In view of long-term transformer insulation resistance and dielectric loss measurement, measurement and according to the national standard formula conversion values are not completely consistent, in this paper, a vari...In view of long-term transformer insulation resistance and dielectric loss measurement, measurement and according to the national standard formula conversion values are not completely consistent, in this paper, a variety of transformers are studied, and the applicable scope of the conversion formula is discussed emphatically, combined with the test results are analyzed of transformer insulation resistance value to temperature and oiliness and dielectric loss tangent to temperature and oiliness, and puts forward suggestions on how to improve the insulation performance of transformer.展开更多
Method IEEE 841 is used to test endurance of insulation system of stators to 100% humidity at 40 ℃ for168 h. Insulation resistance after this test between phases or between phase and frame has not been lover as 5 ...Method IEEE 841 is used to test endurance of insulation system of stators to 100% humidity at 40 ℃ for168 h. Insulation resistance after this test between phases or between phase and frame has not been lover as 5 × 10^6 Ohm. Some producers of motors use this method for determining quality of impregation resin. On such test insulation resistance between phases was lover as between phase and frame. Because between phases is only wire insulation impregnating resins on insulation resistance of insulation system an impregnating resin we observe influence of type of wires and after humidity test. With diagnostic of insulation, the state is dealt. We compare our impregnation resin with competitive impregnation resin. We made test on twisted coils prepared after STN IEC from two parallel wires. In this test, we succeed in demonstrating that the main influence on insulation resistance of insulation system wire and impregnation resin has insulation of wire. Impregnation resin has influenced on data dispersion.展开更多
After successfully growing single-crystal TaP, we measured its longitudinal resistivity （Pxx） and Hall resistivity （Pyx） at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresista...After successfully growing single-crystal TaP, we measured its longitudinal resistivity （Pxx） and Hall resistivity （Pyx） at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresistance （MR） reached 3.28 ×10^5% at 2 K, 176% at 300 K. Neither value appeared saturated. We confirmed that TaP is a hole-electron compensated semimetal with a low carrier concentration and high hole mobility ofμh=3.71 × 105 cm2/V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, because a magnetic field （H） was applied in parallel to the electric field （E）, a negative MR due to a chiral anomaly was observed and reached -3000% at 9 T without any sign of saturation, either, which is in contrast to other Weyl semimetals （WSMs）. The analysis of the Shubnikov-de Haas （SdH） oscillations superimposed on the MR revealed that a nontrivial Berry＇s phase with a strong offset of 0.3958, which is the characteristic feature of charge carriers enclosing a Weyl node. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.展开更多
There has not been an effective method to measure the resistivity of small-size sample of mineral and solid insulating material until now.According to the Chinese National Standard(GB/T1410-2006) and features of digit...There has not been an effective method to measure the resistivity of small-size sample of mineral and solid insulating material until now.According to the Chinese National Standard(GB/T1410-2006) and features of digital high resistance meter,a small electrode experimental installation was developed;it can work with current high resistance meter;the sample decreases to 18 mm from standard size 100 mm in diameter and reduces by 30.86 times in area.A three-electrode system is supported and precisely positioned by two insulating bases whose diameter is 60 mm and height is 20 mm,which ensures accuracy of device structure and reliability of measuring results.The key technological parameters are as follows:diameter of high voltage electrode is 18mm;diameter of measuring electrode is 14.6 mm;internal diameter and external diameter of guard electrode are 16 and 18 mm,respectively;the gap between guard electrode and measuring electrode is set at 0.6 mm.These parameters are adequate for the measurement of flat specimen of mineral and solid insulating material whose diameter is 18 mm.According to the confirmatory experiment on the volume resistivity and surface resistivity,the measuring results are almost the same,using a small electrode experimental installation and a standard electrode.展开更多
文摘In view of long-term transformer insulation resistance and dielectric loss measurement, measurement and according to the national standard formula conversion values are not completely consistent, in this paper, a variety of transformers are studied, and the applicable scope of the conversion formula is discussed emphatically, combined with the test results are analyzed of transformer insulation resistance value to temperature and oiliness and dielectric loss tangent to temperature and oiliness, and puts forward suggestions on how to improve the insulation performance of transformer.
文摘Method IEEE 841 is used to test endurance of insulation system of stators to 100% humidity at 40 ℃ for168 h. Insulation resistance after this test between phases or between phase and frame has not been lover as 5 × 10^6 Ohm. Some producers of motors use this method for determining quality of impregation resin. On such test insulation resistance between phases was lover as between phase and frame. Because between phases is only wire insulation impregnating resins on insulation resistance of insulation system an impregnating resin we observe influence of type of wires and after humidity test. With diagnostic of insulation, the state is dealt. We compare our impregnation resin with competitive impregnation resin. We made test on twisted coils prepared after STN IEC from two parallel wires. In this test, we succeed in demonstrating that the main influence on insulation resistance of insulation system wire and impregnation resin has insulation of wire. Impregnation resin has influenced on data dispersion.
基金supported by the National Basic Research Program of China(Grant Nos.2015CB9210042012CB821404 and 2011CBA00103)+2 种基金the National Natural Science Foundation of China(Grant Nos.11374261and 11204059)Zhejiang Provincial Natural Science Foundation of China(Grant No.LQ12A04007)the Fundamental Research Funds for the Central Universities of China
文摘After successfully growing single-crystal TaP, we measured its longitudinal resistivity （Pxx） and Hall resistivity （Pyx） at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresistance （MR） reached 3.28 ×10^5% at 2 K, 176% at 300 K. Neither value appeared saturated. We confirmed that TaP is a hole-electron compensated semimetal with a low carrier concentration and high hole mobility ofμh=3.71 × 105 cm2/V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, because a magnetic field （H） was applied in parallel to the electric field （E）, a negative MR due to a chiral anomaly was observed and reached -3000% at 9 T without any sign of saturation, either, which is in contrast to other Weyl semimetals （WSMs）. The analysis of the Shubnikov-de Haas （SdH） oscillations superimposed on the MR revealed that a nontrivial Berry＇s phase with a strong offset of 0.3958, which is the characteristic feature of charge carriers enclosing a Weyl node. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.
基金supported by the National Natural Science Foundation of China (Grant No. 50974025)the National Key Technologies R & D Program of China (Grant No. 2004BA810B02)+2 种基金the Applied Foundation of Basic Research in Sichuan Province (Grant No. 07JY029-029)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20095122110015)the Scientific Research Foundation of the Education Ministry for Returned Chinese Scholars, China (Grant No. 2010-32)
文摘There has not been an effective method to measure the resistivity of small-size sample of mineral and solid insulating material until now.According to the Chinese National Standard(GB/T1410-2006) and features of digital high resistance meter,a small electrode experimental installation was developed;it can work with current high resistance meter;the sample decreases to 18 mm from standard size 100 mm in diameter and reduces by 30.86 times in area.A three-electrode system is supported and precisely positioned by two insulating bases whose diameter is 60 mm and height is 20 mm,which ensures accuracy of device structure and reliability of measuring results.The key technological parameters are as follows:diameter of high voltage electrode is 18mm;diameter of measuring electrode is 14.6 mm;internal diameter and external diameter of guard electrode are 16 and 18 mm,respectively;the gap between guard electrode and measuring electrode is set at 0.6 mm.These parameters are adequate for the measurement of flat specimen of mineral and solid insulating material whose diameter is 18 mm.According to the confirmatory experiment on the volume resistivity and surface resistivity,the measuring results are almost the same,using a small electrode experimental installation and a standard electrode.
