问题 单项选择题

某车间负荷采用低压三相电源线路供电,线路长L=50m,允许电压降5%,保护装置0.4s内可切除短路故障,线路发生最大的短路电流Ik=6.8kA。系统采用铜芯交联聚乙烯电力电缆穿钢管明敷,环境温度40℃,电缆导体最高温度90℃,电缆经济电流密度2.0A/mm2,电压损失率降0.5% (kW/km)。车间设备功率数值统计表见表1,有功功率同时系数为0.8,无功功率同时系数为0.93,请回答下列问题。

表1 车间设备功率数值统计表
序号 设备名称 额定功率Pc/kW 额定负荷持续率εr(%) 额定电压Ur/N 需要系数Kx 功率因数
cosφ tanφ
1 数控机床 50 100 380 02 0.5 1.73
2 起重机 22 20 380 0.1 0.5 1.73
3 风机 7.5 100 380 0.75 0.8 0.75
4 其他 5 100 380 0.75 0.8 0.75

若假定Pc=21.5kW,计算供电线路电压损失应为下列哪项数值( )

A.0.054%

B.0.54%

C.5.4%

D.54%

答案

参考答案:B

解析:[解答过程] 根据《工业与民用配电设计手册》第3版P63。
[*]

阅读理解

                     

  Exchange a glance with someone, and then look away. Do you realize that you have made a statement? Hold the glance for a second longer and you have made a different statement. Hold it for 3 seconds, and the meaning has changed again. For every social situation, there is a permissible time that you can hold a person’s stare without being friendly, rude, or aggressive. If you are on a lift, what stare-time are you permitted? To answer this question, consider what you typically do. You very likely give other passengers a quick glance to size them up and to assure them that you mean no harm. Since being close to another person signals the possibility of interaction, you need to send out a signal telling others you want to be left alone. So you cut off eye contacts. That is what sociologist Erving Goffiman calls “a dimming of the lights”. You look down at the floor, at the indicator lights, anywhere but into another passenger’s eyes. Should you break the rule against staring at a stranger on a lift, you will make the other person extremely uncomfortable, and you are likely to feel a bit strange yourself.

  If you hold eye contacts for more than 3 seconds, what are you telling another person? Much depends on the person and the situation. For instance, a man and a woman communicate interest in this manner. They stare at each other for about 3 seconds at a time, and then drop their eyes down for 3 seconds, before letting their eyes meet again. But if one man gives another man a 3-second-plus stare, he signals, “I know you”, “I am interested in you” or “You look peculiar and I am curious about you.” This type of stare often produces hostile feelings.

  60. It can be inferred from the first paragraph that ______.

  A. every glance has its significance

  B. a glance carries more meaning than words

  C. a stare longer than 3 seconds is unacceptable

  D. staring at a person is an expression of interest

  61. If you want to be left alone on a lift the best thing to do is ______.

  A. to look into another passenger’s eyes

  B. to keep a distance from other passengers

  C. to avoid eye contacts with other passengers

  D. to signal you don’t mean to do harm to anyone

  62. By “a dimming of the lights”, Erving Goffiman means ______.

  A. closing one’s eyes         B. turning off the lights

  C. stopping glancing at others     D. reducing stare-time to the minimum

  63. The passage mainly discusses ______.

  A. the limitations of eye contacts

  B. the exchange of ideas through eye contacts

  C. proper behavior in different situations in people’s daily life

  D. the role of eye contacts in communication between people

单项选择题