基本的电气知识。
欧姆定律:流过电阻R的电流I与两端的电压U成正比。其数学表达式:U=R*I
全电路欧姆定律:全电路是指单回路,若单回路中电源的电动势为E,内阻为r,负载电阻为R,则电流等于电动势被回路的全部电阻所除。
其数学表达式为:I=E/(R+r)。
基尔霍夫定律:
电流定律:在任何一瞬间,流进节点的所有电流之和等于从它流出的所有电流之和;
电压定律:沿任何一回路循环一周,各段电压的代数和为零。
电阻的串、并联:
串联:电阻一个接一个连成一串时,称为串联。其特点是各电阻流过的电流相同。串联电阻的等效电阻R为各电阻之和。R=R1+R2+R3+。。。+Rn
并联:各电阻的一端连在一起,另一端也连在一起,称为并联。其特点是各电阻受到同一电压。并联的等效电阻的倒数等于各电阻倒数之和。1/R=1/R1+1/R2+1/R3+。。+1/Rn
二、三相异步电动机变频调速的工作原理。
三相异步电动机由定子绕组所产生的同步旋转磁场的转速为:n0=60f/p转/分。其中f为交流电的频率,p为绕组的极对数。实际上电机以比n0略有差异的转速n(n<n0)旋转,n=(1-s)60f/p,故称为异步电动机。由此公式我们看出,只要适当地改变电机电源的频率f,电机的转速就会相应成比例的改变。这就是变频调速的基本原理。
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