问题 问答题 简答题

什么是次同步振荡?其产生原因和防止措施有哪些?

答案

参考答案:

次同步振荡就是当发电机经串联电容补偿的线路接入电网时,如果串联补偿较高,网络的电气谐振频率容易和大型汽轮发电机的轴系自然扭振频率产生谐振,通常次谐振频率低于同步频率。并造成发电机大轴扭振破坏。

同样高压支流输电线路(HVDC.或静止无功补偿器(SVC.的控制参数选择不当时,也可能激发次同步振荡。

一般防止次同步振荡的措施为:

(1)附加和改造一次设备。

(2)降低串联补偿度。

(3)通过二次设备提供对扭振模式的阻尼(类似于PSS的原理)。

阅读理解

阅读理解。

    A Leg Walking Right

    Here are some signs + - x..., the signs are very different. They mean very different things. When you see

them, you know what to do. This sign + means that you will add some numerals. This sign-means that you

will take one numeral away from another. You will subtract (减去). What will you do when you see x and...? 

    Our signs are easy to read. They are easy signs to remember. Look at these two signs….The ancient

Egyptians used these signs. A picture of a leg walking to the left told them to add some numerals. A picture

of a leg walking to the right told them to subtract.

     In the 1500s people used this printed (印刷的) sign & to add numerals. After a while the sign began to

look like this... Later, the sign became +.

     How much is 2...2?

1. What do you do when you see this sign +? [ ]

A. Walk away

B. Write a numeral

C. Read a sign

D. Add

2. The word in the story that means to take one numeral away from another is _____.

3. The story says, "Our signs are easy to read. They are easy signs to remember".The word "they" 

    means _____.

4. Which of the following does this story lead to believe? [ ]

A. Egyptians could not add numerals together

B. All Egyptians had two left legs.

C. Our signs are not hard to understand

5. What did the sign to add numerals begin to look like (which sentence is exactly like the one in your book)? [ ]

A. After a while, the sign began to look like this...

B. After a while, the sign began to look like this +.

C. After a while, the sign began to look like this &.

6. The main idea of the whole story is that _____. [ ]

A. the signs for adding and subtracting have changed

B. People could not write in the 1500s

C. the old signs were good for Egyptians but not for us

选择题