Praktiċi operattivi ta' ġid fil-kontroll tal-interrutturi u kontatturi tal-apparati elettriki
Praktiċi operattivi ġodda għal switchgear circuit breakers u contactors
Operazzjoni ta’ LV/MV
Switchgear
Il-ġel tal-direttiva huwa biex joffri prattika miftuħa għall-operazzjoni u l-esame ta’ switchgear circuit breakers u contactors ta’ voltiżzi medju (2 - 13.8 kV) u vołtiżzi bażi (200 - 480 V). L-operazzjoni regolata b’mod ġodda hija importanti massanx għal tixtriġxi u l-servizz tal-eqwuipment tal-pjantha, kif ukoll biex is-sigurtà tas-silġa tal-pjantha tkun assikurata.
Din l-artiklu tispjega r-responsabilitajiet tal-personal operattiv, fl-ahwa ma’ l-esami u l-kontrolli tagħhom ta’ switchgear. F’dal-faqar, se tispjega s-sistema optima għall-operazzjoni u protezzjoni ta’ transformers, motors, buses, cables, circuit breakers, u contactors.
Kontrolli tal-Operator
Huwa d-dover tal-personal operattiv li jagħmlu u jiġbuhom kontrolli rutinari regolari ta’ kull switchgear fil-pjantha. Il-circuit breakers, il-contactors, u l-busbars għandhom ikunu żgħar u ħxiesa biex inqassmu r-riskju ta’ fallimenti tal-insulazzjoni li jistgħu jilġu għal esplożjonijiet u nkurar. Fl-ġenerali, huwa sovvigli mill-adviża anki kontrolli waħda l-għarax.
Dawn huma l-kontrolli ta’ kull jorn mill-adviża għal switchgear:
Jekk jikseb anomali sew fis-sistema ta’ esami indikati hawn fuq, work orders ta’ maintenance għandhom jiġu emessi.
Se tispjega l-prattika għal load feeder overcurrent u ground fault protection, kif ukoll source u tie overcurrent protection, u prattiki oħrajn importanti relatati għal transformers. B'asjed, se taddrassa l-issues li jmissu meta jkun hemm transfer ta’ switchgear bus u l-problemi li jmissu meta jsiru parallelism ta’ żewġ sources ta’ energy u f’schemi ta’ switch-time transfer.
Protezzjoni
Il-protective relays huma koordinati b’mod li tikksir biss id-dik circuit breakers u contactors li għandhom jagħmlu biex jisola l-faults. Dan jippermetti li l-numru amkien ta’ eqwuipment jiġi msal saqaf, b’mixxim impact fuq generating units on-line. Dan jgħin ukoll biex tindika l-lokali tal-fault elektriku.
Il-faults elektriki fit-transformers, motors, busbars, cables, circuit breakers, u contactors solitament huma permanenti. Qabel li jirreenergizaw l-equipment, għandhom jiġu eseguita investigazzjonijiet approfonditi dwar l-operazzjoni tal-protective relays.
L-amplitud tal-electrical short-circuit currents solitament toqgħod bejn 15,000 u 45,000 amperes, skont it-tagħba ta’ s-sorg ta’ transformator.
Load Feeder Ground Protection
Id-designs li jlimitaw il-ground fault current (solitament qrib 1000 amps) japplikaw separate ground relays li jkunu jogħġu għal ground faults biss. Dawn il-relays jkunu tripped b’timed delays qasir biex jsilġu l-grounded feeders qabel ma jkunu jogħġu l-source u tie circuit breaker ground relays.
Source and Tie Overcurrent Protection
Il-source breakers u tie breakers mhumiex ekkwippati b’instantaneous tripping elements. Invece, jiddipendu minn timed delays biex jkoordinaw l-replies għal faults mal-downstream buses u loads.
Solitament, dawn il-relays huma settjati bsad ta’ maximum three-phase short-circuit current levels, bl-operating time toqgħod bejn 0.4 u 0.8 sekondi.
Normalment, dawn il-relays jgħandhom characteristic ta’ inverse-time. Hija, levels ta’ current inferjuri jgħoddew proportional longer time delays għal kull relay. Speċifikament, il-tie breaker magħmul ma’ bus oħra huwa settjat biex jopera qrib 0.4 sekondi, mentri l-low-side breaker tat-transformer tas-sorg huwa settjat biex jopera qrib 0.8 sekondi.
