What Are Distribution Lines: Transportation Of Electricity

Do you need information on electrical power distribution lines? Then, read through this article to get all the information you require.

This article carries every information you need on electrical power distribution lines.

To make your reading easy, I will begin with an overview, after which the next section will contain how distribution voltage flows. This section will identify the various voltage levels on distribution lines.

The next section will contain details on the distribution sub-station and its components. After which, we will discuss overhead and underground distribution lines.

In conclusion, I will give answers to some frequently asked questions.

This will be fun. I urge you to read to the end.

Distribution Lines: Overview

Distribution Lines_ Overview

The need for electricity in our homes and offices must not be overemphasized. In addition, most of our domestic and office equipment needs electricity to function effectively.

However, for us to utilize electricity, it goes through different stages. These stages are the generation stage, transmission stage, distribution stage, and utilization or consumption stage.

Nevertheless, the generation stage is at the power generation plant. There are various ways of generating electricity.

The various type of power plants includes the hydroelectric power plant, gas power plant, wind power plant, solar power plant, etc. The generation voltage ranges from 0 to 40kV.

In other to reduce power losses at the transmission stage, the voltage is stepped up to a higher voltage. Hence, this reduces the current. As a result, it reduces power losses due to heat or resistance.

Furthermore, the electricity travels for a long distance at a high voltage. Towers support this transmission line.

However, this high voltage is stepped down at the distribution end with a step-down transformer. Then, this voltage is distributed through cities.

More so, the distribution stage is divided into the primary distribution and secondary distribution. I will discuss this in detail later in this article.

Consumers connect to the secondary distribution line to utilize electricity in their homes. The connection could be in single-phase or polyphase.

Transmission and distribution of electricity are done in 3-phase. This article discusses in detail the distribution stage of electricity.

Therefore, the distribution lines are electrical conductors that distribute electricity through cities to homes and offices. They carry voltages between 2kV and 35kV for primary distribution and about 120volts or 240 volts for secondary distribution.

This electrical distribution can be done in Radial, Loop, or Network.

Distribution Lines: How It Works

In this section, I will discuss the various voltage levels in the distribution lines and how to realize them. However, the distribution lines could be primary distribution lines or secondary distribution lines.

Primary Distribution Lines

The primary distribution line has a voltage between 2kV (2000 volts) and 35kV (35000 volts). At this stage, the high voltage in the transmission line reduces.

A single-phase (phase-to-neutral) primary distribution line could carry a voltage of 2kV to 20kV. While for phase-to-phase, it carries a voltage of 4kV to 35kV.

However, the essence of reducing the voltage level is to reduce the cost of bringing the electricity to consumers and reduce the risk associated with high voltage lines.

Since the distribution is not as far as the transmission, the power losses will not be high. Note that the resistance of a conductor increases as the length increases.

The power loss due to heat or resistance is mathematically calculated using the formula below.

Loss = (current)^2 * resistance.

Thus, Loss = I^2 * R.

The SI unit of power loss is watts.

Secondary Distribution Lines

The secondary distribution lines have voltage levels lower than that of the primary distribution lines. However, this voltage level varies according to region.

Most countries of the world transmit electricity at a frequency of 50Hz or 60Hz. Even so, the voltage at the secondary distribution varies.

Some parts of the world, like Europe, distribute electricity at 50Hz. Also, their voltage level is about 220 or 230 volts for a single-phase or 400 volts for a 3-phase.

Also, they distribute with a 3-phase, 4-wire system.

On the other hand, some other countries like America distribute at a frequency of 60Hz. They use a 120/240 volts split-phase system to power homes and 3-phase for large installations.

In North America, homes are powered with 240 volts. However, since it is a split-phase system, it allows the use of 120 volts in homes.

Furthermore, Japan distributes electricity at 100 volts. More so, they use both 50Hz and 60Hz frequencies.

Let’s assume the phase (phase-to-neutral) voltage to be “Vph” and the line voltage (phase-to-phase) voltage to be “VL.”

Then, the phase voltage relates to the line voltage with the equation below.

VL = √3 * Vph.

Distribution Line Sub-station

The electrical sub-station is an assembly of equipment aiming to either step down or step up electrical quantities like current, voltage, etc., depending on the type. Some electrical sub-stations can correct the power factor of the electrical system.

For the distribution line, the sub-station decreases the voltage to a level consumers utilize. This stepping down is in two stages.

In the first stage, a sub-station steps down the voltage at the transmission line to a primary distribution voltage between 2kV to 35kV, depending on the rating of the sub-station.

More so, this enables the distribution of electricity through cities. Electrical engineers do this either by overhead means or underground.

