When it comes to how we get our electricity, more goes into it than simply flipping a switch.

Electrical transmission is vital to the infrastructure landscape, helping our power get from point A to point B safely and efficiently. While it seems pretty simple at first glance, it is a complex and sometimes dangerous process.

Electricity usually travels a long way from the generation plant to homes and businesses, and each step makes it possible to deliver power without delays or downtime.

Transmission and Distribution

When we think about how electricity is delivered, the process breaks down into two major components: transmission and distribution.

Transmission begins as soon as the power leaves the generation plant and continues until it reaches a substation for distribution. Within this are primary and secondary transmissions, which include:

  • Generation
  • Transformation
  • System protection
  • Switching
  • Voltage support (capacitors)
  • Structural support

Once the power reaches a substation, the high-voltage electricity from the generation plant is ‘stepped down’ to more usable voltages through a series of transformers. Transformers use coils to reduce higher levels of voltage down to safer levels for homeowners and businesses.

Like transmission, distribution can also be primary or secondary. Knowing where the electricity is during distribution will determine its phase. Though both types handle the safe delivery of power to customers, there are some key differences between the two.

Primary Distribution

  • Transformation
  • System Protection
  • Switching
  • Sensing
  • Insulation
  • Structural Support
  • Voltage Support (capacitors and voltage regulators)
  • Power Quality
  • Grounding and Bonding
  • Animal Protection

Secondary Distribution

  • System Health
  • Sensing
  • Transformers
  • Insulators
  • Structural Support
  • System Protection (surge arresters, fuses, etc.), auto and manual
  • Switching
  • Power Quality
  • Tree Mitigation
  • Wildfire Mitigation
  • Grounding and Bonding
  • Animal Protection

“Distribution lines before the transformer on the poles are considered primary,” Justin Solberg with Border States explained. “The low voltage side of the distribution transformer, where it’s below 600v, is a secondary line.”

Combined, transmission and distribution create a unique and expansive system that seamlessly supplies power to millions of homes, businesses, and public buildings daily.

Understanding Voltage Levels

Before diving into electrical power transmission, it’s worth knowing what voltage levels fit into which categories. According to the American National Standards Institute (ANSI), electrical energy voltage levels can be broken down into several buckets.

Low voltage (LV) lines are less than 1,000 volts. These are the wires that power homes, businesses, and public buildings. For the most part, homes use AC systems operating at 120/240 volts.

Medium voltage (MV) lines are more than 1kV but less than 100kV. These are typically electrical distribution voltages.

The rest of the lines are used for electrical transmission and are as follows:

  • High voltage (HV): 100kV to 230kV
  • Extra-High Voltage (EHV): 230kV to 1000kV
  • Ultra-High Voltage (UHV): more than 1000kV

As electricity travels from the power generation facility to transformers, substations, more transformers, and eventually to the meters in our homes, it will move through more than one type of line. High-voltage, medium-voltage, and low-voltage lines will all come into play during the process, with even larger lines coming into play during unique situations.

Primary Electrical Transmission

Primary electrical transmission focuses on electricity generated at a power plant and then sent to substations along massive overhead lines.

High-voltage lines carry power across long distances to substations many miles away. Electricity leaving the generating station is typically less than 35kv but gets boosted to much higher voltages at its first transformer. Transformers use coils and magnets to increase voltages to incredibly high voltages, often higher than 138kV, but can be as high as 1,000kV in certain situations.

Transformers play a massive role in energy transmission because it’s an efficient way of increasing or decreasing power. To maintain power levels and limit loss along the transmission line, power producers can either:

  • Increase conductor size to carry more current.
  • Use a more conductive material for the lines.
  • Increase the voltage.

By increasing the voltage during transmission, generation plants can limit power loss without spending extra money on massive conductors or bringing in more expensive lines.

Even with all the precautions to limit waste, the U.S. Energy Information Administration (EIA) says about 5% of annual electricity is lost during transmission and distribution. Though 5% sounds like a lot, and it is, it’s still less than the waste found in other utilities like water delivery, which loses an average of 14-18% of drinkable water each day.

“Utilities are all about efficiency, because you lose electricity throughout the transmission process,” Solberg explained. “What they’re trying to do is keep as much energy from the power plant to the end user as possible.”

Secondary Transmission (Sub-Transmission)

The second leg of our electricity journey begins when the high-voltage power reaches a substation. In some cases, this form of transmission may be used to move electricity shorter distances than primary transmission lines.

Substations along the transmission line can either step up or down the voltage to prepare it for eventual delivery through a distribution substation.

For the most part, electricity running along these lines is much less than what you’d find in a high-voltage line, typically only measuring between 35-69kV, though it’s possible to see lines carrying 115kV or 138kV. It’s also possible for several secondary transmission lines to feed into a single distribution substation.

Depending on how far the power travels to reach the load center, it may need to be stepped down several times before it’s ready for distribution.

Primary Electrical Distribution

After the initial voltage reduction at the substation, the distribution process begins. Distribution includes a series of voltage drops as the power travels toward its destination, down to about 240 volts for the typical home.

After leaving the substation, the voltage is still higher than most households or businesses can use. The electricity is sent to “load centers,” including cities, neighborhoods, and businesses, for eventual delivery.

When the electricity is in this phase of its delivery, it travels through medium voltage lines ranging from 5kV-35kV, as opposed to the hundreds of thousands of volts primary transmission lines carry.

Secondary Distribution

This is the final leg of the journey. Secondary distribution occurs when the electricity is sent to a specific area from the distribution substation, like a house, neighborhood, or business.

As the electricity gets closer to its destination, whether it’s a house, neighborhood, or business, utilities use lower voltage lines to carry power to customers’ meters.

In this case, the resulting power is considered low, including AC-rated voltages of 100-120 or 230-240 volts at 50-60Hz (hertz).

Electricity from A to Z

It’s one thing to look outside the window and see endless power lines, but getting electric power from A to B is complex and sometimes difficult.

The world of energy is rapidly changing as new technologies like renewables come online. Knowing where our power comes from and how it gets to us is critical to keeping vital infrastructure online and functioning. It’s even more crucial when you stop to consider how vulnerable the grid is due to age and technology.

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