High Side Source Transformer Overcurrent Protection
Il-overcurrent relays fuq is-silġa ta’ high-voltage tat-transformer tas-sorg solitament huma settjati biex joperaw qrib 1.2 sekondi wara li jkun hemm maximum three-phase short-circuit fuq is-silġa ta’ low-voltage. Dan it-timed delay jippermetti l-koordinazzjoni proper mal-overcurrent relays fuq is-silġa ta’ low-voltage jew secondary.
Dawn il-relays solitament għandhom characteristic ta’ inverse-time, hjiel, levels ta’ current inferjuri jgħoddew operating times long. Il-high-voltage-side overcurrent relays tat-transformer tas-sorg jassumu li jista’ jkun hemm fault fit-transformer stess, fit-connecting buses u cables ta’ low-voltage side, jew fi l-low-voltage circuit breaker. Huma jkunu tripped l-equipment necessari biex jsilġu l-fault.
Għal Unitized Automatic Transfer Switches (UATs), li solitament huma ekkwippati b’differential protection, il-high-voltage-side overcurrent relays jistgħu wkoll jiġu cauzati biex it-trip completely l-unit u l-main step-up transformer. Aukoll, jekk l-low-voltage-side breaker iffalli f’interrupting a fault, il-high-voltage-side overcurrent relays jippernu breaker-sticking protection.
Source and Tie Residual Ground Protection
Għal designs li jlimitaw il-ground-fault current (solitament qrib 1000 amps), japplikaw separate ground relays, li jogħġu biss meta jkun hemm ground fault. Il-ground relays tas-sorg u tie breakers mhumiex ekkwippati b’instantaneous tripping elements. Invece, jiddipendu minn timed delays biex jkoordinaw l-replies għal faults mal-downstream buses u loads. Solitament, dawn il-relays huma settjati bsad ta’ maximum ground-fault current levels, bl-operating time toqgħod bejn 0.7 u 1.1 sekondi.
Normalment, dawn il-relays jgħandhom characteristic ta’ inverse-time. Hija, levels ta’ current inferjuri jgħoddew proportional longer time delays għal kull relay. Speċifikament, il-tie breaker magħmul ma’ bus oħra huwa settjat biex jopera qrib 0.7 sekondi għal 100% ground faults, mentri l-low-side breaker tat-transformer tas-sorg huwa settjat biex jopera qrib 1.1 sekondi.
Source Transformer Neutral Ground Protection
Fi d-design schemes li jlimitaw il-ground-fault current (solitament qrib 1000 amps), jemplikaw dedicated ground relays. Dawn il-relays huma speċifikament disegnati biex jisensaw accurate l-ground current li jilfla mill-neutral point tat-transformer. Huma highly targeted u jogħġu biss meta jkun hemm ground fault.
Normalment, is-source transformer neutral-ground relay huwa settjat biex jopera qrib 1.5 sekondi wara l-most severe ground fault. Dan it-timed setting huwa crucial minkejja li jgaranti li l-relay jkoordinaw well mal-ground relays tas-sorg breakers u tie breakers.
Il-neutral-ground relay għandu missjun cruciali. Il-funzjoni kore tal-missjun tiegħu hi biex jisolaw ground faults li jmissu fuq is-silġa ta’ low-voltage (jew secondary side) tat-transformer tas-sorg. Il-lokali possibili tal-faults inkluqu l-low-voltage windings tat-transformer, l-low-voltage circuit breakers, u l-buses u cables li jkonnessjawhom. Aktar importanti, huwa jgħadi wkoll bħala backup protection. Meta l-low-side breaker iffaili f’funzionare proper meta jaffronta ground fault, il-neutral-ground relay jistep in biex jikkorta l-faulty circuit, bil-għas-il li jgħin jassigura l-sigurtà u l-stabilità tal-power system.
