Chaguo na Uwekezaji wa Kitamaduni: Mwongozo Wa Kumiliki kutoka Kwa Viwango vya Msingi hadi Ulinzi wa Chaguo

Vitambulisho vya Circuit Breakers

(1) Air Circuit Breaker (ACB)
Circuit breaker wa hewa, ambao pia unatafsiriwa kama circuit breaker wa mifumo au universal, unaelekea vitu vyote vidakika vikubwa vya metal. Ni mara nyingi open-type, inayoruhusu muundo wa vifaa mbalimbali, na inafanikiwa kurekebisha majanga na vifaa visivyo ya umma. Inatumika sana kama switch mkuu wa mchuzi wa nguvu. Unit za overcurrent zinazotumika ni electromagnetic, electronic, na intelligent. Circuit breaker huu unatoa usalama wa stage nne: long-time delay, short-time delay, instantaneous, na ground fault protection. Kila seti ya usalama inaweza kuruduliwa kwenye ukuta kutegemea kwa saizi ya frame.

Circuit breakers wa hewa ni vizuri kwa mitandao ya 50Hz, voltages zilizotathmini 380V au 660V, na current zilizotathmini kutoka 200A hadi 6300A. Zinatumika kwa ujumla kutoa namba za electrical energy na kupambana na overloads, undervoltage, short circuits, single-phase grounding, na matatizo mengine. Circuit breakers hizi zinatoa multiple intelligent protection functions na inawezesha selective protection. Katika masharti normal, zinaweza kutumika kwa switching ya circuits yenye mara chache. ACBs wenye ratings zaidi ya 1250A zinaweza kutumika kwenye mitandao ya 50Hz, 380V kwa ajili ya kupambana na motors kutokua overload na short circuits.

Circuit breakers wa hewa zinatumika pia kama switches makuu kwenye upande wa 400V wa transformers, bus tie switches, high-capacity feeder switches, na large motor control switches.

(2) Molded Case Circuit Breaker (MCCB)
Pia inatafsiriwa kama plug-in circuit breaker, molded case circuit breaker unaelekea terminus, contacts, arc extinguishing chambers, trip units, na operating mechanisms kwenye enclosure ya plastiki. Auxiliary contacts, undervoltage trip units, na shunt trip units zinazozingatiwa zinaweza kuwa modular. Muundo wake ni mfupi, na huduma ya kutosha si lazima kusikitishwa. Inasimamia usalama wa branch circuits. Molded case breakers zinazo wazi kufanya thermal-magnetic trip units, lakini models zinazozingatiwa zinaweza kuwa na solid-state trip sensors.

Overcurrent trip units kwa MCCBs zinapatikana kama electromagnetic na electronic. Mara nyingi, electromagnetic MCCBs zinabaki non-selective na zinatoa tu long-time delay na instantaneous protection. Electronic MCCBs zinatoa four protection functions: long-time delay, short-time delay, instantaneous, na ground fault protection. Baadhi ya electronic MCCBs mpya zinafanyika zone-selective interlocking.

Molded case circuit breakers zinatumika kwa ujumla kwa usalama wa feeder circuits, switches makuu kwenye upande wa low-voltage wa small distribution transformers, terminal power distribution control, na kama power switches kwa machapisho mengine yoyote.

(3) Miniature Circuit Breaker (MCB)
Miniature circuit breaker ni kitu cha kushindana kwa kutumika sana kama kitu cha usalama cha mwisho katika systems za building electrical terminal distribution. Inatumika kwa usalama dhidi ya short circuits, overloads, na overvoltage katika circuits za single-phase na three-phase zilizotathmini hadi 125A, na inapatikana kama single-pole (1P), double-pole (2P), triple-pole (3P), na four-pole (4P).

MCB unaoperesheni mechanism, contacts, protective devices (matafsiri yake trip units), na system ya arc extinguishing. Contacts makuu hazina mkono kwa kasi au kwa elektroni. Baada ya kufunga, free-tripping mechanism hufuli contacts kwenye namba ya kufunga. Coil ya overcurrent trip unit na heating element ya thermal trip unit zinajulikana kwa series na main circuit, na coil ya undervoltage trip unit inajulikana kwa parallel na power supply.

