Overview: The document provides comprehensive information on S&C Power Fuses, specifically Types SM-4® and SM-5®, designed for outdoor distribution systems with voltages ranging from 4.16 kV to 34.5 kV. These fuses are essential for protecting transformers, capacitor banks, and cables, offering enhanced performance and reliability.

Specifications: SM Power Fuses are available with continuous current ratings of 200, 300, 400, and 720 amperes, and fault-interrupting ratings from 28,000 to 60,000 amperes RMS asymmetrical. They are offered in various ampere ratings and speeds (Standard, Slow, and Coordinating) to ensure optimal protection and coordination.

Construction and Materials: The fuses feature precision-engineered, nondamageable silver or nickel-chrome fusible elements, ensuring precise and permanent time-current characteristics. They are available with Cypoxy® or porcelain station post insulators, meeting ANSI standards for electrical and mechanical strength.

Application and Advantages: The unique solid-material technique in the refill unit provides full-fault-spectrum protection, capable of handling a wide range of transient recovery voltages. SM Power Fuses are not susceptible to damage from transient surges, allowing for close fusing and superior protection against secondary-side faults. Unlike current-limiting fuses, they do not require "safety zones" or "setback allowances," facilitating better coordination with upstream protective devices.

Comparison with Current-Limiting Fuses: SM Power Fuses offer advantages over current-limiting fuses, which are prone to damage from inrush currents and require adjustments to their time-current characteristic curves. SM Power Fuses allow for closer fusing and better protection without the need for large safety margins.

Applications: Suitable for transformer, cable, and capacitor bank protection, SM Power Fuses provide fast operation, minimizing conductor temperature rise and allowing for smaller conductor sizes. They also offer selective isolation of faulted phases, unlike circuit breakers that remove all phases during faults.

Technical Information: The document includes detailed application recommendations, technical information on time-current characteristics, and construction details of the fusible elements, emphasizing their nondamageable nature and precise performance.

Design and Components: The refill unit of the fuse consists of a fusible element, arcing rods, and an arc-extinguishing medium within a glass-epoxy tube. The design ensures efficient fault interruption through the elongation of the arc and deionization by gases from the arc-extinguishing medium.

Fault Interruption: The document explains the process of fault interruption for low and moderate-to-high fault currents, describing how the arc is managed within the fuse to ensure quick and effective fault clearing.

Mounting and Handling: SM Power Fuses are available in different mounting styles, including vertical and inverted. The document details the materials and design features that facilitate installation and ensure reliable operation. Handling instructions emphasize the use of appropriate tools and procedures for safe operation.

Load Switching: The document introduces the Loadbuster tool, which allows for load switching without the need for additional disconnects or interrupter switches, enhancing operational efficiency and reducing costs.

Testing and Ratings: The fuses have been rigorously tested to ensure performance across a range of fault conditions. The document provides interrupting ratings and emphasizes the importance of testing under realistic field conditions.

Testing Procedures: Interrupting ratings are determined according to ANSI Standard C37.41, with tests conducted at an X/R ratio of 20, which is more severe than the standard requirement of 15, ensuring applicability to a wide range of field applications.

Key Data: Tables in the document provide detailed interrupting ratings for various configurations, including different kV levels and system setups. For example, the SM-4 power fuses have ratings for systems ranging from 7.2 kV to 34.5 kV, with corresponding interrupting capacities in MVA.

Recommendations: The document suggests using the provided ratings for systems with matching mounting, holder, and refill units to ensure optimal performance. It also notes adjustments for specific configurations, such as using a 4.16-kV refill unit in a 7.2-kV holder.

Contact Information: S&C Electric Company, headquartered in Chicago, IL, provides contact details for further inquiries.