What is Transformer Protection Fuse and how it works?

The high-voltage current-limiting fuse is one of the main protection components of electrical equipment, and it is used in series in the circuit. Protected objects include transformers, motors, voltage transformers, capacitors and power lines. When the short-circuit current or overload current passes through the circuit, the heat generated by the melt is used to fuse itself and cut off the circuit to achieve the purpose of protection. It breaks a large short-circuit current and can curb its amplitude very significantly, especially it has a quick breaking function.

(1) Basic structure of high voltage current limiting fuse:

The shape and structure of various high-voltage current-limiting fuses for protection are basically the same, and are generally fixed by melting tubes and melts.Column, melt, arc extinguishing material, trigger, metal end cap and so on. Among them, melt, melting pipe and arc extinguishing medium (stone British sand) is the most critical for current-limiting fuses, and its impact mechanism (trigger) generally has two types: spring type and gunpowder formula.

2) How does it work?

Generally speaking, high-voltage current-limiting fuses often use silver as the melt. The melting point of silver has better electrical and thermal conductivity, and it is not easy to oxidize. When the short-circuit current or overload current passes through the melt, the silver melt will heat up and melt, and then gasify. Since the conductivity of metal vapor is much lower than that of solid and liquid metals, the resistance of the melt suddenly increases, and the current in the circuit suddenly decreases, which will generate a high voltage at both ends of the melt, resulting in gap breakdown , an arc occurs, and a large amount of gas is generated under the action of the arc to form a strong deionization effect, so that the arc is extinguished or the arc is in close contact with the surrounding solid medium that is conducive to arc extinguishing and is forced to cool and extinguish.

Generally, the arc-extinguishing material of high-voltage current-limiting fuses is quartz sand, which is because quartz sand has high thermal conductivity and insulation performance, and has a large contact area with the arc, which is convenient for absorbing arc energy. The quartz sand filled into the melting tube forms a large number of small solid medium slits and slits, which can divide, cool and surface adsorb (charged particles) to the arc. At the same time, the sudden increase in gas pressure in the gap also has a strong deionization effect on the arc. , so the arc is quickly extinguished. In the normal working stage, the current passing through the melt is less than its rated current, and the fuse will operate reliably for a long time without malfunction.

(3) Factors to be considered in the selection of high-voltage current-limiting fuses

For fuses, the installation environment used is a very important factor. It not only affects the performance of the fuse, but also affects its ability to safely analyze faults, so it must be properly considered.

A common installation method is to install the fuse in a three-phase closed box. At this time, the rated current of the fuse must be reduced by 15%, and derating may not be considered when the rated current of the fuse is less than 20A.

According to the IEC standard, the fuse can work normally in the range of ambient temperature between -25°C and 40°C. When the temperature is higher than +40°C, the rated current of the fuse should be reduced by 1% for every 1°C increase.

For three-phase installation in a closed cabinet, due to the mutual interference between the temperature rise of the three-phase fuses, the rated current of the fuse should generally be used with a 10% reduction in capacity, and the fuse with a rated current of 20A is not considered.

In order to increase the current level of the fuse, users sometimes use two or three fuses in parallel. At this time, the mutual influence of temperature should be considered. Generally, the fuse can be reduced by 10% to 20%. Furthermore, in high-altitude areas, due to the thin air, the insulation strength of electrical equipment decreases, so the overall dimensions of high-voltage current-limiting fuses generally need to be lengthened.

(4) Installation and replacement of high-voltage current-limiting fuses

Before installation, first check whether the appearance of the fuse is complete, clean, and if the fuse has been dropped Or check its resistance after violent vibration. When installing, pay attention to the striker direction marked on the fuse, so that it is installed in the correct position, if the striker is in the opposite direction, even the best thermal tripping device will not move.

In a three-phase system, when one fuse operates, generally all three fuses should be replaced, mainly because although the other two fuses are not blown, they may have been severely operated and are close to damage.

In addition, it is very important to remind that the correct selection of fuses is also very important. The selection of model and basic parameters, the protection object and the protection characteristics must be considered; some matching with the load must be accurately calculated to ensure that the most suitable high-voltage current limiting is selected Fuses to protect the equipment.

By the way, if you need fuses, kindly contact Vivi: shuguang3@china-shuguang.com/86 18158773357. Thanks