A Cost-Effective Compact Design Expands Capabilities at Major U.S. Dam

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One of the largest power-generating dams on the Columbia River in the northwest United States needed to replace a single-ended unit substation to ensure operational uptime. Built in the mid-1950s, the dam provides a reliable water source for navigation, irrigation, flood mitigation and recreation for regional residents, and has generated over 9.2 million kilowatts (kW) of electrical power to date. Since the dam is owned and operated by a federal agency, the project was put out for a competitive bid. A Lowest Price Technically Acceptable (LPTA) bidding process was launched in 2015 to find the best solution to meet the Agency’s requirements at the lowest possible cost.

The Challenge

The request for proposals (RFP) specified a 480VAC (LCQ) double-ended switchgear for the dam’s navigational lock. With limited space to work, one of the biggest challenges was to closely match the existing footprint of the single-ended unit substation with double-ended switchgear.

In addition to modernizing the installation to help ensure equipment uptime, there was also a need for improved arc flash resistance and longer time intervals between necessary maintenance. Finally, certification from Underwriters Laboratories (UL), an American safety consulting and certification company, was required for the new installation.

The solution was to install metal-enclosed switchgear, which included a vacuum circuit breaker with a disconnect switch and was well suited for this demanding application. This switchgear is designed with the industry’s smallest footprint, more than twelve inches more narrow than competitive solutions. This enabled the installation of a double-ended substation in the same space as the existing single-ended unit.

The Solution

With the ability to trip in three cycles, this switchgear provided the level of safety the Agency required. Through this feature, the solution allows for the addition of arc flash sensors directly to the relay to reduce the risk of arc flash at the transformer and main circuit breaker section. The vacuum breaker design also facilitates the addition of a maintenance switch to provide the Agency an alternative setting to reduce the incident energy when enabled. An arc-resistant enclosure adds additional protection to the application.

In addition, the front-only accessibility of the switchgear allows workers to see the disconnector open ahead of the main medium-voltage breaker. This, along with the Live Line Indicators during maintenance, simplifies processes for personnel.

This switchgear also provides the Agency with maintenance flexibility they needed. With a withdrawable control power transformer and potential transformers mounted in the enclosure, the design allows for removable vacuum circuit breakers which provide flexibility during maintenance or swapping with a spare. In addition, this switchgear also has a ten-year maintenance cycle, decreasing the Agency’s total cost of ownership and eliminating the need for frequent maintenance.

The Results

Through the use of this switchgear all technical criteria for the project was achieved.

The safety and space-saving features, along with the modular design of the medium voltage switchgear provided the Agency with a versatile solution that met their requirements as well as delivered cost savings benefits.

Moving Forward

To continue to serve its customers with reliable power, the Agency also needed to modernize an aging unit substation at one of the largest hydropower dams in the United States. Along with replacing a single-ended unit with double-ended switchgear, they had a goal to:

  • Lower the arc flash incident energy at the transformer.
  • Enable easier maintenance and control.
  • Extend time between maintenance periods.
  • Have a visual means to confirm the circuit breaker is de-energized.

This switchgear was also utilized in its installation, enabling the Agency to reduce costs and increase flexibility. The switchgear is expected to reduce the risk of arc flash, increase the uptime of the distribution network and provide extended product life with longer intervals between maintenance.

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