What is a Power Transmission?
Power transmission is a critical aspect of modern electrical systems, responsible for delivering electrical energy from generation sources to end-users. Power plants generate electricity using various sources, including nuclear energy, fossil fuels, and renewables like hydro, wind, solar, and geothermal. Synchronous power generating plants generally produce electricity at voltages ranging from 5 to 34.5 kV [1].
In the case of inverter-based resources such as solar energy, electricity is produced at even low voltages. For instance, in a large-scale solar photovoltaic (PV) plant using Sungrow SG3600 central inverter, the low voltage AC output is 630 V. A pad mount transformer steps up the LV voltage (630 V) to a medium voltage (MV) range of 12,000 to 35,000 V. These voltages are not suitable for transmission over long distances to reach rural and urban areas due to technical losses.
The infrastructure that facilitates this transportation includes high-voltage transmission lines, substations, and transformers that ensure the voltage is appropriate for distribution.
Components of a Power Transmission
The transmission system is made of several components, such as towers, insulators, conductors, corona rings, and shield wires, among others. The tower is the main structure that supports other components, and they are expected to work together to withstand environmental stresses (wind, ice, or snow loads), maintaining the structural integrity of the power grid. The overhead lines or cables are the current-carrying conductors (aluminum or copper materials). The shield wires provide a path for lightning strike energy to be drained to the ground through a steel structure. In the case of a wooden tower, earthing (ground) wires are run from the shield wire to the ground.
Insulators are key components of transmission lines. They are non-current-conducting components. The overhead lines hang off the insulators, preventing current leakage to the supporting tower. This also ensures safety by electrical isolation from conducting paths, ground wires, and the supporting structure. Insulators are made from materials like porcelain, glass, or polymers.
Image Source: savree.com; Parts of a Power Transmission Structure
Why is a Power Transmission important?
The fundamental principle underlying power transmission is the transformation of voltage levels to minimize energy losses. High-voltage transmission is employed because it reduces the current flowing through the wires, thereby decreasing resistive losses, which are proportional to the square of the current (I²R losses). According to a brief article by the U.S. Energy Information Administration (EIA), the estimated annual mean of electricity transmission and distribution lost is 5% in the United States from 2018 through 2022 [2]. Transmission voltages are further classified based on the voltage level.
Common high-voltage transmission voltages include 115 kV, 138 kV, 230 kV, 345 kV, 500 kV, and 765 kV. For short lines (less than or equal to 50 miles or 80 km), a sub-transmission voltage of 34.5 kV, 46 kV, or 69 kV may be used. This post uses simple examples to demonstrate why transmission at higher voltages reduces technical losses.
How does Power Transmission Work?
Vital substations make the transmission of electricity across the power grid possible. Within these substations are transformers, which play a pivotal role in transmitting power over long distances. They step up the voltage for transmission and step it down when it reaches local substations or customer points. This process enhances an effective and efficient means of flow of electricity throughout the system.
Transmission infrastructures, which are interconnected networks of lines and heavy structures, balance supply and demand across different regions. They allow power plants to share their energy output and provide backup during outages or peak demand times.
This interconnectedness also enables the power grid’s resilience, allowing for more effective management of energy resources and emergency response. Transmission lines are bulk power carriers, and a loss in a major line(s) usually leads to massive devastation or a cascaded effect. Building more resilience and redundancy in transmission systems is crucial to ensure energy security and dependability.
What are some of the Challenges faced by Transmission Systems?
Despite progressive growth in transmission systems, they are not without challenges. Conditions such as aging infrastructure, increasing demand for electricity, and the integration of intermittent renewable energy sources come with challenges that need attention in the medium to long-term reliability and stability.
Moreover, natural or environmental disasters like thunderstorms, excessive heat, wildfires, floods, and earthquakes, among others, could significantly disrupt transmission lines. Errors (or mistakes), intentional vandalism, or cyberattacks from humans could also pose a threat to the smooth operation of a transmission system. To these issues, continuous investment in infrastructure, monitoring systems, and smart grid technologies is essential for addressing these challenges and ensuring the long-term reliability of power transmission networks. In the foreseeable future, power transmission is likely to involve a combination of advanced technologies, artificial intelligence, and sustainable practices.
Innovations such as high-voltage direct current (HVDC) systems offer significant advantages for long-distance transmission, reducing losses even further than traditional alternating current (AC) systems. Additionally, integrating smarter grid technologies can enhance real-time monitoring and control of power flows, thereby improving efficiency and resilience. As the world continues to transition toward renewable energy sources, developing robust power transmission systems will be vital to support sustainable energy goals and meet the ever-growing demand for sustainable electricity.
Summary
In summary, power transmission efficiently transfers electricity from power generation stations to distribution networks and end users. Transmission voltage levels play a critical role in minimizing power losses; that is, at high voltages, typically 69 kV to 765 kV, the current is significantly reduced over long distances, thereby reducing the ohmic losses (I²R losses). Substations step up the voltage for transmission and step it down for distribution, ensuring optimal and safe energy delivery to various customers across the electricity supply chain.
Recent advancements are transforming power transmission systems. Technologies like high-voltage direct current (HVDC) systems enable efficient long-distance energy transfer with reduced losses. Smart grid innovations incorporate sensors, automation, and AI for real-time monitoring and fault detection. Additionally, renewable energy integration has spurred research into advanced transmission solutions, such as superconductors and flexible AC transmission systems (FACTS), which enhance grid stability and efficiency.
- Title: Power Transmission
- Format: PDF
- File Size: 4.14 MB
- Number of Pages: 102
- Source: Western Electricity Coordinating Council (WECC)
References
[1] U.S. Department of Energy (n.d.) How it works: Electric Transmission & Distribution and Protective Measures. Retrieved January 27, 2025, from
[2] U.S, EIA (2023). How much electricity is lost in electricity transmission and distribution in the United States? Retrieved January 27, 2025, from https://www.eia.gov/tools/faqs/faq.php?id=105&t=3#:%7E:text=The%20U.S.%20Energy%20Information%20Administration,in%20the%20State%20Electricity%20Profiles.
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