Mfano mzuri wa utaratibu wa kufanya kazi kwa circuit breakers na contactors za switchgear
Michezo mazuri ya uendeshaji kwa vifungo vya circuit na contactors
Uendeshaji wa LV/MV
Switchgear
Lengo la mwongozo huu ni kutoa ushauri wa michezo muhimu kwa uendeshaji na utafiti wa vifungo vya circuit na contactors vya switchgear vya kuondoka (kati ya 2-13.8 kV) na vya chini (kati ya 200-480 V). Uendeshaji unaohusishwa ni muhimu sana kwa kutengeneza ufanisi na huduma za vifaa vya eneo, pamoja na kupewa mahali maanani wa kazi kwa watumiaji.
Makala haya yataelezea majukumu ya watu walio wakiondoa, pamoja na utafiti wake wa kila siku na utathmini wa switchgear. Pia, itawelezeha michezo bora ya uendeshaji na uhifadhi wa transformers, motors, buses, cables, circuit breakers, na contactors.
Utathmini wa Miondoa
Ni jukumu la watu walio wakiondoa kujenga na kukagua mara kwa mara kwa undani zote za switchgear katika eneo. Circuit breakers, contactors, na busbars yanapaswa kuwa safi na ukame ili kurudisha hatari ya msingi wa insulation ambayo inaweza kuchanganya na kuleta moto. Mara nyingi, ni vizuri kutafuta mara kwa siku.
Yafuatayo ni matumizi ya utathmini wa kila siku ya switchgear:
Ikiwa tayari yoyote inapatikana katika utafiti uliotafsiriwa hapo juu, work orders za ujenzi lazima zatekelewezwe.
Itatambua michezo ya overcurrent na ground fault protection ya load feeders, pamoja na source na tie overcurrent protection, na michezo muhimu mingine zinazohusiana na transformers. Pia, itachunguza transfers za switchgear bus na itajadili suala zinazotokea wakati parallel two power sources na katika switch-time transfer schemes.
Protection
Protective relays zimehusishwa kwa njia ambayo tu vifungo vya circuit au contactors vinavyohitajika kufanya kazi kutekeleza faults zitasimamiwa. Hii inasaidia vifaa vingi kubaki kwenye uendeshaji, kupunguza athari kwenye generating units zinazokuwa online. Pia, hii hutoa taarifa ya mahali pa electrical fault.
Electrical faults katika transformers, motors, busbars, cables, circuit breakers, na contactors mara nyingi ni permanent. Kabla ya kureenergize vifaa, utafiti wa kutosha wa operation ya protective relays lazima ufuliwe.
Ukubwa wa electrical short-circuit currents mara nyingi unakuwa kati ya 15,000 hadi 45,000 amperes, kulingana na ukubwa na impedance ya source transformer.
Load Feeder Ground Protection
Mipango ambayo huweka hatari ya ground fault current (kati ya 1000 amps) hutumia separate ground relays ambazo zitaendelea kwa ground faults tu. Relays hizi huenda kwa time delays fupi sana ili kutekeleza grounded feeders kabla source au tie circuit breaker ground relays zianze kufanya kazi.
Source and Tie Overcurrent Protection
Source breakers na tie breakers hazijahusishwa na instantaneous tripping elements. Badala yake, wanategemea time delays ili kukabiliana na fault responses na downstream buses na loads.
Maranyingi, relays hizi zimefanya kazi kulingana na maximum three-phase short-circuit current levels, na operating time inaruka kati ya 0.4 hadi 0.8 sekunde.
Kawaida, relays hizi zina inverse-time characteristic. Hiyo ni, current levels madogo zitatoa time delays zaidi kwa relays zote. Kwa khusa, tie breaker unayounganishwa na bus nyingine imefanya kazi kwa sekunde 0.4, na low-side breaker wa source transformer imefanya kazi kwa sekunde 0.8.
High Side Source Transformer Overcurrent Protection
Overcurrent relays kwenye high-voltage side ya source transformer zimefanya kazi kwa sekunde 1.2 baada ya maximum three-phase short-circuit kwenye low-voltage side. Time delay hii inasaidia kusambaza vizuri na overcurrent relays kwenye low-voltage au secondary side.
Relays hizi kawaida zina inverse-time characteristic, hiyo ni, current levels madogo zitatoa time delays zaidi. High-voltage-side overcurrent relays za source transformer zinatumai kuwa fault inaweza kuongezeka moja kwa moja katika transformer, kwenye low-voltage-side connecting buses au cables, au kwenye low-voltage circuit breaker. Zitasimamia vifaa vyote vinavyohitajika kutekeleza fault.
Kwa Unitized Automatic Transfer Switches (UATs), ambazo mara nyingi zina differential protection, high-voltage-side overcurrent relays zinaweza kusimamia unit na main step-up transformer kamili. Pia, ikiwa low-voltage-side breaker haiwezi kurejesha fault, high-voltage-side overcurrent relays zinatoa breaker-sticking protection.
Source and Tie Residual Ground Protection
Kwa mipango ambayo huweka hatari ya ground-fault current (kati ya 1000 amps), ground relays zinatumika tu, ambazo zitafanya kazi tu wakati ground fault. Source na tie breaker ground relays hazijahusishwa na instantaneous tripping elements. Badala yake, wanategemea time delays ili kukabiliana na fault responses na downstream buses na loads. Maranyingi, relays hizi zimefanya kazi kulingana na maximum ground-fault current levels, na operating time inaruka kati ya 0.7 hadi 1.1 sekunde.
