The design and construction of these fuses follow the well proven concepts of all high voltage fuses. For pressure resistant encapsulation, a high grade ceramic is utilized. Contact material consists of silver plated high conductivity copper. The pure silver melting elements have appropriate notching profiles to ensure small time-current curve tolerances and low
let through currents. The arc quenching quartz sand is subjected to particular criteria regarding its composition, grain size and water content.

Fuse Applications:

HHB Back Up, Transformer, Capacitor and Motor:
A classical standard current-limiting “Back-Up” fuse for transformer protection, this type series meets the special requirements set for the area of application. As a back-up fuse, it interrupts currents from 3 to 4 times the rated current all the way to the rated breaking current, making short circuit protection its main area of application. HHD-B fuses are available for
rated voltage ranges of 3/7.2kV, 6/12kV, 10/17.5kV, 10/24kV, 20/36kV, 38.5kV and 40.5kV.

HHD-FR – Full Range, Transformer and Capacitor Applications
High voltage current-limiting fuses with “Full-Range” rating with voltage ratings of 6/12kV and 10/24kV are designed to meet the special requirements for transformers requiring this type of rating. These fuses have an interrupt rating of 80kA.

HHD-G – General Purpose, Transformer Application
 “General Purpose” fuses under fixed conditions can interrupt all currents, from rated breaking currents all the way down to the current that in one hour or less triggers the fuse striker. At a melting time of one hour, the melting current usually lies between a multiple of 1.5 to 2 of the rated current. These fuses are therefore deployed for overload protection purposes. These fuses are rated for voltage ranges of 6/12kV and 10/24kV.

HHD-BSSK – Back UP “SSK”, Transformer Application
HV “SSK” current-limiting “Back-Up” fuse model has been specially designed to harmonize with switchgear installations. It was constructed for short fuse-initiated opening times of the switch and low take-over currents.
Together with switch-fuse combinations, and under certain conditions, HHD “SSK” fuses can be used for transformers with higher power ratings. The fuses are available for rated voltage ranges of 6/12kV,10/24kV, 20/36kV and 40.5kV.

Back Up, Motor Applications:
HHM and HHM “R”-rated current-limiting “Back-Up” fuses are designed for the rugged demands of motor circuit protection applications. The fuse elements have been optimized to deal with cyclic loads typical for motor circuits and power dissipation compared to commonly used HV fuses. Fuses are available for rated voltages of 3/3.6kV, 3/7.2kV and 6/12kV. HHD-BR function in the same way as HHD-BM fuses, but are tailored to meet the ANSI C37.46 standard. HHD-BM and BMR series fuses are offered for rated voltages between 2.4kV and 7.2 kV. 

Back Up, Potential Transformers (VT):
HHPT fuses for the protection of PT circuits are current-limiting “Back-Up” fuses designed to interrupt short-circuit currents. Due to the high breaking currents, the fault current will be limited and finally quenched in a few milli-seconds. Some fuses include a striker pin for visual indication. This feature allows remote indication of the fuse operation
for direct tripping of a circuit breaker. Fuses with striker pins have rated currents of 2A, 3.15A, 4A and 5A. Lower rated current 0.5A and 1A fuses are without a striker pin. DIN style PT fuses have a diameter of 53 mm and a length depending on the fuses rated voltage. Fuses are available for a
rated voltage of 3/7.2kV, 6/12kV, 10/17.5kV, 10/24kV, 20/36kV, 38.5kV and 40.5kV.