Analysis of Nonlinear Characteristics for a Three-Phase, Five-Limb Transformer Under DC Bias

• Published in: IEEE transactions on power delivery Vol. 25; no. 4; pp. 2504 - 2510
• Main Authors: Xiaoping Li, Xishan Wen, Markham, P N, Yilu Liu
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.10.2010; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Applied sciences; Bias; Circuit simulation; Circuit testing; DC bias; Direct current; Direct current networks; Electric circuits; Electrical engineering. Electrical power engineering; Electrical power engineering; Exact sciences and technology; Grounding; Harmonics; HVDC transmission; Magnetic circuits; Magnetic cores; magnetic field intensity; Magnetic fields; Maxwell equations; Miscellaneous; no-load current; nonlinear characteristics; Nonlinearity; Phase transformers; Power networks and lines; Studies; three-phase five-limb transformer; Transformer cores; Transformers; Transformers and inductors; Grounding; nonlinear characteristics; Magnetic model; Magnetic circuit; Transformer cores; magnetic field intensity; Algorithm; Electric circuit; Non linear phenomenon; three-phase five-limb transformer; harmonics; Electrical network; Direct current; DC bias; System simulation; Single phase transformer; Non linear effect; HVDC systems; Magnetic field; Maxwell equation; no-load current
• ISSN: 0885-8977; 1937-4208
• DOI: 10.1109/TPWRD.2010.2052837

Monopole HVDC systems create dc current flow in the earth, which can cause the grounding location potential to rise relative to infinite spot and alters the working point of the transformer core. Because of the nonlinearity of the transformer core, the exciting current produces the amount of harmonics under dc bias. Past research has focused almost on simulation and testing dc bias problems of single-phase transformers. However, due to the complicated magnetic circuit structure in a three-phase five-limb transformer, there are some difficulties in studying its dc bias problem. In this paper, a new model and algorithm are proposed to find the nonlinear characteristics for the three-phase five-limb transformer under dc bias. Maxwell's equations are used to replace the magnetic circuit model of the transformer. By combining an electrical circuit with the nonlinear characteristic curve of the core, dc bias problems for a three-phase five-limb transformer are studied. Results show that the waveform of the no-load current and magnetic field intensity of the transformer are distorted under dc current inrush, and low-order harmonics increase with increasing dc current. Finally the interior and exterior nonlinear curve characteristics under dc bias are discussed.