Mipango na mwaka wa nyuma wa Vitufu Vyenye Kasi ya DC ya Kiwango cha Kutwa kati

Jinsi ya kutumia kitambaa chenye nguvu ya kati:
Kitambaa chenye nguvu ya kati linatumia semiconductors za nguvu kuhakikisha kuwa current ya hitilafu imepigwa. Topologia rahisi ya kitambaa chenye nguvu ya kati iliyopewa kama mfano hapa. Nne diodes na IGCT inawakilisha njia kuu ya conduction, wakati surge arrester unatumika kufunga line inductance ikipatikana hitilafu. Wakati kitambaa chenye nguvu ya kati kimepigwa, IGCT inazima. Kwa sababu ya energy iliyohifadhiwa inductive, voltage juu ya semiconductors inaruka haraka na surge arrester anapaza kuanza kubeba current. Ili kukusanya line inductance, protection voltage ya surge arrester lazima iwe zaidi ya nominal grid voltage. Pia, inatafsiriwa kwamba semiconductors zinaweza kudumu protection voltage ya surge arrester. Faida kuu ya kitambaa chenye nguvu ya kati ni kasi ya pigaji haraka na ukosefu wa vifaa vilivyotengenezwa. Tangu semiconductors zipo katika njia kuu ya conduction, on-state losses huonekana.

Fig. 1: Mfano wa utaratibu wa kitambaa chenye nguvu ya kati

Kitambaa chenye nguvu ya kati kunategemea tu kwenye switch solid-state ili kubeba mizigo nominal na kuhakikisha kuwa current imepigwa. Kwa sababu arc electric imetolewa, mekanismo nyingine inahitajika kutoa energy iliyohifadhiwa katika circuit inductance. Hii mara nyingi hutimizika kupitia metal-oxide varistor (MOV) uliounganishwa parallel. MOV una characteristic voltage/current si linear.
Resistance yake inabaki zuri (kutokana na kuwa open circuit) hadi voltage juu yake irasikia kiwango fulani, pale resistance yake inajaribu kubonyeza current kubeba kwa kinyume na device. Wakati ubebaji MOV pia kubonyeza voltage juu yake kwa thamani moja.
Aina hii ya device mara nyingi hutumika katika systems za high voltage kama surge arrester na pia kama protection device kwa components zenye sensitivity voltage.
Mistopo miwili ya bi-directional solid-state circuit breaker yanavyoonyeshwa kwenye Fig. 2. Wakati breaker amefungwa, devices za semiconductors zote zinatumika, kubeba current kwenye sifa mbili. Wakati wa pigaji current, devices zote zinazima, kuboresha voltage juu yao kuruka hadi MOV anapaza kubeba na kubonyeza voltage juu yao. MOV ambaye anabeba anayatoa energy iliyohifadhiwa katika circuit inductance.
Wakati IGCT zinavyoonyeshwa kwenye Fig. 2 (a), GTOs pia zimehitajika katika designs za zamani zinazotumia topology ya circuit ile ile.

 
Fig. 2   a) Bi-directional solid-state circuit breaker yenye msingi IGCT, (b) Bi-directional solid-state circuit breaker yenye msingi IGBT

Fig. 3 inaonesha vipengele kadhaa vya alternative designs vinavyotumia concept hii kwa systems za medium voltage. Katika systems hizi, devices mingi zinajulikana series kuboresha total voltage withstand capability ya solid-state breaker. Diodes pia mara nyingi zinajulikana series na main breaking switches kuboresha reverse block voltage ya system, kutokana na limited reverse blocking capability ya devices kama IGCT na GTO. Circuit unavyoonyeshwa kwenye Fig. 3 (c) ina RC snubbers zinazojulikana parallel ambazo zinahitajika kwa systems za GTO kusaidia kuzima devices, na pia zina vipengele viwili vya interest ambavyo vinaweza kutumika kwa solid-state circuit breakers mengine. Kwanza, ina resistor unaotumika kubainisha fault current wakati wa pigaji current. Wakati wa kazi normal, resistor huo unashort-circuited na main semiconductor switches na hivyo haijihusisha na on-state losses ya breaker. Pili, switch mechanical unajulikana series kutoa isolation physical.
Wakati designs zinazoonyeswa kwenye sekta hii zimeundwa kwa ajili ya ac power systems, inaweza kuwa possible kutumia designs hizi kwa applications za dc na mabadiliko machache.

 
Fig. 3: a) Bi-directional solid-state circuit breaker yenye msingi IGCT, (b) Bi-directional solid-state circuit breaker yenye msingi IGCT, (c) Bi-directional solid-state circuit breaker yenye msingi GTO

Diagram ya block simplified wa solid-state circuit breaker unavyoonyeshwa kwenye Fig. 4. Solid-state current interrupter unajulikana kwa series string of solid-state devices ili kudumu DC bus voltage safely. Fast coordinated inverse-time controller anatoa gate drive signal kwa switches katika interrupter ambayo zinafungwa na kufungwa synchronous. Fast inverse time controller anapokea commands kutoka manual input, kutoka breakers mengine katika network, au kutoka sensors fast ambazo zinapata local fault currents. Inverse-time controller anatoa inverse trip time control kwa overcurrent states, na fast instantaneous trip ikiwa overcurrent limit imefikia. Operational parameters hizi zinaweza kubadilishwa kwa breaker kila moja kulingana na location yake katika network, kutumaini response sequenced kwa conditions za hitilafu.