Furthermore, the second stage transforms the primary distribution voltage into a voltage level suitable for consumers. This voltage varies according to region.

However, the voltage range is between 100 volts and 600 volts. More so, the frequency is either 50Hz or 60Hz.

Components Of A Distribution Substation

Components Of A Distribution Substation

Supply Line

The supply lines are wires (XLPE or PVC cables) that connect the sub-station to a transmission line. More so, the distribution line connects to the transmission line through at least one supply line known as a primary feeder.

For reliability, the distribution sub-station can get its supply from two or more supply lines. This prevents outage when one line is faulty.

Transformers

The distribution substation uses a step-down transformer. This step-down transformer uses the principle of electromagnetic induction to reduce the voltage to a lower magnitude.

More so, it has two windings which are the primary and secondary windings. The primary winding is the input, while the secondary winding is the output.

Furthermore, transformers are classified according to the power rating, insulation, winding connections, voltage rating, cooling, and voltage regulation.

Busbars

These are metal bars used for the termination of cables. They are part of the entire power system – from generation to distribution.

Before now, bare copper busbars supported on porcelain insulators were used. However, in recent times, engineers have used enclosed busbars to achieve higher current densities.

Switchgear And Switching Apparatus

The switchgear is a terminology that covers primary switching and interruption devices. It also encompasses its control and regulating equipment.

Moreover, the switchgear is useful in disconnecting switches, main buses, interconnecting wiring, etc. This switchgear can be outdoor or indoor.

On the other hand, the switching apparatus is useful in connecting and disconnecting elements in a power system. These include switches, isolators, fuses, circuit breakers, etc.

Surge Voltage Protection

Due to a power system’s natural and inherent properties, transient overvoltages do occur. This overvoltage is very dangerous despite its short duration of occurrence.

Furthermore, this surge voltage occurs as a result of lightning or switching. Thus, the presence of surge protection devices will reduce the magnitude and duration of surge overvoltages.

Grounding

This is part of every electrical installation. It creates a part that directs leakages to the general mass of the earth.

More so, it could be equipment grounding or power system grounding. You can also refer to it as “Earthing.”

Overhead Vs. Underground Distribution Lines

Overhead Vs Underground Distribution Lines

Overhead Distribution Lines

In electrical distribution, overhead distribution lines carry electricity on poles. They use bare conductors to carry electricity through cities to the consumers.

However, overhead electricity distribution is very popular because of its simple installation. Also, you can easily detect and correct faults on overhead distribution lines.

Components Of Overhead Distribution Lines

Conductors

A conductor is any material that allows current to pass through them. In an overhead distribution line, conductors play a vital role in delivering electricity to consumers.

However, a good conductor should possess the following properties:

  • Its conductivity should be high.
  • Also, its tensile strength should be high enough to withstand mechanical stress.
  • Even so, it should have less weight per unit volume.
  • Lastly, its cost should be relatively low.

Furthermore, conductors applicable to distribution lines are often stranded. Conductors are products of metallic elements or alloys like copper, aluminum, cadmium-copper, etc.

Copper conductors have high conductivity and tensile strength. Also, they have a high current density which gives them more current-carrying capacity.

Even so, copper is highly durable and has a high scrap value. However, electricians rarely use cooper on overhead lines because of its cost.

Aluminum has a higher conductivity than copper. In other words, aluminum has a higher cross-sectional area for the same resistance.

Also, its tensile strength and weight are less than copper. Even so, aluminum is widely used on overhead lines because of its availability and lesser cost.

The following are the types of conductors used in overhead lines:

  • All Aluminum Conductors (AAC).
  • All Aluminum Alloy Conductors (AAAC).
  • Aluminum Conductors, Steel Reinforced (ACSR).
  • Aluminum Conductors, Alloy Reinforced (ACAR).

Insulators

Insulators are materials that do not allow electricity to flow through them. You might wonder why we need them in an electricity distribution line with this definition.

However, we use insulators to prevent current from leakage or flowing to undesired paths. You see insulators on every pole or tower in overhead lines.

It is to ensure that current flows only through the conductor. Porcelain is the material used in making most of the distribution line insulators.

These insulators could be pot, disk, shackle, stay, or pin insulators. However, the line’s voltage rating determines the insulator’s size.

Line Supports

Line supports are rigid structures that carry the conductors through which current passes. These line supports could be either a pole or a tower.

The distribution lines use poles as their line support. There are two types of poles: wooden and concrete poles.

However, modern electrical installation of distribution lines uses concrete poles. On the top of the pole, metal makes a Tee-shape with the pole.

