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技海拾零 |
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自激反向导通型彩电开关电源变压器的简化工程设计 |
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作者: |
西安电子科技大学
通信系统研究室 杜保明 1988年 4月 |
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前言: |
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1985年~1986年参与了陕西彩电工业配套引进项目〈富平无线电厂彩电开关电源变压器生产线〉 |
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的工作,承蒙省地县有关部门领导和学校的信任,受命担当此项目的技术负责人(也就是人们说的 |
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总工程师吧);在项目技术准备过程中,和工厂的技术人员分析比较收集到的变压器样品,经常讨 |
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论的问题是如何设计开关电源变压器和确保变压器质量的生产工艺方法;这篇小文就是讨论变压器 |
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的设计和计算方法的,当时参考资料非常缺少,写的东西也有好多牵强之处,但总略胜于无吧。 |
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14 |
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20几年过去了,翻看当时打印的文稿,白纸都已变成黄的了,为了不至于忘却,现在将文字照 |
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15 |
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录如下。不知对将要开始搞技术的有否参考价值,希望有点吧。 |
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16 |
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电视机,录放机或小型计算机的功率消耗一般仅有几十瓦,通常都采用电路比较简单的单 |
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端自激式开关稳压电源。在开关电源中,作为电--磁--电转换器件的变压器,对电源的性能有 |
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直接的影响。只有使用良好设计和制作的变压器,才能保证开关稳压电源的高效率,宽输入电 |
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压范围以及安全可靠等优良性能。 |
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对开关电源变压器进行完全的设计将涉及到电,磁,材料等好多方面,比较繁琐。对于实 |
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23 |
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际的生产制作,可以使用简化的工程设计方法来进行。 |
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24 |
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本文所介绍的设计是以“JVC”或“TOSHIBA”14英寸彩电单端自激反向导通型开关电源变 |
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压器为主进行的。电源的电路组成如图
1所示。 |
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L |
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T |
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D1 |
V01 |
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~
220VVac |
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Np |
Ns1 |
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110Vdc |
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n |
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Tr |
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D2 |
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激励电路 |
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V02 |
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NB |
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24Vdc |
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35 |
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保护电路 |
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脉冲调制电路 |
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38 |
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误差信号放大电路 |
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NG |
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39 |
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40 |
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41 |
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42 |
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图 1:单端自激反向导通型彩电开关稳压电源电路的组成 |
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43 |
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根据所使用的交流电网电压,以及电视机正常工作所需的直流电压,最大电流等,可以列 |
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44 |
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出变压器设计的基本条件如下。 |
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45 |
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交流输入电压及输入电压变化范围: |
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46 |
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Vac=185V~
~ 265V~,V0=220V~
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47 |
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整流效率:ηAC/DC≈96%; |
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48 |
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输出整流二极管(D)和绕组线圈(L)的电压降:
Vd = VD + VL≈1.5V; |
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49 |
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输出电压及电流:V01=110Vdc,I01=0.4A; |
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50 |
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V02=24Vdc,I02=0.05A; |
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51 |
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激励电压:VB≈8.0V; |
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52 |
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开关频率:fo≈41kHz,T≈24μS,TON/T≤0.4; |
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53 |
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54 |
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P1 |
55 |
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56 |
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57 |
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环境温度:Tab=45℃; |
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58 |
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最大温升:Δt=35℃; |
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59 |
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根据以上条件和要求,变压器的设计按以下步骤进行。 |
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60 |
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(1)。选择磁心: |
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61 |
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变压器输出功率: |
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62 |
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Pt = |
V01xI01+V02xI02
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46.0(W) |
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63 |
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选择磁心的原则是,首先保证有足够大的传输功率;第二,要有足够的线圈绕制及绝缘空 |
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64 |
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间;第三,磁心要具备适用的磁特性;第四,标准化和低成本。故居以上原则并为了有利说明 |
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65 |
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计算方法,我们选择日本FUJI公司的开关电源变压器磁心H63-EER39/40,传输功率可达100
W |
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66 |
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以上。 |
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67 |
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H63材料的性能如表
1,图 2所示;EER39/40磁心的参数如表 2,图 3所示。 |
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68 |
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表 1:H63材料特性 |
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69 |
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特性 |
使用频率 |
饱和磁通 |
剩余磁通 |
初始导磁率 |
材料功耗 |
居里点温度 |
比重 |
比电阻 |
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70 |
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71 |
