Research On The Multi-Physical Field Analysis And Application Of Dry-Type Air-Core Reactor

As one of the main inductive elements in Ultra-high Voltage AC-DC Transmission Program, Dry-Type Air-Core Reactor (DAR), with advantages of high linearity, simple structure and free maintenance, can work effectively in reactive power compensation, short circuit current limitation, harmonic filtration in power transmission system.With the continuous updating of voltage grade and expansion of electrical transmission network, loads of DAR are used in transmission system. However, as one of the powerful magnetic sources in electrical system, DAR has a severe disadvantage in magnet leakage that will interfere with the neighbor electrical devices on their normal operation and also have an underlying damage to the professional stuff and surrounding people. Magnetic shielding measures of DAR are easy to evaluate in engineering, while the optimal scheme is difficult to obtain. Besides, a coaxial multiple-layer encapsulation structure makes it harder to examine the temperature changing situation of the encapsulation hot point in reactors, plus there are no effective on-line supervision equipment which can solve the reactor operation in a long-term over-heating state. That will shorten the life expectancy and contribute to serious fire accident, all of which pose a great threatening damage to the transmission safe-operation. Time-varying current excitation also has an impact on the mechanical performance of reactors that are forced to vibration resulting in a potential breakdown by the mechanical fatigue damage. On top of this, reactors also produce the structural radiation noise to all around and are becoming the main noise origin in power system.Based on the exposed issues of reactors presented above, the main studies in this paper include magnetic leakage, temperature rise and mechanical vibration characteristics as well as on-line supervision.(1) Studies on magnetic shielding optimization for reactors. Based on the principal of power frequency magnetic shielding, an optimized model for magnetic shielding is built where the hybrid optimization algorithm combining differential evolution algorithm with edge finite element method is put forward to optimize the problem. And the center distance, shielding structure parameters are all comprehensively considered into the object function. Magnetic shielding of three phase reactors with trigonometric form arrangement is optimized, and the optimal shielding results show that increasing the erecting height of shielding board and the diameter can decrease the maximum magnetic induction intensity efficiently while dropping down the center distance properly can improve the average magnetic intensity. This algorithm avoids the limitation of manual single factor-searching methods and provides a reference to magnetic shielding for DAR. Furthermore, the optimized model and algorithm can also be applied to electro-magnetic field study of other high voltage devices.(2) Studies on three-dimensional liquid-solid coupling temperature field of DAR. With reference to the theories of computational fluid mechanics and heat transmission, a mathematical model is established where the eddy loss of star-shaped framework is firstly taken into account as an affecting factor to temperature rise at the encapsulation end. And the three-dimensional model is meshed by application of structural mesh, and finite volume method is also utilized to solve directly the steady flow field and temperature field of DAR, then the temperature distribution property is acquired and the temperature variation characteristics of hot point is concluded. The axial temperature along the encapsulation can be divided into3areas with different temperature gradient and the hot point mainly groups in the top-end area, and the temperature rise from the eddy loss of the framework is appropriately3K. Eventually, forced convection is researched to improve the temperature rise effect of the hot point, the result dedicates that the air flow speed has a nonlinear decreasing relationship with the temperature of the hot point, and if the air flow speed gets growing up, then the effect of heat dissipation will tend to be a saturation state. The calculation model and methodology in this paper can offer foundation to supervise temperature rise of reactors and be applied to the fluid-solid coupling temperature field for other high voltage devices.(3) The experiments on the temperature rise and noise of reactors. Optical fiber thermometry is employed to measure the temperature rise in natural convection condition and the relevant coefficient of measured encapsulation temperature value and calculated value is0.918, which shows an agreement. The experimental results highly verify the accuracy and effectiveness of the numerical calculation of the temperature field. The second experiment, namely the frequency spectrum noise test presents that under power frequency current excitation, the radiated noise derived from electromagnetic vibration is100Hz sound pressure.(4) Numerical calculation of electromagnetic vibration of reactors. According to coupling way between magnet and structural order, the structure mode is discussed by engaging finite element method and both natural frequency and modal shape for DAR are obtained. Based on harmonic response analysis, electromagnetic force under power frequency current excitation is mapped with the structure mesh, the vibration frequency spectrum is gained and the consequences represents that the encapsulation vibration predominates in the radial direction, with less axial vibration.(5) Design on the online temperature monitoring and temperature rise fault prediction system. In order to decrease the operation accidents resulted from over-temperature of DAR and apply the results coming from the liquid-solid coupling temperature field research into practical projects, the online temperature monitoring system is designed where the temperature signal and layout method are all analyzed and fiber grating sensor is selected as the thermometric element. The background temperature, relative humility and solar intensity are all considered in terms of their impacts on the temperature of the hot point. It is less likely to misjudge the over-temperature accidents by combining the regression model, inserted by support vector machine combined with differential evolution algorithm. This monitoring system has an excellent advantage of interference resistance and high accuracy of warning, all of which have made up for the blank in real-time monitoring and protection mechanisms of DAR.