The large transformer is pivotal equipment in an electric power supply system; Its partial discharge test and the induced voltage withstand test on large transformers are carried out at a frequency about twice the wor...The large transformer is pivotal equipment in an electric power supply system; Its partial discharge test and the induced voltage withstand test on large transformers are carried out at a frequency about twice the working frequency. If the magnetizing inductance cannot compensate for the stray capacitance, the test sample turns into a capacitive load and a capacitive rise exhibits in the testing circuit. For self-restoring insulation, a method has been recommended in IEC60-1 that an unapproved measuring system be calibrated by an approved system at a voltage not less than 50% of the rated testing voltage, and the result then be extrapolated linearly. It has been found that this method leads to great error due to the capacitive rise if it is not correctly used during a withstand voltage test under certain testing conditions, especiaUy for a test on high voltage transformers with large capacity. Since the withstand voltage test is the most important means to examine the operation reliability of a transformer, and it can be destructive to the insulation, a precise measurement must be guaranteed. In this paper a factor, named as the capacitive rise factor, is introduced to assess the rise. The voltage measurement error during the calibration is determined by the parameters of the test sample and the testing facilities, as well as the measuring point. Based on theoretical analysis in this paper, a novel method is suggested and demonstrated to estimate the error by using the capacitive rise factor and other known parame- ters of the testing circuit.展开更多
An asymmetric quantum well (AQW) is designed to emit a terahertz (THz) wave by using difference frequency generation (DFG) with the structure of GaAs/Al_(0.2)Ga_(0.8)As/Al_(0.5) Ga_(0.5)As under a doubly resonant cond...An asymmetric quantum well (AQW) is designed to emit a terahertz (THz) wave by using difference frequency generation (DFG) with the structure of GaAs/Al_(0.2)Ga_(0.8)As/Al_(0.5) Ga_(0.5)As under a doubly resonant condition.It is found that the second-order nonlinear susceptibility χ^((2)) varies with the two pump wavelengths,and it can reach the peak value of 1.61 μm/V when the wavelengths are given as λ_(p1) =9.756 μm and λ_(p2) =10.96 μm,respectively.The numerical results show that the refractive index of one pump wave in the AQW is concerned with not only its own wavelength but also the other wavelength.Phase-matching inside the AQW can be obtained through the tuning of the two pump wavelengths.展开更多
文摘The large transformer is pivotal equipment in an electric power supply system; Its partial discharge test and the induced voltage withstand test on large transformers are carried out at a frequency about twice the working frequency. If the magnetizing inductance cannot compensate for the stray capacitance, the test sample turns into a capacitive load and a capacitive rise exhibits in the testing circuit. For self-restoring insulation, a method has been recommended in IEC60-1 that an unapproved measuring system be calibrated by an approved system at a voltage not less than 50% of the rated testing voltage, and the result then be extrapolated linearly. It has been found that this method leads to great error due to the capacitive rise if it is not correctly used during a withstand voltage test under certain testing conditions, especiaUy for a test on high voltage transformers with large capacity. Since the withstand voltage test is the most important means to examine the operation reliability of a transformer, and it can be destructive to the insulation, a precise measurement must be guaranteed. In this paper a factor, named as the capacitive rise factor, is introduced to assess the rise. The voltage measurement error during the calibration is determined by the parameters of the test sample and the testing facilities, as well as the measuring point. Based on theoretical analysis in this paper, a novel method is suggested and demonstrated to estimate the error by using the capacitive rise factor and other known parame- ters of the testing circuit.
基金Supported by National Natural Science Foundation of China under Grant Nos 60801017,61172010,61101058,and 61107086the Science and Technology Committee of Tianjin under Grant No 11JCYBJC01100.
文摘An asymmetric quantum well (AQW) is designed to emit a terahertz (THz) wave by using difference frequency generation (DFG) with the structure of GaAs/Al_(0.2)Ga_(0.8)As/Al_(0.5) Ga_(0.5)As under a doubly resonant condition.It is found that the second-order nonlinear susceptibility χ^((2)) varies with the two pump wavelengths,and it can reach the peak value of 1.61 μm/V when the wavelengths are given as λ_(p1) =9.756 μm and λ_(p2) =10.96 μm,respectively.The numerical results show that the refractive index of one pump wave in the AQW is concerned with not only its own wavelength but also the other wavelength.Phase-matching inside the AQW can be obtained through the tuning of the two pump wavelengths.