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符号 |
f |
Bs |
Br |
μiac |
Pv |
To |
d |
ρ |
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72 |
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条件 |
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80℃ |
80℃ |
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1000G,50kHz,
80℃ |
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73 |
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74 |
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单位 |
kHz |
Gauss |
Gauss |
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mW/cm3 |
℃ |
g/cm3 |
Ω.cm |
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75 |
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H63 |
~
300 |
4250 |
950 |
2500 |
28 |
>230 |
4.8 |
>10 |
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76 |
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77 |
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表 2:H63-EER39/40磁心特性 |
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78 |
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尺寸(mm) |
磁心常数 |
有效磁路长度 |
有效截面积 |
有效体积 |
AL值 |
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80 |
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B |
C |
D |
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F |
C1[cm-1] |
Le[cm] |
Ae[cm2] |
Ve[cm3] |
nH/N2
±25% |
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81 |
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82 |
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40.0+0-1.8 |
29.3+1.6 |
12.8+0-
0.6 |
12.8+0-
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19.8±0.2 |
11.2+0.8 |
7.38 |
9.22 |
1.25 |
11.53 |
3400 |
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83 |
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-0 |
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-0 |
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84 |
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BACDEF |
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(a)工作磁通和功耗的关系10410310-11520kHz40kHz100kHz |
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85 |
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86 |
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87 |
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88 |
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89 |
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90 |
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91 |
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92 |
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93 |
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25℃60℃80℃0246810H (Oe)10002000300040005000B (G) |
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94 |
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95 |
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96 |
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97 |
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98 |
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(b)磁心温升与功耗的关系0864201030405020Δ
t [℃]PC-W |
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99 |
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图 3:
H63-EER39/40磁心的特性曲线(a),(b) |
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100 |
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101 |
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102 |
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103 |
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104 |
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105 |
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106 |
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图 2:H63材料的B-H特性 |
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107 |
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108 |
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109 |
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P2 |
110 |
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111 |
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112 |
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(2)。变压器的允许功耗和工作磁通变化量: |
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113 |
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在变压器温升Δt=35℃时,允许的总功耗约为:Pt=3.8W,工作磁通的最大值约为: |
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114 |
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Bm =3400G,在80℃温度下:Br
=950G(以上参看图 2,图 3的a和b)。 |
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115 |
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由以上,则工作磁通的变化量为: |
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116 |
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ΔBm
= Bm-Br = 2450 G |
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117 |
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(ΔBm也近似地取80℃下Bm的80%)。 |
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118 |
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(3)。输入直流电压: |
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119 |
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最大直流电压: |
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120 |
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Emax = |
2 *Vacmax * ηAC/DC |
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121 |
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= |
2 * 265 * 0.96 |
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122 |
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≈ |
360 (Vdc) |
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123 |
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最低直流电压: |
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124 |
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Emin = |
2 *Vacmin * ηAC/DC |
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125 |
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= |
2 * 185 * 0.96 |
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126 |
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≈ |
252 (Vdc) |
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127 |
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标准直流电压: |
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128 |
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Eo = |
2 *Vaco * ηAC/DC |
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129 |
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= |
2 * 220 * 0.96 |
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130 |
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≈ |
299 (Vdc) |
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131 |
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(4)。初级绕组匝数: |
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132 |
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Np
= |
Emax |
* Ton(max)* 102 |
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(匝) |
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133 |
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Ae*ΔBm |
