A power relay is a device that produces a jump in the output circuit of one or more appliances when the input (or excitation) meets certain specified conditions. It can be used in neutral direct earthing systems as a directional component for zero sequence current protection.

　　The working principle of the power relay is that when the power relay coil ends with a certain voltage or current, the magnetic flux generated by the coil through the core, yoke iron, armature, magnetic circuit work air gap composed of magnetic circuit, under the action of the magnetic field, armature suction to the core pole surface, thus promoting the contact normally closed contact off, normally open contact closed; when the voltage or current at both ends of the coil is less than a certain value, the mechanical reaction force is greater than the electromagnetic suction force, armature When the voltage or current at both ends of the coil is less than a certain value, the mechanical reaction force is greater than the electromagnetic suction, the armature returns to its initial state, the normally open contact is broken and the normally closed contact is turned on.

　　Contact principle of power relays

　　A power relay is a device that can be converted in one or more electrical output circuits when the input (or excitation) meets certain conditions. It can be used in neutral point direct earthing systems as a directional element for zero sequence current protection.

　　The action process of the contacts can be divided into two parts: contact closure and contact break, i.e. the pull-in and release process of the relay, which are cyclically switched at a certain frequency to form the contact break and close phenomena. During contact closure and opening there are many special physical and chemical phenomena such as contact contact resistance, contact jitter and arc discharge.

　　Principle of action during contact closure

　　When the dynamic and static contacts of a relay come into contact with each other, contact rebound occurs, i.e. uncontrolled gap opening and closing. The arcing that occurs at this time and the Joule heat generated by the energising current greatly affect the opening and closing capacity of the relay.

　　Principles of action when contacts are open

　　When the contact opens and the load is cut, dazzling sparks and arcing occur and arcing takes place until the arc voltage drops below the minimum arc voltage value, which causes large damage to the contact. The different contact materials and contact gap sizes directly influence the state of radiation of the arcing electrons and the ease with which they can occur, so they are important conditions for determining the arcing.

　　The role of power relays
　　Power relays have the advantages of fast action, stable operation, long service life and small size. They are widely used in power protection, automation, motion, remote control, measurement and communication devices.