The power grid has always been a dynamic system, but today its dynamic behavior has been come even more challenging for utilities because of the increased deployment of renewable energy sources and COVID-19. In 2020, several research groups identified wind and solar generation as the fastest growing source of electricity generation on the grid and they saw no signs of a slowdown. That may be good for the environment, but these resources are testing the grid’s resilience with their intermittent and variable properties.
In simple terms this means as the amount of renewable generation increase, so does the instability issues facing the grid. These growing numbers can cause frequency disturbances, voltage control problems, and abrupt swings in real and reactive power, but that’s only part of the story. For the past year, the transmission grid and distribution networks have also been challenged by effects of the global COVID-19 pandemic.
Along with the task of keeping employees safe, utilities and grid operators are also dealing with a reduction in demand, fluctuating loads, and continuously shifting energy-use profiles all brought about by the virus. Let’s focus on these fluctuating loads and their additional challenges to the distribution of electricity and the tools available to address the conditions.
Our power delivery system requires a different approach than traditional methods used in the past to keep the grid stable and power flowing. The smart grid’s advanced digital technologies, such as intelligent electronic devices (IEDs) combined with big-data analytics enhanced with artificial intelligence (AI), are a critical resource for addressing shifting demand, but there are more physical methods available that can help. It’s important to explore some of the actual high-tech hardware available to utilities, but with a new twist.
Adding Wheels
Conventional substation equipment has been mounted on trailers and skids for many years to give them the ability to be moved around easily. Those early applications have been adapted into more powerful tools needed specifically to address the issues above like the mobile substation. It has a flexibility that individual trailerized devises don’t have to correct these troublesome electrical characteristics caused by renewable generation and a global pandemic.
It didn’t start out as a mobile substation, but manufacturers like Delta Star, GE, Hitachi ABB, Schneider Electric, Siemens, Southern States, and others morphed a series of specialized trailers consisting of transformers, circuit breakers, switches, etc. into a cohesive mobile substation. These systems address load issues being discussed, which makes this device of prime interest. Mobile substations can provide grid support and they have been used in a variety of roles ranging from grid emergencies, temporary power supplies, and other grid functions.
Typically, the mobile substation contains all the equipment found in the traditional concrete and mortar substation, but it’s portable and mounted on a series of trailers. They use all of the latest technological innovations, which makes their installation fast and provides utilities with a quick method for restoration. It’s a little like plug and play on steroids. One Department of Energy study estimates a mobile substation can be installed in 12 to 24 hours, depending on the complexity of the configuration.
Diverse Solutions
These mobile building blocks come in a wide variety of designs depending on how they are specified. Recently Con Edison (ConEd) announced they had purchased six medium voltage mobile substations from Siemens. The mobile substations are part of ConEd’s US$1 billion grid resiliency plan. ConEd said they could deploy and commission one of these portable substations within days instead of the months required using traditional reinforcement techniques.
In late 2020, Spanish transmission system operator RED ELÉCTRICA DE ESPAÑA awarded a contract for ten mobile substations to GE Renewable Energy’s Grid Solutions. According to the press release, the mobile substations will be used on the Canary and Balearic Islands to support Spain’s decarbonization goals and improve its system’s resiliency. One of the containerized mobile substations is taking advantage of some state of the art technology for mobile substations. It’s the first mobile substation application to use GE’s Green Gas for Grid (g3 - pronounced g cubed) technology making it an SF6 free gas insulated substation.
In addition to the mobile substation there is another mobile device that needs to be examined in relation to the renewable generation and pandemic stratagems. It is the mobile static synchronous condenser (STATCOM). The conventional STATCOM is extremely well suited for dealing with the influx of renewable generation and the continuously shifting energy-use patterns caused by the pandemic, but there are some major benefits to having one that can be relocated.
The STATCOM may be a little unfamiliar, so before moving on, let’s look at the technology. It belongs to the FACTS (flexible AC transmission systems) portion of the power electronics world, and was developed to enhance the transmission grid’s control and to improve its power transfer ability. Hitachi ABB describes the STATCOM as a voltage regulating device that is based on voltage source converter (VSC) technology, and it can act as either a source or sink of reactive AC (alternating current) power.
The STATCOM combines the VSC technology with pulse width modulation and extremely fast switching technologies, which gives the STATCOM several advantages over other FACTS controllers. According to GE, the STATCOM increases system stability and power quality by providing voltage control and support along with reactive power control. In addition, it offers power oscillation damping and increases power transfer capacity. The device has a limited need for harmonic filters, which keeps the size manageable.
The customary STATCOM is an ideal tool for tackling the issues associated with the fluctuating loads and changing energy-use profiles, but they become a permanent part of the substation once installed. In most cases that isn’t an issue, but in today’s dynamic grid it could be a problem because change is the only certainty. What happens if the electrical characteristics of the grid where the STATCOM is located changes? What if the utility finds the STATCOM would be better suited in another location?
Well, the utility ends up with what could be called a stranded resource – in other words, a very expensive device that is no longer needed where it is sitting. That is where the ability to move the STATCOM would pay off big dividends. Breakthroughs in digital technology allowed the already small footprint of the STATCOM to become smaller. They are now compact enough to fit into a container, and the ideas started flowing.
Containerization offered utilities a lot of advantages over a built in place STATCOM that is assembled on location from parts and pieces shipped individually to the utility’s work site. One of the biggest advantages was the fact that each module of the STATCOM would arrive at the utility’s site completely assembled and tested. It only required modules be connected and commissioned.
It did, however, bring up the question - can the containerized STATCOM be trailer mounted (i.e., add wheels)? That would make the STATCOM as portable as the mobile substation. Of course the answer was yes, and Dominion Energy Inc. working with Siemens Energy made it happen. This trailerized adaptation moved this powerful FACTS controller into the plug and play world of mobilized grid equipment.
The first installation of the Siemens mobile STATCOM was at Dominion Energy’s Yorktown power station to support a complex transmission project. It took several trailers to house all the components needed for a complete STATCOM, but that wasn’t a problem. The trailerized modules arrived at the Yorktown power station, where they were quickly arranged, connected, and commissioned. For complete details, see ”Dominion Energy Develops Mobile STATCOM,” T&D World June 2020.
Talking with Mark McVey, principal engineer for Dominion Energy Inc., revealed exactly how valuable a mobile STATCOM has been to Dominion Energy Inc. The Yorktown project ended successfully and the STATCOM was relocated to Northern Neck substation to support a new transmission line rebuild. Mr. McVey said, “The mobile STATCOM has worked so well we are working on the justification of an additional unit.”
It seems the power delivery system is just beginning to scratch the surface of mobile equipment applications, but it’s a growing market. Research and Markets, a marketing research store, estimates the 2020 mobile substation’s global market was about US$824 million. It’s projected to reach US$1.3 billion by 2027 and that is only the mobile substation portion of the mobile equipment market.
The mobile STATCOM can also have a huge impact on a utility’s bottom line once stakeholders understand the economic benefits of a relocatable asset like a FACTS controller. In addition to these two devices, utilities in California are using mobile microgrids as a tool for fighting wildfires. Mobile energy storage systems are smoothing peak demand issues on the edge of the grid and the list is expanding. This is a growing trend that hasn’t quite caught on yet, but it hasn’t been ignored either!