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134 |
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式中Ton(max)为最大导通时间,单位为μS,电压单位为伏特,Ae单位为cm2,ΔBm单位为 |
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135 |
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G(高斯)。 |
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136 |
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由于在开关管导通时间
Ton内,由电源向变压器储存磁能,而在关断时间Toff内,变压器 |
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137 |
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将所储存的磁能转换为磁极输出的电能,为保证变压器磁心在Toff的时间内退磁到初始状态( |
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138 |
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图2中的R点),一般应使Toff≥0.4T,或者Ton(max)≤0.4T。 |
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139 |
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由于T≈24μS,所以Ton(max)=0.4
* T ≈ 9.0μS |
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140 |
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Np
= |
360 |
* 9 * 102 |
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141 |
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1.25*2450 |
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142 |
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≈ |
105.75 (匝) |
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143 |
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(5)。次级绕组匝数(NS1,NS2): |
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Ton(max) |
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144 |
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Ns= |
Np |
Emin |
T-Ton(max)* |
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145 |
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Vo + Vd |
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146 |
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式中各参数单位见Np计算式说明, |
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9 |
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147 |
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NS1= |
105.75 |
252 |
24-9* |
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148 |
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110+1.5 |
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149 |
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≈ |
78.0 (匝) |
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150 |
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由于24V输出的电流仅0.05A,线电压降可忽略,既Vd
= VD = 0.7V,因而: |
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151 |
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NS1= |
105.75 |
252 |
924-9* |
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152 |
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24+0.7 |
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153 |
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≈ |
17.0 (匝) |
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154 |
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(6)。取样电压绕组匝数(NG)激励绕组匝数(NB): |
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155 |
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取样电压一般可取20V左右,由于是电压取样,电流很小,绕组电压降亦可忽略,因而: |
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156 |
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NG= |
105.75 |
252 |
924-9* |
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157 |
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20+0.7 |
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158 |
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≈ |
15.0 (匝) |
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159 |
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160 |
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P3 |
161 |
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162 |
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163 |
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激励电压在标准交流电压(Vo=220V)输入时,应有
8V左右,并且这个电压是在开关管导通 |
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164 |
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时间Ton内产生,因而有: |
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165 |
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NB= |
Np*VB |
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166 |
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Eo |
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167 |
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= |
105.75 *
8 |
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168 |
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299 |
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169 |
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≈ |
3 (匝) 。 |
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170 |
|
|
(7)。各绕组的导线直径: |
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171 |
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变压器的交流输入功率为: |
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1 |
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172 |
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PAC= |
(Pout
+ Pt)* |
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173 |
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η |
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174 |
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η≈95%,为变压器的转换效率,则有: |
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175 |
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PAC= |
(46+3.8)/ 0.95 |
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176 |
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= |
52.4 (W), |
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177 |
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|
输入电流的平均有效值为: |
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178 |
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Ipav= |
PAC / V0
= 52.4/220 = 0.238 A |
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179 |
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取导线的平均载流系数δ=2.1A/mm2,则初级绕组线径为: |
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180 |
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D
= |
Ipav2* |
= |
0.2382* |
= |
0.38(mm), |
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181 |
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π*δ |
|
π*2.1 |
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182 |
|
|
由于在高频工作,考虑电流趋肤效应,在
f=42kHz的频率下,导线直径应增大到低频时的 |
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183 |
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1.09倍(即截面积增大到低频时的1.2倍),因此,使用的导线直径应为: |
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184 |
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Dp= |
1.09 * D |
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185 |
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≈ |
0.42 (mm) |
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186 |
|
|
同样,次级110V电压输出的绕组线径应为: |
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187 |
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DS1= |
