Abstract
The time-domain field-circuit coupled finite element method (FEM) is widely used to analyze the DC effects on transformers. However, the long transient process of calculation will encounter difficulties due to the tremendous requirement of computer memory and CPU time, especially when it comes to ultra-high-voltage (UHV) autotransformers, which has a large time constant due to their less resistance and larger inductance. Besides, compared to the AC voltage, the DC voltage is much smaller, miscalculations usually occur as the component of DC bias can be easily neglected in the simulation. In this paper, a time-domain field-circuit coupling FEM combined with the series resistance and voltage compensation method (SRVCM) is proposed, a large resistance is in series in the circuit model to speed up the convergence of transient process and amplify DC component. Afterwards, the voltage supply is increased to compensate for the reduced voltage drop due to series resistance. The excitation waveform and its frequency characteristics of UHV autotransformer under various DC bias are discussed under no-load condition. Its advantages over conventional decrease the numerical miscalculation and the iterations calculation of the transient process. An experimental verification of the proposed method is carried out by a downscaled autotransformer.
Highlights
The increasing global demand for energy consumption and environmental impact become increasingly prominent, the serious energy crisis is becoming a key focus worldwide [1]–[3]
Eight 1000-kV ultra-high voltage (UHV) AC power transmission projects have been put into operation in China and over 100 units of UHV transformers have been put into service for solving the energy crisis [4]
This paper focuses on single-phase four-limb UHV autotransformer, which consists of two main limbs and two side limbs
Summary
The increasing global demand for energy consumption and environmental impact become increasingly prominent, the serious energy crisis is becoming a key focus worldwide [1]–[3]. For the purpose of increasing the calculation accuracy and speeding up the convergence of the transient process, this paper proposes a new fast solution by making good use of series resistance and voltage compensation method (SRVCM) based on time-domain filed-circuit coupling FEM. (i) Input coil current ik to the transformer magnetic field model, based on edge FEM energy disturbance principle, dynamic inductance L can be calculated. Taking IDC = 100 A as an example, with the increase of series resistance, the DC component in the high voltage winding gradually approximates to the added DC bias current value, and its miscalculation gradually drop from 7.0% of 200 to 2.5% of 500 and 0.7% of 1000. This means the second harmonic could be selected as an indicator sign for monitoring the DC bias current introduced into the transformer windings
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