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          Selection and operation and maintenance of AC contactor

          (1) Selection:
          ① The rated current of the main circuit contact should be greater than or equal to the rated current of the controlled equipment, and the contactor controlling the motor should also consider the starting current of the motor. In order to prevent the main contact of the contactor from being ablated frequently, the rated current of the frequently operated contactor can be reduced.
          ② The rated voltage of the electromagnetic coil of the contactor is 36V, 110V, 220V, 380V, etc. The electromagnetic coil is allowed to be used within the range of 80% to 105% of the rated voltage.

          (2) Operation and maintenance:
          ① Inspection items during operation:
          1) Whether the load current passed is within the rated value of the contactor;
          2) The contactors opening and closing signal indicates whether it matches the circuit status;
          3) Whether the running sound is normal and whether there is a discharge sound due to poor contact;
          4) Whether the electromagnetic coil is overheated, and whether the short circuit ring of the electromagnet is abnormal.
          5) Whether the arc extinguishing cover is loose or damaged;
          6) Whether the auxiliary contact is damaged;
          7) Whether the transmission part is damaged;
          8) Whether the surrounding operating environment has adverse operating factors, such as excessive vibration, poor ventilation, excessive dust, etc.
          ② Maintenance:
          When performing maintenance work on electrical equipment, perform maintenance work on the contactors as well.
          1) External maintenance:
          a. Clean up external dust;
          b. Check whether each fastener is loose, and the conductor connection part, to prevent loose contact and heat;
          2) Contact system maintenance:
          a. Check whether the positions of the dynamic and static contacts are aligned, and whether the three phases are closed at the same time. If there is a problem, adjust the contact spring.
          b. Check the degree of wear of the contacts. The wear depth must not exceed 1mm. The contacts are burnt. When the welding is broken, they must be replaced in time. When the burns are slight, the use is generally not affected. Sandpaper is not allowed when cleaning contacts, and a plastic file should be used;
          c. Measure the insulation resistance between phases, the resistance is not less than 10MΩ;
          d. Check whether the auxiliary contact moves flexibly, the contact stroke should meet the specified value, check whether the contact is loose or fall off, and if a problem is found, it should be repaired or replaced in time.
          3) Iron core maintenance:
          a. Sweep dust, moving parts and the contact surface between iron cores;
          b. Check the tightness of the iron core. Loose cores will cause increased operating noise;
          c. The core short-circuit ring has fallen off or broken, and it should be repaired in time.
          4) electromagnetic coil maintenance:
          a. Measuring coil insulation resistance;
          b. Whether the coil insulation is discolored or aging, and the surface temperature of the coil should not exceed 65 ° C;
          c. Check the coil lead connection, and repair it in time if it is open or damaged.
          5) Partial maintenance of arc shield:
          a. Check whether the arc extinguishing cover is damaged;
          b. Whether the position of the arc extinguishing cover is loosened or changed;
          c. Remove metal particles and debris in the gap of the arc extinguishing cover.