It is a device that can produce jump in one or more electrical output circuits when the input quantity (or excitation quantity) meets some specified conditions, and can be used in neutral direct grounding system as a directional element of zero sequence current protection. It is widely used, today we will talk about the application and working principle of automotive relay. In the application of home appliances such as air conditioning often use automotive relay, and in recent years the rapid development of high-power household appliances, such as automobiles, household appliances and so on are used in this kind of relay. In use, its contact action process can be divided into two parts: contact closure and contact disconnection, that is, the process of the relay's pull-in and release, which circularly switch at a certain frequency to form contact disconnection and closure phenomena. In the process of contact closure and disconnection, there will be many special physical and chemical phenomena, such as contact contact resistance, contact jitter and electric arc. 1. Operation principle of contact closure when the moving contact and the static contact of the relay touch each other, the contact rebound will occur, that is, the uncontrolled gap disconnection and closure. At this time, the arc and Joule heating generated by the current greatly affect the opening and closing ability of the relay. 2. The principle of action when the contact is disconnected when the contact is disconnected and the load is cut off, dazzling sparks and arcs will be generated. The arc will continue until the arc voltage drops below the minimum arc voltage value, which will cause great damage to the contact. The different contact materials and the size of contact gap directly affect the arc electron emission state and the difficulty of occurrence, so they are important conditions to determine the arc.