DC Molded Shell Circuit Breaker Current Limiting Technology Detailed:

1. Overview of current limiting technology of DC plastic circuit breaker:

When the short circuit current is interrupted, a fast-growing arc, usually called dynamic arc resistance, will be generated in a manicure circuit breaker. Maintaining stable arc combustion requires a certain voltage, and the "dynamic arc resistance" is equivalent to a thousand series resistors in the circuit. The arc in the interrupter is divided into several short arcs, which makes the arc voltage rise rapidly. When the arc voltage exceeds the value of the power supply voltage, the power supply voltage can not maintain the arc, so that the arc extinguishing can limit the short-circuit current.

Because there is no zero-crossing point of DC current, it is difficult for DC plastic case circuit breaker to break the arc, so improving the current limiting capacity of DC plastic case circuit breaker is the key to the design of DC plastic case circuit breaker. Current limiting methods of circuit breakers include current limiting by using electro-repulsive contacts and improving static volt-ampere characteristics of arcs. Each current-limiting technology has its advantages and disadvantages. It is very important to choose a reasonable current-limiting method, which should be applied comprehensively in design.

2. Electric repulsive contacts:

Electric repulsive contact is a common and effective current limiting method. Its principle is to repulse the moving contacts by current-oriented mutual repulsion, lead out the arc ahead of time, and restrain the increase of short-circuit current. There are two types of electric repulsion contacts: single repulsion of moving contacts and double repulsion of static and dynamic contacts (see Fig. 1 and Fig. 2). The contact system of plastic case circuit breaker under 250A shelf is this kind of structure. The common type is single repulsion structure, and the high-break type is double repulsion structure. Fig. 1 When the short circuit current comes, the moving contacts will be repulsed by the electric repulsion. Fig. 2 When the short circuit current comes, both the moving contact and the static contact will be repulsed in the upper and lower directions due to the repulsion force. Compared with the structure of Figure 2, the current limiting effect is better, but the height of the circuit breaker will increase. The main design point of this kind of structure is that the movable contacts should have a clamping structure, that is, to prevent the falling of the movable contacts from causing the contact ablation and fusion welding.

Dynamic and Static Contacts Repulse

3. Advanced arc static volt-ampere characteristic method:

The deionized gate method, insulated gate method and narrow slit method are usually used.

1. Deionization grating method:

The arc is divided into several short arcs in series by using metal grid, and the arc is extinguished by using the voltage drop of the short arc to improve the arc voltage.

2. Insulation grid method:

That is to say, the grid is insulated. Its function is to derive the heat of the arc to improve the arc column voltage. At the same time, the grid divides the arc into several short arcs. Each grid is the electrode of the short arc. At the same time, it generates many anode voltage drops and cathode voltage drops. For DC arc, arc is extinguished by using arc voltage drops near the pole and arc column voltage drops together.

3. Narrow slit method:

Multiple narrow slots are usually used to reduce the resistance of arc entering the upper narrow slot, so when the electromagnetic force driving the arc motion is given, smaller slots can be used than single narrow slot interrupter. On the one hand, the arc diameter can be compressed to make the arc contact closely with the slot wall; on the other hand, the area of the arc is increased and the length of the arc is increased, which further strengthens the cold. The arc is extinguished by the action of de-dissociation.

These methods are usually used in combination to achieve better current limiting interruption effect.

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