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Figure 5 Design values of total losses (W) versus transformer rating (kVA) for different laminations. TL= Total losses.

Figure 5 Design values of total losses (W) versus transformer rating (kVA) for different laminations. TL= Total losses.

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Table 1: Parameters influencing transformer excitation current Many parameters impact the excitation currents and as a result, transformer manufacturers sometimes produce transformers with high excitation current that exceeds the standard levels. Consequently, the contribution of this article is very useful during both the design and production phases of transformers. If there is a good industrial control on parameters that impact excitation currents, transformers can be designed and later produced to fulfill the excitation current specifications. excitation current, presented in this paper, are very useful not only during the design stage, but also during the production phase. They allow the appropriate setting of production parameters so as to manufacture transformers with excitation currents within the specifications.
Table 1: Parameters influencing transformer excitation current Many parameters impact the excitation currents and as a result, transformer manufacturers sometimes produce transformers with high excitation current that exceeds the standard levels. Consequently, the contribution of this article is very useful during both the design and production phases of transformers. If there is a good industrial control on parameters that impact excitation currents, transformers can be designed and later produced to fulfill the excitation current specifications. excitation current, presented in this paper, are very useful not only during the design stage, but also during the production phase. They allow the appropriate setting of production parameters so as to manufacture transformers with excitation currents within the specifications.
Figure 1. Arrangement of the core pile after the annealing process. Four superior cores of this pile are fallen due to incorrect movement of the furnace cover and these cores should be re-annealed. annealing process. If the cores are not annealed in a homogeneous way, they will present high gradient of temperature [4]. The industrial experiments carried out by the authors have shown that when the arrangement of the cores in the furnace is not appropriate (the cores should be arranged in such a way that heating of any core is not appreciably affected by others due to obstruction), then the values of excitation current can increase up to 10%.
Figure 1. Arrangement of the core pile after the annealing process. Four superior cores of this pile are fallen due to incorrect movement of the furnace cover and these cores should be re-annealed. annealing process. If the cores are not annealed in a homogeneous way, they will present high gradient of temperature [4]. The industrial experiments carried out by the authors have shown that when the arrangement of the cores in the furnace is not appropriate (the cores should be arranged in such a way that heating of any core is not appreciably affected by others due to obstruction), then the values of excitation current can increase up to 10%.
If during the manufacturing process the cores are not appropriately handled (especially after annealing), then the excitation current is increased due the reintroduction of stresses into the steel [5]. Inadequate handling can occur during storage of the cores, transportation, and assembly of the core-winding set. Fig. 2 shows problems that should be avoided in the process. According to the figure, the steel sheet can lose the insulation when it is hauled over sharp corners. Figure 2. Stress introduced when the steel roll is hauled to manufacture the core.
If during the manufacturing process the cores are not appropriately handled (especially after annealing), then the excitation current is increased due the reintroduction of stresses into the steel [5]. Inadequate handling can occur during storage of the cores, transportation, and assembly of the core-winding set. Fig. 2 shows problems that should be avoided in the process. According to the figure, the steel sheet can lose the insulation when it is hauled over sharp corners. Figure 2. Stress introduced when the steel roll is hauled to manufacture the core.
Figure 3 Excitation current versus transformer rating (kVA) for three lamination thickness for different laminations. All the results have been obtained with a field-validated transformer design optimization computer program that has been used for many years in a mid-size transformer factory using equivalent loss for each transformer rating (See Figs. 4 and 5).
Figure 3 Excitation current versus transformer rating (kVA) for three lamination thickness for different laminations. All the results have been obtained with a field-validated transformer design optimization computer program that has been used for many years in a mid-size transformer factory using equivalent loss for each transformer rating (See Figs. 4 and 5).
Figure 4. Design values of no-load losses (W) versus transformer rating (kVA) for different laminations. NL= No load losses.
Figure 4. Design values of no-load losses (W) versus transformer rating (kVA) for different laminations. NL= No load losses.
As the air gap of the core is increased, the excitation current is also increased. This is validated with the control diagram of Fig. 6. The diagram shows the excitation currents of 32 cores of the same production batch. It is observed that the first 16 cores have higher values of excitation current as compared to the average value because these cores were manufactured with air gaps of the order of 4-5 mm. The remaining 16 measurements give lower values. These last cores have air gap length of the order of 1-2 mm. Figure 6. Control diagram of the excitation current of 32 cores of the same production batch. SL= Superior limit control, [L=Inferior limit control
As the air gap of the core is increased, the excitation current is also increased. This is validated with the control diagram of Fig. 6. The diagram shows the excitation currents of 32 cores of the same production batch. It is observed that the first 16 cores have higher values of excitation current as compared to the average value because these cores were manufactured with air gaps of the order of 4-5 mm. The remaining 16 measurements give lower values. These last cores have air gap length of the order of 1-2 mm. Figure 6. Control diagram of the excitation current of 32 cores of the same production batch. SL= Superior limit control, [L=Inferior limit control
Figure 8. Excitation current (in %) versus magnetic flux density (kG). By increasing the magnetic flux density the excitation current is notably increased; this behavior is explained because the increase of apparent losses in volt ampere of core material is increased with the increase of magnetic flux density. This can be seen in Fig. 8, which was obtained with the use of a field validated transformer design software for distribution transformer. 5) Lamination width for wound-core distribution transformers
Figure 8. Excitation current (in %) versus magnetic flux density (kG). By increasing the magnetic flux density the excitation current is notably increased; this behavior is explained because the increase of apparent losses in volt ampere of core material is increased with the increase of magnetic flux density. This can be seen in Fig. 8, which was obtained with the use of a field validated transformer design software for distribution transformer. 5) Lamination width for wound-core distribution transformers
Figure 7. Magnetic flux lines for an air gap of 3 mm and overlap length of 1 cm, a) Two laminations per layer, b) Eight laminations per layer.
Figure 7. Magnetic flux lines for an air gap of 3 mm and overlap length of 1 cm, a) Two laminations per layer, b) Eight laminations per layer.
Figure 10. Number of turns of low voltage (in %) versus transformer rating (kVA) for single phase transformers. Small circles represent manufactured transformers.
Figure 10. Number of turns of low voltage (in %) versus transformer rating (kVA) for single phase transformers. Small circles represent manufactured transformers.
Figure 9. Excitation current (in %) versus lamination width of the transformer core (mm)
Figure 9. Excitation current (in %) versus lamination width of the transformer core (mm)
Figure 11 Excitation current (in %) versus number of turns of low voltage.
Figure 11 Excitation current (in %) versus number of turns of low voltage.
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EngineeringMaterials SciencePrinted Circuit BoardAdvanced manufacturing technologyElectrostatic InductionAir Bearing
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