1. When selecting a contactor, the following elements are critically considered.
①The AC contactor is used to operate the AC load, and the DC contactor is used for the DC load.
②The stable working current of the main contact point should be greater than or equal to the current of the load power circuit. It should also be noted that the stable working current of the main contact point of the contactor refers to the current that can work normally under specified conditions (voltage in rated value work, application type, actual operation times, etc.). When the specific application standards are different, the current will also change.
③ The voltage during stable operation of the main circuit breaker should be greater than or equal to the voltage of the load power circuit.
④ The rated voltage of the electromagnetic coil should be consistent with the control loop voltage.
2. Operation steps for contactor selection.
①The type of contactor must be selected according to the type of load.
②Select the main parameters of the rated value of the contactor.
Determine the main parameters of the rated value of the contactor, such as voltage, current, output power, frequency, etc.
(1) The electromagnetic coil voltage of the contactor should generally be lower to reduce the requirements of the insulation layer of the contactor and apply relative safety. When the control loop is simple and there are few household appliances, the voltage of 380V or 220V can be selected immediately. If the power circuit is very complicated. When the total number of applied household appliances exceeds 5, 36V or 110V voltage solenoid coils can be selected to ensure safety. However, in order to better facilitate and reduce machinery and equipment, the selection is usually carried out according to the specific power grid voltage.
(2) The operating frequency of the motor is not high, such as refrigeration compressors, centrifugal pumps, centrifugal fans, central air conditioners, etc., the rated current of the contactor exceeds the rated current of the load.
(3) For counterweight daily task motors, such as the main motor of CNC lathes, lifting platforms, etc., the rated current of the contactor exceeds the rated current of the motor when selected.
(4) Motors for unique main purposes. Usually when the operation is turned over, the contactor can be selected according to the service life of the electrical equipment and the amount of running current, CJ10Z.CJ12.
(5) When applying the contactor to control the transformer, the size of the surge voltage should be considered. For example, DC welding machines can usually select contactors based on twice the rated current of the transformer, such as CJT1.CJ20 and so on.
(6) The rated current of the contactor refers to the maximum allowable current of the contactor during long-term operation, the delay time is less than or equal to 8h, and it is installed on the open controller. If the cooling condition is poor, the rated current of the contactor should be selected according to 1.1-1.2 times the rated current of the load.
(7) Select the total amount and type of contactors. The total amount and type of contactors should meet the regulations of the control circuit.
Post time: Apr-09-2022
