Power Distribution Line: How it works and differs from Power Transmission Line


There are complex networks that provide electricity to consumers. The Power plants generate the electricity and transport it through a complicated series of electricity substations, transformers, and power lines together, which you may know as a grid, connecting electricity producers and consumers. Most local grids link together to establish more extensive, dependent networks to improve dependability and economic opportunities. This article will give a good idea of how a power distribution line works.

Table of Contents

Caption: Electricity generation, transmission, and distribution

How do Power Distribution Grids work?

The process of sending the power from transmitters to individual consumers is the Electric power distribution. It might seem like a short task, yet it happens in several phases. Moreover, there is a point where the transmission changes to distribution, known as a Power Substation.

A power substation has the following functions.

  • The transformers inside it step down the voltages of hundred thousand value to distribution voltage of 10000V
  • Inside a substation is a “Bus” that splits the distribution power differently.
  • Moreover, it usually has circuit breakers and switches through which you can disconnect the transmission or distribution lines whenever you need.

Each transformer sends power to the distribution bus. Then the bus is responsible for distributing electricity to local distribution lines. Additionally, the bus does have its transformers, which can lower or boost voltage depending on local energy requirements.

Moreover, there could be two unique sets of distribution lines at the bus, each with a different voltage. For one group of strings, smaller transformers linked to the bus reduce the voltage to standard line voltage (typically 7,200 volts), while power leaves the other way at the greater voltage of the main transformer.

You might observe four wires attached as you pass by an electric pole. The three wires at the top of the utility pole are for three-phase power. Also, the ground wire is the fourth one from the bottom of the bars.

Moreover, you might see some additional cables, such as phones, cable TV, or Internet lines on the same towers in some situations.

In addition to the above steps, you need to further scale down the higher-voltage lines before entering most residential and commercial buildings. For that, you might need a different substation or small transformers further along the line. For instance, you will frequently find a large green box (maybe 6 feet or 1.8 meters on each side) near the entrance to a neighborhood. It would do the subdivision step-down function, thus lowering the greater voltage levels.

As you look into urban distribution systems, they are usually underground. However, the Rural distribution is above the ground, with utility poles connecting the area. Also, the circuity system is distributed over less than 50 ft. for urban areas but 300ft for rural systems normally.

Overhead transmission/distribution

When you need to transmit the energy over more considerable distances, you require overhead transmission lines. Overhead Power lines are made up of aluminum alloy, with several strands bound together by steel. However, there is no insulating layer. Thus, overhead transmission lines rely on air for insulating material. The layout of these lines has to maintain the bare minimum of clearances to guarantee safety. 

Since there is no extra layer, the cost of wires reduces significantly, making the bundle’s prices lower. Also, power outages can occur due to adverse weather conditions such as heavy winds and freezing temperatures. 

In Overhead transmission, you can experience different transmission-level voltages. Usually, it is 110kV or above, But it can be of sub-transmission, rated 66kV to 33kV, going over long transmission lines.

Underground transmission/distribution

On the other hand, the underground transmission lines are less affected by extreme weather conditions. However, it might be costly since it uses heavy cables with an insulation layer.

Moreover, Underground lines are strongly limited by their thermal capacity. As a result, they are less tolerant of overloading or re-rating than their overhead counterparts. Additionally, long underground alternating current cables contain substantial capacitance, limiting their capacity to deliver power to load more than 50 miles from the source.

Thus, to maintain the power flow, you have to monitor the temperature changes constantly while focusing on repairs at every moment.

Power Lines at Sunset

Caption: Power Lines at Sunset

Types of Electric Power Distribution

Customers who require a significant amount of power might directly connect to either the primary distribution level or the sub-transmission level of the power distribution system. Also, service drops are the points at which commercial and residential clients connect to the secondary distribution network.

Primary distribution

Primary distribution lines transport the medium voltage electricity to distribution transformers close to the customer’s residence or industry. Thus, the distribution transformers reduce the voltage to the usage voltage that the lighting, industrial equipment, and residential appliances will consume once again. 

Secondary distribution

Secondary distribution divides the areas into the specific frequency in which it will supply power. Thus, you can deliver the power to a household using a single-phase or three-phase power system


Sub-transmissions rely on relatively lower voltages. Since connecting all substations to high power transmission is not economical, you can use sub-transmission power grids. Also, it ensures that the consumers on the other end get an uninterrupted power supply.

As the power systems evolved, transmission voltages were converted to sub-transmission voltages, which were converted to distribution voltages. The voltages are not fixed between the sub-transmission and distribution lines. They might overlap at some points. Also, Sub-transmission, like transmission, moves relatively large amounts of power and, like distribution, covers an area rather than being limited to a point-to-point connection.

Power Distribution Substation  

Caption: Power Distribution Substation  

History of Transformers

Transmitting electricity over a long distance at a high voltage and then reducing it to a lower voltage for lighting became a well-known engineering obstacle to electric power distribution. Many lighting companies observed it while testing several, if not quite perfect, solutions. 

Hence, the discovery of functioning transformers in the mid-1880s marked a significant milestone in electrical history, allowing alternating current voltages to be “stepped up” to considerably greater voltages and subsequently “stepped down” to a lower end-user voltage. Alternating current (AC) usage proliferated with significantly lower transmission costs and higher economies of scale from substantial production facilities, and alternating current (AC) usage increased.

In the 1970s and 1980s, countries took the step of economic liberalization, which eventually created electricity markets. Hence, even while government regulations will continue to govern the distribution system, they will change the power generation, retail, and occasionally transmission networks into competitive marketplaces.

Caption: Transformer at the power station

Tell Electric power distribution From Electric power transmission

When a large amount of electric current passes from the power-generating grid to the substation, the process is known as electrical power transmission. The power stations use electric lines spread over the area to facilitate communication, termed a transmission network. 

A transmission network is different from the typical wiring in your home. It is more powerful and requires strong cables to support high voltages. Moreover, sending the higher voltages is necessary since the lines might lose power due to their resistance over the distance.  

Both power lines do the same job, i.e., transferring the power from one point to another. When comparing transmission and distribution power lines, the most significant distinction is that transmission power lines transmit high voltages over long distances. In contrast, distribution power lines transmit lower voltages of electricity over shorter distances. 

For instance, transmission lines are the power lines you might see on the side of a highway, tall and big, with lots of cables going over it. On the other hand, distribution lines are the power lines you might see on the side of a street over small utility poles.

Caption: A group of power transmission lines  


Transmission and distribution lines work on the same principle. The difference is their capacity to hold the voltage. No matter which kind of cable you need for your power network, we can help. With our lines,  your connection is made with attention to detail.