Abstract

This paper proposes a nonlinear electromagnetic-thermal-velocity coupling model to study the insulation performance of converter transformer, in which the saddle-like electric-stress dependence is considered under compound alternating current–direct current (AC-DC) voltage situation. Firstly, the conductance of transformer oil and oil-immersed pressboard have been measured through constructed three-electrode experimental system. An interesting electric-stress characteristic, which is saddle-like electric-stress dependence is obtained and counted in the thermal-insulation analysis in the proposed model. Then, the high-order harmonics of compound AC-DC voltage have been considered in the built electromagnetic-thermal-velocity coupling model. Additionally, the impact of non-uniform temperature result has been mapped to the electric field domain through interpolation method, due to different meshes between the flow-thermal and electric fields in accordance with distinct computational characteristics. Finally, the performance of nonlinear thermal-electric coupling properties, including saddle-like electric-stress dependence, have been considered in the proposed coupling model. Results determine that saddle-like thermal-electric dependent properties would considerably change insulation capability, compared with results from the traditional method. Even intensity field of some sampling points could jump more than 1.6 kV/mm. Therefore, it is essential to evaluate the insulation design by practical saddle-like electric-dependent properties.

Highlights

  • Converter transformer in high voltage direct current (HVDC) system is one of the most significant equipment for ensuring electric network security, and its operation condition is different from that of the traditional transformer

  • Where V is the volume conductivity (S/m), due to the leakage current going through the insulation material; R is the measured volume resistance ( ) when the measuring current is stable; A is the effective area of the measuring electrode (m2), which can be calculated on the basis of the national standard [13]; and h is the sample thickness (m), which is equal to the electrode gap when the transformer oil is measured

  • The KI50X mineral oil produced by Kunlun Lubricant, which is widely utilized in HVDC project, has been selected as the oil sample after filter and heat

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Summary

INTRODUCTION

Converter transformer in high voltage direct current (HVDC) system is one of the most significant equipment for ensuring electric network security, and its operation condition is different from that of the traditional transformer. The direct current (DC) component and high-order harmonic current of voltage source have a great influence on insulation state and thermal condition, respectively. Under the compound AC-DC condition of converter transformer, the coupling phenomenon is severe due to larger temperature and electric field. D. Pan et al.: Research on the Thermal-Electric Coupling Behavior Under Compound AC–DC Voltage research of converter transformer. Where V is the volume conductivity (S/m), due to the leakage current going through the insulation material; R is the measured volume resistance ( ) when the measuring current is stable; A is the effective area of the measuring electrode (m2), which can be calculated on the basis of the national standard [13]; and h is the sample thickness (m), which is equal to the electrode gap when the transformer oil is measured

CONDUCTIVITY MEASURED RESULTS
ELECTROMAGNETIC-FLOW-THERMAL COUPLING
Findings
CONCLUSION
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