In our life today, we require electricity so we can survive, that is, it’s part of the basic need of humans. Understanding the electrical power transmission and distribution system is something broad which is what you’ll be learning here today.
An electric power transmission system is a means of transmitting power from a generating source to various load centers. This means where the power is used. Generating stations is where the electrical power is generated, well these generating stations must not be situated where the majority of the power is being consumed.
Today you’ll get to know the definition, components, functions, types, and working of electrical power transmission and distribution systems. you’ll also learn how to construct a power generation station.
What is electric power transmission?
Electric power transmission or electrical transmission is the process of delivering generated electricity. This is usually achieved over long distances to the distribution grid located in populated areas. Electric power transmission can also be seen as a bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines in the system are what facilitate the movement of electrical power. They are known as transmission networks.
Just as earlier explained, the generating stations are not necessarily situated where the majority of the power is being consumed. This is to say, distance is not the only factor that determines the ideal location for a generating station, the place where the power is generated must be quite far away from where it is used.
The reason for this is because land further from the load center, which is generally a high-density central location will be much cheaper per square meter. Another reason is the loud and/or polluting station close to the residential areas.
Finally, Electrical supply systems are the network through which consumers of electricity receive power from a generation source. This is known as a thermal power station.
Components of electrical power transmission
Below are the components of an electrical power transmission
Power transmission system which includes short transmission lines, medium transmission lines, and long transmission lines, and long transmission lines. They all transport the power from the generation source into a power distribution system. This distribution system is what provides electricity to individual consumer premises.
An electrical transmission system consists of power plants, distribution systems, and sub-stations. All these forms what is known as an electrical grid. This grid meets society’s electricity needs.
Power lines or transmission line is what transport electricity from one place to place. The electricity is usually alternating current so that step-up transformers can increase the voltage, which allows efficient transmission for 500 kilometers or less. The three types of lines include:
Overhead lines: these types of transmission lines have a very high voltage that ranges between 100 kV and 800 kV. They are suitable for long-distance transmission and must be high voltage in order to minimize power losses to resistance.
Underground lines: the underground lines are used to transmit power through populated areas, underwater, or anywhere that overhead lines can’t be used. They are less common when compared with the overhead lines due to higher and heat-related losses.
Sub-transmission lines: these types of transmission lines carry lower voltages ranges from 26 kV – 69 kV to distribution stations. This transmission can either be overhead or underground.
Element of a Transmission Line
Below is the main element of a transmission line:
- Conductors: a transmission line conductor must be of proper size (i.e., cross-sectional area), depending on its current capacity. Three for a single circuit line and six for a double circuit line. Aluminium-core steel-reinforced conductors are the most used type.
- Protective devices: these devices include ground wires, lightning, relays, arrestors, circuit breakers, etc. help to protect the power transmission system and ensure reliable operation. Finally,
- Voltage regulators: voltage regulators help to keep the voltage within permissible limits at the receiving end.
- Transformers: step-up transformers are used for stepping up the voltage level and step-down transformers are used for stepping it down.
- Line insulators: the line insulators mechanically support the line conductors as they are electrically isolated from the support towers.
- Support towers: this supports the line conductors suspending in the air overhead.
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Types of electrical power transmission
Below are the major types of transmission system:
The primary transmission is a power transmission type that transfers a large quantity of electrical power from the initial generating station to the substation via overhead electrical lines. Although, some countries use underground cables in situations where transmission takes place at a shorter distance.
In the primary transmission, power is generated at a power station, which supplies electrical energy anywhere between 11 kV and 33 kV. It is then sent to the distribution center through the transmission lines. It stepped up using a transformer to a voltage level that can be anywhere between 100 kV and 700 kV or more, depending on the distance that needs to be transmitted. This means, the longer the distance, the higher the voltage level.
The electrical power is stepped up to an elevated voltage level so that it can be more efficient by reducing the I2R losses that take place when power is transmitted. When the voltage is stepped up, the current reduces relative to the voltage. This helps the power remain constant, thus reducing the I2R losses.
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See diagram of a primary transmission below:
In the secondary transmission, the voltage is stepped back down when electrical power reaches a receiving station. The voltage is stepped down typically between 33 kV and 66 kV. It is then sent to transmission lines from the receiving station to electrical substations closer to “load centers” such as villages, cities, and urban areas. This process is known as secondary transmission.
Furthermore, when electrical power reaches a substation, it is stepped down once again by a step-down transformer to lesser voltages but close to the previous one. This usually around 11kV. At this point, the transmission phase graduates to the distribution phase, and electrical power is used to serve both primary and secondary consumers.
Different Types of Electrical Power Transmission System
Types of the electrical power transmission system can also be seen as:
- Single-phase AC system
- single-phase, two wires
- a single-phase, two wires with midpoint earthed
- single-phase, three wires
- Two-phase AC system
- two-phase, three wires
- two-phase, four wires
- Three-phase AC system
- three-phase, three wires
- three-phase, four wires
- DC system
- DC two wires
- DC two wires with midpoint earthed
- DC three wires
AC and DC Power Transmission
The AC and DC transmission are the two ways by which electrical energy can be transmitted. They are called ‘high voltage DC electrical transmission system and high AC electrical transmission system’. These two methods of energy transmission have their own advantages and disadvantages which will be explained below.
Advantages of using DC transmission system:
Below are the disadvantages of the DC transmission system:
- Just two conductors are required for the DC transmission system. It is even possible to use only one conductor of the DC transmission system, that is if the earth is utilized as the return path of the system.
- In a DC system, inductance, capacitance, phase displacement, and surge problems can be terminated.
- DC transmission systems have reduced insulation costs due to the fact that the potential stress on the insulator of the DC transmission system is about 70% of the equivalent voltage AC transmission system.
Advantages of AC transmission system
Below are the advantages of the AC transmission system:
- Alternating voltages can easily be stepped up and down, which is impossible in DC transmission types.
- Transforming of power in AC electrical substation is much easier than motor-generator sets in a DC system.
- Maintaining an AC substation is quite easy and more economical compared to DC.
Disadvantages of AC transmission system
Despite the good benefits of AC transmission system, some limitation still occurs. below are the disadvantages of AC power transmission:
- AC systems require a higher volume of the conductor when compared to DC systems.
- The reactance of the line usually affects the voltage regulation of the electrical power transmission system.
- These types of transmission systems are more likely to be affected by corona discharge than a DC power transmission system.
- An AC system requires proper synchronizing before interconnecting to or more transmission lines together. However, synchronizing can be neglect in DC power transmission types.
- An AC system can cause skin effects and proximity effects.
- Construction of AC electrical power transmission network is more completed than DC systems.
Watch the video below to learn more about the working of electrical power transmission and distribution system:
Factors to consider when constructing a power generating station
Below are the factors we must consider before building a power generating station:
- Availability of water for power generating station.
- Availability of land for construction of power station including its worker’s township.
- If a hydropower station is to be built, there must be a dam on the river. So, there must river around the station.
- One of the factors to be considered for a thermal power station is fuel.
- Better communication system for good as well as employees of the power station.
- Wide roadways, train communication is required so that very large spare parts of turbines, alternators, etc. can be transported. A deep and wide river must pass away nearby the power station.
Electrical power transmission is one of the important today because it one of the basic needs of humans. Electrical power transmission is a system on how electrical power is transfer to the end-users. Just as promised, this article contained the meaning of electrical power transmission, its component, element, types, working, and factor that should be considered when building a power generating station.
I hope you’ve got a lot from this article, if so, kindly share it with other technical students. Thanks for reading! See you next time.