Uchambuzi wa Kitu kuhusu Matukio ya Kudumisha Mzunguko wa Kiwango cha Hifadhi ya Tumbo la Kupungua Umeme IEE-Business

Ufikio wa upinzani unatafsiriwa kama uhusiano kati ya upinzani wa nyuzi ya mstari wa umeme na ardhi. Katika mfumo wa China wa 35 kV na chini, njia za kawaida zinazotumiwa ni upinzani unaofaa, upinzani wa silau la kupunguza arc, na upinzani wa resistance ndogo. Mfano wa upinzani unaofaa umefanikiwa kutumika sana kwa sababu inayoruhusu utendaji wa muda fupi wakati wa matatizo ya grounding ya single-phase, huku upinzani wa resistance ndogo umekua mzizi kwa sababu ya uondokaji wa matatizo kwa haraka na kudhibiti overvoltage. Maeneo mengi ya substations yanajenga transformers za grounding kwa ajili ya kuimarisha upinzani wa nyuzi, lakini mabadiliko ya magumu ya matatizo yanaathiri protection ya relay, kuchelewesha malipo au kutokulipa.

Makala hii hutaja principles na sifa za transformer wa grounding, huambatianayo configuration/setting ya protection ya current katika mfumo wa resistance ndogo, huanaliza sababu za malipo mbaya, na hujitolea kwa mchakato wa grounding ya single-phase ili kukatanisha actions za protection na mikakati ya matatizo. Inatoa mapendekezo kwa ufadhili/kuhifadhi matatizo, hukubalika staff ya huduma, husonga kwa juu ufanisi wa kutatua matatizo, na kuondoka hatari zisizotarajiwa.

Principle ya Kazi ya Transformer wa Earthing

Wakati wa transformation ya substation yenye mfumo wa delta-connected, neutral-ungrounded kwa mfumo wa small-resistance grounding, kwa ajili ya kuongeza neutral point, tarehe ya kawaida ni kuongeza transformer wa earthing kwenye busbar. Sasa, transformer wa earthing wa Z-type unapochaguliwa kwa ujumla kutoa point ya grounding. Baada ya hayo, principle ya kazi ya transformer wa earthing wa Z-type itahusishwa.

Transformer wa earthing wa Z-type una structurally ni sawa na transformer wa umeme wa kawaida. Lakini, winding kwenye core ya kila phase unachanganyikiwa kwa sehemu mbili za turns sawa, juu na chini, ambazo zinajunganishwa kwa muundo wa zig-zag. Njia yake ya wiring inonekana kwenye Figure 1.

Wakati ground short-circuit unafanyika, zero-sequence current unafikia kwenye neutral point. Uhusiano wa zig-zag wa transformer wa earthing wa Z-type hunaweza kufanya zero-sequence currents za juu na chini kusaidiana, kuteleza magnetic fluxes na kureduce zero-sequence impedance kuihindia overvoltage ya arc-grounding. Kwa positive/negative-sequence currents, electromagnetic properties zake za transformer wa kawaida huchapa high impedance, kuzuia mzunguko wao.

Wakati wa kazi ya normal, transformer wa earthing unategemea karibu na no-load (no secondary load). Wakati wa ground fault, positive, negative, na zero-sequence fault currents hutembelea nje yake. Kwa sababu ya "high positive/negative-sequence, low zero-sequence impedance", device ya protection kuu hutathmini zero-sequence current ya grid.

2 Configuration na Analysis ya Protection ya Current kwa Transformers wa Earthing

Protection ya current ya transformer wa earthing mara nyingi hutumia phase-to-phase na zero-sequence current protection. Hapa ni breakdown:

2.1 Setting ya Protection ya Phase-to-Phase Current
2.1.1 Principles za Setting

Hii protection inajumuisha instantaneous trip na over-current protection:

• Instantaneous Trip: Kuwasiliana na backup over-current protection ya transformer wa power supply upande wa ujumla. Hakikisha sensitivity wakati wa two-phase short-circuits (minimum operation mode) na kuepusha inrush currents (7-10× rated current ya transformer wa earthing) na fault currents ya upande wa low-voltage.

• Over-Current Protection: Set kuepusha rated current ya transformer wa earthing na maximum fault phase current wakati wa external single-phase grounding, hakikisha reliability.

• Operation Logic: Instantaneous trip hutenda mara moja (bila delay); over-current protection (backup for phase-to-phase shorts) na delay fupi na settings chache kwa leveled coordination.

2.1.2 Tripping Modes

Kulingana na connection ya transformer wa earthing na transformer wa power supply:

• Imejulishwa kwenye low-voltage bus: Instantaneous trip/over-current protection hutrip circuit breaker upande wa ujumla kuepusha matatizo haraka.

• Imejulishwa kwenye lead ya low-voltage: Protection hutrip circuit breakers zenye upande kote kutembelea njia ya matatizo na kuepusha escalation.

