Design And Realization Of Assessment Software For DC-bias Of Large Transformers

Magnetic storm caused by violent activities of the sun and single polar earthing current of the HVDC project invade the grounded thansformer neutrals, the large scale-transformer working at the rated state will partially be saturated, and its magnetic current will be distorted accompanying with various of harmonic, increasing reactive power demand, nosie, vibration and some other affiliated phenomnon. It can not reflect the actual hysteresis characteristics and the numerical oscillation problem caused by piecewise linearization, and is hard to quantitative calculation of transformer DC-bias problems becaues the iron core's excitation characteristics are processed using piecewise linear model when study the DC-bias problems using the existing simulation software(such as PSCAD). So it is essential to develop a software system can assess the DC-bias situation of transformers rapidly and conveniently.This paper establishes a transformer saturation circuit model of DC-bias under duality principle basing on J-A theroy which can reflect the hysteresis characteristics of iron core, and develops a software can assess the effects of transformer DC-bias using hybrid programming technology of C#.net and MATLAB with the microsoft.net platform. This software is able to simulate the mangnetizing current of different structures and assess the saturation level of transformers and the influnces of affilicated phenomenon accroding to the rated parameters of transformers and structural parameters of core and the DC current. The reasult is given by calling the drawing program of MATLAB. At the last, analysis the magnetic current, harmonic and reactive power situation of ODFS-250000/500 transformer under normal no-load and DC-bias condition. Then proves the effective of calculation result through compared to the simulation results by PSCAD.