Abstract
Different from a three-winding transformer and ac passive filtering method, this paper proposes an inductive filtering (IF) method with a four-winding inductive filtering transformer (FW-IFT) for power system supplying nonlinear loads. Based on this, the characteristic parameters of the short-circuit impedance for the FW-IFT are studied in detail by theoretical analysis and experimental verification. According to the single-phase equivalent circuit, the voltage equations of the FW-IFT are established at the fundamental and harmonic frequencies. By short-circuit test, the constraint condition of the inductive filtering is obtained, which can satisfy the demand of nonlinear loads in power system. Then, the influences of the filter impedance on characteristic parameter of the short-circuit impedance are analyzed and calculated. The detailed theoretical calculation and the experimental results verified the feasibility and correctness of the aforementioned theoretical analysis and calculation.
Highlights
A three-winding transformer is a key electrical equipment in power systems supplying nonlinear loads
The characteristic parameters of the short-circuit impedance for the four-winding inductive filtering transformer (FW-IFT) are studied in detail by the systematic analysis and the short-circuited test
1) This paper has set up the constraint relationship of characteristic parameters of the short-circuit impedance for the FW-IFT, deduced by the short-circuited test according to the voltage transfer equations, and revealed the special independent filtering winding that the FW-IFT has
Summary
A three-winding transformer is a key electrical equipment in power systems supplying nonlinear loads. Always placed in tertiary winding or low-voltage side of this transformer In such a scheme, the passive filtering method can only alleviate harmonics of the low-voltage (LV) load side, whilst it cannot reduce that of the medium-voltage (MV) load side, and the power quality of the utility grid or high-voltage (HV) supply terminal cannot satisfy the IEEE Standard 519 [16]. Once two conditions are matched, the inductive filtering technique will be implemented In such a way, the main characteristic harmonics generated by nonlinear loads of the MV and/or LV side can be shielded, the harmonic magnetic potential of the transformer can be decreased greatly, and there are few current harmonics at the utility grid, which implies that the bad influences of the harmonic and reactive power on the FW-IFT can be alleviated immensely. The short-circuit impedance is very important characteristic parameters for realizing the IF method
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