant increase in gas pressure within the puffer volume.

• Approach to Current Zero Crossing: As the arc approaches its natural zero crossing (the point where the alternating current passes through zero), the arc's cross-section begins to decrease. This reduction in arc size allows the compressed SF6 gas to flow more freely through the nozzle.

• Powerful Gas Blast: Just as the arcing contacts fully separate, the compressed gas in the puffer volume is released through the nozzle, creating a powerful blast that blows directly onto the arc. This high-velocity gas flow cools the arc rapidly, stretches it, and disrupts the ionized plasma, leading to the extinction of the arc.

4. Extinction sa Arc ug Recovery sa Dielectric Strength 

• Arc Extinguishment: Once the arc is extinguished at the current zero crossing, the flow of current ceases, and the arc no longer exists. The absence of the arc means that the heat source is removed, allowing the SF6 gas to cool down.

• Recombination of Gas Particles: After the arc is extinguished, the decomposed SF6 gas particles (such as SF4, S2F10, etc.) begin to recombine, restoring the original chemical structure of SF6. This recombination process also restores the insulating properties of the gas.

• Dielectric Strength Recovery: The rapid recombination of gas particles and the cooling of the gas lead to a quick recovery of the dielectric strength between the contacts. This ensures that the arc does not reignite when the voltage across the contacts increases after the current has passed through zero.

• Contact Movement Stops: With the arc extinguished and the dielectric strength restored, the movement of the contacts stops. The gas pressure inside the circuit breaker (CB) then stabilizes, and the system returns to a normal, non-conductive state.

Key Points to Note:

• Current Clogging: At high short-circuit currents, the arc cross-section can be larger than the nozzle throat diameter, temporarily blocking the gas flow. This phenomenon is called current clogging. Despite this, the gas pressure continues to build up due to mechanical compression and heat transfer from the arc.

• Puffer Volume and Nozzle Design: The puffer volume is a crucial component that stores the compressed SF6 gas, which is then released through the PTFE nozzle. The nozzle is designed to direct the gas flow precisely onto the arc, ensuring effective cooling and arc quenching.

• Rapid Dielectric Strength Recovery: One of the key advantages of SF6 gas is its ability to quickly recover its insulating properties after the arc is extinguished. This ensures that the circuit breaker can safely interrupt high currents without risking arc reignition.

Conclusion

The puffer-type SF6 circuit breaker's arc quenching process is a highly efficient and reliable method for interrupting high currents, especially during short-circuit conditions. The combination of mechanical compression, gas flow, and the unique properties of SF6 gas ensures that the arc is rapidly extinguished, and the dielectric strength between the contacts is quickly restored. This design allows the circuit breaker to handle large fault currents while maintaining the integrity and safety of the electrical system.