2.2 Setting ya Protection ya Zero-Sequence Current kwa Transformers wa Earthing
2.2.1 Principles za Setting

• Thamani ya current setting inapaswa kuweka sensitivity ya kutosha wakati ya single-phase-to-ground fault.

• Kuwasiliana na thamani ya long-delay protection kwa full-line sensitivity ya lower-level zero-sequence current protection.

• Kwa time limit ya zero-sequence current ya first, itafauti lazima ziwaelezwe kuelekea successive occurrence ya single-phase-to-ground faults kwenye mstari wa mbili.

• Operating time lazima iwe zaidi ya operating time maximum ya Section Ⅱ ya zero-sequence current ya kila component yenye connection ya bus.

Tangu protection ya zero-sequence current ya transformer wa earthing isiyotumika kama protection msingi, kuna time limits tatu, ambazo zinavyoonyeshwa chini:

Katika formula: t0¹, t0², t0³ ni time limits ya 1, 2, na 3 ya protection ya zero-sequence current ya transformer wa earthing respectively; t_0I' ni thamani ya time setting ya Section I ya zero-sequence current ya outgoing line; t_0II' ni thamani ya time setting ya longest ya Section II ya protection ya zero-sequence current ya kila equipment kwenye busbar isipokuwa transformer wa earthing; Δt imepelekwa 0.2-0.5 s.

2.2.2 Tripping Modes

• Wakati transformer wa earthing unajulishwa kwenye busbar yake ya bus, protection ya zero-sequence current hutenda: time limit ya 1 hutrip circuit breaker ya bus tie au section circuit breaker na kuepusha automatic standby power supply input device (kurudiwa kwa "automatic standby input" kwa furaha); time limit ya 2 hutrip circuit breakers upande wa ujumla wa transformer wa earthing na transformer wa power supply.

• Wakati transformer wa earthing unajulishwa kwenye lead yake ya power supply transformer, protection ya zero-sequence current hutenda: time limit ya 1 hutrip circuit breaker ya bus tie au section circuit breaker na kuepusha automatic standby input; time limit ya 2 hutrip circuit breaker upande wa ujumla wa transformer wa power supply; time limit ya 3 hutrip circuit breakers zenye upande wote wa transformer wa power supply.

2.3 Analysis ya Operation ya Protection ya Current kwa Transformers wa Earthing

Analysis ya configuration ya protection ya transformer wa earthing inatafsiriwa tofauti kali katika tripping modes kati ya phase-to-phase na zero-sequence current protections: zero-sequence protection huelimisha auto-standby input wakati anatenda, hata hivyo phase-to-phase protection haielimishi.

Ikiwa zero-sequence current uliyomuweka kwa device ya protection unafika thamani ya operation na ground fault unafanyika (na transformer wa earthing kuwa njia pekee ya zero-sequence current kwenye mfumo wa small-resistance grounding), device hutambua matatizo lakini haiwezi kuthibitisha. Ikiwa matatizo yanaonekana kwenye mstari wa outgoing, baada ya protection kuhutrip transformer wa earthing, auto-standby input hutenganishwa kwenye standby busbar. Ikiwa standby busbar hutengeneza tena mstari wa faulty, transformer wa earthing upande wake bado hutambua zero-sequence current, kuleta another trip. Tangu auto-standby input haije imeshindwa charging, range ya outage inaweza kuboresha. Hivyo, zero-sequence protection lazima ielimishe auto-standby input.

Wakati protection ya phase-to-phase hutenda (lakini zero-sequence protection haiendi), device hukaza kwamba short-circuit ya phase-to-phase imefanyika kwenye transformer wa earthing mwenyewe. Hutrip transformer wa earthing, parallel-trips circuit breaker upande wa ujumla wa transformer wa power supply, na auto-standby input hutenganishwa kwenye standby busbar. Tangu matatizo yanaonekana kwenye transformer wa earthing aliyehutrip, standby busbar hutenganishwa kwenye mstari wa sahihi, kurudi umeme.

Kwa ufupi, protection ya phase-to-phase na zero-sequence current kwa transformers wa earthing inatafsiriwa tofauti kali katika judgment ya sababu na location ya matatizo, inahitaji settings na configurations tofauti. Hata hivyo, wakati wa ground short-circuit, protection ya phase-to-phase inaweza kutenda vibaya kwa sababu ya zero-sequence components iliyomuweka. Kutokana na logics zao za auto-standby input tofauti, malipo yasiyopaswa inaweza kuboresha range ya matatizo au hata kuchelewesha blackout kamili ya substation.

3 Case Analysis
3.1 Fault Process

Diagram ya primary wiring ya 110 kV substation inavyoonekana kwenye Figure 2. Kabla ya matatizo, circuit breaker ya 018 upande wa low-voltage wa Transformer 1 ulikuwa umefungwa, circuit breaker ya 032 upande wa low-voltage wa Transformer 2 ulikuwa umefungwa, na circuit breaker ya 034 ulikuwa kwenye position ya test.

