In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Current...In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Currently the value of over-voltage on transformer neutral point and the corresponding protection strategy is based on theoretical formula. This article uses the PSCAD/EMTDC software to calculate the over-voltage on the neutral point of 4 ungrounded power transformers in Chongqing 220 kV power grid. The result shows that the power frequency transient over-voltage on the neutrals may reach 178 kV. If the single-phase grounding fault occurs in ungrounded power system, the power frequency over-voltage on the neutrals will be more serious and rise to 138.6 kV. Non-full phase operation may cause serious ferro-resonance over-voltage on the neutrals of no-load transformer, which may last for seconds and may rise to 723.7 kV, causing serious threat to the transformer neutrals and line-side equipment. The article also studies the gap parameter which should be taken on the neutrals of 220 kV transformers at the end.展开更多
Three electrodeposited Fe-Ni,Fe-Co,and Fe-Ni-Co cores of thin film transformer are prepared on silicon(100) substrates,which are sputtered a 90 nm thick film of Cu acting as the seed layer.The core films consisting of...Three electrodeposited Fe-Ni,Fe-Co,and Fe-Ni-Co cores of thin film transformer are prepared on silicon(100) substrates,which are sputtered a 90 nm thick film of Cu acting as the seed layer.The core films consisting of Fe-Ni 20:80,Fe-Co 60:40 and Fe-Ni-Co 10:60:30,respectively,are deposited using direct current electrodeposition.The surface texture,electrical and magnetic properties are surveyed by scanning electron microscopy(SEM),superconducting quantum interference device(SQUID),etc.The wave transmission ability and efficiency of thin film transformer with these cores,inputting the sine wave,are compared.All the analyses indicate that FeNi alloy films display the optimal magnetic properties and excellent transformer performance.展开更多
文摘In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Currently the value of over-voltage on transformer neutral point and the corresponding protection strategy is based on theoretical formula. This article uses the PSCAD/EMTDC software to calculate the over-voltage on the neutral point of 4 ungrounded power transformers in Chongqing 220 kV power grid. The result shows that the power frequency transient over-voltage on the neutrals may reach 178 kV. If the single-phase grounding fault occurs in ungrounded power system, the power frequency over-voltage on the neutrals will be more serious and rise to 138.6 kV. Non-full phase operation may cause serious ferro-resonance over-voltage on the neutrals of no-load transformer, which may last for seconds and may rise to 723.7 kV, causing serious threat to the transformer neutrals and line-side equipment. The article also studies the gap parameter which should be taken on the neutrals of 220 kV transformers at the end.
基金supported by the National Natural Science Foundation of China (Grant No. 60874101)
文摘Three electrodeposited Fe-Ni,Fe-Co,and Fe-Ni-Co cores of thin film transformer are prepared on silicon(100) substrates,which are sputtered a 90 nm thick film of Cu acting as the seed layer.The core films consisting of Fe-Ni 20:80,Fe-Co 60:40 and Fe-Ni-Co 10:60:30,respectively,are deposited using direct current electrodeposition.The surface texture,electrical and magnetic properties are surveyed by scanning electron microscopy(SEM),superconducting quantum interference device(SQUID),etc.The wave transmission ability and efficiency of thin film transformer with these cores,inputting the sine wave,are compared.All the analyses indicate that FeNi alloy films display the optimal magnetic properties and excellent transformer performance.
