The selection of AC contactor should be based on the type of load and the main working parameters. It is divided into the following processes

1. Select the type of AC contactor

AC contactors are generally divided into class I, class II, class III and class IV according to the load type, which are respectively recorded as AC1, ac2, AC3 and Ac4. The first type of AC contactor is used to match the operation target of non inductive or micro inductive load, such as fluorescent lamp, electric heating furnace, etc.; the second type of AC contactor is used to start and terminate the wound induction motor; the typical main purpose of the third type of AC contactor is to break the bangs during the operation of wound induction motor; the fourth type of AC contactor is used to start and terminate the cage induction motor Connect the brake system reversely, turn over and start light out.

2. Select the rated value and main parameters of AC contactor

According to the measured target and main parameters such as working voltage, current, output power, frequency and working time system, the main parameters of rated value of AC contactor are defined.

1) Generally, the working voltage of electromagnetic coil of AC contactor should be lower, so that the insulation layer of AC contactor can be reduced and the application is safer. But in order to facilitate and reduce the cost of machinery and equipment, often according to the specific power grid working voltage selection.

2) The actual operation frequency of motor is not high, such as refrigeration compressor, centrifugal pump, centrifugal fan, central air conditioner, high speed punch, etc. the rated current of AC contactor can exceed the rated current of load. The type of AC contactor can be cjl0, cj20, etc.

3) The average actual operating frequency of counterweight daily task motors, such as the main motor of CNC lathe, lifting platform, winch, pulverizer, etc., exceeds 100 times / min. The cjl0z and cjl2 AC contactors can be selected for starting, light emitting, positive and negative facing braking system, reverse connecting braking system, etc. In order to ensure the service life of electricity, the capacity of AC contactor can be reduced. When selecting, the rated current of AC contactor exceeds the rated current of motor.

4) For special duty motors, such as printing equipment and boring machine, the actual operation frequency is very high, reaching 600-12000 times / h. they often operate in starting, reverse braking system, reverse direction and other situations. AC contactor can be selected according to the service life and starting current, and contact models are cjl0z, cjl2, etc.

5) When the power capacitor in the AC control circuit is put into or removed from the power network, the impact current of power capacitor reclosing should be considered in the selection of AC contactor. Generally, the rated current of AC contactor can be selected as 1.5 times of the rated current of power capacitor, and CJ10, cj20, etc. can be selected as the model and specification.

6) When operating the transformer with AC contactor, the size of surge current should be considered. For example, AC arc welding machine, resistance welding machine, etc. generally, AC contactor can be selected according to 2 times of rated current of transformer, and cjl0, cj20, etc. can be selected for model and specification.

7) For electric heating equipment, such as electric heating furnace, electric water heater, the load of hot resistor is small, so the starting current is relatively large. When selecting AC contactor, it is not necessary to consider (starting current), but select according to the rated load current immediately. Cjl0 and cj20 can be selected as models and specifications.

8) Due to the large starting current and long starting time of gas discharge lamp, AC contactor can be selected according to 1.1 ~ 1.4 times of rated current, and cjl0, cj20, etc. can be selected for the operation of lighting lamps.

9)The rated current of AC contactor refers to the larger allowable current of AC contactor in long-term work, with delay time ≤ 8h, and is installed on the opened controller. If the refrigeration standard is weak, when AC contactor is selected, the rated current of AC contactor shall be selected according to 110% ~ 120% of rated current of load. For long-term operation of the motor, because the air oxide film has no chance to be eliminated, the circuit resistance is expanded, resulting in the contact point scalding beyond the allowable temperature rise. When selecting, the rated current of AC contactor can be reduced by 30%.