Electric grids

Summary: Electric grids are networks that connect electric generation plants to individual customers. Recent developments in alternative energy, involving wind and solar plants in remote areas, have increased interest in long-distance transmission networks and new grid technologies.

Electricity transmission is in general considered to be the bulk transfer of electrical power or energy. The lines that connect the bulk transmitters of power (generating stations) to their substations are typically called a grid. The wires or connections from substations to consumers are typically called a power distribution network. There are many types of electric grids, including DC grids, AC grids, international grids, hyper grids, smart grids, and micro grids. Grids vary depending on the type of power being transmitted.

In grid systems there must be some power to put into the grid at the beginning of the process. Generating plants produce electricity using different means including coal, natural gas, nuclear, hydropower, renewable energy, and petroleum. In general, electricity moves through the grid in stages as it is: (1) generated, (2) stepped up, (3) transmitted, (4) stepped down, and (5) delivered to the end user consumer.

Usually transmission lines transmit electricity in the 110 kV range. This may be done with overhead wires or underground wires. In order to move electricity from one region to another there is often a system in place to match up the various systems of energy. This is typically referred to as an HVDC power transmission system (HVDC stands for High Voltage Direct Current). An HVDC system has the ability to adjust so that different systems can work together.

AC and DC Power

There are two main types of power: DC power (DC stands for direct current), and AC power (AC stands for alternating current). With DC power the charge goes in one direction, but not both. AC power alternates its direction of flow. In a lot of AC utility circuits it changes direction approximately 60 times every second. DC current is most commonly thought of in the sense of batteries; AC current is most commonly thought of as the wall outlets in a house. DC power does not go as far with as much strength as AC power does. This is important for electrical grids, as this difference is central to the discussion of centralized grids or decentralized grids. Decentralized grids most often refer to their power usage and generation as localized power generation or localized grids. Centralized power is more typically the big power generating plant producing power that is sold and used throughout a region of the country.

AC grid systems are at the moment the common systems of choice. AC grid systems are used by a majority of countries to a greater or lesser extent. DC grid systems are broken down into two sets of systems: (1) HVDC, which is used fairly universally as a bridge or interpreter helping to match AC grid systems together, and low voltage DC systems. Low voltage DC systems are either on or off of the main grid of a country. In many cases a low voltage grid exists as either a remnant of earlier times, when DC power was used more extensively in grid systems than today. Another case is in remote or industrial settings. For example, in Africa and in Italy and other countries, remote places like mining towns may be on their own town-wide low voltage DC grid. Finally, the issue with DC is that since it costs more to transmit it great distances, it is usually kept close to its area of use. In many cases equipment or appliances used on a daily basis operate on DC, and when plugged into an AC outlet, there is a rectifier or inverter changing the cycle of power so the DC equipment can use it.

The problem of how to combine DC grids into an AC grid system or switch back to DC systems has been revived because of increased generation of alternative energy, which is often DC, not AC. In some countries like India, Denmark, Norway, and Germany they have already begun to make DC grids. These countries are working on either integration with their existing AC grid or parallel use of a DC grid with the existing grid infrastructure.

The US Grid

The US grid system is made up of three regional interconnection areas, with the the Eastern Interconnection serving states east of the Rocky Mountains, the Western Interconnection grid covering states west of the Rockies to the Pacific Ocean, and a third grid for the state of Texas. Each of these regions is, in turn, made up of smaller local energy grids.

Each of the three regional interconnection areas has its own voltage level, plus an interpreter, which is a fourth voltage level. The regional interconnections or voltages carried are (1) 345-499kV, (2) 500-699kV, and (3) 700-799kV, all of these being AC current, and then 1,000 kV (HVDC serves as the “interpreter,” able to change the speed or rate of transfer when needed). The three regional interconnection grid areas are called a “wide area synchronous grid.” Each regional interconnection area interconnects AC power operating at the same frequency and phase within its area or region. These regions are overseen by various reliability councils and the members of these reliability councils are in part utility companies, power producers, and distributors.