Saa 06:14 tarehe 30 Julai 2023, protection ya over-current I section ya No. 2 earthing transformer ilianza, hutrip circuit breaker ya No. 2 earthing transformer 022. Pia, ilikuwa interlocked kutoka circuit breaker ya 032 upande wa low-voltage wa Transformer 2, kuchelewesha umeme wa 10 kV Section II na III busbars. Device ya automatic standby power supply (auto-standby) ilianza kufunga 10 kV Section I/II bus tie 020 circuit breaker.

Saa 06:36, protection ya over-current I section ya No. 1 earthing transformer ilianza, hutrip circuit breaker ya No. 1 earthing transformer 015 na interlocking kutoka circuit breaker ya 018 upande wa low-voltage wa Transformer 1, kuchelewesha umeme wa 10 kV Section I, II, na III busbars zote. Device ya auto-standby kisha ifunga circuit breaker ya 032 upande wa low-voltage wa Transformer 2 na No. 2 earthing transformer 022 circuit breaker. Hata hivyo, matatizo yakurudi, kuanza protection ya over-current I section ya No. 2 earthing transformer tena. Circuit breaker ya 022 hutrip na interlock kutoka circuit breaker ya 032, kuchelewesha umeme kamili wa 10 kV system ya substation.

3.2 On-site Equipment Inspection Results
Matokeo ya utafiti wa vifaa vya primary:

• Earthing transformer body: Hakukuwa na tofauti kwenye transformers wa earthing wa No.1 na No.2, hakuna athari za matatizo zenye windings au cores.

• 10 kV Section III bus PT interval (040 switchgear):

• Water stains zinazowebeka juu ya switchgear cabinet, kunainishia penetration ya mvua.

• Ablation yenye nguvu kwenye position ya C-phase ya shutter baffle ya handcart chamber, na holes miwili kwenye shutter chenye juu.

• Contact box na static contact wa C-phase chenye juu walikuwa wamecharred na damaged, na maji ya liquid vilikuwa vimekunyoka ndani ya box.

• Arc burn marks kwenye moving contacts ya C-phase chenye juu na chini ya arrester handcart, springs zenye annealed, na insulating cylinders za contact arm zenye damage.

• Outer insulating sleeve ya C-phase busbar kwenye bus chamber ilikuwa burned na cracked. Water stain penetration ilionyeshwa kwenye eneo la C-phase la backplate ya bus chamber, na water droplets vilikuwa vimekunyoka kwenye sensor ya live display.

• Maji kidogo vilikuwa vimekunyoka chini ya voltage transformer chamber, hata hivyo PTs za three-phase haikuwa na tofauti za nje zenye wingi.

Leakage ya mvua kutoka steel support juu ya 10 kV Section III bus PT chamber ilifika kwenye switchgear, kushinda insulation na kuleta discharge ya C-phase iliyokua metallic ground fault. Katika mfumo wa low-resistance grounding, transformer wa earthing wa No. 2 alidetected zero-sequence currents za ~4.3 A/phase (zisizozidi 2.5 A overcurrent I-section setting), kuanza tripping. Protection ya overcurrent haielimishe 10 kV auto-standby, kuleta operations zinazokurudi. Tripping ya mwisho ilianza auto-standby isipokuwa imecharge, kuchelewesha umeme kamili wa 10 kV.

Sababu muhimu: Control word ya "phase current zero-sequence cancellation" ilikuwa imezimwa (imepelekwa "0"), kuepusha software filtering ya zero-sequence components kwenye phase currents. Na zero-sequence current wa 13 A, protection ya overcurrent iliteleza vibaya. Ingawa imewekwa vizuri, hii control inaweza kuepusha matatizo. Badala yake, protection ya zero-sequence overcurrent I-section (imepelekwa 1.4 A) ilianza: time limit ya 1 hutrip bus tie na kuepusha auto-standby; time limit ya 2 hutrip transformers wa earthing na main, kuepusha Sections II/III ingawa Section I ikarudi umeme.

Sababu asili: Control word ya zero-sequence cancellation imezimwa iliyeruhusu misinterpretation ya phase current.

4 Conclusion

Makala hii hutaja settings za protection ya transformer wa earthing, huanaliza risks za malipo vibaya under high zero-sequence currents, na hujitolea kwa case study. Kuepusha recurrence:

• Weka features za zero-sequence cancellation za software-based (mfano wa "phase current zero-sequence cancellation" control word) kwenye mfumo wa low-resistance grounding.

• Ikiwa features hizo hazipo, optimize coordination kati ya settings za overcurrent na zero-sequence protection.

Key takeaway: Upatikanaji wa awali wa protection software ni muhimu sana kuepusha malipo vibaya wakati wa ground faults.