Kikomo cha Mfululizo wa Tiaji | Teknolojia & Athari kwa Ustawi wa Mtandao

1 Utangulizi kuhusu Teknolojia ya Fault Current Limiter (FCL)

Mfumo wa kawaida wa kuzuia mfululizo wa viwango vya umeme kutumia njia za kawaida kama kutumia transformers wa kiwango cha juu, reactors maalum, au busbar za kujifunza hupata changamoto za asili, ikiwa ni kuchelewesha muktadha wa mtandao, kuongeza ukunguaji wa mfumo wa kiwango cha kawaida, na kupunguza usalama na ustawi wa mfumo. Njia hizi zinapopungua ufanisi katika mitandao ya umeme yasiyofaa sana kwa mitandao ya umeme makubwa na magumu ya leo.

Kwa upande mwingine, teknolojia za kuzuia mfululizo wa viwango vya umeme yenye fursa, inayoreprezentwa na Fault Current Limiters (FCLs), huonyeshwa kiwango cha chini wakati wa kazi ya kawaida ya mitandao. Waktu mfululizo unafanyika, FCL anapokagua kwenye hali ya kiwango cha juu, kusaidia kukidhi mfululizo wa viwango vya umeme kwa kiwango cha chini, kwa hivyo kukabiliana na uongozi wa mfululizo wa viwango vya umeme. FCL zimetoka kutoka kwa ufumbuzi wa zamani wa kuzuia mfululizo wa viwango vya umeme kutumia reactor zilizojumuishwa na teknolojia za juu kama elektroniki ya nguvu, superconductivity, na uongozi wa magnetic circuit.

Misingi ya FCL yanaweza kurudiwa kwa modeli iliyotolewa katika Figure 1: wakati wa kazi ya kawaida ya mfumo, switch K unafungwa, na hakuna impedance ya kuzuia mfululizo inayotolewa na FCL. Tu wakati mfululizo unafanyika, K unafunguka haraka, ikifuatilia reactor ili kukidhi mfululizo wa viwango vya umeme.

Ingawa zaidi ya FCL zinatumia modeli hii ya misingi au aina zake zenye uzito, tofauti kuu kati ya FCL mbalimbali yanapatikana katika tabia ya impedance ya kuzuia mfululizo, utaratibu wa switch K, na mikakati yake ya uongozi.

2 Mfano wa Kutatua FCL na Hali ya Tumia

2.1 Superconducting Fault Current Limiters (SFCLs)

SFCL zinaweza kugrupishwa kama aina ya quench au non-quench kulingana na kama wanatumia mabadiliko ya superconductor kutoka kwenye hali ya superconducting hadi normal (S/N transition) kwa kudhibiti mfululizo wa viwango vya umeme. Kwa kihitimu, zinaweza kugrupishwa kama resistive, bridge-type, magnetically shielded, transformer-type, au saturated-core types. SFCL za aina ya quench hutumia S/N transition (kutokana na temperature, magnetic field, au current yakijitokezea kiwango cha juu), ambapo superconductor hungebadilika kutoka resistance ya sifuri hadi resistance ya juu, kusaidia kukidhi mfululizo wa viwango vya umeme.

SFCL za aina ya non-quench zinajumuishia coils za superconducting na component nyingine (kama vile elektroniki ya nguvu au magnetic elements) na mikakati ya uongozi ya kudhibiti mfululizo wa short-circuit. Matumizi ya SFCL yanaweza kupata changamoto za superconducting kama vile gharama na ufanisi wa kupunguza moto. Pia, SFCL za aina ya quench huanza kurejelea muda mrefu, ambayo inaweza kushindana na reclosing ya mfumo, wakati SFCL za aina ya non-quench changes ya impedance zinaweza kusababisha matatizo ya coordination ya relay protection, inahitaji kurekebishwa.

2.2 Magnetic Element Current Limiters

Hizi zinagrupishwa kama aina ya flux-cancellation au magnetic saturation switch. Katika aina ya flux-cancellation, windings watatu wenye polarity tofauti hutengenezwa kwenye core moja. Wakati wa kazi ya kawaida, flux equal and opposite hutolewa, kusaidia kupunguza leakage impedance.

Wakati mfululizo unafanyika, winding moja hutolewa, kusababisha imbalance ya flux na kuonyesha impedance ya juu. Aina ya magnetic saturation switch hutumia biasing ya winding ya kudhibiti current kwenye hali ya saturation (kutumia DC bias, ndc.) wakati wa kazi ya kawaida, kutoa impedance ya chini. Wakati mfululizo unafanyika, current ya mfululizo hupeleka core kutoka kwenye hali ya saturation, kusaidia kukidhi mfululizo wa viwango vya umeme. Kwa sababu ya mikakati ya uongozi magumu, limiters za magnetic element zinatumika kidogo.

