Increased electric transmission capacity using existing infrastructure and with limited environmental impact: That may sound too good to be true, but it is a possibility that proactive utilities are evaluating today.

High-voltage direct current (HVDC) is a proven form to not only transmit power with minimal loss but also to rapidly and accurately control the power direction and level. Whether using overhead transmission lines or underground cables, HVDC technology is a viable way to increase the power transmission within the grid.

The Lowdown on HVDC

Alternating current (AC) is the primary form in which electricity is transmitted and distributed. But with new energy production sources, smart device technologies, and greater demand placed on the transmission and distribution networks, there is a driving interest among utilities to explore the potential of converting existing AC systems to HVDC.

HVDC offers a constant flow of electricity that doesn’t change over distance or time. This cost-effective electrical superhighway results in minimal energy loss and more efficient transmission, with power potential that can operate above 100 MW, and often in the 1,000-to-3,000-MW range.

HVDC uses a converter station to change AC to DC and then another station to return DC to AC. Standard system design and configuration options depend on existing asset infrastructure and budget. However, all upgrade options involve altering existing tower heads and using current rights-of-way. Substation modifications, or sometimes new substations, are also required for converters.

Evaluating Energy Options

Assessing cost and operating benefits between AC and HVDC systems must take into account the unique operating characteristics of the utility.

The advantage of using HVDC as a technology to transmit bulk power comes from the lower losses and controllable power levels and, as a result, a more economical transmission of power. If large power transfer is required, lower losses can offset associated costs of an HVDC system upgrade.

While upgrade evaluation includes any required system components, substation requirements or other capital costs, there also are intangibles and cost benefits to be considered. Reutilizing existing towers and other infrastructure limits environmental impacts, and using existing rights-of-way allows HVDC systems to be established faster and deliver improvements, even in densely populated areas.

Weighing the decision about converting to HVDC requires experienced analysis to determine how effectively this solution would work for different regions. For example, while HVDC offers the value of smaller towers and fewer conductors, a project must consider converter DC station costs as termination points over AC substations.

Converting existing assets to HVDC systems incurs cost, and a staged evaluation to identify the right approach is key. Verifying the technical capability of existing structures, determining if assets can accommodate modifications, and validating the system’s ability to meet the utility’s need will help determine if HVDC is the right solution.

Utilities need to consider their unique needs and operating environments as they look to transfer power more economically over long distances, achieve lower operating costs from reduced energy loss, or realize system improvements with less environmental impact. As with any utility infrastructure project, careful evaluation of options and a stage-gate review process can help determine the right path forward.

 

Learn how a systematic approach to HVDC conversion evaluations avoids cost surprises.

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Marianne Goldsborough is a project manager for Burns & McDonnell, overseeing the design, engineering and construction of substation and transmission line projects. With more than 30 years of experience in the electrical utility sector, Marianne specializes in HVDC and HVAC conversions, substations, transmission and distribution lines, and underground AC systems.