Open phase in three phase induction motors is a common fault that can occur as a result of a fuse blowing or a pro- tective device failing on one phase of the motor. This paper introduces a new method,which is based o...Open phase in three phase induction motors is a common fault that can occur as a result of a fuse blowing or a pro- tective device failing on one phase of the motor. This paper introduces a new method,which is based on the transient mea- surement and can distinguish the fault of one phase connecting ground. The method has been proved to be in correspondence with the simulation results by Matlab and LabVIEW in practice, The method has merits of simplicity, accuracy and ease of USe.展开更多
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
文摘Open phase in three phase induction motors is a common fault that can occur as a result of a fuse blowing or a pro- tective device failing on one phase of the motor. This paper introduces a new method,which is based on the transient mea- surement and can distinguish the fault of one phase connecting ground. The method has been proved to be in correspondence with the simulation results by Matlab and LabVIEW in practice, The method has merits of simplicity, accuracy and ease of USe.
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.
