1. When choosing a contactor, start from the working environment, and mainly consider the following factors
AC contactors shall be selected for ① control AC load and DC contactors for DC load
The rated working current of the ② main contact should be greater than or equal to the current of the load circuit, and also note that the rated working current of the contactor main contact is under the specified conditions (rated working voltage, use category, operation frequency, etc.) can work with normal current value, when the actual use conditions are different, the current value will also change accordingly.
The rated operating voltage of the ③ primary contact shall be greater than that of the load circuit.
The rated voltage of the ④ coil shall be consistent with the control circuit voltage
2. Specific steps of contactor selection
① selects the type of contactor, requiring the type of contactor based on the type of load
The ② selects the rated parameter of the contactor
Determine the rated parameters of the contactor according to the charged object and working parameters, such as voltage, current, power, frequency, etc.
(1) The coil voltage of the contactor should generally be lower, so that the insulation requirements of the contactor can be reduced, and it is also relatively safe when using. When the control circuit is simple and the use of electrical appliances is less, 380V or 220V voltage can be directly selected. If the circuit is complex. When the number of electrical appliances used exceeds 5, a 36V or 110V voltage coil can be used to ensure safety. But in order to facilitate and reduce the equipment, often according to the actual power grid voltage selection.
(2) The operation frequency of the motor is not high, such as compressor, water pump, fan, air conditioning, etc., the rated current of the contactor is greater than the load rated current.
(3) For the heavy task-type motor, such as the main motor of the machine tools, lifting equipment, etc., the rated current of the contactor is greater than the rated current of the motor
(4) For special purpose motors. When often running in the state of start and reversal, the contactor can be roughly selected according to the electric life and starting current, optional CJ10Z, CJ12,
(5) When controlling the transformer with a contactor, the surge current should be considered. For example, the electric welding machine can generally select the contactors by 2 times of the rated current of the transformer, such as CJT1, CJ20, etc.
(6) The rated current of the contactor refers to the maximum allowable current of the contactor under long-term work, with a duration of 8H, and is installed on the open control board. If the cooling condition is poor, the rated current of the contactor is selected by 1.1-1.2 times of the rated current of the load when selected.
(7) Select the number and type of contactors. The number and type of contacts shall meet the requirements of the control circuit.
Post time: Oct-13-2022