1.09*2* |
IS1av |
= |
1.09*2* |
0.4 |
≈ |
0.536(mm), |
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188 |
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|
π*δ |
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|
π*2.1 |
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189 |
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|
为便于绕制,初次级使用一个规格的导线三股并绕,则每股导线的线径为: |
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190 |
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D1X3= |
DS1 |
≈0.31(mm)。 |
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191 |
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3 |
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192 |
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NS2,NG,NB各绕组的电流都很小,可统一采用0.35~0.5mm直径的导线绕制。 |
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193 |
|
|
(8)。初次级电感量和磁心气隙(GL): |
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194 |
|
|
V0输入时,变压器初级绕组内的峰值电流为: |
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195 |
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Ipmax= |
|
2*Ipav* |
T |
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196 |
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|
TON(MAX) |
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197 |
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= |
2 * 0.238 * 24/9 |
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198 |
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|
≈ |
1.27 (A) |
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|
199 |
|
|
因此,初级的标准电感量应为: |
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200 |
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Lp= |
Eo |
*TON(MAX)*
10-3 (mH) |
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201 |
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|
Ipmax |
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202 |
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= |
299 |
*
9 *10-3 |
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203 |
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|
1.27 |
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204 |
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≈ |
2.12 |
(mH) |
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205 |
|
|
次级NS1绕组的标准电感量应为: |
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|
206 |
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|
LS1= |
Lp |
*NS12 |
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|
207 |
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Np2 |
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208 |
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= |
2.12 |
*782 |
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209 |
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|
(105.75)2 |
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210 |
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≈ |
1.16 |
(mH) |
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211 |
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212 |
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213 |
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P4 |
214 |
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215 |
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216 |
|
|
为了保证NP绕组流过要求的电流而又不使磁心饱和,需要在磁心中制造间隙,增大磁阻, |
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217 |
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|
降低AL值。不同方式的间隙(三足隔垫或中足开气隙)尺寸和实效AL值的对应关系或曲线,一 |
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218 |
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|
般由磁心生产厂给出,变压器制造厂可以根据设计要求选用(可参阅日TDK公司软磁性磁心手 |
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219 |
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|
册等)。目前,我国的磁心生产厂还没有给出这方面的标准参数,一般要由变压器制造厂和磁 |
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220 |
|
|
心生产厂协同用试验的方法确定。因此,下面进行的计算及结果,仅供中足开气隙时的参考。 |
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221 |
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|
初级绕组的计算用最小电感量: |
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222 |
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Lpmin= |
|
Emin *Vacmin *Tonmax2 |
|
|
*10-3
(mH) |
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223 |
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|
|
2*PAC*T |
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224 |
|
|
式中,电压为V(伏特),功率为W(瓦),时间为μS(微秒),则有: |
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225 |
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|
Lpmin= |
|
252 * 185
* 92*10-3 |
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226 |
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|
2*52.4*24 |
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227 |
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≈ |
1.50 |
(mH) |
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228 |
|
|
计算用磁心实效导磁系数μe为: |
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229 |
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μe= |
|
C1 * Lpmin
* 104 |
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230 |
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|
|
0.4*π*Np2 |
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231 |
|
|
式中,C1单位为cm-1,Lpmin单位为m
H,则有: |
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232 |
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|
μe= |
|
7.38*1.50*104 |
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233 |
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|
|
0.4*π*(105.75)2 |
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234 |
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≈ |
7.87729 |
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|
235 |
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|
由以上,则磁心中足气隙的参考值GL为: |
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|
236 |
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|
GL= |
Le*(1 |
- |
1)*10-1 |
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237 |
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|
μe |
μiac1 |
1 |
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238 |
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= |
9.22*( |
|
|
)*10-1 |
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239 |
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|
7.877 |
2500 |
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240 |
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|
≈ |
0.11668 |
(cm) |
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241 |
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|
= |
1.17 |
(mm) |
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|
242 |
|
|
因为磁心的性能不可能作到绝对没有变化,而存在一个允许的误差范围。所以实际上在开 |
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243 |
|
|
磨气隙时,可在1.17mm~1.20mm之间由试验确定。 |
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244 |
|
|
(9)。变压器工作温升的估算: |
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|
245 |
|
|
变压器温升主要由变压器本身产生的功耗,环境温度和工作环境的散热条件等因素决定; |
