Functional Analysis Of Drop-out Fuse And Power Protection Mechanism
As a unique protection device in the power system, High Voltage Fuse is named after its special action structure characteristics. It plays the dual role of overload and short-circuit protection in the 10kV distribution network. This article will deeply analyze its name connotation and protection mechanism, and reveal its core role in the safe operation of the power grid.
1. Engineering interpretation of the name
The name "drop-out" comes from its unique mechanical action characteristics: when the fuse melts, the fuse tube automatically detaches from the bracket under the action of gravity to form a clearly visible fracture. This mechanical design meets the requirements for visible fractures in the GB/T 15166 "High Voltage AC Fuse" standard, and its status indication is more intuitive than that of enclosed fuses.
The "RW" code in the standard model has a professional meaning: "R" stands for fuse (Recloser), and "W" represents the outdoor (Weatherproof) use characteristics. In the IEC standard system, this device is classified as a "drop-out fuse", emphasizing its physical state change characteristics after a failure.
2. Structural characteristics and protection mechanism
The core components of the equipment are melting tube, melt, moving and static contacts and supporting porcelain bottles. The melt is made of zinc/silver alloy, and its diameter tolerance is controlled at ±0.02mm to ensure the accuracy of the fusing characteristics. When the current exceeds the set threshold, the melt undergoes metallurgical phase change under the Joule heat effect, and the melting time and current value have an inverse time characteristic relationship.
During overload protection, the melting time of the melt at 1.3 times the rated current does not exceed 1 hour; during short-circuit protection, the 6kA fault current can be cut off within 20ms. The gas-generating material inside the melting tube generates a longitudinal arc blowing airflow under the action of the arc, accelerating the arc extinguishing process, and its dielectric strength recovery speed can reach 3kV/μs.
3. Power system Functional Positioning
In radial distribution lines, drop-out fuses mainly undertake three core functions:
Overcurrent protection: Cut off the fault branch by melting the fuse to protect the safety of the main line
Equipment isolation: Construct a visible break to meet the safety isolation requirements of electrical maintenance.
Load control: Manual operation can be performed for planned power outages, and the operating torque is usually less than 200N·m
In the ring network power supply system, its action selectivity needs to be coordinated with the upper circuit breaker, and the time difference is generally set to 0.3-0.5 seconds. For access points of distributed power sources such as wind power, it is necessary to select reinforced products with a breaking capacity of more than 16kA.
In mountainous areas, its windproof structure can withstand 12-level strong wind loads; the salt spray-proof model used in coastal areas has an enclosure protection level of IP65. For chemically polluted areas, contacts with special coating treatment can increase the electrical life to more than 2,000 operations. The intelligent improved product integrates a wireless temperature measurement module, which can monitor the temperature rise of the contacts in real time and automatically warn when the temperature exceeds 80°C. Some models have arc protection function, and its action response time is shortened to 8ms, which can meet the needs of rapid protection of photovoltaic power stations.
V. Summary
As the first line of defense for power systems, drop-out fuses still play an irreplaceable role in areas where distribution network automation has not yet been fully covered through their unique mechanical structure and precise fusing characteristics. With the application of new materials and sensor technologies, Enbima's classic equipment is gradually evolving towards intelligence and digitalization, and continues to protect the safe operation of power networks.
