|转至：电工之家
电机的功率并不大，也只有200瓦，完全可以改为单相电机使用。我们知道电动机从原来的三相运转改变成单相运转，一般都是采用串接电容的方法。我们利用电容在电路中它的电流超前电压的这一特性，进行移相，达到分开电流相位的目的，这样在电机的内部才能产生旋转磁场。由于三相电机内部没有离心开关，我们只能把这种电机接成电容运行的方式，下面我们来聊聊这样大的电机需要配多大的电容，电容如何与电机定子三相绕组进行连接。
电容容量的确定
我们知道对于1KW以下的三相异步电动机可以通过接电容的方式改成单相电动机。我们国家规定对于3KW以下的三相异步电动机，它的绕组接法都是采用星型的连接方式，其连接方法如下所示。对于这种千瓦以下，绕组连接方式为星型的电机，我们可以用经验公式估算出该配置多大的运行电容，一般是按照C=(800~1600)I/U来估算电容的大小，我们这个式子上的C就是指电容的容量大小，单位为微法（UF），U是指电动机上的电压，一般是指220V；I是指三相电动机的相电流额定值，单位为安培（A）。
对于200瓦的三相电机，它的额定电流大约在1.4A左右，我们把这些数值带入经验公式可以得到C=(800~1600)X1.4/220=5.1~10.1UF，为了电机能够正常运行，我们可以选择8微法的启动电容。对于它的耐压值可以按照Uc=1.6U来计算，这样的话Uc=1.6U=1.6X220=352V，我们可以取电容器的耐压值为400V就可以了。至于电机的转动方向，如果只需要一个方向就不用在外部接倒顺转换开关了，当220V电源从U1、V1端子接入时，电机会顺时针转动；当电源从U1、W1端子接入时，电机会逆时针转动。
对于三角形接法的三相异步电动机它所配的电容大小也可以根据经验公式得到，我们一般用
C=(2400~3600)I/U，其耐压值估算不变，还是Uc=1.6U。有时为了得到较好的工作特性，我们可以配置两个电容，一个电容用于启动电机；另一个电容用于运行，当启动结束后，启动电容可以与电路断开，在单相电机中一般是采用离心开关来实现的。
对于启动电容的容量可以不考虑电动机的接法，它的容量一般取工作电容容量的2.5倍左右，对于200瓦的电机，运行电容配8微法的话，那么其启动电容可以配20微法左右。
专栏：行业资讯
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