The short-circuit electromagnetic force in radial direction induces critical mechanical stress on a power transformer. In this paper, the radial short-circuit forces which are exerted on transformer low voltage (LV) windings are investigated. Firstly, the mechanisms of leakage flux and short-circuit electromechanical forces in transformer coils are analyzed. Afterwards, based on IEC standards followed by short-circuit tests, calculations of radial short-circuit forces and evaluations of the ability to withstand short currents in LV windings are developed. The case studies and comparisons with improved measures show that the evaluation and calculation method is feasible and effective, and this method also offers three useful ways to strengthen the ability to withstand short-circuit currents for transformer windings.
Due to the large capacity of large power transformers, normally the power capacity of a load test is difficult to meet the test requirement, which makes the ancillary devices such as induction regulator, intermediate transformer etc. difficult to meet the test demands too. The transformer factories with limited power capacity can only perform load test under less than fifty-percent of the rated load current, which not obeys the standards and technical protocols. Thus, a field load test method for large power transformers is proposed in this paper. It carries out the reactive power compensation with compensation capacitors, which reduces the capacity of test power supply and makes the field load test possible. This method also gives a guarantee for the safe and stable operation of power transformers.
Sensorless control system for Permanent magnet synchronous motor (PMSM) has been widely used in many areas for its simple installing and easy realizing advantages. This paper mainly analysis sensorless control system of PMSM, estimate the angel of rotor and speed based on flux observation initially, PLL and state observer were used to obtain the accurate angle. Use Simulation toolbox design of MATLAB to implement the simulation of control system and analyze the simulation results. The results verify the correctness and feasibility flux observation method that used in paper.
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