Design of arc extinguishing chamber and wiring of DC plastic case circuit breaker:

I. Overview of DC Molded Case Circuit Breaker Arc Extinguishing Chamber:

The arc extinguishing chamber is a metal grid type arc extinguishing chamber. Melamine plate is used as insulation plate on both sides, cold rolled steel plate is used as grid, and the chamber is designed with slit and staggered upper and lower. When the arc enters the arc extinguishing chamber and is cut into short arcs in series by grids, each short arc has positive and negative polar voltages. The total arc voltage will increase. When the arc voltage is greater than the recovery voltage between contacts, the arc will extinguish the daughter-in-law, as shown in Figure 3.

Picture of Metal Grid Arc Extinguishing Chamber for DC Molded Case Circuit Breaker

arc voltage

U=NU. +EL (1)

In the formula, U is the arc voltage; N is the number of short arcs divided by the grid; U. It is near pole voltage drop; E is arc electric field strength; L is arc length. Formula (1) shows that increasing the number of short arcs in series and the length of arcs L can effectively increase the arc voltage.

2. Metal grid design of arc extinguishing chamber:

The cold-rolled steel plate with 1.5 2.5 mm gap and 2 5 mm gap is selected for the grids. Nickel plating and zinc plating can also be applied on the surface of the grids. However, the experiment proves that nickel plating on the surface is more effective for arc extinguishing. The number of grids varies according to the volume and breaking capacity of the product. For 250A shelf products, the number of grids of Icu=25kA DC plastic shell circuit breaker is 8 pieces and 13 pieces. The comparative test shows that the arc extinguishing effect of 13 pieces is obviously better than that of 8 pieces. Of course, the choice of the number of grids is not the more the better. When the size of circuit breaker is determined, too many grids in arc extinguishing chamber will lead to too small gap between grids, which will cause great resistance to arc entering the arc extinguishing chamber, resulting in the burning of grids by arc.

3. Design of insulation support plate for arc extinguishing chamber:

The insulation support plate of the arc extinguishing chamber not only plays the role of supporting the metal grid of the arc extinguishing chamber, but also plays the role of arc isolation. Material selection is very important. When short-circuit current is interrupted, gas will be generated, which is beneficial to gas blowing arc extinguishing, mainly epoxy glass cloth board and melamine board. Melamine board is superior to epoxy glass cloth board in arc resistance and heat resistance, but its price is higher.

4. Connection Design of DC Plastic Tank Circuit Breaker:

Because DC current is not like zero-crossing characteristic of AC, the short-circuit current of DC (even fault current with small multiples) is interrupted, and the arc extinguishing is difficult, especially for DC plastic case circuit breakers with DC 500V or above. Because of the high voltage, the arc extinguishing is more difficult. Therefore, the juice wiring of the product should adopt the method of series connection, increase the fracture, so that each fracture can bear part of the voltage and arc energy. Cooperating with arc extinguishing chamber can improve the breaking ability of products. Figures 4 and 5 are common series connection modes.

三、四极直流塑壳断路器串联接线方法图

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