DC Biased Transformer Research Articles

Determination of Parasitic Capacitance of High-Power Medium Frequency Transformers: Case Study of a High Voltage DC Biased Transformer for Wind Power Application

Determination of Parasitic Capacitance of High-Power Medium Frequency Transformers: Case Study of a High Voltage DC Biased Transformer for Wind Power Application

Research on excitation current and vibration characteristics of DC biased transformer

In practical engineering, DC disturbance will lead to excitation saturation and vibration intensification on transformer core, as well as affecting the normal operation of equipment and power grid. According to the problem, a new idea is proposed in this paper. Based on the electromagnetic characteristics of DC biased transformer, excitation saturation and core vibration are studied by using excitation-vibration harmonic response analysis method. Excitation current is identified through electromagnetic coupling to characterize the excitation saturation degree. Then, vibration harmonic response model is established to analyze core vibration. Electromagnetic characteristics of DC biased Y/Δ transformer are simulated. The variation of excitation current and core vibration at different DC levels are studied. Excitation-vibration characteristics of three-phase group transformer and three-phase three-limb transformer are compared and summarized. With experimental platform built, the correctness of simulation results is verified by experimental data, and the effectiveness of the proposed method can be proved.

Magnetization Research in Time-Domain Magnetic-Circuit Coupled Computation for DC-Biased Transformer

By revised method of fitting magnetization curve in segment, technique of simulating the nonlinear characteristic of laminated core is enhanced. The DC-bias problem is computed based on the time-domain magnetic-circuit coupled model while considering the saturated and unsaturated magnetizing characteristics of the laminated core. Experiments are designed to verify the validity of the proposed method, and then the volt-ampere feature of unsaturated magnetization is learned. Consequently, the results indicate that the improved method is more accurate and efficient by contrast.

Vibration and Audible Noise Characteristics of AC Transformer Caused by HVDC System Under Monopole Operation

When the HVDC system works in monopole ground return mode, dc current flows through the neutral of ac power transformer with the neutral grounded, which will enhance its vibration and audible noise. In this paper, dc bias experiments on ac power transformers carried out on 500-kV power transformers both in the transformer factory and the substation are described; the experimental results show how the vibration and audible noise of the transformer change under the dc bias current or windings voltage. The frequency characteristics of the vibration and audible noise of the dc-biased transformer are discussed under the conditions with and without loads. The direct connections between the vibration peak value and the dc bias current, and between the sound pressure and the dc bias current are revealed. Long-term online monitoring shows that the vibration of the transformer changes seriously even if there is not a dc system operating in monopole earth return mode, so when we analyze the influence of dc bias on the vibration and audible noise of the transformer, other influential factors should be expelled.

Harmonics generated from a DC biased transformer

Harmonic characteristics of transformer excitation currents under DC bias caused by geomagnetically induced currents (GICs) are presented. A saturation model for a single phase shell-form transformer based on 3-D finite-element analysis is used to calculate the excitation currents. As a consequence, the variation of excitation current harmonics over an extended range of GIC bias is determined. The results of this study are useful in understanding transformers as harmonic sources and their impact on power systems during a solar magnetic disturbance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>