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|
246 |
|
|
散热主要通过变压器表面的热辐射和自然对流进行。一般情况下,最不利于散热的情况是在夏 |
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|
247 |
|
|
季,若环境温度Tab
= 45℃,变压器磁心表面温升Δt=35℃;则变压器表面最高温度应在80℃ |
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|
248 |
|
|
以下。 |
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|
249 |
|
|
热辐射形式的热耗散速率为: |
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250 |
|
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|
P1 = |
5.67*10-8*E*(TM4-Tab4) |
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(W/m2) |
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251 |
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E: |
表面辐射率,黑色表面
E=0.95; |
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252 |
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TM: |
磁心表面最高温度(绝对温度); |
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253 |
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Tab: |
环境温度(绝对温度); |
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254 |
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|
因为变压器的磁心为黑色,则有
E=0.95,并且TM=273+80=353,Tab=273+45=318,代入计 |
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255 |
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算式,则有: |
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256 |
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P1≈ |
285.557 |
(W/m2) |
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257 |
|
|
自然对流热耗散速率: |
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258 |
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|
对于垂直放置的表面,散热速率为: |
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259 |
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P2≈ |
2.17*(Δt)1.25 |
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260 |
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= |
184.733 |
(W/m2) |
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261 |
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|
对于水平向上放置的表面,散热速率为: |
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262 |
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P3≈ |
1.27*P2 |
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263 |
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= |
234.611 |
(W/m2) |
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264 |
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265 |
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P5 |
266 |
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267 |
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268 |
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|
对于水平向下放置的表面,散热速率为: |
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269 |
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P4≈ |
0.82*P2 |
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270 |
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= |
151.481 |
(W/m2) |
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271 |
|
|
绕制好的变压器立式安装(如图
4),线包为圆形,最大外径27mm左右,则有: |
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272 |
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S2= |
4*D*E + 4*D*F + 4*P*(A-B)+4*A*(E-F)+2*Φ*π*F |
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273 |
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≈ |
5.527*10-3 |
|
(m2) |
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274 |
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S3= |
D*(A-B)+π*(Φ/2)2 |
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275 |
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≈ |
0.693*10-3 |
|
(m2) |
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276 |
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|
S4= |
D*(A-B)+π*(Φ/2)2 |
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277 |
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≈ |
0.693*10-3 |
|
(m2) |
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278 |
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|
S1= |
S2+S3+S4 |
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279 |
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|
≈ |
6.913*10-3 |
|
(m2) |
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|
|
280 |
|
|
代入散热速率计算式,则总的热耗散速率为: |
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|
281 |
|
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|
PΣ≈ |
P1*S1+P2*S2+P3*S3+P4*S4 |
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282 |
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= |
1.974+1.021+0.163+0.105 |
|
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283 |
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|
= |
3.263 |
(W) |
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284 |
|
|
变压器的功耗主要是由磁心的功耗(铁损)和变压器线圈的功耗(铜损)两大部分组成。 |
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285 |
|
|
H63-EER39/40磁心,材料铁损在80℃,50kHz时的最大值为PL=28mW/g;材料比重d=4.8g/cm3, |
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|
286 |
|
|
磁心体积Ve=11.53cm3,因此,总铁损为: |
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|
287 |
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|
PZ= |
PL*d*Ve |
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|
288 |
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≈ |
11.53*28*4.8 |
|
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|
289 |
|
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|
≈ |
1549.632 |
(mW) |
|
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|
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|
|
290 |
|
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|
= |
1.55 |
(W) |
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291 |
|
|
绕制好的线圈,初级最大电阻RP=0.7Ω,次级最大电阻RS=0.6Ω,则铜损值约为: |
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|
292 |
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|
|
PC= |
Ip2*Rp2+Is2*Rs2 |
|
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|
293 |
|
|
|
≈ |
(0.24)2*0.7+(0.45)2*0.6 |
|
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|
294 |
|
|
|
= |
0.16182 |
(W) |
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|
295 |
|
|
考虑到其他绕组(24V绕组,取样及激励绕组等)和介质损耗等,将变压器的功耗增大至 |
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|
296 |
|
|
1.2倍,则变压器功耗变为: |
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|
297 |
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|
PK≈ |
(PZ+PL)*1.2 |
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|
298 |
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≈ |
2.05418 |
(W) |
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|
299 |
|
|
变压器的热耗散能率为3.263W,而变压器的最大功耗为2.054W,散热能力和损耗功率相比 |
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300 |
|
|
有近60%的余量;因此,即便在45℃的环境温度下,变压器的温度也会远底于80℃。 |
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|
301 |
|
|
(10)。标准状态下的开关工作频率验算: |
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|
302 |
|
|
单端自激反向导通型开关稳压电源,在其输出功率不变和开关导通比维持恒定的情况下, |
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303 |
|
|
开关管的工作频率的约值为: |
