关于定子接地保护的几个问题

Some Problems Concerning the Stator Earth - Fault Protection Device

以几次事故为例说明用"允许接地电流"来决定定子接地保护投运方式是不合理的。对于双水内冷发电机及没有匝间保护的大中型发电机，其定子接地保护应投跳闸。3ω接地保护的动作可靠性低的原因是：调整不当、工作环境条件差、回路及继电器本身有缺陷。为提高其动作可靠性，应掌握机组的US3与UN3变化规律、改善环境、以及更换不良的3ω保护等。发电机中性点经配电变压器接地，降低了定子接地保护的动作灵敏度。对经计算没有产生过电压可能的发电机，应将配电变压器换成单相PT或消弧线圈。无条件换时，尽量增加二次并联电阻。3U0接地保护的定值应为5V～10V。

Taking some occurred faults as example,this paper explains that it is unreasonable to determine the conditions of putting into operation of the stator earth - fault protecting device by using 'allowable earth-fault current '. For double- water inner-cooled generators,as well as the large and medium sized generators without turn-to-turn breakdown protection,the stator earth-fault protecting device should enable the generator tirp. Low operational reliability of 3ω earth-fault protecting device is caused by inappropriate adjustmemt,unfavorable working environments,as well as the inherent defects of circuit and relay. In order to enhance the operational reliability of 3ω earth-fault protecting device,we should find out the various patterns of generator's U3and UN3, improve the working environments and replace unproper 3ω earth-fault protecting device. Generator's neutral point earthed througn distribution transformer descreases the operational sensitivity of the stator earth-fault protecting device. For generator without possibility of overvoltage occurrence after calculation,the single phase PT or arc-supperession coil should be used instead of the distribution transormer. When this requirement is not satisified, the secondary shunt resistance should be increased as more as possible. The setting value of 3u0 earth-fault protecting device should be 5~10V.