The Bulls Bridge Hydroelectric Plant in New Milford, Connecticut first came online in 1903 and today stands as a testament to early twentieth-century hydroelectric engineering. Although much of its original structure and machinery remains in service today, a recent breaker upgrade illustrates how thoughtful modernization and modern equipment built “like it used to be” can sustain aging infrastructure.
Today, the plant utilizes six original horizontal double-runner Model F-1 Francis turbine units installed in 1903, each coupled to General Electric generators. While the turbine-generator units performed as intended, one area that required retrofitting was the downstream circuit breakers.
These devices connect or disconnect the generator from the broader electrical system, provide isolation for maintenance, and protect the generator against internal faults such as stator or rotor failures, as well as against abnormal operating conditions like overcurrent, overvoltage, or unbalanced loads.
However, older breakers, such as oil, air-magnetic, or air-blast types, can become unreliable as contacts erode, insulation degrades, and maintenance costs rise. Today, these types of breakers are considered outdated due to modern safety standards and advances in breaker technology.
Because of these factors, the 1903-era breakers were replaced with updated designs that utilize advanced vacuum interrupter technology.
For the retrofit, National Breaker Services (NBS) was called in to replace all six breakers with draw-out style vacuum circuit breakers. NBS is a specialized provider operating from Middlebury, Connecticut, that engineers, designs, manufactures, retrofits, and services medium-voltage switchgear and circuit breakers.
What sets the company apart is their focus on ruggedness, utility-grade engineering, and adaptability to legacy systems. Their flagship offering, The Citadel, allows utilities to upgrade aging medium-voltage infrastructure without a full system replacement, maintaining or exceeding original equipment ratings while enabling modern maintenance practices.
Initially developed as fixed-mounted vacuum breaker elements to retrofit aging U.S. mediumvoltage systems, The Citadel components are dimensioned to fit virtually any 5 kV or 15 kV legacy breaker chassis, with conservative ratings such as 15 kV – 95 kV BIL, and current capacities of 1600 A at 31.5 kA or 2500 A at 40 kA.
Over time, this platform evolved into a drawout breaker design featuring remote racking options and rollin replacement capabilities, meeting high performance levels including up to 38 kV – 63 kA – 5000 A. NBS also offers indoor and outdoor switchgear, including dog houses, freestanding units, walkin commonaisle substations, generator accessory cubicles, and modular EPC lineups.
In this case, the Bulls Bridge project involved retrofitting the 1903 breakers with modern circuit breaker systems.
After careful on-site measurements were gathered to ensure the new equipment could be engineered and designed to fit the very tight footprint, NBS removed the old breakers and installed six new custom enclosures with draw-out style breakers. A draw-out breaker is designed to be inserted into and withdrawn from a switchgear cubicle or breaker compartment without having to disconnect the wiring or bus connections manually.
The custom Citadel enclosures also incorporate draw-out potential transformer assemblies, a modern feature that did not exist on the original 1903 breakers.
The modernization of Bulls Bridge highlights the lasting value of historic infrastructure when combined with targeted upgrades, demonstrating that legacy systems can continue to deliver reliable power when supported by the right technical interventions.
Read the full article here as published in POWER Magazine: https://www.powermag.com/major-retrofit-restores-early-1900s-hydropower-dam/
For more information call (475) 316-3471, email jduggan@nationalbreaker.com, or visit www.nationalbreakerservices.com.