An example of an HVDC VSC valve hall. Source: Hitachi Energy.
An example of an HVDC VSC valve hall. Source: Hitachi Energy.

Rethinking Transmission ROW

Dec. 14, 2022
What’s delaying 1,400 gigawatts of renewable energy projects from being added to the grid?

How will 2023 change the power grid and its modernization goals? That’s a big question that’s being discussed around the watercoolers as we leave 2022 behind. It doesn’t take a crystal ball to realize that 2023 will be a demanding time for the transmission system. The climate crisis and its extreme weather events are major forces driving change in the power grid.

Transitioning from fossil-fuel to carbon-free energy sources is another heated topic, which brings up another subject that’s keeping stakeholders awake at night. What can be done to connect all the proposed renewable projects to the transmission system in a timely manner? The simplest answer would be to add transmission, but that hasn’t happened.

According to J.P. Morgan’s 2022 Annual Energy Paper, the U.S. transmission infrastructure’s growth has been flat for several decades at about 2% per year. If that isn’t bad enough, the last couple of years have seen this number drop to about 1% per year. The recently passed Infrastructure Investment and Jobs Act and Inflation Reduction Act promises relief, but there is still the quagmire of the interconnection queues needing attention.

Endless Queues

FERC (Federal Energy Regulatory Commission) reported at the end of 2021, there were over 8,000 active interconnection requests in the queues. That doesn’t include the projects waiting to get into queues. Those active projects in the queues represent over 1,400 gigawatts of generation and storage projects waiting to be studied. It has been pointed out that while some of the projects are considered to be “shovel-ready,” others in the queue are less than ready.

A report last year from Berkeley National Labs said, “Only 23% of projects seeking connection from 2000 to 2016 subsequently reached commercial operation.” Under today’s rules, it is a “first come, first served” procedure. Last year, FERC proposed changing the rules governing the interconnection process. One item on their list of changes would be to make the process a “first ready, first served.”

There are other proposed revisions, but changing rules and regulations takes time, and time is the big issue. Why not use some off-the-shelf technologies that are available right now? One of those technologies that has been leading the pack is HVDC (high-voltage direct current) transmission technology. It’s been a cost effective way to deliver large blocks of electricity over extreme distances for decades and today’s HVDC is more than just a power-pusher.

T&D World published its first special supplement on HVDC technology a little over 10 years ago. The first article in that supplement started off saying, “Sometimes technological advancement is not about a new discovery, it is about steady progress, hard work, and improvement of existing technologies.” A decade later, HVDC transmission technology is still doing that.

There are two types of HVDC technologies available today: LCC (line commutated converter) systems and VSC (voltage source converter) systems. VSC-based HVDC systems offer many benefits to a transmission starved power grid. Without getting too deep into the subject, VSC technology allows underground and submarine cables to be used without polarity reversals, which increases the cable’s dielectric withstand strength to almost twice the DC (direct current) voltage.

This is particularly important for today’s applications where utilities and operators wish to remove the HVDC transmission line from the view plain. In addition, VSC-based transmission and converter stations are more compact and environmentally friendly. Also VSC facilities don’t require AC (alternating current) or DC filters and they provide the operators with black start capabilities, plus they offer independent active and reactive power flow control.

Innovative ROWs

HVDC transmission line projects are popping up worldwide, and these aren’t small projects. To get a better understanding of the tangible aspects of VSC-based transmission lines on the grid, “Charging Ahead” spoke to Roger Rosenqvist, vice president, business development, HVDC at Hitachi Energy about the Champlain Hudson Power Express (CHPE) project.

Rosenqvist said, “New York state has set a goal of having 70% of their electricity coming from renewable energy resources by 2030 and the HVDC CHPE interconnection project is a key element in reaching that goal. Hitachi Energy is supplying an HVDC Light converter station for the U.S. portion of the CHPE project. The converter station will be connected to a ±400 kilovolt (kV) underground/underwater transmission line. It will be buried for its entire length — more than 372 miles (600 kilometers). When completed, the CHPE project will transmit up to 1,250 megawatts (MW) of clean, hydropower from Hydro-Quebec to the New York City metro area.”

