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 ...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
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.
