(1) Selection of overload protection device The overload protection device of the soft start device should choose a thermal overload relay with overload protection, phase failure protection and temperature compensation functions. When selecting, the working current of the motor should be within the range of the setting current of the thermal element. For equipment that is easy to be overloaded during operation, the rated current value of the motor should be close to the lower limit of the setting current range of the thermal element.
(2) The electrical wiring and component arrangement of the low-voltage soft-start cabinet The general electrical wiring of the low-voltage soft-start cabinet is shown in Figure 2. The electrical components in the cabinet are arranged in the order shown in the figure, so that the main wiring is short and does not cross, which is convenient for the connection of copper bars. The soft starter is installed on the right side of the contactor and is not affected by the heating of other components. The distance between the soft starter and the side wall of the control cabinet and other components is required to be 2100mm, which is convenient for the soft starter to dissipate heat.
(3) Selection of bypass contactor At the end of the soft start, the motor has been running at the rated voltage, so the AC contactor can be selected according to the rated current of the motor to meet the requirements. It should be noted that when wiring the cabinet, the soft starter and the contactor should be connected in the same phase, and do not connect the wrong phase sequence.
(4) The isolator and fuse are selected as the isolation electrical appliances in the soft start cabinet. You can choose an isolating switch or a molded case circuit breaker with an isolation function. The low-power soft-start cabinet should choose a combination of isolating switch and fuse, a knife fuse switch. It not only plays the role of isolation and protection, but also reduces the project cost. The rated current of the isolating switch is greater than the rated current of the motor to meet the operation requirements.
(5) Verification of transformer load capacity and protection setting value In addition to the above requirements when selecting a soft-start device, attention should also be paid to the load capacity of the transformer that supplies power to the equipment. If the transformer is close to full load beforehand, the soft-start equipment should be carefully selected. Especially when adding equipment with relatively large power, it is necessary to check the load capacity of the transformer and the setting of the protection.
(6) In addition to the comparison of technology, performance and price, the selection of soft starters should also consider specific conditions such as the power grid capacity of the equipment site, the light and heavy starting load of the equipment, and the frequency of starting. Public Account: Electrical Knowledge Classroom, for equipment with lighter starting loads such as pumps, soft starters with simple functions, lower prices and easy operation can be selected. According to the rated power of the motor, this kind of equipment can meet the needs by selecting the soft starter of the same capacity as specified in the sample.
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