Split-winding Transformer Research Articles

Measurement of Circulating Currents in Split-Winding Transformer and Comparison with Numerical Calculation

Split-winding transformer is a one of the common transformer types with one low-voltage winding placed above the other low-voltage winding and with the jointly high-voltage and regulation winding. The paper investigates circulating currents that occur in high-voltage and regulation windings in case of nonsymmetric load. In addition, measurement of circulating currents for a case of 240MVA, 220 kV transformer is presented along with a numerical calculation of circulating currents and compared with the measurement.

Analysis of Turn-to-Turn Fault on Split-Winding Transformer Using Coupled Field-Circuit Approach

The turn-to-turn faults (TTF) are also inevitable in split-winding transformers. The distorted leakage field generated by the TTF current results in large axial forces and end thrusts in the fault windings as well as affecting other branch windings normal operation, so it is of significance to study TTF of split-winding transformers. In this paper, the characteristics analysis of the split-winding transformer under the TTFs of the low voltage winding at different positions are presented. A 3600 KVA four split-windings transformer is taken as an example. Then, a simplified three-dimensional simplified model is established, taking into account the forces of the per-turn coil. The nonlinear-transient field-circuit coupled finite element method is used for the model. The leakage field distribution under the TTFs of the low voltage winding at different positions is studied. The resultant force of the short-circuit winding and the force of the per-turn coil are obtained. Subsequently, the force and current relationship between the branch windings are analyzed. The results show that the TTF at the specific location has a great influence on the axial windings on the same core, and the distorted leakage magnetic field will cause excessive axial force and end thrust of the normal and short-circuit windings. These results can provide a basis for the short-circuit design of split-winding transformer.

Multi-Conductor Transmission Line Model of Split-Winding Transformer for Frequency Response and Disk-to-Disk Fault Analysis

For transformer designers, split-winding transformer modeling in different frequency ranges is of great importance. In this paper, for the first time, a multi-conductor transmission line model is proposed for high-frequency modeling of the split-winding transformer. In this model, all the turns in layers and disks have been considered and the model's parameters have been calculated using the finite element method. In order to validate the proposed model, the results are compared with the result of a model, which is based on finite element and coupled field-circuit. It is shown that the introduced model has good accuracy and it can be employed for split-winding transformer modeling in different frequency ranges. In addition, using the validated multi-conductor transmission line model, the frequency response of the split-winding transformer and disk-to-disk short circuit fault are analyzed.

Research of Short-Circuit Performance of a Split-Winding Transformer With Stabilizing Windings

Short-circuit faults are inevitable in split-winding transformers with stabilizing windings, and the resulting transient electromagnetic force may cause detrimental damages to the equipment. This paper focuses on a comprehensive analysis of the characteristics of the split-winding transformer with stabilizing windings under different short-circuit faults. In this regard, a FEM based on a field-circuit coupled approach is proposed. Also, a SFFZ10-88000-kVA split-winding transformer with stabilizing windings is used as a prototype to investigate its transient performances with both full-crossing and half-crossing conditions under different short-circuit faults. The symmetrical component method is presented to compute short-circuit currents to compare with the simulation ones, and a prototype test model is established to verify the correctness of the proposed method. The results reveal that the axial forces exerted on the winding in half-crossing short-circuit faults are generally larger than those in full-crossing short-circuit faults. Moreover, there is a considerable short-circuit force in the stabilizing winding in cases of a single-phase earthed fault and a two-phase earthed fault and there is no current in the stabilizing winding under other short-circuit fault cases. The numerical modeling approach dealt with in this paper is expected to be useful in the design of the split-winding transformer with stabilizing windings.

Split‐winding transformer design using new hybrid optimisation algorithm based on PSO and I‐BB‐BC

Split-winding transformer design is a time-consuming and complicated procedure. Considering the number of windings and their geometries, the design parameters of the split-winding transformer cannot easily be determined to reach an acceptable and low-cost scheme. Their manufacturing and operational costs are very higher than the usual two-winding transformers and they may be subjected to multidimensional restrictions. The split-winding transformer design needs to select around 20 parameters to achieve different goals such as windings leakage inductances, four windings temperature rises, no-load and load losses, transformer dimensions, windings coordination. A new hybrid algorithm based on particle swarm optimisation (PSO) and an improved big bang-big crunch (I-BB-BC) algorithm (named PSO-IBB), is introduced for optimisation (optimal design) of split-winding transformer. Using this novel algorithm, the optimal designs are extracted and compared to the results obtained by PSO and I-BB-BC algorithms. By analysing the divergence of the extracted results, it is seen that the proposed hybrid PSO-IBB optimisation algorithm has good performance and it can reach the global optima very fast.

Nonlinear behavior analysis of split-winding dry-type transformer using a new star model and a coupled field-circuit approach

AbstractRegarding the importance of short circuit and inrush current simulations in the split-winding transformer, a novel nonlinear equivalent circuit is introduced in this paper for nonlinear simulation of this transformer. The equivalent circuit is extended using the nonlinear inductances. Employing a numerical method, leakage and magnetizing inductances in the split-winding transformer are extracted and the nonlinear model inductances are estimated using these inductances. The introduced model is validated and using this nonlinear model, inrush and short-circuit currents are calculated. It has been seen that the introduced model is valid and suitable for simulations of the split-winding transformer due to various loading conditions. Finally, the effects of nonlinearity of the model inductances are discussed in the following.

Research on Numerical Simulation of 3D Leakage Magnetic Field and Short-circuit Impedance of Axial Dual-low-voltage Split-winding Transformer

It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.

Analysis of Short-Circuit Performance of Split-Winding Transformer Using Coupled Field-Circuit Approach

The split-winding arrangement requires special short-circuit design considerations. During short-circuit conditions, there is a considerable distortion of the leakage field, which in turn produces high axial short-circuit forces. This paper deals with the computation and analysis of electromagnetic forces in windings of split-winding transformers. A nonlinear-transient field-circuit coupled finite element model is used to simulate the split-winding transformer. A 70-MVA, three-phase, 220/6.9/6.9-kV split-winding transformer is modeled under preset and postset short-circuit test conditions. Under the preset condition, the transformer is analyzed with one as well as both the LV windings short circuited to compare the axial forces produced in the windings for these two cases. The results show that there is a considerable rise in the axial forces when one winding is short circuited as compared with the case when both windings are short circuited. The effect of initial magnetization of core on axial short-circuit forces is calculated and discussed. It is also shown that even though postset method eliminates inrush related problems there is not much respite in short-circuit forces

Split winding transformers

A discussion of the application of and advantages derived from the use of split winding transformers for separating bus sections and for avoiding undue concentration of power from high voltage lines. An explanation is given of the characteristics of these units with respect to the reactances and the effect of load unbalance on the windings.

Split Winding Transformers

A discussion of the application of and advantages derived from the use of split winding transformers for separating bus sections and For avoiding undue concentration of power from high voltage lines. An explanation is given of the characteristics of these units with respect to the reactances and the effect of load unbalance on the windings.