Common fault analysis of AC contactors

- Jul 25, 2019-

AC contactors are a widely used electrical component that is often encountered by maintenance electricians in their work. Now I have encountered several typical cases in the work, to share with you. These cases fall broadly into the following categories:

First, ac contactor coil voltage level problem

In our work, the voltage levels of the commonly used AC contactor coils are: AC36V, AC220V, AC380V.

 When servicing or controlling the circuit design, it is important to pay special attention to the coil voltage level, otherwise errors can be easily.

 1, when the low voltage AC contactor, connected in the high voltage control circuit, the coil will burn out.

 2, when the high voltage AC contactor, connected in the low voltage control circuit, AC contactor can not be reliably absorbed, and the noise is very loud. Example: the coil voltage AC380V AC 380V AC contactor, mistakenly connected to the AC220V control circuit, when powered up will find that the AC contactor can not fully absorb, but also make a very large "buzzing" sound. And at this time the main circuit voltage is low, simply can not reach the rated voltage.

Second, frequent communication contactors



This type of AC contactor is characterized by frequent movements, such as pressurized booster pumps that pressurize high-rise buildings. The AC contactor that controls the pump, which absorbs and disconnects a lot, so its main contacts are easily melted. After melting, poor contact contact, resulting in a decrease in the voltage of the main circuit, resulting in a heat overload of the pump motor. There are many AC contactors like this, such as the upper, lower, left, right control in the car, the control of the upper, lower, left, right, and so on in the electric hoist. Such as such AC contactors, during service, it is important to pay special attention to its main contact stoin.

Third, the size of the larger AC contactors


As shown in the figure, ac contactors such as these are generally used in electric motors with high power. And under normal circumstances, it should be the Star Triangle Buck Start.

The distinctive feature of this type of contactist is that the vibration is large when sucking or disconnecting! The vibration is large, which will cause the junction pile head, the terminal to loosen, the light causes the line contact is poor, and the heavy cause the contactor main contact burned.

 So it is necessary to tighten the terminal head and terminal slyly on a regular basis. Another point is that these large AC contactors should not be installed next to the drive. Because of its heavy load current, frequent movements, will cause a lot of interference to the inverter, often make the inverter wrong action.

Four, the working environment dust-multi-AC contactors


Because of the more dust, it enters the AC contactor's spring, contacts and other internal, will make the contactor stuck. Scenario 1: The suction contactor, when the coil is off, because of more dust, can not reliably rebound reset, there will be a control circuit power off, the main circuit still has electricity.

 This situation is very dangerous because although the stop button is pressed, the device is still powered!

 Scenario 2: Coil power, because of more dust, contactors can not reliably absorb, the main contact contact is poor, will cause the main circuit voltage is low, or even lack of phase! In this case, we have to seal the distribution box to prevent dust from entering.

 In addition, the distribution box should be regularly blown and cleaned to ensure reliable electrical components. Thank you, if there are deficiencies, please criticize the right!