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Wasu Masu Gano-ganar da Aiki na Tashar Tsakiyar Wuri

A takaici masu gano-ganar da aiki (CSDs) suna kawo a matsayin yanke da za su iya taimakawa wajen kadan wasu abubuwan da suka faruwa a kan tsakiyar wuri masu yawan karamin da suka dace zuwa shunt reactors da capacitor banks. Kafin bayan haka, littattafai sun fiye masu amfani da su a cikin transmission lines da power transformers. Daga baya, wannan wasu sun yi tasirin yaɗuwar rike a kan waɗannan fasahoyi na musamman game da independently pole-operated circuit breakers (IPO).

Har zuwa, ziyukan talabarta masu kyau ta duniya ya haɓaka inganci a yi amfani da renewable energy sources a cikin grids na distribution na tashar tsakiyar wuri ba kawai a kan systems na transmission na yawan karamin (HV). Wannan haruffa ya bukata mu bi gaba a yi karfin daidaitun inrush currents da ba a kontrola ba a lokacin transformer energization.

Wasu switchgear na tashar tsakiyar wuri suna yi aiki a kan tsohon fasahoyi ɗaya, wanda yana bambanta da aiki na musamman a cikin applications na HV. Wannan ya buƙata yadda CSD technology ya dogara don iya yi gudanar da inrush currents na transformer energization da amfani da standard switches da fasahoyi ɗaya. Yanzu, wannan takardun ya fi amfani a cikin renewable energy installations kamar wind farms da photovoltaic solar plants, kuma a cikin industrial setups da transportation networks, inda kontrolin inrush currents yana da muhimmanci don in yi karfi da tsarin transformer na tashar tsakiyar wuri da yawan karamin.

Inrush Current a Cikin Transformers Na Tashar Tsakiyar Wuri

Yadda da yake inrush current a lokacin transformer energization yana da muhimmanci saboda flux na residual a cikin core na transformer; yadda da yake yawan flux na residual yana iya haifar da yawan inrush currents a lokacin random energization. Yanayin yanayin da za su iya taimakawa suna da muhimmanci don in kara disturbances operational da in tabbatar da grid stability.

Daga baya, da amfani da controlled switching techniques masu ilimi, ana iya haifar da ko kare inrush currents. Wasu hanyoyin haka suna iya sa system reliability, kuma suna kare taurari da equipment, kare costs maintenance, da kuma sanar da efficiency overall a cikin grids na distribution na tashar tsakiyar wuri. Amfani da technologies masu haka yana nuna babban farko a cikin adana da talabartun modern electrical distribution networks.

Ingantaccen Residual Flux Da Inrush Current Na Transformer

Bayanan field collected a lokacin commissioning na Controlled Switching Devices (CSDs) a cikin circuit breakers da switchgear da fasahoyi ɗaya suna tabbatar da ingantaccen residual flux da inrush current na transformer. Amfani da CSDs yana iya haifar da inrush current 3:1 kafin a taka random energization, wanda yana kare disturbances potential.

Hanyoyin Inrush Current Mitigation Da Gang Operated Circuit Breaker

Tushen da aka bayyana na yauke na neman inrush current mitiga applied to power transformers:

Idan phase R na transformer na demagnetized an energize a zero crossing na voltage (kamar yadda aka bayyana a kafa na Figure 1), zai iya kare core na transformer deep into saturation, kuma zai iya add 2 per-unit (p.u.) na flux a cikin core. Ingantaccen haka zai iya haifar da inrush currents saboda core saturation.

Amma, idan transformer an energize a positive voltage crest, initial positive quarter cycle yana iya add 1 p.u. na flux a cikin core. Idan voltage yana ƙare zuwa negative half-cycle, ita zai ƙare kare flux a cikin core. Saboda transformer ba ya samu saturation limit under conditions hakan, core saturation an kare, wanda yana kare inrush current.

Wannan scenario yana nuna steady-state energization na transformer, inda core flux lagging voltage by 90 degrees. Daga baya, da zama da timing careful ya kunshi moment na energization zuwa points optimal a kan waveform na voltage, risk na inrush currents an haifar, wanda yana tabbatar da transformer operation smoother da kuma more stable.

