Newnes Electrical Engineers Handbook
D.F. Warne
Chapter 1 Introduction
There seems to be a trend in the public perception of engineering and technology that to be able to operate a piece of equipment or a system is to understand how it works. Nothing could be further from the truth. The gap between the ability to operate and a genuine understanding is, if anything, widening because much of the complexity added to modem electrical equipment has the specific aim of making it operable or lsquo;user-friendlyrsquo; without special training or knowledge. The need for a basic explanation of principles, leading to a simple description of
how various important and common classes of electrical equipment works , has never been stronger. Perhaps more so than in its predecessor, Newnes Electrical Pucker Book, an attempt is made to address fundamentals in this book, and the reader is encouraged to follow through any areas of interest using the references at the end of each chapter. More comprehensive coverage of all the subjects covered in this pocket book is available in the Newnes Electrical Engineerrsquo;s Reference Book. More so now than ever before, the specification and performance of electrical equipment is governed by national and international standards. While it would be inappropriate in a pocket book to cover standards in any detail, a summary of key standards is included for reference purposes at the end of each chapter.
The need for a basic explanation of principles, leading to a simple description of how various important and common classes of electrical equipment works, has never been stronger. Perhaps more so than in its predecessor, Newnes Electrical Pucker Book, an attempt is made to address fundamentals in this book, and the reader is encouraged to follow through any areas of interest using the references at the end of each chapter. More comprehensive coverage of all the subjects covered in this pocket book is available in the Newnes Electrical Engineerrsquo;s Reference Book.
More so now than ever before, the specification and performance of electrical equipment is governed by national and international standards. While it would be inappropriate in a pocket book to cover standards in any detail, a summary of key standards is included for reference purposes at the end of each chapter. The structure of the book is based around three groups of chapters, which address:
- fundamentals and general material
- the design and operation of the main classes of electrical equipment
- special technologies which apply to a range of equipment
The first group comprises three chapters which set out fundamentals and principles running through all aspects of electrical technology.The opening chapter deals with fundamentals of electric and magnetic fields and circuits, with energy and power conversion principles.
This is followed by a review of the materials that are so crucial to the design of electrical equipment, and these are grouped into sections on magnetic, insulating and conducting materials. In each of these areas technology is moving ahead rapidly. The great increases in the strength of permanent magnets in the past ten years has done much to make possible the miniaturization of equipment such as the Sony Walkman and the introduction of so many small motors and actuators in our homes and motorcars. Developments in insulating mataids mean that increased reliability and operation at higher temperatures can now readily be achieved. Under the heading of conductors there are continuing advances in superconductors, which are now able to operate in liquid nitrogen, and of course semiconductor development has transformed the way in which equipment can be controlled and the processing power in computers.
Finally in this opening group there is a chapter on measurement and instrumentation. A classical textbook on electrical measurement would in the past have included sections on moving iron and moving coil instruments, but these have been omitted here in favour of the oscilloscope and sensors which now dominate measurements in most areas.
The following group of nine chapters make up the main core of the book and cover the essential groups of electrical equipment found today in commerce and industry.
The opening five chapters here cover generators, transformers, switchgear, fuses and wire and cables. These are the main technologies for the production and handling of electrical energy, from high power and high voltage levels down to the powers and voltages found in the household. Exciting developments in this area include the advances made in high voltage switchgear using SF6 as an insulating medium, the extension of polymer insulation into high voltage cables and the continuing compaction of miniature and moulded-case circuit breakers. A new section in the wire and cables chapter addresses the growing technology of optical fibre cables; although the main use for this technology is in telecommunications, which is outside the scope of the book, a chapter on wires and cables would not be complete without it and optical fibres have a growing number of applications in electrical engineering.