2.3 PTC Resistor Current Limiters

Resistors za Positive Temperature Coefficient (PTC) zinashow nonlinear; wakati wa kazi ya kawaida, wanavyoonyesha resistance chache na heating chache. Wakati short circuit unafanyika, temperature yao hurudi haraka, kusababisha resistance ya juu kwa mara 8-10 orders of magnitude kwenye milliseconds. FCL zinazotumia PTC resistors zimeanza kutumiwa kwa biashara katika matumizi ya voltage chache.

Lakini, changamoto zinazozingatia ni: overvoltages ya juu zinazotolewa wakati ya kudhibiti mfululizo wa inductive (inahitaji overvoltage protection parallel), stress ya mekani ya resistor kwa sababu ya expansion wakati wa kazi, ratings ya voltage/current zinazopungua (hundreds of volts, a few amps), inahitaji series-parallel connections na kupunguza matumizi ya high-voltage, na recovery times mrefu (several minutes) na muda wa huduma mdogo, kusababisha matumizi kubwa.

2.4 Solid-State Current Limiters (SSCLs)

SSCL ni aina mpya ya kudhibiti mfululizo wa short-circuit kubwa kwenye elektroniki ya nguvu, mara nyingi inajumuisha reactors za kawaida, devices za elektroniki ya nguvu, na controllers. Wanaweza kutoa topologies nyingi, response haraka, endurance ya kazi ya juu, na uongozi rahisi. Kwa kudhibiti hali ya devices za elektroniki ya nguvu, equivalent impedance ya SSCL hupunguza ili kukidhi mfululizo wa viwango vya umeme. Kama FACTS device mpya, SSCL zinapata msingi zaidi. Lakini, wakati mfululizo unafanyika, devices za elektroniki ya nguvu hazitaweza kubeba mfululizo mzima, kuhitaji performance na capacity ya juu. Uhusiano kati ya multiple SSCLs au na miundombinu nyingine ya FACTS bado ni changamoto muhimu.

2.5 Economical Current Limiters

Hizi zinatoa teknolojia ya kutosha, usalama wa juu, gharama chache, na switching automatic isiyohitaji uongozi wa nje. Zinaweza kugrupishwa kama aina ya arc-current transfer au series-resonant. Aina ya arc-current transfer inajumuisha vacuum switch parallel na current-limiting resistor. Wakati wa kazi ya kawaida, current ya load hufuata switch. Wakati short circuit unafanyika, switch hupeleka, kusababisha current kugeukia resistor kwa kudhibiti mfululizo wa viwango vya umeme.

Matatizo yanayozingatia ni: transfer current unayozingatia voltage ya vacuum arc na stray inductance, transfer time unayezingatia speed ya switch, na ugumu wa kugeukia current wakati arc voltage ni chache, inahitaji devices za auxiliary kuboosta voltage ya arc na kufanya current zero-crossing. Series-resonant FCL zinatumia saturated reactors au surge arresters kama switches. Wakati wa kazi ya kawaida, capacitor na inductor hupiga series resonance na impedance chache. Wakati mfululizo unafanyika, current ya juu hufunga reactor au kusababisha arrester, kusababisha resonance kuteleza na kuingiza reactor kwenye line kwa kudhibiti mfululizo wa viwango vya umeme. Fast switches za electromagnetic repulsion pia zinaweza kugeukia capacitor haraka.

2.6 Hali ya Tumia ya FCL Engineering Applications

Kwa thamani ya kawaida, FCL zinapaswa si tu kuidhi impedance haraka wakati mfululizo unaonekana, lakini pia kufanya reset automatic, operations mingi za kawaida, generation ya harmonics chache, na gharama ya investment na operations inayotolewa. Sasa, zinazolimitwa na changamoto za teknolojia na gharama ya kutosha, ingawa prototypes nyingi zimeundwa duniani, matumizi ya grid halisi zimetulia, zinazolimika kwa projects za pilot za low-voltage, small-capacity.

