使用三相电源的电气设备在缺相的情况下不能正常工作,因而引出了许多缺相保护电路。有的电路简单,但灵敏度和可靠性不高;有的电路灵敏度和可靠性高,但线路复杂成本高。本电路使用“555”元件,其灵敏度高(20ms以内有反应动作),成本低,易于制作,不妨一试。 如附图所示,R_1～R_3,C_1～C_3接Y形。正常情况下a点无电压,如果三相电源中的一相或二相无电,则a Electrical equipment that uses three-phase power supplies can not function properly in the absence of phase loss, thus leading to many phase loss protection circuits. Some circuit is simple, but the sensitivity and reliability is not high; some circuits have high sensitivity and reliability, but the circuit complexity is high. The circuit uses “555” components, its high sensitivity (response action within 20ms), low cost, easy to make, may wish to give it a try. As shown in the drawing, R_1 ~ R_3 and C_1 ~ C_3 connect to Y shape. Under normal circumstances, there is no voltage at point a. If one or two phases in the three-phase power supply have no electricity, a