The following four chapters describe different groups of equipment that use or srore electrical energy. Probably the most important here is electric motors, since these use almost two-thirds of all electrical energy generated. Static power supplies are also of growing importance in applications such as emergency standby for computers; this technology is now based on power electronics and the opportunity is taken in this chapter to explain the fundamentals of power electronic design and technology. Rotating converters were important for many of the duties now handled by power electronic
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纽恩斯电气工程师手册
利物浦大学D.W.Shimmin博士著
- 简介
人们对工程技术的认识，就是我们使用一台设备或一个系统都是要知道它是如何工作的，这与实际情况是相悖的。实际动手操作能力和对其真正理解之间的唯一区别，就是许多日益添加到的庞杂电气元件这一特定目标使其具有可操作性或具有“用户友好”，而不需要经过特殊训练或拥有专门的知识。
这种对事物本源认识的需要,促成了简单描述电气设备的工作。我们完全没有必要在其原理上做冗杂的解释。在我们编著的上一版《纽恩斯电气口袋书》里，着重解决了基本原理问题，并且在每章的最后，我们还列出了参考文献，供读者钻研自己感兴趣的领域。更全面的覆盖所有领域的知识的手册是《电气工程师参考书》。
电气设备的规格和性能有国家及国际标准规范。一个袖珍手册里不能覆盖这些标准的任何细节，我们只在每一章的结尾把关键性的标准做了描述。
本书包括以下三个部分，分别是：
- 基本原理和主要材料
- 主要电气设备的设计和操作
- 适用于一大类设备的特殊技术
第一部分包括三章，主要是对基本原理的陈述和贯穿各个方面的电气技术。
开篇第一章处理基本的电、磁、绝缘和电路,包括能量等方面的电气技术。
这是设计至关重要的电气设备（如磁、绝缘、导电材料）很好的参考材料,我们将分成章节来讲述。上述这些每一个科学技术的领域都在迅猛的朝着领先的方向发展。在过去的十年中，这种伟大的迅猛发展的力量已经促成了很多使小型化成为可能的设备（如索尼随身听），并引进如此多的小型电动机与执行器在汽车上。绝缘材料的发展意味着现在在较高的温度下增加可靠性和运行安全性可以轻易地实现。之中有持续改进的导体以及超导体材料,比如液态氮,而且半导体的发展改变了这个可以控制设备和计算机处理能力的方法。
这部分的最后，我们还安排了一章关于测量和仪表，检测方面的内容。作为一本有关电测量的经典教材，也就是对前面章节我们所介绍的,如软铁和仪器的截面的测量,这些示波器和传感器等测量设备的测量值是至关重要的。
接下来的九章构成这本书的核心内容和覆盖现代商业和研究用途的大部分重要电气设备。
在这九章中的前五章我们将分别介绍发电机、变压器、开关、保险丝和电线电缆。这些是为生产和处理电能的主要技术,适用于高功率、高电压水平和日常供电电压等不同方面。在这一领域所取得的令人兴奋的发展,包括使用SF6作为高压开关的绝缘介质,把聚合物绝缘材料延伸到高压电缆和模型化的微型断路器。在电线电缆这一章将谈到日益增长的光纤电缆技术。尽管这项技术的主要用途是在电信 ,但电线电缆尤其是光学纤维越来越多的应用在电气工程领域。
而后的四章描述不同设备消费或储存电能的情况。可以说最重要的是电动机,因为它所要消耗的电能几乎占到了2/3。静态电力供应也越来越起着重要的应用，如计算机的应急备用供电；现在这项技术都是基于电力电子发展起来的，我们有幸在本章解释电力电子设计的基本原理和技术。现代电力电子技术中，旋转调速器的重要性也很突出，但这项技术目前却仍待提高。一系列的铅蓄电池被开发并且在各种场合广泛应用,这一章将研究电池充电技术的诞生相关技术和新兴的燃料电池。如果燃料电池能够在未来发挥更大的作用,那我们可以期待在下一版电气工程师手册中见到它更进一步的发展。另一个主要的电力消费是所谓的电热技术。另外一个特别的章节，还会看到一套通过微波加热干燥技术对紫外线的光谱的电弧炉技术。
