1. The voltage level of the AC contactor should be the same as the load, and the type of contactor should be suitable for the load.
2. The accounting current of the load should be less than or equal to the additional working current of the contactor.
The turn-on current of the contactor is greater than the starting current of the load, the breaking current is greater than the breaking demand current when the load is running, and the accounting current of the load should consider the practical working environment and working conditions.
3. Check the dynamic and thermal stability for a short time.
The three-phase short-circuit current of the line should not exceed the dynamic and thermal stability current promised by the contactor, and the breaking ability of the contactor should also be verified when the contactor is used to disconnect the short-circuit current.
4. The additional voltage, current and the number and current capacity of the auxiliary contacts of the contactor suction coil should meet the wiring requirements of the control loop. It is necessary to consider the length of the line connected to the control loop of the contactor, the operating voltage value of the general introduction, and the contactor should be able to work at an additional voltage value of 85-110%. If the line is too long and the voltage drop is too large, the contactor coil may not reflect the closing instruction; Because the line capacitance is too large, it may not work for trip commands.
5. Check the operation frequency promised by the contactor according to the number of operations. If the operating frequency exceeds the specified value, the additional current should be doubled.
6. The parameters of short-circuit maintenance components should be selected in cooperation with the parameters of the contactor. When selecting, you can refer to the sample manual, which generally gives the cooperation table of contactor and fuse.
The cooperation between the contactor and the circuit breaker should be decided according to the overload coefficient of the circuit breaker and the current coefficient of short-circuit maintenance. The agreed heating current of the contactor should be less than the overload current of the circuit breaker, and the on-on and disconnection current of the contactor should be less than the short-circuit maintenance current of the circuit breaker, so that the circuit breaker can maintain the contactor.
In practice, the ratio of heating current and additional working current of the contactor is between 1 and 1.38 under a voltage level, and the overload coefficient parameters of the circuit breaker are more than 1, and different types of circuit breakers are different, so it is difficult to have a specification for the cooperation between the two, and the cooperation table cannot be formed, and the demand is calculated in practice
7. The installation interval of contactors and other components should comply with relevant national standards and specifications, and the repair and wiring spacing should be considered.
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