Difference Between DC Circuit Breaker and AC Circuit Breaker

July 25,2022

The structural composition of the two is different:

Structural composition of AC circuit breaker: AC high-voltage circuit breaker includes a shell, high-voltage porcelain insulator arranged on the shell, three-phase high-voltage input end, and three-phase high-voltage output end. Linear electromagnetic actuator, movable electrode, fixed electrode, and controller are arranged in the shell. The linear electromagnetic actuator includes an iron core, coil, permanent magnet, armature, push rod, and electromagnetic positioning lock. The push rod is arranged between the movable electrode and the linear electromagnetic actuator.

Structure composition of DC circuit breaker: the topology principle of DC circuit breaker is complex and diverse. According to the different key breaking devices in DC circuit breakers, DC circuit breakers can be divided into three categories: mechanical DC circuit breakers, all solid-state DC circuit breakers, and Hybrid DC circuit breakers combining mechanical switches and solid-state switches.

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Structural characteristics of AC circuit breaker: the circuit breaker adopts a three-phase pillar structure, which has the characteristics of stable and reliable braking performance, no combustion and explosion hazards, maintenance-free, small volume, lightweight, and long service life.

Structural characteristics of DC circuit breakers: the difficulties in the development of DC circuit breakers are shown in two aspects. First, the DC system currently has no natural zero crossing, and the mature arc extinguishing technology in the AC circuit breaker cannot be applied; Secondly, the inductive components in the DC system store huge energy, which significantly increases the difficulty of DC fault current breaking.

Overview of AC circuit breaker: AC high voltage circuit breaker is the main power control equipment of the substation. When the system operates normally, it can cut off and connect the no-load and load current of lines and various electrical equipment; When the system fails, it can quickly cut off the fault current in cooperation with the relay protection to prevent expanding the scope of the accident. Therefore, the working quality of high-voltage circuit breakers directly affects the safe operation of the power system.

Overview of DC circuit breaker: DC circuit breaker combines power electronic devices. It is a circuit breaker used to disconnect the DC circuits. The time to realize DC disconnection is the current zero crossing. DC circuit breakers can generally be divided into mechanical DC circuit breakers, solid-state DC circuit breakers, and Hybrid DC circuit breakers. Among them, the control of power electronic devices and DC arc extinguishing are the key technologies of DC circuit breakers.

DC circuit breaker and AC circuit breaker are not universal.

The main reason is the arc extinguishing problem. The arc extinguishing performance of the DC air switch is better than that of the AC air switch because the arc generated by DC is large. If the AC air switch is used to replace the DC air switch, it shows that the arc extinguishing performance meets the requirements, which will cause the accident of burning the contact or burning the air switch.

For large capacity air switches; There are few DC special products, which are generally replaced by AC air switches. When selecting products from well-known manufacturers at home and abroad, DC breaking parameters and relevant test data must be available. Its protection can only choose the electromagnetic port mode, not electronic protection. In addition, it is mainly determined by the breaking capacity of the switch, which is the product of the rated voltage and current of different properties that the switch can break.

There are such signs: AC 220V 1a, DC 48V 0.5A. The nature of the current of the same pair of contacts is different, and the interrupting capacity is also different. The relay contact does not know whether it is connected to DC or AC in advance. Once used in the 48V DC circuit, its interrupting capacity is DC 48V 0.5A. If the DC voltage is grounded, the corresponding current value can be larger. Back to the air, that's it.

At present, the rated voltage of the air switch is mostly about 690V AC. if it is used above 48 V DC, although the voltage at both ends of the switch is DC, the DC voltage is far lower than the AC-rated voltage, so there will be no major electrical problems in actual use.

Generally, the DC air switch of the same grade can be temporarily used on AC occasions, but it is best not to use the AC air switch casually on DC occasions. It is easy to produce large sparks in case of a short circuit. Therefore, when we don't have an AC circuit breaker on hand, we can use a DC circuit breaker to temporarily fill the position, but we can't use it all the time, because the arc extinguishing capacity of the DC air switch is high.