毕业论文英文翻译：基于工频电流变化量的中性点不接地

毕 业 设 计（论 文）
英 文 翻 译
课题名称 基于工频电流变化量的中性点不接地
电网单相接地保护的研究
系 部 电信学院
专 业 电气工程及自动化

2 0 1 2年 6 月 4 日

Ground fault protection of the importance of the line selection

1.Ground fault protection of the importance of the line selection
In the substation (station), switching stations and power plants, 66 kV, 35 kV, 10 kV, 6 kV and 3 kV distribution lines is a major component of the electric power system.In these voltage levels of the system,The neutral point of transformers and generators have been taken the way of Ungrounded or through arc-suppression coil or Resistance grounding Transmission and distribution.And another multi-output or input distribution lines connected to
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ulation resistance obviously too low to ground. Due to the system of main transformer neutral point grounding or arc-suppression coil, high resistance grounding. When on the same bus when there have multiple distribution lines, no matter which piece of single phase grounding, is not directly connected with the primary winding of the transformer coil form loop, the line does not appear in the large current phenomena such as short circuit and overload. Only a line between the Earth and the formation of capacitance current change, characterized by weak appears in each line of zero-sequence current. This current is very small, ranging from a few milliamps to hundreds of milliamps or amperes, and is proportional to the length of the lines under normal conditions, each kilometers long overhead line is about 15 Ma. In the electric power industry power supply system known as such: "little Earth current system" or "small current grounding system". In the system, because of the voltage transformer (PT) Y0 ways a winding of wire connected to the system bus, when any line when there is a single phase grounding, triangular openings in the secondary winding of zero-sequence voltage, you can set the zero-sequence voltage alarm but you cannot select a line. Grounding Shi due to non-grounding phase line on to voltage rose can up phase voltage of √ 3 times times, dang system then with has iron magnetic resonance produced Shi, on will makes phase voltage rise 1-5 times, even more high, formed had voltage, accelerated has power device insulated material of aging, shortened has using life, to led to insulated device is breakdown, on will appears two-phase or more phase while grounding and occurs short circuit accident, increased has power device of damage degree.Therefore, often occur in power system voltage transformer e*plosion, circuit breakers, power distribution transformer burn, power cable and insulator breakdown, accident. Has some following electric protection or integrated automation protection device in the of "short circuit protection", and "had current protection" and "zero sequence current" protection, are belonging to large current started protection device single phase to Shi of small current cannot drive this class protection device action, so, cannot action Yu high pressure switch (circuit breaker device) trip, fault line and non-fault line also on cannot is isolation.
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