Katika ubuni wa electrical design ya nyumba, miniature circuit breakers zinatumika kwa ujumla kwa usalama na malengo ya operation kama overloads, short circuits, overcurrent, loss of voltage, undervoltage, grounding, leakage, automatic transfer of dual power sources, na motor starting chache.

Mipangilio Mfano ya Circuit Breakers

(1) Rated Operating Voltage (Ue)
Voltage iliyotathmini ya rated operating ni nominal voltage ya circuit breaker, kwenye ambayo breaker anaweza kukabiliana na kufanya kazi kwa muda wa muda kwa masharti mapema na performance.

Katika China, kwa voltage levels zilizohuru 220kV, maximum operating voltage ni 1.15 mara ya system rated voltage; kwa 330kV na zaidi, maximum operating voltage ni 1.1 mara ya rated voltage. Circuit breaker lazima iweze kudumu insulation na kufungua na kugongwa kwenye system's maximum operating voltage.

(2) Rated Current (In)
Current iliyotathmini ni current ambayo trip unit inaweza kukabiliana na kwa muda wa muda kwenye temperature ya ambient chini ya 40°C. Kwa breakers wenye adjustable trip units, inatafsiriwa kama current iliyotathmini zaidi ambayo trip unit inaweza kukabiliana na kwa muda wa muda.

Wakati hutumika kwenye temperature ya ambient zaidi ya 40°C lakini isisogope 60°C, breaker anaweza kufanya kazi kwenye load imara kwa muda wa muda.

(3) Overload Trip Current Setting (Ir)
Kwenye current zinazoelekea zaidi ya setting Ir ya trip unit, circuit breaker hutrip baada ya muda. Inatafsiriwa pia kama current iliyotathmini zaidi ambayo breaker anaweza kukabiliana na bila kugongwa. Hii inapaswa kuwa zaidi ya maximum load current Ib lakini chini ya maximum allowable current Iz ya circuit.

Kwa thermal-magnetic trip units, Ir inaweza kubadilishwa kwenye 0.7–1.0In. Kwa electronic trip units, ufunguo wa badiliko ni zaidi, mara nyingi 0.4–1.0In. Kwa breakers wenye overcurrent trip units isiyobadilika, Ir = In.

(4) Short-Circuit Trip Current Setting (Im)
Short-circuit trip unit (instantaneous au short-time delay) huchukua circuit breaker kwenye muda wa muda kwenye currents za faults kubwa. Im ni threshold ya trip.

(5) Rated Short-Time Withstand Current (Icw)
Hii ni current value inayoruhusiwa kujitokeza kwenye conductor kwa muda uliotathmini bila kusababisha damage kwa sababu ya overheating.

(6) Breaking Capacity
Breaking capacity ya circuit breaker inatafsiriwa kama uwezo wake wa kugongwa kwa safe fault currents, ambayo si lazima kusalia na current iliyotathmini. Ratings zinazozingatiwa ni 36kA na 50kA. Mara nyingi inaeleka kwa ultimate short-circuit breaking capacity (Icu) na service short-circuit breaking capacity (Ics).

Mistari ya Chaguo Circuit Breaker

Kwanza, chagua aina na poles kulingana na utaratibu; basi chagua current iliyotathmini kulingana na maximum operating current; hasa, chagua aina ya trip unit na vifaa. Maagizo yanayotarajiwa ni:

• Rated operating voltage ya circuit breaker ≥ rated voltage ya line.

• Rated short-circuit making/breaking capacity ya circuit breaker ≥ calculated load current ya line.

• Rated short-circuit making/breaking capacity ya circuit breaker ≥ maximum possible short-circuit current kwenye line (marani kama RMS value).

• Single-phase-to-ground short-circuit current kwenye mwisho wa line ≥ 1.25 mara ya instantaneous (au short-time delay) trip setting ya circuit breaker.

• Rated voltage ya undervoltage trip unit = rated voltage ya line.

• Rated voltage ya shunt trip unit = control power supply voltage.

• Rated operating voltage ya electric operating mechanism = control power supply voltage.

• Wakati hutumika kwenye lighting circuits, instantaneous trip setting ya electromagnetic trip unit ni mara nyingi 6 mara ya load current.

• Wakati hutumika kwa short-circuit protection ya single motor, instantaneous trip setting ni 1.35 mara ya motor starting current (kwa DW series) au 1.7 mara (kwa DZ series).

