When using DC contactor, there are often some faults problems, which need us to understand first then judge.

1) DC voltage should be a fixed value, but it is often obtained by rectifying filtering AC voltage. Because the filtering is clean, there will be residual AC components. Even if the battery is used for power supply, ripple will occur due to load fluctuation. In fact, even a good voltage reference device, its output voltage is ripple. That is, the AC components with different frequencies amplitudes.

2) The DC power supply capacity of substation is limited. In particular, small simple substations are DC transformer battery high-frequency switching power supply. In the process of charging discharging, with load (electromagnetic mechanism model: cd-10-ii, the impact current of closing coil is 99A), it is easier to produce AC components with different frequencies amplitudes.

3) The operation power supply the closing power supply are on the DC power bus at the same time. The instantaneous changes of voltage current during operation are quite large, which also leads to the different effects of electromagnetic force on the current carrying conductor in the magnetic field. The number of coil turns of DC contactor is large, the coil is a large inductance, reactance current. Although it is less affected by the change of DC frequency, it is greatly affected by the AC component of different frequency amplitude.

Due to various reasons, in practical application, after the electromagnet (iron core) of DC contactor coil is affected by AC components of different frequencies amplitudes to a certain extent, the iron core produces residual magnetism, forming a large resistance, which affects the movement of the iron core. It will cause equipment burn out affect the high quality reliable power supply of power grid.

DC contactor needs us to grasp, often read some books, constantly improve our knowledge.