According to the requirements of IEC 60384-14, safety capacitors are divided into X capacitors and Y capacitors, which filter the common mode and differential mode interference respectively.Among them, the X capacitor is connected between the two lines of the power line (LN), and the Y capacitor is connected between the two lines of the power line and the ground (LE, NE), respectively. The X capacitor and the Y capacitor only indicate the location of use, not the material of the capacitor. .The discharge of safety capacitors is different from that of ordinary capacitors. Ordinary capacitors will retain their charge for a long time after the external power supply is disconnected. If they are touched by hand, they will be charged, but safety capacitors do not have this problem.Because the safety standard stipulates that when the power cord of the working machine is unplugged, within two seconds, the charged voltage (or ground potential) at both ends of the power cord plug must be less than 30% of the original rated working voltage.X capacitor and connection position The position of the X capacitor connection is more critical, and more attention is paid to the withstand voltage level, and there is no fixed limit value on the capacitance value.The capacitance value of the X capacitor is allowed to be larger than that of the Y capacitor, but at this time, a safety resistor must be connected in parallel at both ends of the X capacitor to prevent the power cord plug from being damaged due to the charging and discharging process of the capacitor when the power cord is unplugged and inserted. Charged for a long time.As one of the safety capacitors, the X capacitor must be certified by a safety testing agency. Generally, it is marked with a safety certification mark and the words AC250V or AC275V withstanding voltage, but its real DC withstand voltage is as high as 2kV or more.According to the pulse voltage, X capacitors can be divided into X1, X2, X3.Among them, the high voltage resistance of X1 is greater than 2.5kV and less than or equal to 4kV; the high voltage resistance of X2 is less than or equal to 2.5kV; the high voltage resistance of X3 is less than or equal to 1.2kV.According to the insulation level, Y capacitors are divided into Y1, Y2, Y3, and Y4.Among them, Y1 withstands high voltage greater than 8kV, Y2 withstands high voltage greater than 5kV, Y3 withstands high voltage n/a, and Y4 withstands high voltage greater than 2.5kV.The two Y capacitors are all safety capacitors, the capacitance value should not be too large, and the withstand voltage must be high.Under normal circumstances, the machine working in the subtropical zone requires that the leakage current to the ground should not exceed 0.7mA, and the machine working in the temperate zone requires that the leakage current to the ground should not exceed 0.35mA.Therefore, the total capacity of Y capacitors generally cannot exceed 4700PF (472).The capacitance of the Y capacitor must be limited, so that under the action of rated frequency and rated voltage, the amount of leakage current flowing and its impact on the EMC performance of the system can be effectively controlled.GJB151 stipulates that the capacity of the Y capacitor should not be greater than 0.1uF.In addition to complying with the corresponding power grid voltage withstand voltage, the Y capacitor is also required to have sufficient safety margin in terms of electrical and mechanical properties to avoid breakdown short-circuit phenomenon under extremely harsh environmental conditions, which is of great significance to protect personal safety.Similarly, Y capacitors must also be certified by a safety testing agency.Y capacitors are mostly orange or blue in appearance, and are generally marked with safety certification marks (such as UL, CSA, etc.) and withstand voltage AC250V or AC275V.However, its true DC withstand voltage is above 5kV.It should be noted that due to some differences in the safety standards of various countries, the safety capacitors produced by the manufacturer must meet the safety standards of the country of use.A safety capacitor can meet the requirements of Y capacitors, and some can meet the requirements of X capacitors at the same time. Some safety capacitors have labels such as X1Y1 and X1Y2.Link: https://mbb.eet-china.com/blog/uid-me-3975615.html