Kawaida, relays hizi zina inverse-time characteristic. Hiyo ni, current levels madogo zitatoa time delays zaidi kwa relays zote. Kwa khusa, tie breaker unayounganishwa na bus nyingine imefanya kazi kwa sekunde 0.7 kwa 100% ground faults, na low-side breaker wa source transformer imefanya kazi kwa sekunde 1.1.
Source Transformer Neutral Ground Protection
Katika vipimo ambavyo huweka hatari ya ground-fault current (kati ya 1000 amps), ground relays zinatumika tu, ambazo zitafanya kazi tu wakati ground fault. Relays hizi zimeundwa kwa ufupi ili kusikia ground current unayofika kwenye neutral point ya transformer. Wanaweza kuzingatia tu wakati ground fault inatokea.
Kawaida, source transformer neutral-ground relay imefanya kazi kwa sekunde 1.5 baada ya fault ya ground fault ya nguvu zaidi. Time-delay setting hii ni muhimu sana kwa sababu inasaidia relay kuwa na coordination vizuri na ground relays za source breakers na tie breakers.
Neutral-ground relay ana shughuli muhimu. Funguo yake ni kutekeleza ground faults zinazotokea kwenye low-voltage side (secondary side) ya source transformer. Fault locations zinaweza kuwa kwenye low-voltage windings ya transformer, low-voltage circuit breakers, na buses na cables zinazounganisha. Zaidi ya hayo, inatosha kama backup protection. Ikiwa low-side breaker haiwezi kufanya kazi vizuri wakati anapata ground fault, neutral-ground relay atastep in mara moja kutembelea circuit faulty, kwa hivyo kuaminika na stable operation ya power system.
Alarm-Only Ground Schemes
Alarm-only ground schemes huiweka hatari ya ground-fault current kwa amperes machache tu. Aina zinazozingatia ni 1.1 amperes kwa systems za 480-volt na 3.4 amperes kwa systems za 4 kV. Kwa transformers za source zenye wewe, neutral point mara nyingi imegrounded kwa grounding transformer. Kwa transformers za source zenye delta, ground-fault current zinatoka kwa tatu transformers, zinazounganishwa kwa grounded wye configuration kwenye primary side na open-delta configuration kwenye secondary side.
Katika mwanachama wote, voltage relays zimeundwa kwenye secondary sides za grounding transformers kwa ajili ya kutoa alert kwa ground-fault conditions. Kwa transformers za source zenye delta, blown primary fuses za ground-detector transformers zinaweza kutoa alert.
Mipango yote miwili hutoa alarms (kawaida na sensitivity ya 10% au zaidi) kwa vifaa vyote vilivyoground katika electrical system fulani. Hii inajumuisha low-voltage au secondary windings za source transformer, pamoja na buses, cables, circuit breakers, potential transformers, na loads zote zinazounganisha.
Switchgear Bus Transfers
Paralleling Two Sources
Kutumia tofauti mbili za chanzo ni njia inayopendekezwa kwa kutumia moja kwa moja. Njia hii haipeleki stress kwa motors, husaidia transition smooth, na haiwezi kuwa na hatari kwa vifaa vya kazi. Lakini, katika mipango mengi, short-circuit current unayotokea wakati wa paralleling unaweza kuwa zaidi ya interrupting capacity ya feeder breakers.
Source breakers na tie breakers hawana athari, lakini feeder breakers zinaweza kuwa na changamoto kutekeleza close-in faults na zinaweza kuharibiwa wakati huo. Kwa hivyo, duration ya paralleling lazima iwe chache (kati ya sekunde chache) ili kupunguza exposure time na probability ya feeder faults.
Maranyingi, tatizo hili linajumuisha zaidi wakati generating unit anayotoa umeme kwa system moja na standby au startup transformer unayopewa kwa system nyingine. Kutokosea power output ya generator mara nyingi huchanganya phase angles zaidi, kwa sababu angle ya power ya generator huenda chini kwa kutokosea load.
Drop-Pickup Transfers
Drop-pickup transfers, ambazo pia zinatafsiriwa kama switch-time transfer schemes, zinaweza kuharibu motors. Ikiwa source breaker mpya haiwezi kufunga baada ya source breaker iliyopo ikatoka, inaweza kusababisha running unit kupunguza au process inayofanya kazi kupunguza. Wakati busbar inapoteza umeme, motors zinazounganishwa zinatoa residual voltage kwenye busbar.
Residual voltage hii mara nyingi huenda kwenye sekunde moja.
Lakini, drop-pickup transfers hutokea zaidi ya sekunde moja, na residual voltage inaweza kuunganishwa na voltage ya chanzo mpya. Ikiwa vector sum ya voltage zote mbili zinazopata zaidi ya 133% ya rated voltage ya motor, transfer inaweza kupunguza service life ya motors zinazowasiliana.
Automatic Bus Transfer Schemes
Automatic bus transfer schemes zinatumika kuboresha stress kwa motors wakati wa transfer na kusambaza na fault relays. Usambazaji na over-current relaying unafanyika kwa kutumia transfer baada ya source circuit breaker ikatoka. Ikiwa over-current relays zinaweza kusababisha source breaker kutoka (kuelezea bus fault), automatic transfer itapigwa kwenye block.
Pia, mipango haya mara nyingi hutumia residual voltage relays na/or high-speed synchronizing check relays. Transfers zinaweza kufanyika tu ikiwa vector sum ya residual voltage na voltage ya chanzo mpya ni chache kuliko 133% ya rated voltage ya motor. Ikiwa transfer ipigwa kwenye block na 86 lockout relays, mipango haya mara nyingi hutokosa.
Lakini, ikiwa si hivyo, watumiaji wanapaswa kuthibitisha ikiwa automatic transfer scheme imezima kabla ya kurejelea bus 86 lockout relays.