Once the generating plant has produced electricity, it is prepared for transmission by going to a generating station step-up transformer to increase the voltage for better transmission. Once the power is packaged, it is transmitted into transmission lines at a voltage within one of the three regional voltage ranges. When it reaches its destination, since it is carrying so much energy it needs to be stepped down through a substation step-down transformer so that it may be distributed to users with much smaller voltage needs (for example, American homes with 120v outlets). These smaller distributed networks are on an AC grid.

Smart Grids

The term smart grid refers to the addition of types of artificial intelligence to electric grid systems. These software programs track, read, compute, and determine the most optimal ways and means for our grid systems to work. Smart grids are important in that they can make determinations without manual intervention. They must be protected from corruption or viral invasion; this area is typically called cyber security. Since grids are now being made smart we must be able to identify if grids are connecting to each other through the interpreter (HVDC) or if other grids are interfering. In the area of international or hyper grids these identifications and protections are going to be critical to how the smart grid works.

The US smart grid was first established under Title XIII of the Energy Independence and Security Act of 2007 (EISA). According to the U.S. Department of Energy’s original estimates, the smart grid was supposed to cost $468 billion over the course of 20 years, but was expected to save much more than that in energy costs. There are infrastructure costs at all levels, such as changing from mechanical meters on houses to digital meters linked wirelessly or through some other means. The benefit is in better service, fewer outages, less leakage of power resources, and more. The consumer and the vendor also have better control over their expenses. According to a 2022 report from the US  Department of Energy, US electric utilities companies spent $6.4 billion on smart grid technology in 2020, up from $3.1 billion in 2014.  

Micro Grids

Micro grids are created when like or dissimilar renewable energy resources are tied together before being attached to the grid, either through corporate or community efforts. Resources may be tied to the grid through a common access point, or through a common corporate access point. In the case of a common energy system in which a community runs on solar power and wind power, the need to buy energy from the main grid may be removed or substantially lowered. In this case the main reason for being tied to the grid is to purchase power either individually or through an association like an energy cooperative when power is needed. These configurations draw on energy systems, but if the houses have more energy being produced by solar and wind than they can consume, the users are creating cheap energy for the utility system to buy and then resell. Sometimes a loose confederation of users allow a company to manage all of their energy issues, and all usage and data goes to that entity first and then it reports that data to the utility companies attached to the grid.

Renewable energy sources of power are typically DC. Homes with renewable energy sources usually have either a DC power-using home or an AC home with an inverter (which converts DC power to AC) between the power source (solar cells and the house) and its point of energy use. This is important for the grid as a whole because you usually cannot put renewable energy directly into the grid. The US FERC (Federal Energy Regulatory Commission) controls licensing for people or entities wishing to attach to the US grid to give the grid power.

Grid management systems, sensors, and flexibility are paramount in the new smart grid and micro grid world. Micro grids are useful in rural and remote areas where laying transmission lines is a challenge for the local or regional power companies, especially in rugged terrain or in disaster areas. Micro grids will, however, have to meet some form of standard as continually regulated by FERC. Nonetheless, there are some real advantages to them. For example, in a micro grid or local power distribution scenario the whole grid or region is less vulnerable to one large catastrophic event. Hospitals, police, and military may be on localized micro grids, a configuration that makes it harder for a negative event to affect the whole of the grid, or even a significant portion of it depending upon how the micro grids are constructed. Micro grids would most likely be DC-based since they tend to be in the low power generation cycles and this would also free up current power generation for other more immediate high power needs and use.

Bibliography

Berger, Lars T., and Krzysztof Iniewski. Smart Grid Applications, Communications, and Security. Hoboken, NJ: John Wiley & Sons, 2012.

"Electricity Grids and Secure Energy Transitions." International Energy Agency, October 2023, www.iea.org/reports/electricity-grids-and-secure-energy-transitions. Accessed 30 July 2024.

"Smart Grid System Report 2020." US Department of Energy, January 2022, www.energy.gov/sites/default/files/2022-05/2020%20Smart%20Grid%20System%20Report‗0.pdf. Accessed 30 July 2024.

Sorebo, Gilbert N., and Michael C. Echols. Smart Grid Security: An End-to-End View of Security in the New Electrical Grid. Boca Raton, FL: CRC Press, 2011.

"US Grid Regions." Environmental Protection Agency, 15 Jan. 2024, www.epa.gov/green-power-markets/us-grid-regions. Accessed 30 July 2024.