The level of prosperity of a community is related to its capability to produce
goods and services. But producing goods and services is strongly related to the
use of energy in an intelligent way.
Motion and temperature (heat) control are paramount in energy usage.
Energy comes into use in a few forms such as thermal, mechanical and
electrical.
The level of prosperity of a community is related to its capability to produce1 }$ T6 Y5 V9 `
goods and services. But producing goods and services is strongly related to the9 n! J% |. w$ T# D% ?. ~
use of energy in an intelligent way.) R5 M( a3 ?* U h. L) _% K
Motion and temperature (heat) control are paramount in energy usage.$ U' p7 @, v+ f. s
Energy comes into use in a few forms such as thermal, mechanical and : ^6 K) E0 b, r% _ a6 nelectrical. & u8 E) P6 C8 c1 IElectrical energy, measured in kWh, represents more than 30% of all used ' i: q0 D. B3 [* [6 W, Kenergy and it is on the rise. Part of electrical energy is used directly to produce " d4 K% J6 U" B2 c! Xheat or light (in electrolysis, metallurgical arch furnaces, industrial space 8 ]4 {% T- ]4 E. X# ?heating, lighting, etc.).3 J5 O0 ]5 `8 K" p- W7 x y' |, O" M- O
The larger part of electrical energy is converted into mechanical energy in5 o9 v5 H3 z# |3 p( B6 |: A& m
electric motors. Among electric motors, induction motors are most used both for. }% C, n4 C' k7 t
home appliances and in various industries [1-11]. 8 f3 p0 l; v( O" z+ Y4 D4 GThis is so because they have been traditionally fed directly from the threephase . }! @, U8 j5 R$ T6 ha.c. electric power grid through electromagnetic power switches with) O _% _ W; }1 c# S& A9 n
adequate protection. It is so convenient. # B- M# f8 e; w0 R: T2 ESmall power induction motors, in most home appliances, are fed from the4 e" {) `8 h+ X
local single phase a.c. power grids. Induction motors are rugged and have6 Z& o+ t& u; |# P! W }# j
moderate costs, explaining their popularity. & j d. A9 G1 c+ B+ @2 p7 oIn developed countries today there are more than 3 kW of electric motors ! D P4 L$ C3 g3 ]6 ~per person, today and most of it is from induction motors.' ?4 B" p* w- g$ x6 C
While most induction motors are still fed from three-phase or single-phase7 n' t$ j, Q& t, _
power grids, some are supplied through frequency changers (or power 4 ?8 N, w# x6 v- \5 y# E# x1 r! Lelectronics converters) to provide variable speed.- x, V& o% x' t' i% Z& J3 `7 I6 a6 t! z
In developed countries, 10% of all induction motor power is converted in2 b3 b. Z3 R$ Y: n/ d/ q/ c' ^
variable speed drives applications. The annual growth rate of variable speed % @, t, a- F' ]drives has been 9% in the last decade while the electric motor markets showed2 z q9 P! G0 d
an average annual growth rate of 4% in the same time.- }# p( [/ N& G& W3 Q
Variable speed drives with induction motors are used in transportation,. z) u, j# [! z% f; F9 S. ]
pumps, compressors, ventilators, machine tools, robotics, hybrid or electric $ {' i2 u9 C) a+ Qvehicles, washing machines, etc.* Q3 k% Q: {' g: n: x) T5 l; e
: W+ o6 p$ d& l: g
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发表于 2007-12-22 11:09:33
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