问题 单项选择题 案例分析题

某车间有一台不频繁起动的笼型异步电动机,电气参数为:额定功率160kW,额定电压为交流三相380V,额定功率因数0.85,额定效率0.93,额定起动电流倍数7倍。该电动机由一台额定容量500kVA,电压10/0.4kV,阻抗电压4%的变压器供电。变压器到电动机由电缆连接,线路阻抗为0.01Ω。变压器一次侧短路容量为25MVA。变压器二次母线上其他负荷的无功功率为178kvar。电动机起动前变压器二次母线电压为额定电压380V,试计算电动机起动时有关参数并判断电动机是否可以采用全压起动。

该笼型异步电动机的额定起动容量为()。(选最接近的一个数据)

A.1353kVA

B.1120KVA

C.1204kVA

D.1420kVA

答案

参考答案:D

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单项选择题

Motherhood may make women smarter and may help prevent dementia in old age by bathing the brain in protective hormones, US reseachers reported on Thursday.

Tests on rats show that those who raise two or more litters of pups do considerably better in tests of memory and skills than rats who have no babies, and their brains show changes that suggest they may be protected against diseases such as Alzheimer’s. University of Richmond psychology professor Craig Kinsley believes his findings will translate into humans.

"Our research shows that the hormones of pregnancy are protecting the brain, including estrogen, which we know has many neuroprotective effects," Kinsley said.

"It’s rat data but humans are mammals just like these animals are mammals," he added in a telephone interview. "They go through pregnancy and hormonal changes. "

Kinsley said he hoped public health officials and researchers will look to see if having had children protects a woman from Alzheimer’s and other forms of age-related brain decline.

"When people think about pregnancy, they think about what happens to babies and the mother from the neck down," said Kinsley, who presented his findings to the annual meeting of the Society of Neuroscience in Orlando, Florida.

"They do not realize that hormones are washing on the brain. If you look at female animals who have never gone through pregnancy, they act differently toward young. But if she goes through pregnancy, she will sacrifice her life for her infant—that is a great change in her behavior that showed in genetic alterations to the brain. \

How do scientists know "motherhood may make women smarter"()

A. Some researchers have told them.

B. Many women say so.

C. They know it by experimenting on rats.

D. They know it through their own experience.