Winding Impulse Voltage Distribution Based on Transformer Scale Model
2017-05-02 16:33:46 click: 780
Power transformers as the core equipment of the power grid, in the actual operation often need to withstand lightning and operation and other impact voltage role. It is of great practical significance and engineering application value to calculate and measure the winding voltage distribution of the power transformer under the action of the impulse voltage for the design and manufacture of the transformer insulation structure. However, the actual operation of the power transformer winding does not measure the tap, it is difficult to directly in the actual transformer winding to measure its voltage distribution. Therefore, by designing a transformer scale model with similar electrical characteristics and measuring tap, on this basis, the measurement of the winding voltage distribution is carried out. The result can not only be effectively pushed back to the prototype transformer, but also the winding voltage distribution under the impact voltage The mechanism analysis provides basic data. Key Content Transformer Zoom Ratio The transformer scale ratio is different from the simple scale model, and it is necessary to determine the shrinkage relation of each physical quantity. The key to establishing the scaling criterion is the selection of the scaling factor, which is the same as the original model. The dielectric constant, the conductivity, the permeability and the resistivity ρ of the shrinkage model are consistent with the original model, that is, the scaling coefficients of these physical quantities are both 1. Also assume that the electric field strength E remains constant, that is, the scaling factor kE is 1. According to the constitutive relation of current density J and electric field intensity E, kJ = kE = 1 is obtained. Note that the winding current density of the model and the original model remains constant. In the production of shrinkage model, the length, width and radius in accordance with the ratio of shrinkage ratio k reduced, so the rectangular and circular area S and other two-dimensional parameters of the shrinkage factor are k2. The scaling factor kt of time t is 1. Voltage and current parameters such as the ratio can be determined according to the relationship between the physical quantity. Transformer parameters of the transformer scale ratio transformer design of the transformer scale design includes transformer core structure design, transformer winding turns design and winding taps structure design. In this paper, the original model of the power transformer is 80MVA and the scale ratio is 10kVA. According to the shrinkage criterion, the final design of the transformer is made of silicon steel sheet, and the core structure is Column for the square column, left and right column is about cylindrical. Winding is located outside the core, the core diameter of 105mm, transformer high and low voltage winding is located in the diameter of 116mm outside, the middle of the epoxy cloth and epoxy tube. Transformer high voltage winding a total of 960 turns, divided into two parts, each part of the 480 turns, located in the core around the two cylinders. Winding every 48 turns as a layer, continuous around the core. And every 48 turns leads to a tap, a total of 20 taps. Transformer low-voltage winding a total of 176 turns, the average distribution of the core on the left and right two cylinders. Transformer winding taps The transformer is used to calculate the electric field distribution and magnetic field distribution of the original transformer and the scaling model. The finite element simulation of the electric field distribution and the magnetic field distribution of the original model and the scale model is carried out according to the similarity principle. , The original model and the scale model apply similar boundary conditions. When the electric field and the magnetic field work together on the transformer, the electromagnetic field distribution of the transformer original model and the scale ratio model show that the potential distribution and magnetic flux density distribution of the scaling model are consistent with the original model. Transformer Shifting Model Winding Impulse Voltage Distribution Based on the transformer scale model, the test platform is used to measure the impulse voltage distribution of the transformer high voltage winding. Based on the transformer voltage ratio model, the pulse width of the nanosecond pulse generator is 1400ns, and the voltage of different voltage amplitude is applied to the high voltage side of the winding, the low voltage winding in series and the low voltage winding connected by Measure the voltage waveform of each tap voltage of the high voltage winding to obtain the winding voltage distribution under different external voltage. From the test results can be seen: the impact voltage under the winding voltage distribution is very uneven, different voltage voltage distribution trend is basically the same, and the high voltage winding bear the end of the larger voltage. Mainly because the existence of stray capacitance between the winding makes the winding voltage distribution is very uneven, the shunt of the high voltage winding voltage distribution is extremely uneven and high voltage winding end to withstand a larger voltage. Conclusion 1) Considering the same skin depth, the ratio of the scale model is 400 times of that of the original model and the magnetic flux density B is 1/20 of the original model. 2) Based on the design of the transformer scale model, the design parameters, the original model and the shrinkage model of the transformer are simulated by COMSOL according to the requirements of this paper. The correctness of this paper is verified. 3) When the impulse voltage is applied, the winding voltage distribution is extremely uneven and the voltage at the head end is large. The shrinkage criterion proposed in this paper can be applied in the measurement of transformer winding voltage distribution test.
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