Rosenqvist explained, “On the land portion, the cables will be buried along railroad and highway rights-of-way (ROW). This also enables designers to utilize compact design reducing the width of the ROW. Also HVDC has no control or safety issues for signal interference along the railroad’s ROW. The U.S. portion of the project starts at the northern end of Lake Champlain. The HVDC transmission line will go underwater via submarine cables at that point.”

Rosenqvist continued, “The cables will exit the lake on its southern end and continue underground along highway and railroad ROWs until they reach the Hudson River in the Catskills area. The transmission line resumes its underwater routing until it reaches a sensitive fish spawning area (the Haverstraw Bay). At that point, it comes onshore until it has cleared the spawning area. It returns underwater to the Harlem River, where it comes onshore in the Bronx for a short distance. After crossing the East River in a long horizontal directional drill, it reaches its final destination in Astoria, Queens, NY.”

Rosenqvist said, “HVDC systems can bring large amounts of electricity directly into large cities like New York without visual impact and associated public concerns by exploiting compact ROW design and underground/submarine cables. Generally, siting is less challenging for underground HVDC than for traditional overhead transmission lines in densely populated areas where land is scarce. Also going underground protects the transmission system from extreme weather events.”

Rosenqvist continued, “The converter station in New York City will be designed with physical characteristics to resist extreme weather events too. In addition, the reactive power and AC voltage support characteristics of the HVDC Light technology also play well with the existing power transmission grid in the area, which will experience a deficit of such characteristics as more and more of the traditional fossil fuel-based generation retires. Furthermore, the HVDC converter station will be a new and powerful resource for black-start of the New York City power grid in case a major system-wide blackout event.”


According to a report by Transparency Market Research Inc., the global HVDC transmission market was worth about US$16.96 billion in 2021. It is expected to reach about US$33.54 billion by 2031. This increase is expected because of growing electricity consumption and growing demand for cost-effective solutions for long-distance power transmission. That viewpoint is supported by the number of VSC-HVDC transmission projects currently in planning or under construction.

National Grid’s Viking Link HVDC ±525 kV, 1,400 MW project will utilize two Siemens Energy HVDC Plus voltage-sourced converters in a modular multilevel converter arrangement. It is expected to be commissioned in late 2023. The project will connect Britain and Denmark with a bidirectional underground/submarine cable power system. The marine section of the project is approximately 385 miles (620 km) of submarine cable. The Danish onshore portion is about 46 miles (75 km) of underground cable, and the UK onshore portion is approximately 40 miles (65 km) of underground cable. The Viking Link  will allow the two countries to share clean electricity.

Last year, Adani Electricity Mumbai Infra Ltd announced it had awarded a contract to Hitachi Energy for an HVDC ±320 kV transmission system linking Kudus to Mumbai on India’s west coast and is expected to go into service in 2025. The link will supply up to 1,000 MWs of electricity using Hitachi Energy’s HVDC Light technology. Because of the area’s high population density, the transmission system will use a compact design that includes 31 miles (50 km) of underground transmission rather than using overhead for the entire 50 miles (80 km) length.

Traditionally, HVDC transmission lines have been built much like the standard HVAC (high-voltage alternating current) overhead transmission lines, but schemes like the projects cited are changing that perspective. Today’s technological advancements allow the utilization of compact transmission designs, existing railroad ROW, and highway ROW. Developers are thinking outside the box, and these are the types of approaches that will speedup transmission projects.

The regulatory/interconnection hurdles are the same for HVAC and HVDC, but using existing ROW and going underground can aid in permitting. There are also proposals to convert HVAC transmission lines into HVDC transmission lines. Having a network of HVDC overlaid on the HVAC system is a step in the direction of National Renewable Energy Laboratory’s Interconnection SEAMS macrogrid proposal. It has the potential of supercharging the interconnection queues!  

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