What are the common failure causes of drop-out fuses?

What are the common failure causes of drop-out fuses?

The fuse is not normally blown. The fuse blows and causes the tube to drop. In theory, the fuse protection has played a role.

However, it can be clearly seen from the statistical charts of previous years that abnormal fusing has time and climatic rules, which are reflected in July to August each year. The temperature is high, the power load is large, and the distribution transformer load rises quickly. Fuse tube failure occurs frequently.

This shows that the fuse is abnormally blown. The reasons are as follows: 1. The fuse capacity and the distribution transformer capacity are not properly configured, which fails to meet the technical standards for fuse configuration. 2. The quality of the fuse is not off, and the fusing characteristic is relatively poor.

It can be seen from the statistical charts of previous years that there is no special time rule and climate rule for the fuse tube drop due to rolling damage. From the analysis of the broken position of the fuse body, it is found that one is the fuse. The second is the fuse at the corner of the metal casting at both ends of the fuse tube.

1. Reasons for Fuse Broken

1. When tightening the bolt, the end of the fuse will revolve and break the strand with the rotation of the bolt.

2. Since the corners of the metal castings at both ends of the fuse tube have concave-convex sharp edges, after the fuse is fixed and tightened, after a period of operation, affected by mechanical vibration, the fuse is cut and broken.

When the fuse loosening fuse is used on the drop-out fuse, it is under stress for a long time.

When replacing the fuse, if it is too tight or too loose, after a period of operation, due to the influence of natural environment, mechanical vibration and long-term force, the fuse will be pulled out in an over-tight state, or The fuse is elongated and loosened compared to the original replacement, causing tube drop failure.

Second, the cause of the failure

1) When replacing the fuse, the adjustment force is inappropriate.

2). The fuse is loosely pulled out, which mainly means that the fuse body is pulled out from the crimping place with the multi-strand tail wire. This kind of problem belongs to the product quality problem of the manufacturer.

3). The drop-out fuse has been running for a long time, especially for the distribution transformer with a small load for a long time, and the fuse tube has the phenomenon of water and damp.

3. Device defects

1) The product process is rough, the manufacturing quality is poor, and the elasticity of the contact spring is insufficient, resulting in poor contact and spark overheating.

2) The manufacturing of the rotating shaft of the molten tube is rough and inflexible, which makes the angle of the molten tube fail to meet the requirements of the regulations, especially the size of the equipped molten tubes does not meet the requirements of the regulations. If the molten tube is too long, the duckbill will die and cause melt. After fusing, the fuse tube cannot drop quickly, and the arc is cut off and extinguished in time, causing the fuse tube to burn or explode; the fuse tube is short in size, difficult to close, poor contact contact, and sparks. The “6.7″ accident of the Guangling Electric Power Bureau was one of these reasons, which caused the staff to be impatient, suddenly thinking of the closing dynamics of the fusion tube with their hands, and being electrocuted.

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. 10kV outdoor drop-out fuse is divided into three types, namely 50A, 100A, 200A. The upper limit of the breaking capacity of the 200A drop-out fuse is 200MVA, and the lower limit is 20MVA. According to its ability to interrupt the capacity, it is not difficult to see that the arc cannot be extinguished in time after the melt is blown in the case of a short-circuit failure, and it is also easy to cause the fuse tube to burn or explode.

4). The size of some new switch fuses does not match the size of the fixed contact part of the fuse, and it is easy to loosen. (House of Electrical Engineering www.dgjs123.com) Once encountered external force, vibration or windy weather during operation, It will accidentally move and fall, which not only reduces the amount of electricity sold, but also makes it difficult to guarantee the reliability of the power supply.

The existence of the above-mentioned defects not only increases the workload of maintenance personnel, but also promotes the improper use of maintenance personnel (especially agricultural electricians), which completely loses the protection function of the drop-out fuse and causes a short circuit in the line. Only the scope of the power outage can be expanded, and the 10kV outgoing main circuit breaker of the substation will be tripped, causing power outages across the entire line.