Medium-Voltage Switchgear and Automatic Transfer Control Modernization

Project Overview

Shermco supported a major electrical modernization project at a corporate campus in Illinois, addressing aging medium-voltage equipment and automatic transfer controls within an existing, interconnected power distribution system.

The project focused on modernizing legacy medium-voltage switchgear through circuit breaker retrofits. The modernization strategy was developed to improve system reliability, maintainability, and long-term performance while leveraging portions of the facility’s existing electrical infrastructure.

The Challenge

Modernizing an existing electrical distribution system presents significantly different challenges than designing a new installation. Existing equipment dimensions, bus configurations, control schemes, protection requirements, equipment condition, and interfaces with downstream and upstream systems all influence the available modernization options.

For this project, Shermco evaluated the existing medium-voltage switchgear lineup, equipment section dimensions, single-line diagrams, site power loop, and associated control systems to determine how new equipment and controls could be integrated into the existing infrastructure.

The facility’s ATO system added another level of complexity. The controls interface with multiple components of the broader electrical system, including the power plant master controls, generator controls, ATO control house, and main low-voltage switchgear. Changes to one portion of the system therefore had to be evaluated in the context of the complete power distribution and control architecture.

Medium-Voltage Switchgear Modernization

The existing medium-voltage switchgear utilized aging Merlin Gerin circuit breaker technology. Rather than replacing the complete switchgear lineup, the modernization strategy included retrofilling six existing medium-voltage circuit breaker positions with new vacuum circuit breaker technology.

A retrofill approach allows critical switching components to be modernized while retaining serviceable portions of the existing switchgear structure. When properly engineered and implemented, this strategy can reduce the extent of equipment replacement required while improving maintainability and extending the useful life of the electrical distribution system.

The project required careful evaluation of the existing switchgear configuration to confirm physical compatibility, electrical requirements, control interfaces, and integration with the facility’s existing distribution architecture.

Safety and Existing System Conditions

Working within legacy electrical infrastructure also requires careful consideration of existing system hazards and operating conditions. Available equipment documentation identified arc flash incident energy levels throughout portions of the electrical distribution system, making these conditions an important consideration during planning and execution.

Evaluating the existing system alongside the proposed modernization allowed safety, equipment condition, system configuration, and operational requirements to be considered as part of the overall project strategy.