Common faults and preventive measures of the hotte

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Common faults and preventive measures of drop fuse

drop fuse is the most commonly used overload and short-circuit protection equipment on high-voltage distribution lines. It has the characteristics of simple structure, low price, convenient operation and strong adaptability to outdoor environment. It is widely used in 10kV distribution lines and the primary side of distribution transformers as protection. It is installed on the branch line of 10kV distribution line, which can reduce the scope of power failure. Because it has an obvious disconnection point and has the function of isolating switch, it creates a safe working environment for line maintenance. Installed on the distribution transformer, it can be used as the main protection of the distribution transformer. Therefore, it has been popularized in 10kV distribution lines and distribution transformers. Its working principle is: insert the fuse into the fuse tube, tighten both ends, and make the fuse located above the middle of the fuse tube. The upper moving contact tilts vertically to the fuse tube due to the tension of the fuse, and push the upper moving contact into the upper static contact with an insulating pull rod to form a closed state (closed state) and maintain this state. When the protected line breaks down and the fault current causes the fuse to fuse, an arc will be formed. The arc suppression tube will decompose a large amount of gas under the action of high temperature of the arc, which will sharply increase the pressure in the tube, and the gas will be sprayed out at a high speed, forming a strong longitudinal arc blowing on the arc, so that the arc will be quickly lengthened and extinguished At the same time, because the fuse is fused, the tension of the fuse disappears, releasing the locking mechanism. Under the action of the elastic force of the upper static contact and its self weight, the fuse tube overturns and falls around the lower shaft, forming an obvious disconnection distance. Disconnect the circuit, cut off the faulty line or faulty equipment, and talk about how Stora Enso changes to meet the new personalized needs of consumers and the development needs of green cycle.

I. main faults of drop out fuse

1. Fuse burning and non coincidence with the main pin

common fuse tube burning faults occur after the fuse is blown, because the fuse cannot fall automatically after it is blown, At this time, the arc is not cut off in the pipe, forming a continuous arc and burning the pipe. The fuse is often installed incorrectly on the upper and lower rotating shafts, blocked by sundries, and the rotating shaft is rough, so the resistance is too large and inflexible. As a result, when the fuse is fused, the fuse remains in the original state for a short time and cannot fall quickly, and the arc extinguishing time is extended, resulting in pipe burning

    2. The main reason for the abnormal fall of the fuse tube is that the size of the fuse tube of some switches does not match the size of the fixed contact part of the fuse, which is very easy to loosen. Once there is a strong wind, it will be blown down, and sometimes it will fall down by itself after a little vibration because it is not checked after operation; The spring pressure of the upper contact of the fuse is too small, and the right angle protrusion in the duck beak (upper cover of the fuse) is burned or worn, and the failure to block the tube is also the reason for the accidental fall of the fuse; When the installation angle of the fuse (i.e. the included angle between the axis of the fuse and the vertical line) is not appropriate, it will also affect the time of the tube falling. Sometimes, because the fuse accessories are too thick and the hole of the fuse tube is too thin, even if the fuse is blown, the fuse element is not easy to fall out of the tube, so that the tube cannot fall quickly

    3. The rated breaking capacity of the fuse is small, and its lower limit is less than the three-phase short-circuit capacity of the protected system, and the fuse is blown by mistake. If it happens repeatedly, it is often because the fuse is too small or improperly matched with the capacity of the next level fuse, which leads to skip level and false breaking and fusing. This kind of accident may be caused by the failure to replace the high-capacity fuse after replacing the high-capacity transformer. The fuse is of poor quality, and its welding joint will be disconnected under the action of temperature and mechanical force, which will also cause false disconnection. In addition, tin alloy welded and old fuse with wire string or spring will change its performance after being affected by temperature, and it is easy to oxidize and rust, which is most prone to false fusing

II. Main measures to prevent the failure of drop fuse

1. Reasonable selection of drop fuse

10kV drop fuse is suitable for outdoor places where the ambient air is free of conductive dust, corrosive gas, flammable, explosive and other dangerous environments, and the annual temperature change ratio is within ± 40 ℃. The selection is based on the two parameters of rated voltage and rated current, that is, the rated voltage of the fuse must match the rated voltage of the protected equipment (line). The rated current of the fuse shall be greater than or equal to the rated current of the melt. The rated current of the melt can be 1.5 ~ 2 times of the rated load current. In addition, the selected fuse shall be checked according to the three-phase short-circuit capacity of the protected system. Ensure that the three-phase short-circuit capacity of the protected system is less than the upper limit of the rated breaking capacity of the fuse, but must be greater than the lower limit of the rated breaking capacity. If the rated breaking capacity (generally refers to its upper limit) of the fuse is too large for Xinlun composite to reach a strategic cooperation with Funeng technology, it is likely that the three-phase short-circuit capacity of the protected system will be less than the lower limit of the rated breaking capacity of the fuse, which will make it difficult to extinguish the arc when the melt melts, and eventually cause accidents such as fuse tube burning and explosion

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