最后的一组三章涵盖前面没有涉及到的的多种技术和设备。有一章关于描述以发电机、开关、变压器、线路、电缆连接和控制以及传输消费电能等方式组成的电力系统。国有企业民营化的电力供应格局给世界各国带来了巨大的改变。第二章讲述电磁兼容(emc)问题；目前随着大量的电子和高频设备使用，应采取必要的预防措施甚至立法来防止干扰，追踪的技术复杂,需要一大批设备。最后一章描述设备的设计以及在危险和不正常运行下的使用操作方法，其中包含了对很多设备进行的保护。
- 电工原理 （利物浦大学D.W.Shimmin博士著）
2.1 命名和单位
此书所使用的符号是按照当前英国及国际标准生产制造的。工程量的单位是标准罗马数值和单位组成,单位各字母之间不留空隙,例如，275 KV。复合单位,单位元素之间有空间,圆点或者“/”作为间隔，例如：1.5 N m， 300m/s，9.81 m·s-2。用斜体印刷的字体来表示变量的符号,如V。对交流量,瞬时值按小写斜体印刷、在小写斜体基础上加符号(^)表示峰值,均方根值用大写字母表示,例如：i，，I。重要电气量的符号和单位列在表2.1,表示数量级别的小数前缀符号列在表2.2。
2.2 电磁场
2.2.1 电场
任何一个物体，都可以带电或者带静电电荷。当物体带正电荷时，它必然失去了电子；同样，如果物体带负电，那么它必然有过剩的电子。电子所包含的电量是人类已知最小的电荷，为-1.602 x 10-19 C。带电的物体能够产生电场，在空气或真空中，孤立的点电荷在不同距离下的电场强度E（v/m）由以下公式给出：
（2.1）
在真空中，介电常数ε0=8.854times;10-12F/m。在绝缘介质中的介电常数应该乘以一个相对介电常数εr，那么电场强度E（V/m）则由以下公式计算
(2.2)
任何带点物体或粒子处于其内部都要受到电场力的作用。这个力F(N)与所带电荷Q(C)和电场强度E(V / m)有关，其计算公式为:
F=QE (2.3)
电场力是一个向量。力的方向有两个，分别是引力和斥力。同种电荷相互排斥，异种电荷相互吸引。
要使两个同种电荷在一起，就必须克服电场力做功。这个功是用来表征电场电压或者静电势（通常以地面为零势能点）。相对于地面，正电荷的电势为正。
若一带正电物体与地面有一定的距离，那么在地球和物体之间的点的电压高于地面电压，所以，地球和被控对象之间有一个电位梯度。同样，也有电场指向
图 2.1 常用的图形符号
地面。电场强度与电势梯度数值相等，方向相反。
(2.4)
|
表 2.1 标准符号和单位 |
|||
|
符号 |
物理量 |
单位 |
单位符号 |
|
A |
几何面积 |
米 |
m2 |
|
B |
磁通量密度 |
特斯拉 |
T |
|
C |
电容 |
法拉 |
F |
|
E |
电场强度 |
伏每米 |
F/m |
|
F |
机械力 |
牛顿 |
N |
|
Fm |
磁动势 |
安培 |
A |
|
G |
电导 |
西门子 |
S |
|
H |
磁感应强度 |
安培每米 |
A/m |
|
I |
电流 |
安培 |
A |
|
J |
电流密度 |
安培每立方米 |
A/m3 |
|
J |
惯性矩 |
千克每米平方 |
Kg/m2 |
|
L |
自感 |
亨利 |
H |
|
M |
互感 |
亨利 |
H |
|
N |
匝数 |
||
|
P |
功率 |
瓦 |
W |
|
Q |
电荷 |
库伦 |
C |
|
Q |
无功功率 |
乏 |
Var |
|
R |
电阻 |
欧姆 |
Omega; |
|
Rm |
磁阻 |
安培每韦伯 |
A/wb |
|
S |
视在功率 |
伏安培 |
V·A |
|
T |
机械转矩 |
牛米 |
N·m |
|
V |
电位或电压 |
伏特 |
V |
|
W |
能量 |
焦耳 |
J |
|
X |
电抗 |
欧姆 |
Omega; |
|
Y |
电纳 |
西门子 |
S |
|
Z |
阻抗 |
欧姆 |
Omega; |
|
f |
频率 |
赫兹 |
Hz |
|
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