HTSS242125CN is an ABB backup current-limiting fuse of the Trans‑Guard OS Shorty type, rated 17.2 kV / 125 A and built for installation inside oil-immersed distribution transformers. It is a partial-range back-up current-limiting fuse as defined in IEEE C37.40 — it does not cover the full current range on its own and must always be applied in series with a correctly sized low-current protective device.

How the Two-Fuse Scheme Works

Inside a distribution transformer the two protective devices divide the fault-current range between them, so each one operates only where it performs best:

Why the Energy-Limiting Duty Matters

A transformer protected only by an expulsion fuse has a very low interrupting capability — typically between 600 A and 3,500 A. If a fault exceeds that capability the arc keeps burning inside the tank until another device reacts, which is how disruptive tank ruptures and torn-off accessories happen. The current-limiting fuse interrupts the fault and, more importantly, limits the let-through energy to a value below the withstand capability of the transformer tank. No other protective device performs that function.

Construction & Testing

▪  Oil-submersible and hermetically sealed — sealed against oil ingress; every unit passes a helium mass-spectrometer leak test to prove seal integrity.

▪  100% factory tested for resistance and seal before packing.

▪  Threaded end terminals — 1/4‑20 threaded hole, 1/2 in deep, at both ends, matching standard under-oil mounting hardware.

▪  Back-up design — partial-range construction keeps the physical size down while delivering full interrupting capability on high-magnitude faults.

▪  Parallel-capable range — where a higher continuous rating is needed, OS Shorty fuses can be paralleled; the manufacturer publishes parallel-application ratings separately.

Selection & Application Notes

▪  Always coordinate HTSS242125CN with an expulsion fuse of the correct link rating. The combination — not the current-limiting fuse alone — provides full-range protection.

▪  Coordinate against two curves: the minimum melting curve of this fuse and the total clearing curve of the expulsion fuse, so that the expulsion fuse clears every current below the minimum interrupting current.

▪  Ratings shown on this page are single-fuse values. Peak arc voltage and I²t figures are stated at the rated maximum voltage and maximum interrupting current; they fall at lower voltages and currents.

▪  Final selection, installation and maintenance must be carried out by qualified personnel using the current manufacturer data sheet, the project protection study and the published time-current curves.

Standards

▪  IEEE C37.40 — definition and application of back-up current-limiting fuses.

▪  ANSI/IEEE distribution fuse standards; tested by the manufacturer to the applicable ANSI/IEEE requirements.

Cross Reference & Ordering

Inquiries are quoted against the exact catalog number. Lead time is typically 4–8 weeks; confirm price, availability and documentation for the specific quantity before ordering.