Safety capacitors are divided into x type and y type. The AC power input consists of three terminals: live Line L/ Neutral line N/ Ground line G, (L=Line,N=Neutral, G=Ground). Between the "L-N", that is, between the "firewire and neutral wire" is the X capacitor; Straddling the "L-G/N-G", that is, between the "live wire - ground wire or neutral wire - ground wire" is the Y capacitor. The indirect capacitance of the live line and the neutral line is like "X", and the indirect capacitance of the live line and the ground line is like "Y", which are not divided by what material.
X capacitor: Because the location of this capacitor connection is also more critical, it also needs to meet the relevant safety standards. The X capacitor is also one of the safety capacitors. According to actual requirements, the capacity of the X capacitor is allowed to be larger than that of the Y capacitor. In this case, a safety resistor must be connected to both ends of the X capacitor in parallel to prevent the plug of the power cable from being charged and discharged for a long time when the power cable is removed and inserted. Safety standards stipulate that when the power cord of the working machine is unplugged, the voltage (or potential to the ground) at both ends of the power cord plug must be less than 30% of the original rated operating voltage within two seconds.
As one of the safety capacitors, the X capacitor is also required to obtain the certification of the safety testing organization. X capacitors are generally marked with safety certification marks and voltage AC250V or AC275V words, but its real DC voltage is up to 2000V or more, do not use ordinary capacitors such as nominal voltage AC250V or DC400V when used.
Generally,X capacitors are mostly polyester film capacitors with relatively large ripple current. This type of capacitor has a larger volume, but the current it allows for instantaneous charge and discharge is also large, and its internal resistance is correspondingly small.
Y capacitor: The location of the connection of the two Y capacitors is more critical, and must meet the relevant safety standards to prevent leakage of electronic equipment or housing charging, which is easy to endanger personal safety and life. They are all safe capacitors, which requires that the capacitance value cannot be too large, and the voltage must be high. Under normal circumstances, the machine working in the subtropical zone requires that the earth leakage current should not exceed 0.7mA; Working in the temperate zone machine, the earth leakage current should not exceed 0.35mA. Therefore, the total capacity of the Y capacitor generally cannot exceed 4700PF (472).
The capacitance of the Y capacitor must be limited, so as to control the size of the leakage current flowing through it and the impact on the EMC performance of the system under the action of the rated frequency and rated voltage. GJB151 stipulates that the capacity of Y capacitor should not be greater than 0.1uF. In addition to complying with the corresponding power grid voltage withstand voltage, the capacitor is also required to have sufficient safety margin in terms of electrical and mechanical properties to avoid breakdown and short circuit in extremely harsh environmental conditions. The voltage withstand performance of the Y capacitor is of great significance to protect personal safety. In particular, it is pointed out that the Y capacitor, as a safety capacitor, must be certified by a safety testing institution. The appearance of Y capacitors is mostly orange or blue, and they are generally marked with safety certification marks (such as UL, CSA, etc.) and the words AC250V or AC275V. However, its true DC withstand voltage is up to 5000V or more. It must be emphasized that Y capacitors must not be arbitrarily used to substitute ordinary capacitors such as nominal voltage AC250V or DC400V.