Thermal Protection

How does it work?
inter-teknik’s thermal protection feature activates the striker pin, in case the fuse body temperature exceeds a certain limit. The striker will trip the switching device in combination, before thermal damage can occur to adjacent switchgear components, and also prevent fuse malfunction.

Why the fuse body becomes dangerously hot?
Apart from the particular GIS challenges, the primary protection is against the loads in the forbidden range (between the nominal current and the minimum breaking current).

If the current limiting fuses are loaded within this forbidden range, this will inevitably result in overheating, which may lead to explosions.

Are there any other reasons for the temperature rise?
Experience shows that wrong fuse selection or mistakes at the site by installing the wrong fuse may also cause this.

Although overlooked, thermal damages can again occur even at normal operating currents. Why?

  • Mechanical damages: High-voltage fuses usually exhibit several precisely manufactured but fragile fuse-elements connected in parallel to carry the rated current. Under normal service conditions, there is no risk of overheating with properly selected fuses. However, individual fuse-elements may accidentally be damaged either mechanically, when dropped on the floor
  • Electrical damages: Inrush currents or lightning strikes may result in damaged fuse-elements
  • Overuse of fuses: As well-known, in case of a short-circuit fault, fuses on all three phases should be replaced with new ones. Even if they look completely perfect from outside, they very likely contain damaged fuse-elements. When this is overlooked, the fuse will likely not possess the original characteristics and has a high risk of overheating.
Figure 4 highlights the correlation between the temperature rise in the fuse body and the number of damaged fuse elements, caused by one of the above. For all above reasons, use of thermal protection is highly recommended whenever fuses are used in combination with on-load switching devices.

Warning: The fuses should head the right direction for thermal protection to operate!

Related Links:

Switch-Fuse combinations
Electrical Utilities
Air Insulated Switchgears
Gas Insulated Switchgears