VV fuse-links are designed to provide a stable and reliable time-current characteristic. The body of the insert is a porcelain, glazed tube with very high mechanical and temperature resistance. The clamps are made of copper, electrolytically coated with nickel, and silver on request. The clamp is fixed on the grooves located at the ends of the pipes by sufficiently firm clamping. The strength of the connection is ensured by the use of an appropriate adhesive resistant to temperature changes. The highly advanced production method of the fuse link element ensures accurate and stable time-current characteristics of the fuse link. The fusing element is wound on a porcelain insert located inside the tube. The insert is filled with quartz sand with appropriately selected granulation. A very important element of the cylinder design is the striker mechanism. For the TERMO version with a thermal trigger (VV D and VV E versions), an integral part of the device is a thermal element, which is triggered by an increase in temperature. The thermal release always occurs regardless of whether the temperature increase is due to overload or external factors. Operation takes place at a temperature of about 120oC. The mechanism works in such a way that short-term overloads do not cause unnecessary disconnection of the circuit. Only when the temperature rises too high, the striker is activated. The insert with a thermal switch is primarily used as protection for medium voltage power switchboards in SF6 insulation. Medium voltage VV fuse-links have a t-I short-range time-current characteristic.
Advantages:
→ small temperature rises associated with low power losses,
→ high short-circuit capacity - 50 and reliability of breaking at critical current,
→ wide range of striker systems - 80 N, 120 N for fuse-links with a thermal switch - VV D and VV E version and 50 N for the standard VV C version, reliable operation of the striker system,
→ high resistance to moisture,
→ both internal and external use,
→ reliable tripping with minimum pick-up current,
→ stable time-current characteristics,
→ the switch-off voltages are lower than the recommended value,
→ fusible elements of very good quality.