Muhimmanen, hanyoyin controlled switching suna amfani da timing precise don in haifar da inrush currents effectively. Daga baya, da kare core saturation through strategic energization points a cikin voltage cycle, wasu hanyoyin haka suna tabbatar da reliable transformer performance, enhance grid stability, da kuma kare disturbances operational. Wannan approach yana nuna babban farko a cikin technology na medium voltage switchgear, offering benefits substantial for both new installations and upgrades of existing systems.

Abin da ya fi yawa a lokacin da ake amfani da 3-phase switch da fasahoyi ɗaya. Bisa ga, selecting the energization instant that minimizes the inrush current on one phase can be detrimental to the other two phases. Wannan yana nuna a Figure 2, inda mitigating the inrush current for phase R na transformer na demagnetized (left) adversely affects phases Y and B (right).

Daga baya, da zama da optimize the energization moment for one phase to reduce its inrush current, the conditions for the other two phases may inadvertently lead to increased inrush currents, highlighting the need for a balanced approach in multi-phase systems.

Kamar yadda aka bayyana, pattern na residual flux a cikin power transformer yana nuna result na previous de-energization.

Idan transformer an re-energize, dynamic flux induced by the applied voltage is added to or subtracted from the residual flux depending on the polarity of the applied voltage. According to the principles of controlled switching, the optimal energization moment for a power transformer phase occurs when the induced prospective flux matches the existing residual flux (Figure 3, left). For instance, in the presence of positive residual flux, applying negative voltage would first decrease the core flux to zero at the negative voltage peak and then immediately reach the steady-state operation of the transformer without saturating its core.

Conversely (Figure 3, right), energizing the phase at a positive zero crossing of the voltage would add 2 p.u. of positive flux into the core on top of the existing 0.5 p.u. residual flux. This pushes the power transformer core into deep saturation, resulting in excessive inrush current. Therefore, the presence of residual flux increases the maximum inrush current when the transformer's energization is uncontrolled.

Precisely selecting the energization instant to match the induced flux with the residual flux can effectively prevent core saturation, thereby reducing inrush currents and ensuring smooth transformer operation. This strategy not only enhances system reliability but also extends equipment lifespan and reduces maintenance costs. Proper timing of energization is especially critical in multi-phase systems to balance performance across phases, ensuring grid stability and efficiency.

This approach underscores the importance of considering the effect of residual flux when designing and implementing controlled switching technologies for power transformers, aiming to achieve more efficient and reliable power transmission networks.

When there is residual flux in the transformer core, the situation with a gang-operated circuit breaker becomes even more complex. The optimal energization instant must consider the simultaneous operation of all three phases according to the magnitude and polarity of the residual flux. However, for each possible residual flux pattern, there is always an optimal energization instant that results in minimal transformer saturation (Figure 4).

In the following example, the residual flux pattern is 0, -0.5, and +0.5 p.u. in phases R, Y, and B, respectively. Energizing the power transformer at 90° (the voltage crest of phase R) results in the minimum saturation of the phases. However, closing the blue phase (assuming phase B) at the positive zero crossing of the voltage (240°) would cause the worst inrush current, which would be 6.5 times higher than the optimal switching instant calculated by a Controlled Switching Device (CSD).

This highlights the importance of accurately determining the optimal energization moment for each specific residual flux condition to minimize transformer saturation and inrush currents. Proper timing ensures smoother operation and enhances the reliability and efficiency of the power system.

When not controlling the energization of a power transformer, the worst possible inrush current will always appear on the phase with the highest residual flux. A Controlled Switching Device (CSD) minimizes the energization inrush current by computing the optimal pole-closing instant based on the residual flux pattern. Consequently, under specific high residual flux conditions, the inrush current can be entirely eliminated.

Figure 5 illustrates the theoretical relative inrush current during energization as a function of the highest of the three residual fluxes measured in the transformer (with a saturation knee at 1.2 p.u.). The peak inrush current is normalized to the maximum energization current of the demagnetized core. When the core residual flux is high (on the horizontal axis), the CSD eliminates the inrush current by preventing the transformer from entering saturation (bottom area of the blue line). Conversely, energizing the power transformer at a random moment can push the transformer into full saturation (red line), leading to excessive inrush current and subsequent voltage dips on the grid. This diagram thus demonstrates the effectiveness of inrush current mitigation provided by a CSD compared to random or uncontrolled energization.