• Wakati hutumika kwa short-circuit protection ya multiple motors, instantaneous trip setting ni 1.3 mara ya starting current ya largest motor plus operating currents za motors zingine.

• Wakati hutumika kama switch mkuu kwenye upande wa low-voltage wa distribution transformer, breaking capacity yake inapaswa kuwa zaidi ya short-circuit current kwenye upande wa low-voltage wa transformer. Rated current ya trip unit inapaswa si chini ya rated current ya transformer. Short-circuit protection setting ni mara nyingi 6–10 mara ya rated current ya transformer; overload protection setting sawa na rated current ya transformer.

• Baada ya chaguo la awali la aina na rating ya circuit breaker, coordination na upstream na downstream protective devices inahitajika ili kuzuia cascading tripping na kupunguza scope ya accident.

Selectivity ya Circuit Breakers

Katika mitandao ya distribution, circuit breakers zinachaguliwa kama selective au non-selective kulingana na performance ya usalama. Selective low-voltage circuit breakers zinazozingatiwa zinatoa two-stage au three-stage protection. Instantaneous na short-time delay characteristics zinatumika kwa short-circuit protection, na long-time delay characteristics zinatumika kwa overload protection. Non-selective breakers zinazozingatiwa zinatumika tu kwa short-circuit protection, au long-time delay, zinatumika tu kwa overload protection.

Katika mitandao ya distribution, ikiwa upstream breaker ni selective na downstream breaker ni non-selective au selective, selectivity inapatakiwa kwa kutumia time delay ya short-time delay trip unit au differences kwenye settings ya time delay. Wakati upstream breaker anafanya kazi kwa time delay, tafakari kuhusu:

• Chanzo kwa downstream breaker kuwa selective au non-selective, instantaneous overcurrent trip setting ya upstream breaker inapaswa kuwa sawa au zaidi ya 1.1 mara ya maximum three-phase short-circuit current kwenye output ya downstream breaker.

• Ikiwa downstream breaker ni non-selective, ili kupambana na upstream short-time delay overcurrent trip unit kuwa first due to insufficient sensitivity ya downstream instantaneous trip unit wakati ya short circuit, short-time delay overcurrent trip setting ya upstream breaker inapaswa kuwa sawa au zaidi ya 1.2 mara ya downstream breaker's instantaneous trip unit.

• Ikiwa downstream breaker pia ni selective, ili kupata selectivity, short-time delay operating time ya upstream breaker inapaswa kuwa zaidi ya 0.1 sekunde zaidi ya downstream breaker.

Marani, ili kupata selectivity kati ya upstream na downstream low-voltage circuit breakers, upstream breaker inapaswa kuwa na short-time delay overcurrent trip unit, na operating current lake inapaswa kuwa zaidi ya moja ya downstream trip unit. Minimum, upstream operating current Iop.1 inapaswa kuwa sawa au zaidi ya 1.2 mara ya downstream operating current Iop.2, i.e., Iop.1 ≥ 1.2Iop.2.

Cascading Protection ya Circuit Breakers

Katika ubuni wa mitandao ya distribution, coordination kati ya upstream na downstream circuit breakers inapaswa kupata "selectivity, speed, na sensitivity." Selectivity inaunganisha breakers, na speed na sensitivity zinazozingatiwa zinatumika kwa characteristics ya protective device na mode ya operating ya circuit.

Coordination nzuri kati ya upstream na downstream breakers inawezesha selective isolation ya faulty circuit, inaweza kupata other non-faulty circuits kufanya kazi kwa normal. Coordination chache kinapunguza reliability ya system.

Cascading protection ni application ya practical ya current-limiting characteristics ya circuit breakers. Principle yake ni kutumia effect ya current-limiting ya upstream breaker (QF1), ambayo inaweza kupata downstream breaker (QF2) una lower breaking capacity, kwa kufanya hii kusaidia kupunguza gharama. Upstream breaker QF1 unaweza kugongwa kwa maximum prospective short-circuit current kwenye installation point lake. Tangu upstream na downstream breakers zinajulikana kwa series, wakati ya short circuit kwenye output ya downstream breaker QF2, actual short-circuit current inapungua sana kwa effect ya current-limiting ya QF1, chini ya prospective short-circuit current kwenye point hiyo. Hivyo, breaking capacity ya QF2 inaweza kupata QF1, zaidi ya rated breaking capacity lake.

