بەشداری بە شەرەوەکان لە گشتی کورت کردنی جاری بۆ ئامێری کارکردن
Nehatina Rastîn a Wergerandina Baranê û Paşeyên Pre-Strike da Switchgear
Da switchgear, bêyî tekerî da circuit breakers (CB) û load break switches (LBS), wergerandina baranê ji rewşa ku pêkhatên di dema kevankirin de destpêkirin. Ev proses nabeş e ku li dema ku pêkhatên fisikî têkêvin da destpêkirin, lê dikarin çend milesekûn pêş ve bigereke yên pre-strike. Li jêr heye rastîna nehata bi vê rengayê û piştgiriyên wê.
Pre-Strike: Destpêkirina Arc Pêşda Têkêvekirina Pêkhatan
Dielectric Breakdown: Di dema ku pêkhatan xwe berhêl bikin da kevankirin, mediuma izolatekirina (wisa air, SF6, an vacuum) di navbera wan de divê breakdown bide. Ev li gor ê ku dengiya elektrikî li navbera pêkhatan da ku hêsan dikin zêdetir bike. Wanke dengiya dibejînê ji dengiya dielectric strength ya mediuma izolatekirina veguhere, navbera wan breakdown bide û arc îlavekirin.
Build-Up Dengiya Elektrikî: Dengiya elektrikî di navbera pêkhatan de zêdetir bike wanke hêsan bikin. Dengiya yê li gor ê ku bi tensiona di navbera pêkhatan de proporsiyonal û bi derexa navbera wan de inversely proportional be. Wanke dengiya bêdibejîne, hêsan bike ionization ya moleculeya gas di navbera wan de, li ser ber vê yekam rota transparan bide ji bo baranê da ku bergebe.
Destpêkirina Arc: Arc destpêkirin wanke pêkhatan fisikî têkêvin, lê çend milesekûn pêş. Ev destpêkirina arc ê li navenda pre-strike nîse. Da pre-strike, arc di navbera mezin a pêkhatan de form bide, û baran ê li ser arc bergebe ne ji bo wait kirina pêkhatan da ku fisikî têkêvin.
Piştgiriyên Pre-Strike
Melting Excessive ya Surfaceyan Pêkhat: Eger energya di pre-strike de yeke mezin be, divê melting excessive ya surfaceyan pêkhat bide. Ev li gor ê ku tekerî da short-circuit conditions, ku baranê zêde ye. Metala molten li ser surfaceyan pêkhat dikare weldan bide, ku surfaceyan du têkêvin.
Welding of Contacts: Contacts welded dikare prevent bike switching device ji bo respondkirina wekhevî da opening command. Eger mechanisma operasyonê da switchgear force enough nabeş da breaking welded points, device dikare fail bike open properly, li ser ber potential safety hazards û equipment damage.
Short-Circuit Current Characteristics: Short-circuit currents zêdetir component DC din, ku dikare peak value ya current da bibe zêde yên pure AC short-circuit current. Peak current increased dikare exacerbate effects of pre-strike, leading to more severe contact damage and welding.
Arc Voltage Dependence: Voltage across the arc (arc voltage) highly dependent on interrupting medium used in switchgear. Even with very short arc lengths, can be significant voltage drops near electrodes. This because arc resistance not uniform along length, and regions near electrodes tend have higher resistance due concentration heat and ionized particles.
Making Under Short-Circuit Conditions
Circuit Breakers (CB): In circuit breakers, making operation under short-circuit conditions particularly challenging. High current levels and presence of DC component can lead intense arcing and contact damage. Modern circuit breakers designed with advanced materials and cooling mechanisms to mitigate these effects, but pre-strike remains concern.
Load Break Switches (LBS): Load break switches also susceptible to pre-strike during making operation, especially high-current applications. However, LBS devices typically used lower-voltage and lower-current applications compared circuit breakers, so risk severe contact damage generally lower.
Stages of Making Operation in Switchgear
Making operation of switchgear divided into several stages, as shown figure:
Stage 1: Initial Approach of Contacts: Contacts begin move toward each other, and electrical field between them starts build up. At stage, no current flows, but potential for pre-strike increasing.
Stage 2: Pre-Strike Arc Formation: As contacts get closer, electrical field exceeds dielectric strength insulating medium, causing dielectric breakdown. Pre-strike arc formed, and current begins flow through arc before contacts touch.
Stage 3: Contact Touch and Arc Transfer: Contacts finally make physical contact, and arc transfers from gap between contacts to contact surfaces. Current continues flow through now-closed circuit.
Stage 4: Steady-State Operation: After contacts fully closed, system enters steady-state operation, and current flows through closed contacts without any arcing.
Mitigation Strategies
To minimize effects of pre-strike and contact welding, several design and operational strategies can employed:
Use of High-Dielectric-Strength Insulating Mediums: Using insulating mediums high dielectric strength, such as SF6 gas or vacuum, can reduce likelihood of pre-strike by requiring higher electrical field initiate breakdown.
Advanced Contact Materials: Using contact materials high melting points and good thermal conductivity can help reduce contact damage during pre-strike. Materials like copper-tungsten alloys commonly used high-voltage switchgear.
Cooling Mechanisms: Incorporating cooling mechanisms, such as puffer systems or forced gas flow, can help dissipate heat from arc and reduce temperature contact surfaces, minimizing risk welding.
Mechanical Design Enhancements: Ensuring operating mechanism provides sufficient force break any welded points during opening operation can prevent switchgear failing open properly.
Protection Systems: Implementing protection systems, such as overcurrent relays fault detection mechanisms, can help detect and respond short-circuit conditions quickly, reducing duration intensity arc.
Conclusion
Pre-strike phenomenon, where arc initiated before contacts physically touch, critical aspect making operation in switchgear. Can lead excessive contact damage, welding, potential failure switching device. Understanding factors contribute pre-strike, such as electrical field build-up characteristics insulating medium, essential designing operating reliable switchgear. By employing appropriate mitigation strategies, such using high-dielectric-strength insulating mediums, advanced contact materials, cooling mechanisms, effects pre-strike minimized, ensuring safe reliable operation switchgear both circuit breakers load break switches.
