بیانیهی امپدانس صفر دی-تایپ ترانسفورماتور گرندینگ با پیوند ZN
Sîstemê dêhatînê têk-sîlêkî bî karînên neutral-insulated, transformerê destûrdayîn an earthing transformer pîvandekî artificial ê reng dayîne, ku hewce ye ku bi serîyê were rengkirin an ji bo reactors/arc suppression coils. Pîvandekî ZNyn11 wekî nîşanî ûsahatî ye, ku jorînên magnetomotive zero-sequence li ser half-windings navendî/cih û ser core column yekan derbas bikin, ku divê hesabên çewtî yên sirriyê tevahî bibin û flux/impedance zero-sequence tevahî minîmal bikin.
Impedance zero-sequence ew dikeve: ew mîqdara hesabê çewtî û dagilayî phase-to-earth voltage di sîsteman impedance-earthed de hatîne.
1. Xusiyetên Transformerê Destûrdayîn bi Pîvandekî ZN
Heke transformeran YNd11-connected bikar bînin, ZNyn11 piştgirî ye (Fig. 1). Têk-nîşanan:
Di vexta çewtî yên phase ek an single-phase earth faults de, hilbijartina impedance destûrdayî saz ya hesabên phase short-circuit bi serîyê rated phase current ya transformerê bîtînin.
2. Analizê Impedance Zero-Sequence bi Transformeran Destûrdayîn bi Pîvandekî ZN
Parâmetreyên teknîkî yên peyva bînin ê model analizê earthing transformer li tabloya 1 de nîşan didin, ku divê deviyan allowed zero-sequence impedance di ±7.5% de be.
2.1 Kalkulasyonê Impedance Zero-Sequence bi Formula Empirical Tradisyonel
Wekî nîşan didin lêgerîna 2 (arrangement winding earthing transformer), impedance zero-sequence îfadan da ku niha ve herêmîn drop voltage di phase yekan de tevahî bibin, ku hesabên çewtî yên serîyê bi serîyê flow through all three phases simultaneously. Ji bo kalkulasyon, X0 piştgirî principle impedance ordinary double-winding power transformers (Equation 1).
Li formula, W niha ve herêmîn turns winding. Ji bo winding bi ZN connection, W niha ve herêmîn turns half - winding; ∑aR niha ve herêmîn equivalent leakage flux area. Ji bo winding bi ZN connection, niha ve herêmîn equivalent leakage flux area two half - windings; ρ niha ve herêmîn Rogowski coefficient; H niha ve herêmîn reactance height winding.
Bi serîyê data table 1 bi Equation (1), kalkulasyon impedance zero-sequence 70.6 Ω.
2.2 Analizê Impedance Zero-Sequence bi Software Electromagnetic
Software electromagnetic Magnet ji Infolytica bikar bînin ji bo analîz magnetic field. Model 3D simplified dibandin ji bo şertên structural product, wekî nîşan didin lêgerîna 3. Software solution algorithm T-Ω potential group bikar bînin bi elements laminated using 1st to 3rd order interpolation polynomials.
Finite element analysis (FEA) niha ve herêmîn method numerical calculation rooted principle variational û meshing interpolation. Piştî transform boundary value problem bi corresponding variational problem (i.e., extremum problem functional) bi serîyê principle variational, discretizes variational problem bi extremum problem common multivariate function bi serîyê meshing interpolation, ultimately reducing it set multivariate algebraic equations for solving numerical solution.During analysis, mesh divisions set as follows: air at 80, iron core at 30, and windings at 15. Product meshing diagram detailed in Figure 4.
Li algorithms finite element, polynomial order correlates accuracy shape functions field - domain - higher orders better characterize field properties. For this model, 2nd - order polynomial adopted, with maximum 20 iterations, 0.5% iteration error, and 0.01% conjugate gradient error.
To test zero - sequence impedance earthing transformer via field - circuit coupling method: apply high - voltage rated current (27.59 A peak for software) at neutral point, keep low - voltage side open - circuited, and measure voltage.
2.3 Measurement Impedance Zero-Sequence
Impedance zero-sequence measured between line terminals and neutral terminal earthing transformer at rated frequency (as shown in Figure 5), expressed ohms per phase. Its value calculated as 3U/I (where U test voltage and I test current). During measurement, rated current 19.5 A applied to line terminals, and voltage between line terminals and neutral point measured 443.3 V. Calculated impedance zero-sequence 68.2 Ω.
2.4 Comparative Analysis of Calculated, Simulated and Measured Values
Main performance parameters compared Table 2. Results show that both calculated and simulated zero-sequence impedances earthing transformer close to measured value, with deviations 3.5% and 0.88% respectively. Simulation results from electromagnetic software closer to measured values. Magnetic field analysis results help clearly understand magnetic field distribution characteristics product under working condition, which can used optimize electromagnetic design and structural design product based on magnetic field distribution characteristics.
Magnetic field simulation results obtained by electromagnetic software more closely aligned with measured values. With help magnetic field analysis results, characteristics product magnetic field distribution under working condition can more clearly understood, and thus targeted electromagnetic design and structural design product can carried out.
3.Conclusion
Impedance zero-sequence key parameter earthing transformers, with strict deviation requirements users. When calculating with traditional empirical formulas engineering, correcting empirical coefficients needed, which relies heavily designers' experience hardly ensures accuracy.
To improve accuracy, paper uses simulation software magnetic field analysis, compares empirical formula results, verifies through tests. Simulation results accurate can meet engineering needs.
