问题 问答题 简答题

在非正常及特殊情况运行方式下对发电机的要求有哪些?

答案

参考答案:

(1)发电机应能监视双向无功功率和功率因数,具备进相能力,如100MW及以上火电机组在额定出力时,功率因数应能达到超前0.95~0.97;励磁系统采用可以在线调整低励磁限制的微机励磁装置。

(2)发电厂应根据发电机进相试验绘制指导实际进相运行的P—Q图,以编制相应的进相运行规程,并根据电网调度部门的要求进相运行,此时根据可能的进相深度,当静稳定成为限制进相因素时,应监视发电机功角进相运行。

(3)新投产的大型汽轮发电机应具有一定的耐受带励磁失步震荡的能力,发电机失步保护应考虑既要防止发电机损坏又要减少失步对系统和用户造成的危害,为了防止失步故障扩大为电网事故,应当为发电机解列设置一定的时间延迟,使电网和发电机具有重新恢复同步的可能性。

(4)发电厂应制定完备的发电机带励磁失步震荡故障的应急措施。并按有关规定做好保护定值整定,具体包括如下两点。

1)失步震荡中心在发电机—变压器组内部时,应立即解列发电机。

2)当发电机电流低于三相出口短路电流的60%~70%时(通常震荡中心在发电机---变压器组外部),发电机组应允许失步运行5~20个周期,此时,应立即增加发电机励磁,同时减少有功负荷,切换厂用电,延迟一定时间,争取恢复同步。

(5)在发生过严重失步振荡(失步振荡时间超过上述规定)以后应当及时检查发电机组的健康状况,重点检查发电机组的轴系震动和疲劳寿命损失、轴系裂纹等情况,同时详细检查定子绕组端部的紧固情况,当发现存在松动和磨损以及端部整体动态特性性能劣化时必须及时加以处理。再运行半年至一年后应利用停机机会再一次检查端部紧固情况。有条件的发电机建议加装扭应力检测和分析设备,对轴系寿命损耗进行在线监视。

(6)当发电机失磁异步运行时,只有在电网有足够的无功余量去维持一个合理电压书评,且机组能迅速减少负荷(应自动进行)到允许水平,同时机组所带厂用电供电系统可以自动切换到另一个电源时,发电机才具备失磁异步运行条件。此时应严格限制失磁异步运行的时间和运行条件(汽轮发电机实际失磁异步运行的能力,与电网容量、机组容量、有否特殊设计等有关)。发电机失去励磁后是否允许机组快速减负荷并短时运行,应当根据电网和机组的实际情况综合考虑,电网运营部门应当与电厂就具体机组失磁后可能的运行方式达成协议。对于发生严重失磁运行事故的发电机,例如超过规定的负荷和时间,或引起强烈系统振荡,应当尽快对发电机组进行停机检查,重点检查发电机组的轴系振动和疲劳寿命损失、轴系裂纹等情况,同时详细检查定子绕组端部的紧固情况,当发现存在松动和磨损以及端部的紧固情况,当发现存在松动和磨损以及端部整体动态特性性能劣化时必须及时加以处理。再运行半年至一年后应再一次利用停机机会检查端部紧固情况。

(7)为防止电网频率一场时发生电网崩溃事故,发电机组应当具有必要的频率异常运行能力。汽轮发电机组在带负荷运行(不包括启动和停机等)情况下,允许频率异常的运行能力主要受汽轮机调频叶片的限制,因此发电机应装设低频保护,保护动作于信号并有低频累计时间显示。特殊情况下当低频保护需要跳闸时,保护动作时间可按汽轮机和发电机制造厂的规定进行整定,但必须符合表2-5规定的每次允许时间。同时,机组低频保护整定一定要与系统频率降低特性协调,即系统频率降低情况一定不能使机组保护动作而引起恶性连锁反应;系统的低频减载配置和整定应能保证系统频率动态特性的低频持续时间符合相关规定,并有一定裕度。

阅读理解与欣赏

阅读下文,完成题目 (12分)

