A、100Ω
B、200Ω
C、300Ω
答案:A
解析: (The first question): 题目解析 (Analysis of the question): 为保证接地后备最后一段保护可靠地有选择性地切除故障, 220kV线路接地电阻最大按( )考虑 Translation: In order to ensure the reliable and selective removal of faults by the last backup protection segment, the maximum grounding resistance of a 220kV line should be considered as ( ). 答案 (Answer): A. 100Ω Explanation: The answer is A (100Ω) because having a lower grounding resistance helps to ensure better selectivity in fault clearance. Lower grounding resistance results in higher fault currents during ground faults, which improves the ability of the backup protection to detect and clear the fault while avoiding unnecessary tripping of healthy sections of the power system.
A、100Ω
B、200Ω
C、300Ω
答案:A
解析: (The first question): 题目解析 (Analysis of the question): 为保证接地后备最后一段保护可靠地有选择性地切除故障, 220kV线路接地电阻最大按( )考虑 Translation: In order to ensure the reliable and selective removal of faults by the last backup protection segment, the maximum grounding resistance of a 220kV line should be considered as ( ). 答案 (Answer): A. 100Ω Explanation: The answer is A (100Ω) because having a lower grounding resistance helps to ensure better selectivity in fault clearance. Lower grounding resistance results in higher fault currents during ground faults, which improves the ability of the backup protection to detect and clear the fault while avoiding unnecessary tripping of healthy sections of the power system.
解析:在发电机中性点附近不可能发生绝缘破坏,因为发电机运行时中性点对地电压近似为零。 答案: B (错误) 解析: 中性点对地电压虽然很小,但并不是绝对为零的。在发电机运行时,中性点对地电压会有一定的值,通常被称为“接地电流”。如果存在绝缘缺陷或故障,这个接地电流可能导致中性点附近的绝缘破坏。
A. 应填用第一种工作票
B. 应填用第二种工作票
C. 口头或电话命令
解析:二次接线回路上工作,无需将高压设备停电者() 答案: B.应填用第二种工作票 解析: 二次接线回路是指保护设备与被保护设备之间的接线回路,用于传递保护信号而不是电力。在维护或检修二次接线回路时,无需将高压设备停电,因为二次接线回路与电力设备的运行相互独立。在这种情况下,可以选择第二种工作票,即不需要停电的工作票,来保证施工人员的安全,并确保高压设备持续供电。
A. 转子滑环附近
B. 励磁绕组一点
C. 励磁机正极或负极
解析:按直流电桥原理构成的励磁绕组两点接地保护,当()接地后,投入跳闸 答案:B 解析:这道题目考察的是按直流电桥原理构成的励磁绕组两点接地保护的触发条件。根据直流电桥原理,当励磁绕组的一点接地(选项B)时,会导致绕组电流的不平衡,从而使电桥不平衡,触发保护跳闸动作。选项A中的转子滑环附近接地通常与励磁绕组两点接地保护无关,选项C中的励磁机正极或负极接地也不涉及直流电桥保护的原理。因此,选项B是正确的答案。
解析:电抗器差动保护动作值应考虑躲过励磁涌流问题。答案解析: B 这题的答案是错误 (B)。电抗器差动保护是一种保护设备,用于保护电抗器免受内部故障的影响。励磁涌流是在电抗器启动时可能出现的暂态过程,但它不会导致电抗器内部故障。因此,在设置电抗器差动保护的动作值时,并不需要考虑励磁涌流问题。