بەکارهێنانی دەستگری کۆنتڕۆڵ بۆ کاهێنانی چاکانی سەرچاوەی ترانسفۆرمەری نیمی هەژارە ولت
Kontrolkirîn Cihazên Binyînî yên Dîmena Nîvendî
Pêş de tirsan sê dêh, Cihazên Binyînî Kontrolkirî (CSD) hêjir kirin bi sedeya piştguhên binyînî yên çavkaniya li ser reaktoran paralel û bankên kapasitorkan. Li dawiyê zanistina herî vir di wan vê cihazan de hatiye pelandin bi ser rêtên transmetisyon û transformatoran. Di destpêkir, wan cihazan demên binyînî bi rêza her pêve bi ser circuit breakers-ê pol-operated independently (IPO) hatiye kontrolkir.
Di demên derbarê, çavkanî energiya jîyayî di navbera sisteman distribûsyon nîvendî da ku ji lêserîna sîsteman transmetisyon dîmena bilind ên vir. Vê guherandê hate dixwazin da ku pirsgirêka problemên dipên voltajê ya ji bar wekîna inrush currents di dema energizasyonê de transformatoran.
Switchgear nîvendî yekêker bi sê pole hatiye kar kird, ku ji bo operasyonê independent di dîmena bilind de nehatiye. Vê hate dixwazin biguherîneke teknolojî CSD bi sedeya xwe ye ku binişanîna inrush currents bi ser switchên standart bi operasyonê yekbûyî pole. Di roja heyî de, vê innovasyonê yekêker bi ser instalasyonên energy jîyayî wêgeha wind farms û plants solar photovoltaic, da ku heta di setupên industriyey û networkên transportasyon de, ku kontrolkirina inrush currents yekêm eku bi ser energizasyonê yekparast bike transformatoran nîvendî û dîmena bilind.
Inrush Current di Transformatoran Nîvendî de
Mîqdara inrush current di dema energizasyonê de transformatoran yekêker bi fluxê residual di nav core transformator de; mîqdara fluxê residual bi berdewam zêde dikare ku bi ser energizasyonê random inrush currents zêde bike. Strategîyan efektîvan mitigaşûnê zêde dirayînin ku bi tenê bikar bînin ku bi şopandina operasyonê û amana stabilitê gridê.
Bi implementasyonê teknikên binyînî kontrolkirî piştguh, mumkin e ku minimiz bikin an elimin bikin inrush currents. Yekêker bi ser metoda wan, systemê bi amanî hatiye pelandin, ji bo dema cihazan ve hatiye pelandin, xarcên maintenance hatiye kevîn, û efektivîyatê yekêker bi ser gridan distribûsyon nîvendî hatiye pelandin. Bi qebûlkirina teknolojiyan sê tiştê nişan dike hevdengîn pivînîn di ser peyvên moderna sistemên distribûsyon elektrik de.
Parastnîsha Fluxê Residual û Inrush Current Transformator
Data field di dema komisyonkirina CSDs li ser circuit breakers û switchgear bi operasyonê yekbûyî pole hatiye teyit kirin parastnîsha fluxê residual û inrush current. Bi ser bikar bînin CSDs dikare ku 3:1 reduksiyon bi ser inrush current bi ser energizasyonê random bide, ku bi tenê bikar bînin ku bi şopandina potensiyelên disturbs.
Metodên Mitigaşûnê Inrush Current bi Circuit Breaker Gang Operated
Têrsibina jêrîn ilustration dike konseptê binyînî kontrolkirî bi ser inrush current mitigation applied to power transformers:
Ji dema transformator demagnetized R phase bi ser zero crossing of voltage (wêne li ser şopê çep Figure 1), force dikare ku core transformator bi ser saturation, bi ser adding 2 per-unit (p.u.) flux into the core. This condition can lead to significant inrush currents due to core saturation.
However, when the transformer is energized at the positive voltage crest, this initial positive quarter cycle only adds 1 p.u. of flux into the core. As the voltage then transitions to its negative half-cycle, it begins to decrease the flux within the core. Since the transformer does not reach its saturation limit under these conditions, core saturation is avoided, thereby preventing the occurrence of inrush current.
This scenario corresponds to the steady-state energization of the transformer, where the core flux lags the voltage by 90 degrees. By carefully timing the moment of energization to coincide with optimal points in the voltage waveform, the risk of inrush currents is minimized, ensuring smoother and more stable transformer operation.
In summary, controlled switching techniques leverage precise timing to mitigate inrush currents effectively. By avoiding core saturation through strategic energization points in the voltage cycle, these methods ensure reliable transformer performance, enhance grid stability, and reduce operational disturbances. This approach represents a critical advancement in medium voltage switchgear technology, offering substantial benefits for both new installations and upgrades of existing systems.
The situation becomes more complex when using a 3-phase switch with simultaneous pole operation. In fact, selecting the energization instant that minimizes the inrush current on one phase can be detrimental to the other two phases. This is illustrated in Figure 2, where mitigating the inrush current for phase R of a demagnetized transformer (left) adversely affects phases Y and B (right).
By optimizing 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.
As explained previously, the residual flux pattern in a power transformer is the result of its previous de-energization.
When a transformer is re-energized, the 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.