魏文侯燕饮,皆令诸大夫论己。或言君仁,或言君义,或言君之智也。至于任座,任座曰:“君不肖君也。得中山不以封君之弟,而以封君之子,是以知君之不肖也。”文侯不说,知于颜色。任座趋而出。次及翟黄,翟黄曰:“君贤君也。臣闻其主贤者,其臣之言直。今者任座之言直,是以知君之贤也。”文侯喜曰:“可反欤?”翟黄对曰:“奚为不可?臣闻忠臣毕其忠,而不敢远其死。座殆尚在于门。”翟黄往视之,任座在于门,以君令召之。任座入,文侯下阶而迎之,终座以为上客。

(选自《吕氏春秋》)

【注】①燕:通“宴”,宴请。②次及:依次轮到。③毕:竭尽。

小题1:解释下列句中划线词(4分)

(1)皆令诸大夫己(       )           (2)文侯不(       )

小题2:下列对文中画线句翻译正确的一项是(3分)

A.您得到了中山国,不把它封赏给您的弟弟,而把它封赏给您的儿子,我因此知道您不像个君王。

B.您得到了中山国,不把它封赏给您的弟弟,却把它封赏给您的儿子,我因此知道您不像个君王。

C.您得到了中山国,不把它封赏给您的弟弟,却把它封赏给您的儿子,我因此知道您不是个贤明的君王。

D.您得到了中山国,不把它封赏给您的弟弟,而把它封赏给您的儿子,我因此知道您不是个贤明的君王。小题3:本文中任座的人物形象可以概括为     和     两个字。(请用原文回答)(2分)

小题4:请具体分析一下“或言君仁,或言君义,或言君之智也”这句话对于塑造任座或翟黄形象的作用。(3分)

阅读理解

A book review tells not only what a book is about,but also how successful it is at what it is trying to do.Professors often assign book reviews as practice in careful analytical(分析的) reading.

As a reviewer,you bring together the two strands of accurate,analytical reading and strong,personal response when you indicate(指出) what the book is about and what it might mean to a reader(by explaining what it meant to you).In other words,reviewers answer not only the WHAT but the SO WHAT question about a book.Thus,in writing a review,you combine the skills of describing what is on the page,analyzing how the book tried to achieve its purpose,and expressing your own reactions.

Most book reviews start with a heading that includes all the basic information about the book,like:

Title.

Author.

Place of publication,publisher,date of publication.

Number of pages.

Like most pieces of writing,the review usually begins with an introduction that lets your readers know what the review will say.The first paragraph usually includes the author and title again,so your readers don’t have to look up to find this information.You should also include a very brief description of the contents of the book,the purpose or audience for the book,and your reaction and evaluation.

Then you move into a section of background information that helps place the book in context and discusses how to judge the book.Next,you should give a summary of the main points,quoting(引用) and explaining key phrases from the author.Finally,you get to the heart of your review—your evaluation of the book.In this section,you might discuss some of the following issues:

•How well the book has achieved its goal.

•What possibilities are suggested by the book.

•What the book has left out.

•How the book compares with others on the subject.

•What specific points are not convincing.

•What personal experiences you’ve had related to the subject.

It is important to use labels to carefully distinguish your views from the author’s,so that you don’t confuse your readers.

Then,like other essays,you can end with a direct comment on the book,and tie together issues raised in the review in a conclusion.

There is,of course,no set form,but a general rule is that the first one­half to two­thirds of the review should summarize the author’s main ideas and at least one­third should evaluate the book.

小题1:According to the text,personal response of a book reviewer refers to “________”.

A.accurate and analytical reading

B.the reviewer’s indication of what the book is

C.the reviewer’s indication of what the book meant to a reader

D.skills of describing what is on the page小题2:What is the most important part of a book review?

A.The heading.

B.The evaluation.

C.The conclusion.

D.The introduction.小题3:Readers will get puzzled if ________.

A.there is no heading in a book review

B.the book review is not complex enough

C.the reviewer’s point of view is mixed with the author’s

D.there are some different issues listed in the book review小题4:What does the text mainly tell us?

A.Steps to read a book.

B.Tips for writing a book review.

C.The way to develop your idea.

D.Things not to be avoided in a book review.