More so, the insulators are installed on this metal bar, and it’s held to the pole with bolts and a tie-strip. This metal is known as the Cross arm.

Protective Devices

These protective devices include lightning arrestors, circuit breakers, line fuses, and even earthing. These devices protect the system from one fault or the other.

Stay Wire

A stay wire is a wire capable of withstanding mechanical stress. It is made from strands of galvanized steel wire.

You find it at the end of a distribution line. Also, it provides support to the last pole on the line and keeps it erect.

Pros Of Overhead Distribution Lines

  • Its cost is lower.
  • Also, its construction is easier and quicker.
  • Even so, it is easy to spot and clear faults on overhead lines.
  • Furthermore, it is easy to maintain.
  • Lastly, you can easily extend overhead lines.

Cons Of Overhead Distribution Lines

  • Due to its exposure to the environment, its risk level is high.
  • It is vulnerable to lightning strikes.
  • Also, vehicle collisions could damage it.
  • Trees and vegetation could damage it.
  • Lastly, it is less attractive.

Underground Distribution Lines

Environments without electric poles and wires use underground distribution lines. The underground distribution system is a method of distributing electricity through cables under the ground.

This system is neat and attractive, but it is costly. Also, it carries a limited amount of voltage.

Furthermore, this system is not very popular because of its complex nature. You install underground distribution lines using cables, often Armoured Cables.

The armored cable is a cable with different layers that perform different functions. It has conductors which allow the flow of current.

However, its other parts include a lead sheath, armor, serving, etc.

Pros Of Underground Distribution Lines

  • They are safer than overhead lines.
  • Also, lightning does not affect them.
  • Even so, they are very attractive.
  • Lastly, they are not vulnerable to trees, animals, vehicles, etc.

Cons Of Underground Distribution Lines

  • They are very expensive.
  • Also, it isn’t easy to install.
  • Even so, it is challenging to locate and clear faults.
  • Furthermore, it is susceptible to flooding.
  • It is not easy to maintain.
  • Lastly, it could be vulnerable to diggings.

Frequently Asked Questions

Frequently Asked Questions
1. What’s the difference between distribution lines and transmission lines?

Transmission lines are for long-distance and high voltage electrical power transportation. On the other hand, Distribution lines are for low voltage and shorter transportation of electricity.

2. How do you identify a transmission line and a distribution line?

Transmission lines travel for long distances on towers. They have large suspension insulators.
On the other hand, distribution lines travel short distances on poles. Therefore, they use pots and disks insulators.

3. What is distribution line voltage?

The distribution line voltage is 13kV (13000 volts). However, our household electricity is 110 volts.

4. What is a distribution power line?

The distribution line is the final stage of the electrical grid. It brings electricity to consumers at a safe voltage level.

5. What is the difference between kVA and kW?

kVA (kilovolts-ampere) is a unit for apparent power, while kW (kilowatts) is a unit for real or active power.

6. What is the difference between distribution and substation?

Distribution lines are low voltage lines that take power from a sub-station to the consumers. In contrast, a distribution sub-station steps down high voltage to a lower and safe voltage for consumption.

7. How do we distribute electricity?

Distribution starts from the sub-station where the transformer steps down the transmission voltage to the distribution voltage. Then, the distribution line distributes the voltage.

8. Which conductor is used in the 11kv line?

The conductor that is often used on distribution lines is the All Conductors, Steel Reinforced (ACSR).

9. What is a kV in electricity?

kV is a unit of potential difference. 1kV equals 1000 volts.

10. Are power lines AC or DC?

Power lines carry alternating current (AC), not direct current.

Distribution Lines: My Final Thoughts

Distribution Lines_ My Final Thoughts

The utilization of electricity needs a distribution line to bring the high voltage of the transmission line to a distribution voltage level. This is to allow the consumers to use safe voltage.

However, the voltage at the distribution line could be in a single-phase or polyphase system. Depending on the region, it could be a 2-wire, 3-wire, or 4-wire system.

Therefore, this article has every information you need on electricity distribution lines. It also gives details on the distribution sub-station.

I hope this article is useful to you.

So, fill out the “Leave A Reply” form at the end of this article to share your thoughts.

Finally, you may find other helpful articles on our Tech Explain page

You can as well visit the following pages:

What Is An Atom?: The Smallest Unit of Matter

Pulse Generator: Explanation in Details

What Is A Battery: Cells That Produce A Direct Electric Current (DC).

Christian Jerome
Akan Christian writes for PowerVersity.com. He holds an HND in Electrical/Electronic Engineering. Christian enjoys reading, listening to solemn music, singing, and playing sports. For PowerVersity.com, Christian writes reviews, buying guides, and best pick articles.
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