PT and PN cartridges are designed for use in high-voltage fuses, providing protection for electrical equipment against overloads and short circuits. They are widely used in 6 and 10 kV power networks.

Construction and operating principle:

A cartridge consists of a ceramic tube with metal caps at the ends, containing a fuse element inside. The cartridge's cavity is filled with fine-grained quartz sand to extinguish the electric arc when the fuse element melts.

Differences between PT and PN cartridges:

• PT Cartridges: Used in PKT fuses to protect power transformers. The fuse element is calibrated for nominal current and voltage. The cartridge length depends on the nominal voltage: the higher the voltage, the longer the cartridge.
• PN Cartridges: Applied in PKN fuses to protect voltage measuring transformers. The fuse element is designed solely for short-circuit protection and is not calibrated for nominal current. Selection is based only on nominal voltage.