如何选用热继电器为电动机作过载保护？
参考答案：
热继电器主要用于电动机的过载保护，选择热继电器时应考虑电动机的工作环境、起动情况、负载性质等因素：
（1）热继电器结构型式的选择星形联结的电动机可选用两相或三相结构热继电器；三角形联结的电动机应选用带断相保护装置的三相结构热继电器。
（2）根据被保护电动机的实际起动时间选取6倍额定电流下具有相应可返回时间的热继电器。一般热继电器的可返回时间大约为6倍额定电流下动作时间的50%~70%。
（3）热元件额定电流的选取一般可按下式选取：IN=（0.95～1.05）INM。
| With the understanding of phobias has come a magic bag of treatments: exposure therapy that can stomp out a lifetime phobia in a single six-hour session; virtual-reality programs that can safely simulate the thing the phobia most fears, slowly stripping it of its power to terrorize; new medications that can snuff the brain’s phobic spark before it can catch. In the past year, the U. S. Food and Drug Administration approved the first drug—an existing antidepressant. Most psychologists now assign phobias to one of the three broad categories: social phobias, in which the sufferer feels paralyzing fear at the prospect of social or professional encounters; panic disorders, in which the person is periodically blindsided by overwhelming fear for no apparent reason; and specific phobias—fear of snakes and enclosed spaces and heights and the like. If you are living with a generalized sense of danger, it can be profoundly therapeutic to find a single object on which to deposit all that unformed fear—a snake, a spider and a rat. A specific phobia becomes a sort of backfire for fear, a controlled blaze that prevents other blazes from catching. But a condition that is so easy to pick up is becoming almost as easy to shake, usually without resort to drugs. What turns up the wattage of a phobia the most is the strategy the phobias rely on to ease their discomfort: avoidance. The harder phobics work to avoid the things they fear, the more the brain grows convinced that the threat is real. Progress in treating social-anxiety disorder is also providing hope for the last—and most disabling—of the family of phobias: panic disorder. Panic disorder is to anxiety conditions what a tornado is to weather conditions: a devastating sneaks havoc and then simply vanishes. Unlike the specific phobic and the social phobic who know what will trigger their fear, the victim of panic attacks never know where or when one will hit. Someone who experiences an attack in, say, a supermarket will often not return there, associating the once neutral place with the traumatic event. But the perceived circle of safety can quickly shrink, until sufferers may be confined entirely to their homes. When this begins to happen, panic disorder mutates into full-blown agoraphobia. The treatment for agoraphobia is much the same as it is for social phobia: cognitive-behavioral therapy and drugs. |
What is the purpose of the author in writing the passage
A．To describe different kinds of phobias.
B．To expound phobia and their possible treatments.
C．To help the phobia sufferers to get better.
D．To tell readers how to prevent such phobias.