问题 问答题 简答题

双电源自动切换系统执行的国家标准是什么,分为哪两种?

答案

参考答案:

GB14048.11-2002为新颁布的国家标准,主要适应于额定电压交流不超过1000V或直流不超过1500V的自动转换开关电器。适用于紧急供电系统,在转换电源期间中断向负载供电的ATSE。操作程序有两个自动转换过程组成,即自投自复开关。被监测的电源偏差为:电源电压或频率的非正常改变。分类两种:PC级和CB级。PC级:能够接通、承载但不用于分段短路电流的ATSE。CB级:配备过电流脱扣器ATSE,它的主触头能够接通并用于分断短路电流。PC级主要指接触器,隔离开关等组成的ATSE,CB级指由两个断路器组成。

单项选择题

Personality is to a large extent inherent. A-type parents usually (1) A-type offspring. But the environment must also have a profound effect (2) if competition is important to the parents, it is (3) to become a major factor in the lives of their children.

One place where children (4) A characteristics is school, which is, (5) its very nature, a highly competitive institution. Too many schools (6) the "win at all costs" moral standard and measure their success by sporting achievements. The current (7) for making children compete against their classmates or against the (8) produces a two-layer system, in which competitive A types seem in some way better than their B type fellows. Being too (9) to win can have dangerous consequences: remember that Pheidippides, the first marathon runner, (10) dead seconds after saying. "Rejoice, we conquer!"

(11) the worst form of competition in schools is the disproportionate emphasis on examinations. There is, for example, a (12) school that allows pupils to concentrate on those things they do well. The (13) of competition by examination are somewhat questionable, but competition in the certain (14) of failure is positively harmful.

(15) , it is neither practical nor desirable that all A youngsters change into B’s. The world needs types, and schools have an important duty to try to (16) a child’s personality to his possible future employment. It is top management.

If the preoccupation of schools with academic work was (17) , more time might be spent teaching children surer values. Perhaps selection (18) the caring professions, especially medicine, could be made less by good grades in chemistry and more by such (19) as sensitivity and sympathy. It is surely a mistake to choose our doctors exclusively from A type stock. B’s are important and should be (20) .

12()

A.responsible

B.reliable

C.scarce

D.rare

单项选择题