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Safety capacitor
YTF websit:www.ytfcapacitor.com
The discharge of the safety capacitor is different from the ordinary capacitor. The charge will remain for a long time after the external power supply is disconnected. If it is touched by hand, it will be charged, and the safety capacitor will not have this problem. At the AC power input, it is generally necessary to add three safety capacitors to suppress EMI conducted interference.
Safety capacitors are divided into x and y types. The AC power input is divided into 3 terminals: FireWire L/Neutral N/Groundline G, (L=Line, N=Neutral, G=Ground). Between the “LN”, that is, between the “hot line and the zero line” is the X capacitor; between the “LG/NG”, that is, between the “fire line - ground line or neutral line - ground line” is Y capacitance. A capacitor between the live and neutral lines is like an “X”, and a capacitor between the live and ground lines is like a “Y”.
X capacitor: According to the actual needs, the capacitance of the X capacitor is allowed to be larger than the capacitance of the Y capacitor. However, a safety resistor must be connected in parallel with the X capacitor to prevent the power cord from being plugged in. The power cord plug is energized for a long time during the discharge process. The safety standard stipulates that when the working power cord is unplugged, the voltage charged at both ends of the power cord plug (or ground potential) must be less than 30% of the original rated operating voltage within two seconds.
As an X capacitor of safety capacitors, do not use the ordinary capacitors such as AC250V or DC400V at random. In general, X-capacitors use a polyester film capacitor with a large ripple current. This type of capacitor is bulky, but it allows a large amount of current to be instantaneously charged and discharged, and its internal resistance is correspondingly small.
Y capacitor: Under normal circumstances, the machine working in the subtropical zone requires that the earth leakage current should not exceed 0.7mA; when working in a temperate machine, the earth leakage current should not exceed 0.35mA. Therefore, the total capacity of the Y capacitor generally cannot exceed 4700 PF (472). The capacitance of the Y capacitor must be limited to achieve the purpose of controlling the leakage current flowing through it under the rated frequency and rated voltage and the impact on the EMC performance of the system. GJB151 specifies that the capacity of the Y capacitor should be no more than 0.1uF.
In addition to the corresponding grid voltage withstand voltage, the Y capacitor also requires sufficient safety margin for electrical and mechanical performance to avoid breakdown and short circuit under extreme environmental conditions. The pressure resistance of the Y capacitor is correct. Protecting personal safety is of great significance. The appearance of the Y capacitor is mostly orange or blue, and the Y capacitor must not be used as a substitute for a common capacitor such as a nominal withstand voltage of AC250V or DC400V.