Cascading protection ina masharti: mfano, adjacent circuits hawapaswi kuwa na critical loads (kwa sababu ya tripping ya QF1 ingeweza kufanya QF3's circuit kuwa de-energized), na instantaneous settings ya QF1 na QF2 inapaswa kuwa properly matched. Cascading data inaweza kupatikana experimental, na coordination kati ya upstream na downstream breakers inapaswa kupewa na manufacturer.

Sensitivity ya Circuit Breakers

Ili kupata reliable operation ya instantaneous au short-time delay overcurrent trip unit kwenye minimum system operating conditions na wakati wa mildest short-circuit fault kwenye protection range lake, sensitivity ya circuit breaker inapaswa kuepatana na requirements za "Low-Voltage Electrical Distribution Design Code" (GB50054-95), ambayo inaeleka sensitivity si chini ya 1.3, i.e., Sp = Ik.min / Iop ≥ 1.3. Hapa, Iop ni operating current ya instantaneous au short-time delay overcurrent trip unit, Ik.min ni single-phase au two-phase short-circuit current kwenye mwisho wa protected line kwenye minimum system operating conditions, na Sp ni sensitivity ya circuit breaker.

Wakati wa chaguo la circuit breaker, sensitivity lake inapaswa pia kutathmini. Kwa selective breakers wenye both short-time delay na instantaneous overcurrent trip units, sensitivity ya short-time delay trip unit tu inapaswa kutathmini; sensitivity ya instantaneous trip unit haipaswi kutathmini.

Chaguo na Setting ya Circuit Breaker Trip Units

(1) Setting ya Operating Current ya Instantaneous Overcurrent Trip Unit
Baadhi ya electrical equipment zinazolinda kwa circuit breaker zinapata peak currents kubwa wakati ya startup, mara kadhaa ya rated current, kusababisha breaker kufanya kazi kwa peak currents chache. Operating current Iop(o) ya instantaneous overcurrent trip unit inapaswa kuwa zaidi ya circuit's peak current Ipk, i.e., Iop(o) ≥ Krel·Ipk, ambapo Krel ni reliability factor. Wakati wa chaguo la circuit breaker, hakikisha setting ya instantaneous overcurrent trip yake inapita peak current ili kupunguza nuisance tripping.

(2) Setting ya Operating Current na Time ya Short-Time Delay Overcurrent Trip Unit
Operating current Iop(s) ya short-time delay overcurrent trip unit inapaswa pia kuwa zaidi ya circuit's peak current Ipk, i.e., Iop(s) ≥ Krel·Ipk, ambapo Krel ni reliability factor. Short-time delay trip times ni mara nyingi 0.2s, 0.4s, au 0.6s, determined kulingana na selectivity na upstream na downstream protection devices, inaweza kupata upstream device kufanya kazi baada ya downstream kwa one time step.

(3) Setting ya Operating Current na Time ya Long-Time Delay Overcurrent Trip Unit
Long-time delay overcurrent trip unit ni muhimu kwa overload protection. Operating current Iop(l) lake inapaswa kuwa zaidi ya circuit's maximum load current (calculated current I30), i.e., Iop(l) ≥ Krel·I30, ambapo Krel ni reliability factor. Operating time inapaswa kuwa zaidi ya duration ya allowable short-term overloads ili kupunguza nuisance tripping.

(4) Coordination Requirements Kati ya Operating Current ya Overcurrent Trip Unit na Protected Circuit
Ili kupunguza damage ya insulation au fire kwa overloads au short circuits bila circuit breaker kugongwa, operating current Iop ya overcurrent trip unit inapaswa kupata condition: Iop ≤ Kol·Ial. Hapa, Ial ni allowable current-carrying capacity ya insulated cable; Kol ni allowable short-term overload factor—typically 4.5 kwa instantaneous na short-time delay trip units, 1.1 kwa long-time delay trip units zinazotumika kwa short-circuit protection, na 1.0 wakati zinatumika tu kwa overload protection. Ikiwa coordination requirement hii haipepo, trip unit setting inapaswa kubadilishwa, au cross-section ya conductor au cable inapaswa kuongezeka.