Chapter4-Transformer讲解.ppt

Chapter 4 Transformer; Function of transformer ; 在能量传输过程中，当输送功率P =UI cos? 及负载功率因数cos? 一定时：; 发电厂 1.05万伏;1. 按用途分类 电力变压器、配电变压器、整流变压器、 电焊变压器、船用变压器、电源变压器等。 2. 按相数分类 三相变压器、单相变压器。 3. 按每相绕阻的个数分类 双绕阻变压器、三绕阻变压器、自耦变压器。 4. 按冷却方式分类 干式变压器、油浸式变压器。 5. 按结构分类 心式变压器、壳式变压器。;6;7; 将电压降低到电气设备工作电压的变压器称为配电变压器，该类变压器作为日常照明和工厂动力用，一般低压为0.4kV及以下。电力网中所用到的所有变压器统称为电力变压器，即为配电前用的各级变压器，一般低压为3kV及以上。;4.1 变压器的基础知识;一、磁路基础;*;5. 安培环路定律（全电流定律）：;磁路：主磁通所经过的闭合路径。;对于均匀磁路;磁路和电路的比较（一）;欧姆定律;电路方程：;假设;二、 变压器的基本结构; 心式变压器 （绕组包围铁心） ; 壳式变压器 （铁心包围绕组） ;单相变压器原理图;（1） 变压器的型号;? 额定电压 U2N—原边接U1N时，副边绕组的开路电压 ;容量 SN 输出功率 P2 ;A transformer is a device that couples two AC circuits magnetically rather than through any direct conductive connection and permits a “transformation” of the voltage and current between one circuit and the other. Transformers play a major role in electric power engineering and are a necessary part of the electric power distribution network.;＋ u2 － ;一、变压器的空载运行 ： 原边接入额定正弦电源，副边开路。;= －E1＋Z1I1;结论：改变匝数比，就能改变输出电压。;二、变压器的负载运行 ：;2、电流变换 ;(1) i1 与 i2 反相位 i1＞0 时，i2 ＜0，即 i2 是去磁的。保持主磁通不变。 (2) i1 与 i2 的大小关系;3、电压变换 ; 规定 U1 = U1N 时， U20 = U2N 。 如铭牌上标注： 10 000 / 230 V U1N / U2N;（2）高压绕组匝数多，电流小；低压绕组匝数少，电流大。;The Ideal Transformer;The Ideal Transformer;When a time-varying current flows in the primary winding, a corresponding time-varying voltage is generated in the secondary because of the magnetic coupling between the two coils. The relationship between primary and secondary current in an ideal transformer is very simply stated as follows: (3.8.1) N1, the transformer is called a step-up transformer N1, the transformer is called a step-down transformer. ;Example Problem ;Problem Solution;A very common and rather general situation is that depicted in Figure 7.40, where an AC source, represented by its Thevenin equivalent, is connected to an equivalent load imped