Why DC fuse is hard for fuse manufacturers?

DC fuses hotspots

At present, the DC current limiting fuse research hotspots include the research of arcing process, arcing model and hybrid fuse.

Research on the arcing process of DC fuse. In the study of the arc burning process of DC fuse, the relationship between DC arc voltage gradient and current density is studied. 

The results show that: 

1), The arc voltage gradient of high voltage current limiting DC fuse is related to the current density, the greater the current density, the higher the arc voltage gradient; but when the current density reaches a certain value, the arc voltage gradient rises slowly. 

2), The relationship between arc voltage gradient and current density is different for different fuse structures. The greater the fuse pressure is, the higher the arc voltage gradient is. The results show that the maximum value of arc energy occurs when the arc voltage is equal to the grid voltage. In the actual working condition, the power grid plays an important role in the process of DC fuse arcing. Its value may be equal to or even more than the energy stored in the inductor.

(2) Research on the arcing model of DC fuse. The process of breaking DC short-circuit current of linear fused silica sand fuse is studied, and the empirical formula of arc voltage in arcing and quasi stable arcing stages is obtained.

In the arcing stage, the arc voltage is combined with the DC circuit equation by using these empirical formulas

It can be found that the DC fuse flows through the fuse in the process of breaking

The current and voltage at both ends of the DC fuse vary with time

Process [17].

Research on hybrid fuse. A DC fuse guy -Dai Chao designed an arc triggered hybrid current limiting DC fuse. He developed the Engineering DC fuse prototype with rated 640 VDC / 2000AMP,

At the same time, the on state loss is reduced, also, he did the temperature rise and the current limiting experiment. Principle of arc triggered hybrid current limiting DC fuse.

The figure is shown in Figure 10. In case of short circuit happened, the arc trigger starts, The arc voltage is used to trigger the detonator in the high-speed breaker.

Fast breaking forces current to transfer to the branch fusing limit of arc extinguishing DC fuse flow. These test proved that the scheme with low power loss, Strong current limiting ability, big breaking capacity. 

At the same time, Mr Liu Siyuan designed a DC fuse based on the No load switch series hybrid fuse, used for the circuit full range protection. When the current is small, it is loaded by vacuum, The switch is responsible for breaking; When the current is large, the DC fuse is responsible for it.

Mersen designed a kind of DC fuse with power switch;

Hybrid fuse with parallel breakers [21]. Set up by Mersen.

The mixed fuse is shown in Figure 1. In which power is cut off,  The conductive part of the device is a copper bar and is equipped with an insulating piston triggered by electricity.

When the insulated piston is triggered, the piston acts to cut off the copper bar, and the current flows from The copper bar branch is transferred to the DC fuse branch, and finally to the DC fuse branch disconnect.

Key problems of DC fuse

And the direction of DC fuse development

At present, the overload breaking capacity of DC fuse is limited, Key issues of the exhibition. This includes pre arc time under overload current

It is difficult to extinguish the arc under long and overload current and after the arc is extinguished, And so on.

The DC fuse is to turn on and power off by breaking the fuse sliver belt inside.

The higher the current is, the more heat is generated per unit time and the melt is narrow

The faster the temperature rise of the neck, the shorter the corresponding fusing time. So,

DC Fuse has a great advantage in breaking short-circuit current. 

However, the overload breaking current is smaller and the DC fuse is broken.

The pre arc time of the device is very long, which can not meet the requirements of breaking.

By the way, The current carrying d'c K is very small and the quartz sand around the melting belt  is overheated

The arc breaking capacity is also very weak, which is easy to cause arc re strike through the continuous arc. 

Therefore, the overload of DC fuse is increased.

Current breaking characteristic is a key problem.

From the perspective of application, the weak overload breaking capacity also limits the development of fuse. 

In electric vehicles, the power battery is its core components. At present, hydrogen is used for power battery protection Gas switch and DC fuse in series. Among them, hydrogen turns on and off is responsible for breaking rated current and small overload current,

 While DC fuse  is responsible for breaking large overload current and short-circuit current. But, in the process of practical use, it is found that the current DC fuse on the market,

It can only effectively cut off the electricity above 3-5 times of rated current,

When the overload current is less than 3-5 times, its breaking capacity is very high.

when the breaking time is long, even can not be broken. 

For hydrogen switches,

With the increase of overload current multiple, its breaking life is greatly shortened,

Moreover, the contact may be fused during the breaking process. Therefore, 2-5 times overload current area is blind to the battery protection of electric vehicles.

. The interruption of overload current is protected by the power battery of electric vehicle Problems.

So, when you select DC fuse, you should consider these factors, to choose the fuse manufactureres with longer DC fuse manufacturing experience is better, to choose those manufacturers with more practical use experience are better,  to choose those with more DC fuse certifications manufacturers are better.