Overview: This document provides comprehensive information on S&C Power Fuses, specifically models SMD-1A, SMD-2B, SMD-2C, SMD-3, and SMD-50. These fuses are designed for transformer and capacitor-bank protection in outdoor substations with voltages from 34.5 kV to 138 kV. They feature precision-engineered, nondamageable fusible elements made of silver or nickel-chrome, ensuring reliable performance and system coordination.

Specifications: SMD Power Fuses offer continuous current ratings from 100 to 300 amperes and are available in various speeds (Standard, Slow, Very Slow) for optimal coordination with other protective devices. They handle a wide range of fault conditions and provide visible air gap isolation after operation. The fuses are constructed with silver-clad contacts and an articulated latch mechanism for secure latching.

Applications:

• Transformer Protection: These fuses provide economical and reliable protection for small to medium-sized transformers, eliminating the need for auxiliary equipment and reducing installation costs. They offer full-fault-spectrum protection and handle transient recovery voltages.
• Capacitor Bank Protection: Suitable for high fault current scenarios, these fuses ensure rapid isolation of faulted capacitor banks to prevent unnecessary outages.

Construction and Operation: The fuses include a fusible element, a spring-driven arcing rod, and a solid-material arc-extinguishing medium within a glass-epoxy tube. This design ensures precise time-current characteristics and nondamageability, allowing for close fusing and superior protection.

Key Advantages:

• Superior transformer protection with close fusing capabilities.
• High service continuity by eliminating unnecessary fuse operations.
• Close coordination with other protective devices due to precise fusible elements.
• Operating economies by reducing the need for replacing unblown fuses.

Additional Considerations: SMD Power Fuses are not voltage critical and can be applied at any system voltage equal to or less than their rated voltage. They allow for reduced phase spacing and ground-clearance requirements, making them suitable for space-constrained applications.

Fault Interruption Mechanism: The fuses achieve fast fault interruption through high-speed arc elongation and deionizing gas generation. This involves the rapid movement of an arcing rod and the thermal reaction of solid materials to efficiently extinguish arcs and ensure high dielectric recovery rates.

Mounting Styles and Ratings: Various mounting styles are outlined, including Vertical, Vertical-Offset, Upright, Right-Angle, and Inverted, each with specific voltage and current ratings. Detailed tables provide interrupting ratings for different fuse types across various voltage levels.

Handling Procedures: Instructions are provided for opening, closing, installing, and removing fuse units using specific tools like the S&C Distribution Prong and S&C Round Socket. Safety and control during handling, particularly for high-voltage fuses, are emphasized.

Interrupting Ratings: The document includes tables with short-circuit interrupting ratings, tested under rigorous conditions to simulate real-world scenarios. Ratings are provided for different X/R ratios, reflecting the asymmetry and transient recovery voltage conditions expected in field applications.