Classification structure and selection principle o

Classification, structure and selection principle of thermal relay

thermal relay (FR) is mainly used for overload protection of motor load in electric drive system

in actual operation, the motor often encounters overload, but as long as the overload is not serious, the time is short, and the winding does not exceed the allowable temperature rise, this overload is allowed. However, if the overload is serious and lasts for a long time, it will accelerate the aging of the motor insulation, shorten the service life of the motor, and even burn the motor. Therefore, overload protection must be carried out for the motor

(1) relay structure and working principle thermal relay to the layout of the whole industrial chain of terminal products such as lithium-ion power batteries and lithium-ion electric vehicles. Electrical appliances are mainly composed of thermal elements, bimetallic sheets and contacts. As shown in Figure L, thermal elements are made of thermal resistance wires. Bimetallic sheet is rolled by two metals with different thermal expansion coefficients. When the bimetallic sheet is heated, Hongyu new material (300345) is a high-tech enterprise specializing in the research and development of new materials and technology utilization in the wear-resistant material industry; It is a country in the field of metal component surface strengthening technology 9 When the operation is completed and the machine is completely stopped, the door can be opened to take the leader in the test article and the international leader. Bending deformation will occur. When in use, the thermal element is connected in series in the main circuit of the motor, and the normally closed contact is connected in series in the control circuit of the motor

Figure 1 Schematic diagram of thermal relay

1-thermal element 2-bimetallic sheet 3-guide plate 4-contact reset

when the motor operates normally, although the heat generated by the thermal element can bend the bimetallic sheet, it is not enough to make the contact of the thermal relay act. When the motor is overloaded, the bending displacement of the bimetallic sheet increases, and the guide plate is pushed to disconnect the normally closed contact, so as to cut off the motor control circuit for protection. Generally, the thermal relay cannot be reset automatically after action. Press the reset button to reset after the bimetal plate cools down. The adjustment of the action current of the thermal relay can be realized by rotating the cam at different positions

(2) model and selection of thermal relays

at present, thermal relays produced in China mainly include jr0, jr1, jr2, jr9, R10, jrl5, jrl6 and other series. Jrl, jr2 series thermal relays adopt indirect heating method, and its main disadvantage is that bimetallic sheets are indirectly heated by heating elements, resulting in poor thermal coupling; The bending degree of bimetallic sheet is greatly affected by ambient temperature, which can not correctly reflect the over-current condition of load

jrl5, jrl6 and other series thermal relays adopt composite heating mode and temperature compensation elements, so they can accurately reflect the working condition of the load

jrl6 and jr20 series thermal relays have thermal relays with phase failure protection and differential phase failure protection mechanism. The selection of thermal relay mainly determines the model of thermal relay according to the connection mode of motor stator winding. In the circuit of three-phase asynchronous motor, the thermal relay of two-phase or three-phase structure can be selected for the motor with Y connection. Generally, the thermal relay of two-phase structure is adopted, that is, the thermal elements are connected in series in the two-phase main circuit. For three-phase induction motors, thermal relays with open phase protection must be used for motors with delta stator windings. The graphic and literal symbols of the thermal relay are shown in Figure 2

Figure 2 graphical and textual symbols of thermal relay

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