电气工程专业英语电机

Electric

MachineryPerformance

Characteristics

of

Induction

MotorsThe

rotating

field

travels

around

the

air-gap

at

aspeed

ofr

f=s

p(4-1)Where

r

/

s

=

revolutions

per

second

of

the

rotatingmagnetic

field;f

=

frequency

of

excitation,

Hz;p

=

number

ofpoles.The

speed

of

rotation

is

more

commonly

expressedin

revolutions

per

minute

and

is

called

synchronousr/min,

whereSynchronous

r/min=

60

f/p（4-2）Section

2Performance

Characteristics

of

Induction

MotorsSynchronous

speed,

defined

in

Eq.(4-2),

is

thespeed

at

whichrotor

is

revolving

insynchronism

withthethe

rotating

magnetic

fieldgenerated

by

the

stator

windings,

and

there

istherefore

no

rotor

current

and

no

electricallygenerated

torque.同步转速，正如公式4-2所定义的那样，是转子的旋转速度，该速度与由定子绕组产生的旋转磁场速度同步，因此就不会有转子电流和电磁转矩。Section

2Performance

Characteristics

of

Induction

MotorsSlip

is

the

difference

in

speed

between

the

rotorand

the

air-gap

rotating

magnetic

field

and

isdefined

bySlip

=

(synchronous

r/min

–

rotor

r/min)/synchronous

r/min

(4-3)Eq.

(4-3)

yields

slip

as

a

per-unit

value,

although

itis

often

expressed

as

a

percentage.

At

speeds

abovesynchronous

speed

the

machine

operates

asinductiongenerator.Section

2Performance

Characteristics

of

Induction

MotorsSlip

values

for

speeds

above

synchronous

speedare

negative,

as

is

evident

from

Eq.(4-3).

Operationin

the

generating

region

results

from

overhaulingloads

or

from

the

motor

being

driven

by

a

primemover.For

induction

generating

action

to

occur,

themachine

must

have

a

source

of

leading

excitingcurrent.从式（4-3）可以看出，当转速大于同步转速时，转差率为负值。工作在发电机状态要有被动拖曳型负载或被原动机驱动的电机。要工作在感应发电机状态还必须要有一个励磁电流。Section

2Performance

Characteristics

of

Induction

MotorsThis

excitation

can

be

supplied

from

the

powersystem

if

the

motor

is

connected

to

such

a

system.In

recent

years,

induction

generators

have

foundapplication

as

wind-driven

generators;

they

areconnected

to

a

power

line

and

deliver

power

to

thesystem

whenever

wind

velocities

reach

a

certainminimum

value.为了使译文表达通顺，使词与词、句与句之间前后连贯，可增加一些起连贯作用的词。例如英语中的分词短语或从句作定语或状语，而含有明显的条件、时间、原因、让步等意义时，可分别增加连词“由于”，“

如果”，“假使”，“只要”，“一旦”，“当……时”，“……时”，“虽然……”，“但……”等；对于陈述句可增添“的”，“了”，“哩”，

“啦”等字。(1)

Using

a

transformer,

power

at

low

voltage

can

betransformed

into

power

at

high

voltage.如果使用变压器，低电压的电力就能转换成高电压的电力。增加表达语气起连贯作用的词Many

persons

learned

to

program

with

littleunderstanding

of

computers

or

applications

to

whichcomputers

could

or

should

be

applied.许多人虽然已经学会了编程序，但对计算机以及计算机能够或必备的种种用途所知甚少。This

question

is

really

a

circuit

design

rather

thana

layout

problem.这个问题是属于电路设计方面的，而不是布局方面的。Do

not

leave

dead

batteries

in

the

battery-box

asthis

may

cause

malfunction.注意不要将废电池留在电池盒内，以免引起故障。增加表达语气起连贯作用的词ExercisesAnswer

the

following

questions

according

to

thetextWhat

relation

is

among

revolutions

per

second

ofthe

rotating

mag