electrical power transmission: the middle child (part 1)
transmission! the middle child of the energy. part 1 in a series on transmission, bottlenecks, & solutions
I most recently wrote about the generation layer of the energy stack, providing overviews of the 6 most relevant (in my very humble opinion) sources of clean energy generation currently, their bottlenecks, and companies building those sources today.
Part 1 covered solar, wind, and hydropower.
Part 2 covered biomass, geothermal, and nuclear + a bottleneck and upfront cost comparison across them.
This brings us to the next layer of the energy stack: transmission.
Transmission is the essential, underappreciated infrastructure that connects electricity generation to the power outlets in our homes.
In this mini-series, I’ll cover first what transmission actually is, before diving into bottlenecks the sector faces in part 2 and onto some possible solutions and the companies building them in part 3. Welcome to part 1!
what is transmission?
When you see tall metal towers stretching across the landscape on road trips, you're looking at part of the transmission system.
More precisely, transmission is the bulk movement of electricity from where it’s generated to the substations that prepare it for distribution. It happens through a network of overhead and underground high-voltage lines which bridge the high-voltage world of generation with the lower-voltage world of end users.
Below is a more holistic visualization of how the pieces of the system fit together:
Because transmission is responsible for shuttling electricity about, and is interconnected in so many ways across many different geographies - often crossing state lines - it is one of the most highly regulated parts of the US energy system.
the policy + permitting landscape
Most of transmission is thus handled by utilities and regional planners (RTOs, ISOs), which are vestiges of our historically monopolized, centrally-planned energy system (more on grid history in a separate post coming soon). As such, costs to construct and maintain these systems are typically recouped through customer billing charges.
While FERC (the Federal Energy Regulatory Commission) oversees interstate transmission planning and cost allocation, it has limited backstop authority (referring to the federal government's ability to step in and approve the construction of transmission lines when state authorities have denied permits or taken too long to make a decision) to approve transmission projects within “national interest” corridors (referring to a geographic area designated by the DOE where lack of adequate transmission capacity is harming consumers and hindering the development of new energy sources), according to the Energy Policy Act of 2005. Basically, the federal government has very little power here (no pun intended).
This means states generally have primary jurisdiction over intra and interstate transmission siting and permitting, placing heavy emphasis on the role of local authorities. This makes transmission permitting very piecemeal and haphazard.
I’ll dive deeper into the permitting process in part 2 (the bottlenecks), but I’m calling this out now because it provides some context on the complexity that defines the transmission sector, ultimately causes lags in its expansion and innovation.
anatomy of a transmission system
There are 3 main components to our energy transmission system:
transmission lines
substations
associated equipment for the above
transmission lines
Transmission lines are the highways electricity travels on, forming the backbone of the grid. The below components form the transmission network:
Conductors are wires, often made of aluminum or copper that carry electrical current.
Busbars are the central point for connecting and distributing electrical power. They are a solid, conductive metal bar (copper or aluminum) used to distribute electrical power. Often found in switchgear, circuit boards, and busway boxes.
Insulators are materials like porcelain and glass, or composite polymers preventing electrical current from flowing. They support conductors by acting as insulating barriers between conductors and other equipment, and act as supporting structures.
Towers + poles are the tall structures that support conductors by keeping them elevated
Ground wires, aka shield wires, protect the system when lightning strikes
Line hardware includes clamps, brackets, spacers, vibration dampers. These maintain line integrity
substations: where voltage changes
Substations change voltage levels. They either step up voltage levels for high-voltage transmission over long distances, or step down voltage levels for safe distribution to end users. Substations therefore act as connection points between segments of the grid:
(1) generation → substation → (2) transmission → substation → (3) distribution.
There are two main types of substations:
Transmission substations: connect two or more high-voltage transmission lines.
Distribution substations: step down voltage and deliver power to local distribution networks.
inside a substation
There are many components in a substation. Here’s a visual for what substations typically look like and how the energy flows:
Transformers: adjust voltage via electromagnetic induction.
How transformers work: Voltage is stepped up or down using two adjacent coils of wire. As voltage changes in one coil, it creates a magnetic field that induces voltage in the second coil. The output voltage depends on the ratio of loops e.g., 1000:100 loops = 10x reduction.
Switchgear: a control the flow of electricity and protects circuits.
Circuit breakers: a type of switchgear that interrupts or continues the flow of electricity automatically. They are designed to protect electrical circuits from damage caused by excess current from an overload or circuit short. Think “emergency switches.”
Insulators: prevent arcing (when electricity jumps out of the bounds of wiring and uses air as a conductor, which is super dangerous) and ground faults at high voltages.
Often, dielectric materials (non-conductive) are used to extinguish arcs.
Instrument transformers: used for measurement and monitoring.
Voltage regulators: fine-tune voltages on feeder lines to consumers. These often have multiple taps that adjust output voltage up or down depending on demand and line load.
Control & protection systems: employ protective relays, comms equipment, and control panels to operate and monitor the substation
Grounding systems: ensure safety and uniform voltage across components by connecting everything through wires into the ground.
how electricity flows through the grid
generation
Electricity is produced at large power plants, typically at voltages between 10–30 kilovolts (kV).
This low-voltage power is not efficient for long-distance travel, so it needs to be stepped up.
step up voltage via transformers (at substation)
Transformers at the generation site increase the voltage to hundreds of kilovolts for efficient transmission.
transmission
High-voltage electricity is transmitted across the country via overhead or underground lines.
These lines connect large power stations to substations near population centers
up next: transmission bottlenecks + solutions
In part 2, I’ll dive into the challenges slowing transmission buildout, from fragmented permitting to supply chain constraints, and explore who is trying to solve them.
visualization tools
How Substations Work (YouTube) – I liked this explanation of how substations operate in practice, as well as this IRL walkthrough
U.S. Transmission Line Map by Charlie Cone – This is a really cool interactive map showing transmission infrastructure across the U.S!