为什么逆调压可以提高电网运行的经济效益？
参考答案：
从电网的组成可以看出，造成电网有功电力和电能损耗的主要元件是输电线和变压器，其有功功率损耗主要由两部分组成，一部分为线路和变压器阻抗回路上流过的电流时的损耗，即I2R，称为可变损耗；另一部分则发生在变压器、电抗器、电容器等设备上的不变损耗，也成为固定损耗。负荷大时，可变损耗大，电网中可变损是主要的，此时中枢点提高电压运行，使传输同等功率负荷时电流减小，从而减小了可变损耗；
相反，负荷小时，电网中的变压器固定损耗（如铁损等）占有较大比值，例如非农排季节时，广大的农村配电网就是这种情况，此时为数众多的配电变压器都在轻负荷下运行，其固定损耗远大于电网的可变损耗，而变压器的固定损耗又正比于电压的平方，此时为减少轻负荷时配电电网的固定损耗，中枢点应当降低电压运行。而这种调压方式正是逆调压方式，因此可以说逆调压方式对于降低配电网线损是很有效的，这也就是逆调压方式的经济效果。
| 阅读理解 | |
| Jim suffered heart problems. In conversation he expressed little joy and it seemed that his life was drawing to a close. When his heart problems led to operation, Jim went through it successfully, and a full recovery was expected. Within days, however, his heart was not beating properly. Jim was rushed back to operation, but nothing was found to explain the cause of his illness. He died on the operating table on the day before his 48th birthday. Dr. Bruce Smoller, a psychologist (心理学家), had had many conversations with him, and the more he learned, the stranger he realized Jim's case was. When Jim was a child, his father,a teacher, suffered a heart attack and stayed home to recover. One morning Jim asked his father to look over his homework, promising to come home from school at noon to pick it up. His father agreed, but when Jim returned his father had died. Jim's father was 48. "I think all his life Jim believed he killed his father, "Dr. Smoller says. "He felt that if he had not asked him to look at his homework, his father would have lived. Jim had been troubled by the idea. The operation was the trial(判决) he had expected for forty years. "Smoller believes that Jim willed himself not to live to the age of 48. Jim's case shows the powerful role that attitude (态度) plays in physical health, and that childhood experiences produce far-reaching effect on the health of grownups. Although most cases are less direct than Jim's, studies show that childhood events, besides genes, may well cause such midlife diseases as cancer, heart disease and mental illness. | |
| 1. Jim was sent back to operation because . | |
| A. his heart didn't work well B. he expected a full recovery C. his life was drawing to a close D. the first one wasn't well performed | |
| 2. What made Dr. Smoller feel strange about Jim's case? | |
| A. Jim died at a young age. B. Jim died on the operating table. C. Both Jim and his father died of the same disease. D. Jim's death is closely connected with his father's | |
| 3. From Smoller's words, we can infer that . | |
| A. Jim's father cared little about his study B. Smoller agreed that Jim did kill his father C. Jim thought he would be punished some day D. Smoller believed Jim wouldn't live to the age of 48 | |
4. Which of the following could have strong effect on one's physical health according to the text?
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| A. a,b,d B. a,b,e C. a,c,e D. b,c,d |