Affiliations: [a] State Key Laboratory of Transmission and Distribution
Equipment and System Security and New Technology, School of Electrical
Engineering, Chongqing University, Chongqing, China | [b] Zibo Power Supply Company, Shandong Electric Power
Corporation, Zibo, Shandong, China
Correspondence:
[*]
Corresponding author: Fan Yang, State Key Laboratory of
Transmission and Distribution Equipment and System Security and New Technology,
School of Electrical Engineering, Chongqing University, Chongqing 400044,
China. Tel.: +86 139 9628 9198; E-mail: yangfancqu@gmail.com
Abstract: When HVDC transmission lines operate in the monopole ground return
mode or asymmetric bipolar mode, DC current flows in the earth and DC magnetic
bias will arise in neutral point grounding (NPG) transformers. In this work, the model to calculate the potential distribution for multi-layer soil
structure is set up, then the magnetic bias current (MBC) is calculated. The
magnetic field distribution in the NPG transformer is obtained according to
MBC, and electromagnetic energy and force in the transformer are calculated.
Finally, the influence on MBC, electromagnetic energy and force caused by soil
parameters are investigated. Results indicate that thickness of the first layer
and resistivity of the second layer have a greater contribution to MBC,
electromagnetic energy and force. To avoid excessive vibration of the NPG
transformer, the soil at grounding electrode with a greater thickness in the
first layer and lower resistivity in the second layer is preferred.
Keywords: DC current, electromagnetic energy, force, magnetic bias current (MBC), transformer