Alarm-Only Ground Schemes
Il-alarm-only ground schemes jlimitaw il-ground-fault current għal kelk amper. Valuri tipici huma 1.1 ampera għal sistemi ta’ 480-volt u 3.4 ampera għal sistemi ta’ 4 kV. Għal transformers tas-sorg wieda, il-neutral point solitament huwa grounded permezz ta’ grounding transformer. Għal transformers tas-sorg delta, il-ground-fault current solitament jvien minn tre transformers, li huma connected fi konfigurazzjoni ta’ grounded wye fuq is-silġa primarja u open-delta fuq is-silġa sekondarja.
Fid-due scenari, voltage relays huma installed fuq is-silġa sekondarja tal-grounding transformers biex jalertaw dwar ground-fault conditions. Fi kas transformers tas-sorg delta, primary fuses blown tal-ground-detector transformers jistgħu wkoll jkunu causati biex jagħmlu alarm.
Dawk kollox schemi ta’ relays jemmnu alarms (solitament b’sensitivity ta’ 10% jew iktar) għal kull grounded equipment fi sistema elettrika partikular. Dawk inkluqu l-low-voltage jew secondary windings tat-transformer tas-sorg, kif ukoll kull connected buses, cables, circuit breakers, potential transformers, u loads.
Switchgear Bus Transfers
Paralleling Two Sources
Il-paralleling ta’ żewġ sources differenti ta’ power huwa l-approċċ preferut għal switching minn wieħed għal ieħor. Din il-metodu ma timposex stress fuq motors, tassegura transizzjoni smooth, u ma tħallasx riskju għal l-running equipment. Imma, fid-disigns ħafna, il-short-circuit current li jmiss meta jsir paralleling huwa akbar mill-interrupting capacity tal-feeder breakers.
Is-source breakers u tie breakers ma jiġux affettwati, imma l-feeder breakers jistgħu jiġu incapaxi ta’ clear close-in faults u jistgħu jkunu damaged fl-proċess. Għalhekk, il-duration ta’ paralleling għandha tkun minimized (qrib ftit sekondi) biex tinqassam l-exposure time u probability ta’ feeder faults.
Typikalment, din il-problema hija aktar prominent meta generating unit jfornixxi power lis-sistema wahda, mentri l-standby jew startup transformer huwa fed from sistema differenti. It-tneħħija tal-output ta’ power mit-generator solitament tapprossima l-phase angles, skont it-tneħħija tal-load.
Drop-Pickup Transfers
Id-drop-pickup transfers, anki ma kjentu bħala switch-time transfer schemes, jistgħu jiġu damage motors. Jekk il-new source breaker iffalli f’close wara li l-previous source breaker jtrip open, dan jista’ jkun cauzi ta’ running unit li tistop jew process operattiv li tiġi interrupted. Meta busbar jisperd power, il-connected motors jagħmlu bħala generators u jfornixxu residual voltage lill-busbar.
Dan il-residual voltage solitament jdecays wara qrib sekonda waħda.
Imma, id-drop-pickup transfers jiġu mult fast kemm qrib sekonda waħda, u l-residual voltage jista’ jittagħmil ma’ voltage mil-new source. Jekk il-vector sum ta’ dawn żewġ voltages jissover 133% tal-rated voltage tal-motor, il-transfer jista’ jirriduci l-service life tal-motors involuti.
Automatic Bus Transfer Schemes
Is-schemi ta’ automatic bus transfer huma ġenerali disegnati biex jiġu mitigated it-tensioni fuq motors waqt it-transfer u biex jkoordinaw mal-fault relays. Il-koordinazzjoni mal-over-current relaying tissab b’initiation tal-transfer wara li l-source circuit breaker jitrip open. Jekk over-current relays jcausaw is-source breaker jitrip (indicating bus fault), l-automatic transfer ser tkun blocked.
Aktar, dawn is-schemi solitament jemplikaw residual voltage relays u/o high-speed synchronizing check relays. It-transfers huma permessi biss meta l-vector sum tal-residual voltage u l-voltage mil-new source huwa inqas minn 133% tal-rated voltage tal-motor. Jekk it-transfer tkun blocked permezz ta’ 86 lockout relays, is-scheme solitament timeout.
Imma, jekk dan ma jkunx, l-operators għandhom verifika li l-automatic transfer scheme huwa deactivated qabel ma jirresetjaw l-bus 86 lockout relays.
