(1) type selection
Generally, two phase structure of thermal relay can be selected, but when the balance of the three-phase voltage is poor, the working environment is bad or the unattended motor, it is suitable for the thermal relay of three phase structure. For a triangular connection motor, a thermal relay with a phase protection device shall be selected.
(2) selection of rated current for thermal relay
The rated current of the thermal relay should be greater than the rated current of the motor. Then select the type of the thermal relay according to the rated current.
(3) the selection and setting of the rated current of the thermal element
The rated current of the heat element should be slightly larger than the rated current of the motor. When the starting current of the motor is 6 times the rated current and the start time is not more than 5S, the thermal integral current of the motor is adjusted to the rated current of the motor. When the starting time of the motor is longer, the impact load is dragged or no parking is allowed, the setting current of the thermal element is adjusted to 1.1-1.15 times of the rated current of the motor.
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