Selection and operation maintenance of AC contactor

(1) Selection:

1 Select the type of AC contactor, which should be selected according to the type of load current and the weight of the load, that is, AC load or DC load, light load, general load or heavy load.

2 The rated current of the main circuit contact should be greater than or equal to the rated current of the controlled device. The contactor of the control motor should also consider the starting current of the motor. If the AC contactor controls the motor to start, brake or reversing frequently, the rated current of the contactor main contact is generally reduced to one level. In addition, the rated current of the main contact can be calculated according to the empirical formula:

Ie main contact ≥ (A)

3 The rated voltage of the main contact, the voltage marked on the nameplate of the contactor refers to the rated voltage that the main contact can withstand, not the voltage of the electromagnetic coil. When used, the rated voltage of the main contact of the contactor should be greater than or equal to the rated voltage of the load. .

4 The choice of operating frequency, the operating frequency refers to the number of times the contactor is turned on and off every hour. When the on-off current is large and the switching frequency is too high, the contact may be seriously overheated or even welded. If the operating frequency exceeds the specified value, a contactor with a rated current of one level should be used.

5 AC contactor electromagnetic coil rated voltage selection, the contactor's electromagnetic coil rated voltage is 36V, 110V, 220V, 380V, etc., the electromagnetic coil is allowed to use within the range of 80% ~ 105% of the rated voltage. The voltage of the electromagnetic coil of the contactor can be directly selected from 380V or 220V, which can be selected according to the voltage of the control circuit.

(2) Operation and maintenance:

1 running check items:

1) Whether the passing load current is within the contactor rating;

2) The split signal of the contactor indicates whether it matches the state of the circuit;

3) Is the running sound normal, and whether there is a discharge sound due to poor contact;

4) Whether the electromagnetic coil is overheated or not, and the short circuit of the electromagnet is abnormal.

5) Whether the arc extinguishing cover is loose or damaged;

6) Whether the auxiliary contacts are burnt or not;

7) Whether the transmission part is damaged or not;

8) Whether there are adverse operating factors in the surrounding operating environment, such as excessive vibration, poor ventilation, and excessive dust.

2 maintenance:

When performing maintenance work on electrical equipment, maintenance work should be performed on the contactor.

1) External maintenance:

a. Clean up external dust;

b. Check whether the fasteners are loose, especially the conductor connection parts, to prevent loose contact and heat;

2) Contact system maintenance:

a. Check whether the position of the moving and static contacts is aligned, and whether the three phases are closed at the same time. If there is any problem, adjust the contact spring;

b. The contactor contact surface should be kept clean and no oil is allowed. When the surface of the contact has formed a metal bead due to the action of the arc, it should be removed in time, but the oxide film produced on the surface of the silver and silver alloy contacts has little contact resistance and does not need to be repaired, otherwise the life of the contact is shortened.

c. Check the degree of contact wear, the wear depth should not exceed 1mm, the contact burns, when the welding is off, it must be replaced in time; when it is slightly burnt, it generally does not affect the use. Sandpaper should not be used when cleaning the contacts, and plastic files should be used;

d. Measuring the insulation resistance between phases, the resistance is not less than 10MΩ;

e. Check whether the auxiliary contact action is flexible. The contact stroke should meet the specified value. Check whether the contact is loose or not. When the problem is found, repair or replace it.

3) Core maintenance:

a. Sweeping dust, especially between moving parts and core contact surfaces;

b. Check the tightening of the iron core, and the loose iron core will cause the running noise to increase;

c. If the iron core short-circuit ring is detached or broken, it should be repaired in time.

4) Electromagnetic coil maintenance:

a. Measuring the insulation resistance of the coil;

b. Whether the coil insulation has discoloration or aging, and the surface temperature of the coil should not exceed 65 °C;

c. Check the coil lead connection. If there is open welding or burning, it should be repaired in time.

5) Partial maintenance of the arc extinguishing cover:

a. Check if the arc chute is damaged;

b. Whether the position of the arc extinguishing cover is loose or positional;

c. Remove metal particles and debris from the gap of the arc chute.