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304 |
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|
f
= |
(VIN - VCE)2 |
(kHz) |
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305 |
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|
|
8*LP*V0*IOMAX |
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|
306 |
|
|
式中,VIN为加在开关管上的直流电压Eo=299V,VCE为开关管的饱和压降(约0.7V),VO为主 |
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|
307 |
|
|
输出电压(即:V01+绕组线电压降和续流二极管的压降
),IOMAX为输出直流脉冲电流的最大值: |
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|
308 |
|
|
|
IOMAX= |
Io* 3 |
ToffT |
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|
309 |
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|
310 |
|
|
将所得到的各参数值代入,则在交流220V时,开关工作频率的约值为: |
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|
311 |
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|
f
= |
(Eo-0.7)2 |
|
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|
312 |
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|
|
8*2.12*(110+1.5)*0.4*
3 /0.6 |
|
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313 |
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|
≈ |
40.8 |
(kHz) |
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314 |
|
|
即与设计时预设的开关频率基本相同。 |
|
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|
|
315 |
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|
316 |
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317 |
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|
P6 |
318 |
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|
319 |
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320 |
|
|
实际情况下,彩电的功率消耗是一个变量,大多数时间低于POUT(45W);因而,开关工作 |
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321 |
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|
频率在大多数情况下低于41kHz,大约在25kHz~38kHz之间随机变化。 |
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322 |
|
|
彩电开关电源输出电压的稳定,是由电源电路自动调整开关管的开关频率和导通比来完成 |
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323 |
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|
的。为了使交流电网输入电压的下限降低,初级绕组的电感量可尽量取在负误差允许范围内, |
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|
324 |
|
|
以增大低输入电压时的储能电流。当初次级的匝数在±2%~±4%范围内变化时,对电源的实际 |
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325 |
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|
工作并无多大的影响;但在生产中,作为产品,必须保证各绕组匝数一致不变,电感量也必须 |
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326 |
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|
尽量作到在设计值上,使产品具有良好的电气一致性。 |
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327 |
|
|
以上计算若有不妥,望指正。 |
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328 |
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329 |
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|
1988年 4月于西安 |
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330 |
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331 |
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332 |
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333 |
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334 |
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|
335 |
|
|
注: |
关于变压器的温升 |
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|
336 |
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|
一般情况下,对同一物体而言,单位表面积需要发散的热功率按55%的热辐射和45%的 |
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|
337 |
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|
热对流组合实现(即Ws=0.55×Wr+0.45×Wc),当预知环境空气温度后,可以得到如下的 |
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338 |
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|
|
发热物体的温升概算式: |
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|
339 |
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|
|
ΔT=(0.55×Δr
+ 0.45×Δt)/
2 |
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|
340 |
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|
= ( 0.55×(
( ( Ws + k1 ) / ( 5.13×10-12
) )1/4 – k2 ) + 0.45×( Ws / ( 2.7×10-4 ) )1/1.2
) / 2 |
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|
[ ℃
] |
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|
341 |
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|
式中:Ws 单位表面积需要耗散的热功率 ( W / cm2) |
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|
342 |
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|
k1 |
和环境空气温度有关的系数(见下表) |
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|
343 |
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|
k2 |
和环境空气温度有关的系数(见下表) |
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|
344 |
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|
|
表: |
不同环境空气温度时系数k1,k2的值: |
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|
345 |
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|
|
环境温度℃ |
-10 |
0 |
20 |
30 |
40 |
50 |
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346 |
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347 |
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|
k1 |
0.02454 |
0.02850 |
0.03781 |
0.04324 |
0.04924 |
0.05584 |
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348 |
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|
k2 |
263 |
273 |
293 |
303 |
313 |
323 |
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349 |
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|
在上文关于变压器的工作温升的计算中,我们已得到变压器的总损耗PK≈2.054W,变 |
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350 |
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|
压器的总的散热面积是S1≈6.913*10-3(m2),变压器单位面积(cm2)需要耗散的热功率Ws为 |
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351 |
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|
Ws=0.029725(W/cm2);假定变压器的工作环境温度为40℃,则按上面算式计算得到的变压 |
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352 |
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|
器温升为ΔT≈22.1℃(达到热平衡后的变压器表面温度约为62℃)。 |
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|
353 |
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354 |
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|
DuBao |
2006年12月31日于西安 |
|
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355 |
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356 |
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357 |
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358 |
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359 |
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360 |
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361 |
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362 |
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363 |
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364 |
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365 |
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366 |
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367 |
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368 |
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|
|
|
|
|
369 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
370 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
P7 |
371 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|