Shughuli hiyo ilianza mapema nchi za nje, na maendeleo muhimu katika commercialization ya solid-state na superconducting FCL. Mnamo 1993, breaker wa 6.6 MW wa solid-state using anti-parallel GTOs uliwekwa kwenye feeder wa 4.6 kV kwenye Army Power Center nchini Marekani, anayecheza faults kwenye seconds 300 μs. Mnamo 1995, FCL ya 13.8 kV/675 A ya solid-state aliyotengeneza EPRI na Westinghouse ilihitaji commissioning kwenye substation ya PSE&G. Kwa SFCL, hybrid AC/DC FCL iliyotengeneza ACEC-Transport na GEC-Alsthom mnamo 1998, imetengeneza commercialization. Mnamo 1999, SFCL ya 15 kV/1200 A aliyotengeneza General Atomics na wengine iliyotengeneza ilihitaji deployment kwenye substation ya Southern California Edison (SCE).

Utafiti wa FCL wa kimataifa ulianza baada, lakini ulipanda haraka. Mnamo 2007, China's 35 kV superconducting saturated-core FCL, aliyotengeneza Tianjin Electromechanical Holdings na Beijing YunDian YingNa Superconductor Cable Co., Ltd., ulihitaji grid-connected trial operation kwenye Puji Substation, Yunnan - then the world's highest-voltage, highest-capacity superconducting limiter in trial operation. Kwa series-resonant FCL, China's first 500 kV device, jointly developed by China Electric Power Research Institute, Zhongdian Puri, and East China Grid, was commissioned at the 500 kV Bingyao Station in late 2009, reducing short-circuit current to below 47 kA.

Duniani, matumizi ya FCL zimetulia kwa projects zote, lakini zinapata msingi zaidi. Potential kubwa zinazobaki ni katika utafiti wa kuongeza ubora, voltage withstand, material improvements, heat dissipation, cost control, na topology optimization.

3 Athari ya Integration ya FCL kwa Usalama na Ustawi wa Mfumo wa Umeme

Idhinisha haraka ya FCL wakati mfululizo unaonekana, ingawa inaweza kudhibiti current effectively, inabadilisha parameters za network, inaathiri transient stability, voltage stability, relay protection settings, na reclosing. Uongozi chache unaweza kusababisha athari negative. Uongozi coordinated na optimal configuration ni muhimu kwa multiple FCL kufanya kazi kwa ubora.

3.1 Athari kwa Relay Protection na Reclosing Settings

Kwa SFCL za aina ya saturated-core, muda mrefu wa recovery unamaanisha impedance ya juu imebaki baada ya mfululizo, inahitaji kurekebishwa ya automatic reclosing na relay protection. Literature inasema kuhakikisha quench-type SFCL zinatumika kwenye generator na main transformer branches; ingawa re-setting ya protection inahitajika, high impedance ya persistent wakati wa recovery inaweza kutumika kama braking resistor, inasaidia transient stability. Various distance protection setting methods accounting for SFCLs have been proposed. Solid-state FCLs can use thyristor trigger signals, bypass breaker contacts, FCL switch positions, and GAP circuits to switch zero-sequence current protection settings, addressing sensitivity issues after FCL insertion.

3.2 Athari kwa Transient Power-Angle Stability

Ingawa FCL zinajaribu kufanya kazi kwa impedance chache kawaida na impedance ya juu wakati mfululizo, tabia yao ya kazi na structure zinaweza kusababisha athari tofauti kwa transient power-angle stability. Solid-state na superconducting FCL, kwa kuidhi high impedance wakati mfululizo, inaweza kuboresha electromagnetic power output ya generator na kuboresha transient stability.

Resistive-type FCL zinaboresha ustawi zaidi kuliko aina za inductive kwa kutoa damping resistance ambayo hutumia nguvu zaidi ya generator. Lakini, values ya resistance chache zinaweza kusababisha reverse power flow kwenye generator, kusababisha power deficits. Analysis inasema kuwa kwa mfululizo wanaoonekana mbali na generator, inductive SFCL zinaweza kuwa na faida zaidi tangu total transfer reactance ipungue. Resistive SFCL pia zina show characteristics similar beyond a threshold resistance.

Athari inategemea location na aina ya mfululizo; FCL zinaweza kusababisha athari kwa power-angle stability tu wakati mfululizo unafanyika kwenye lines zinazotengenezwa. Kwa mfululizo asymmetrical kwenye start ya line, FCL inductance inaweza kuwa na faida, inarudi kwa value ya inductance. Kwenye mwisho wa line, ikiwa mfululizo unachukua muda mfupi, FCL inductance inaweza kusababisha athari hasi, lakini negative impact inapungua kwa inductance ya juu kwa phase-to-phase na two-phase-to-ground faults. Kwa single-phase au phase-to-phase faults karibu na mwisho wa line, extending fault clearing time vizuri vinaweza kuwa na faida, significantly reducing swing curve amplitude compared to fast clearing.