 
Fig. 4: Diagram ya system simplified ya typical MVDC solid-state circuit breaker

Solid-state interrupter anatoa primary functionality ya complete circuit breaker assembly fast fault protection na isolation. Complete circuit breaker assembly lazima pia anatoa means ya safe disconnecting interrupter kutoka power network wakati maintenance au service inahitajika.
Preliminary layout kwa 8 MW load-level circuit interrupter unavyoonyeshwa kwenye photo 1. Interrupter huyu
unajulikana na six 4,500 V IGBTs (CM900HB-66H) zinazojulikana series. Interrupter wa 8 MW
ni umbali wa takriban 23” wide x 9” high  11” deep na anavuta takriban 60 lb. IGBTs zimezinduliwa
katika water-cooled aluminum cold plates, ambazo zinazinduliwa kwenye frame mechanical yenye electrical insulation. Water lines non-metallic zinaresistance suficiente kutolimita current leakage down the lines.
Hii itahitaji small, closed-loop cooling system na long-lasting ion-exchange cartridge kudumisha resistivity ya cooling water.
Hii itahitaji small, closed-loop cooling system na long-lasting ion-exchange cartridge kudumisha resistivity ya cooling water.
Kwenye photo 1 inaoneshwa preliminary mechanical layout ya 10 kV, 8 MW (800 A) IGBT interrupter. IGBTs zimezinduliwa katika water-cooled cold plates. Non-metallic cooling lines kati ya adjacent cold plates zimeundwa kusimama full switch voltage wakati switch imefungwa.
Parallel arrays ya assemblies haya zinatumika kutosha overall current requirements kwa load.

 
Photo 1: Preliminary mechanical layout ya 10 kV, 8 MW (800 A) IGBT interrupter. IGBTs zimezinduliwa katika water-cooled cold plates

Kulinganisha faides na adhabu za Solid-State Circuit breakers na circuit breakers mengine kwa ufupi:
Wakati solid-state circuit breakers zinaweza kupata interruption speed haraka sana zaidi kuliko conventional electro-mechanical-based circuit breakers, drawdown kuu wa solid-state breakers ni on-state losses zao zisizo magumu. Na contact resistance ndogo kama mikro-ohms chache, electro-mechanical contacts katika classical circuit breakers hufanya on-state losses zisizo magumu. Ingawa, most solid-state devices hufanya voltage drop of at least two volts, kwa hiyo wakati current mkubwa unapofika kwenye breaker, on-state losses za solid-state circuit breaker zinaweza kuwa zaidi sana kuliko za classical circuit breaker. The increased energy loss pia hunyanyasa maagizo matumizi ya cooling. Traditionally large metallic heatsinks zinatumika kuzuia passively power semiconductor devices, lakini zinaweza kuchangia portions substantial za size na weight za systems.
Wakati installation ya active cooling systems kama forced air (fan) au liquid cooling inaweza kusaidia kupunguza size na weight ya system kamili, zinatoa complexities additional kama acoustic signature, energy losses, na issues za maintenance.
Kulingana na Fig. 5, values zinapatikana kulingana na highest value per group.
Kwa criterion chochote, small values zinaweza kuwa preferable. Small area, hivyo inaonyesha performance nzuri ya switching concept.
Kulingana na findings, solid-state circuit-breaker unatoa performance nzuri. Kwa sababu ya fast switching capabilities, turn-off time ni ndogo na current amplitudes ndogo tu hupatikana. Pia, reliability na complexity ya switching process zinaweza kuwa nzuri. Lakini, solid-state breaker ana suffer from high losses, kumpika na mechanical au hybrid switches.
Concept alternative na low losses, medium relative costs, na good reliability ni snubber mechanical breaker. Pia, conventional hybrid breaker unatoa performance medium. Anasuffer from high peak currents kutokana na mechanical switch. Concepts zinazoenda kutoka HVDC systems hazito na performance nzuri katika voltage na power levels zilizotathmini. Lakini, kwa voltages na powers zaidi, hii inaweza kubadilika. Finally, concept ya pure mechanical-breaker bado ni interesting kwa applications za low na low-medium voltage kwa sababu ni well-proven tu.

Fig. 5: Overview of all switching concepts for DC circuit breakers

Table 1 inachukua characteristics za four circuit breaker technologies:
Inapaswa kuzingatia kuwa time of preparation ya table hii ni 2012.

 
Table 1: Summary of circuit breakers technologies for low power DC applications