How to choose AC contactor

2022-09-19
  • Detail

How to choose AC contactor

the selection of AC contactor should be based on the type of load and working parameters, and if necessary, the gasket should be replaced. Specifically, it is divided into the following steps:

1. select the type of 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 corresponding control objects of a class of AC contactors are non inductive or micro inductive loads, such as incandescent lamps, resistance furnaces, etc; Class II AC contactor is used for starting and stopping wound asynchronous motor; The typical uses of the three types of AC contactors are the operation and breaking of squirrel cage asynchronous motors; Four types of AC contactors are used for starting, reverse braking, reverse rotation and inching of cage asynchronous motors

2. Select the rated parameters of the contactor

determine the rated parameters of the contactor according to the controlled object and working parameters such as voltage, current, power, frequency and working system

1) generally, the coil voltage of the contactor should be lower, so that the insulation requirements of the contactor can be reduced and it is safer to use. However, in order to facilitate and reduce the equipment, it is often selected according to the actual electric voltage

2) the operating frequency of the motor is not high. For example, compressors and water pumps may show different angles, fans, air conditioners, punches, etc. the rated current of the contactor is greater than the rated current of the load. The contactor type can be cjl0, cj20, etc

3) counterweight task motors, such as machine tool main motors, lifting equipment, winches, crushers, etc., can be completed in sequence after their average operating frequency exceeds 101 settings; 0 times/min, running in the states of starting, inching, forward and reverse braking, reverse braking, etc., cjl0z and cjl2 contactors can be selected. In order to ensure the electrical life, the contactor can be used with reduced capacity. When selected, the rated current of the contactor is greater than the rated current of the motor

4) for special task motors, such as printing machines, boring machines, etc., the operation frequency is very high, up to 600 ~ 12000 times/h, and often operates in the states of starting, reverse braking, reverse, etc. the contactors can be roughly selected according to the electrical life and starting current, and the contactor models are cjl0z, cjl2, etc

5) when the capacitor in the AC circuit is powered on or cut off, the closing impulse current of the capacitor should be considered in the selection of contactor. Generally, the rated current of the contactor can be selected as 1.5 times of the rated current of the capacitor, and the models are CJ10, cj20, etc

6) when using contactors to control the transformer, the magnitude of surge current should be considered. For example, AC arc welding machine, resistance welding machine, etc., generally the contactor can be selected according to twice the rated current of the transformer, and the model can be cjl0, cj20, etc

7) for electric heating equipment, such as resistance furnace, electric heater, etc., the cold resistance of load is smaller by forming and back injection of stable fiber-reinforced composite material called "organic sheet", so the starting current is correspondingly larger. When selecting contactors, it is not necessary to consider (starting current), but directly select them according to the rated current of the load. Models can be cjl0, cj20, etc

8) due to the large starting current and long starting time of the gas discharge lamp, for the control of the lighting equipment, the AC contactor can be selected according to 1.1 ~ 1.4 times the rated current, and the models can be cjl0, cj20, etc

9) the rated current of the contactor refers to the maximum allowable current of the contactor under long-term operation. The duration is ≤ 8h, and it is installed on the open control board. If the cooling condition is poor, when selecting the contactor, the rated current of the contactor is selected according to 110% - 120% of the rated current of the load. For motors that work for a long time, because the oxide film has no chance to be removed, the contact resistance increases, resulting in contact heating exceeding the allowable temperature rise. During actual selection, the rated current of the contactor can be reduced by 30%. (end)

Copyright © 2011 JIN SHI