3.3 Athari kwa Transient Voltage Stability

Short-circuit faults huchukua voltage dips, inasababisha athari kwa equipment operation na kuwa na losses za kiuchumi. Analysis based on PSCAD shows that larger FCL inductance improves voltage dip suppression within a certain range. The inherent ability of FCLs to improve fault voltage varies with network structure. On radial feeders, FCL reactance >0.5 pu can maintain voltage above 0.8 pu during faults. Local generation or reactive support near the fault bus reduces dependency on FCLs.

3.4 Coordination with Traditional Limiting Measures

Coordinating FCLs with traditional measures (e.g., reactors, high-impedance transformers) is key to practical application. An automatic optimization method using 0–1 variables for measure deployment and integer variables for capacity forms a mixed-integer programming problem, solvable by branch-and-bound methods, to guide coordinated configuration.

3.5 Optimization of Configuration

With multiple FCLs, optimizing location, number, and parameters for cost-effective performance is a research hotspot. For small grids, enumeration or methods based on power change/loss rate suffice. For large grids with multiple nodes exceeding short-circuit limits, enumeration becomes computationally intensive and inadequate for multi-objective problems (impedance, number, location).

Weighted multi-objective optimization using genetic or particle swarm algorithms is common, but results heavily depend on weight selection. Sensitivity-based methods, calculating short-circuit current changes relative to branch impedance, avoid weight dependence and help determine optimal FCL placement, number, and impedance. Since the primary goal is current limiting, optimization can focus on limiting effectiveness, ensuring selected FCL locations affect all nodes with insufficient short-circuit margin. Cost and operational losses are also critical factors in real-world optimization.

4 Development and Application Trends of FCLs

4.1 FCL Technology Research Trends

To leverage advantages and mitigate weaknesses, new research directions are emerging. Combining superconducting FCLs with energy storage is a hot topic—absorbing energy during faults and supplying it to improve power quality during normal operation, achieving dual benefits. The key lies in power conditioning system design.

To address high capacity demands, cost, and harmonics in solid-state limiters, improved topologies like transformer-coupled three-phase bridge SSCLs with bypass inductors have been proposed. Conventional FCLs lack dynamic adjustability and steady-state compensation.

A multi-functional FCL with dynamic series compensation has been proposed: normal operation uses capacitor bank switching for stepwise line compensation; during faults, GTOs or IGCTs control the limiting degree via a series inductor, enabling multi-purpose use. Series compensation must be chosen carefully to avoid sub-synchronous oscillations.

4.2 FCL Application Trends

FCLs not only limit short-circuit currents but, under suitable conditions, can enhance power-angle and voltage stability, expanding their application scope. Emerging trends include improving DC receiving-end transmission capacity, reducing commutation failure risk, enhancing power quality, and supporting large-scale renewable integration.

In multi-terminal DC systems, FCLs can limit current without affecting normal operation. For DC receiving-end grids, FCLs installed on fault propagation paths can isolate regions, block fault propagation, shorten commutation failure duration, accelerate DC power recovery, and mitigate power imbalances and power flow transfers from simultaneous multi-infeed DC failures, enhancing overall transient stability. For large asynchronous motors, integrating SFCLs in the stator circuit enables soft starting and suppresses fault current contribution, reducing voltage dips and improving transient voltage stability.

For large-scale wind integration, FCLs at wind farm connection points can improve fault ride-through capability and reduce disconnection risks. Resistive FCLs require less impedance than inductive types for stability under the same fault duration, but inductive types offer better improvement near critical stability.

As FCL technology matures, these fast-responding, multi-functional devices—limiting faults, enhancing stability, and isolating faults—will find broader applications.

5 Conclusion

FCLs effectively limit short-circuit currents but may impact power-angle/voltage stability, relay protection, and reclosing settings. Optimized configuration and coordinated control of multiple FCLs or with FACTS devices promise significant benefits. Future FCLs will extend beyond current limiting to enhancing DC transmission, reducing commutation failures, improving power quality, and supporting renewable integration.

However, technical and economic barriers delay large-scale application of high-voltage, high-capacity FCLs. Solid-state limiters, limited by device capacity and voltage ratings, are currently restricted to distribution networks. Advances in high-power self-commutating devices may overcome these bottlenecks and reduce costs.

Superconducting FCLs offer fast response and self-triggering but face high cooling costs, heat dissipation challenges, and long quench recovery times. Considering near-term feasibility and economics, economical FCLs based on conventional equipment are the preferred solution. Solid-state limiters, with lower technical barriers and maturity, represent the mainstream future direction.