The new Thomas & Betts Hi-Tech 38kV Trans-Guard OS Shorty Backup Current-Limiting Fuse provides risk reduction of disruptive transformer failure. Designed for use in 26.4 to 34.5kV distribution and wind farm transformers that have a primary or secondary delta connection or that feed more than 50 percent delta-connected loads, it significantly reduces fault energy and offers a high interrupting capability for protection against ever-increasing available fault currents. This reduction in fault energy results in a reduction in arc-flash potential.
As a backup current-limiting fuse, the 38kV Trans-Guard OS Shorty fuse must always be applied in series with a properly sized, low-current protective device such as an expulsion fuse or the Elastimold Molded Vacuum Interrupter (MVI). Both devices provide fault protection over a given range of currents. The expulsion fuse or MVI clears low-magnitude currents, such as those caused by faults external to the transformer and high-impedance faults inside the transformer, which are generally below the minimum interrupting current rating of the current-limiting fuse.
Backup current-limiting fuses, such as the 38kV Trans-Guard OS Shorty fuse, clear all other currents, such as those resulting from low-impedance faults within the transformer and, most importantly, limit the amount of energy from the fault source to a value below what the transformer tank is capable of withstanding. The 38kV Trans-Guard OS Shorty fuse is capable of interrupting fault currents as high as 50,000 amperes symmetrical.
“By limiting the amount of energy from the fault’s source, the Hi-Tech 38kV Trans-Guard OS Shorty fuse minimizes the likelihood of disruptive equipment failure,” said Dan Gardner, Thomas & Betts director of engineering. “These examples include transformer tank ruptures, damaged accessories and accessories broken from the mountings."
The 38kV Trans-Guard OS Shorty fuse’s L-L voltage rating allows smaller backup fuses to be used to reduce arcing time and the amount of energy originating from a fault. In addition to increasing transformer protection, this feature greatly improves upstream coordination.
The 38kV Trans-Guard OS Shorty fuse provides current-limiting protection for transformers as large as 2,850KVA at 26.4kV; 3,000KVA at 27.6kV; and 3,800KVA at 34.5kV. It meets ANSI and IEEE standards that include 100 percent physical inspection, resistance measurement and helium mass spectrometer leak testing.
