Transmission System
Nowadays, “electric energy” is a basic necessity of life. Besides, electric energy development has pushed forward the changes across several sectors, such as industry, medicine, public health, transportation, education, tourism, and communication, etc.
The route of electric energy development has continued to advance through quality-driven mechanisms that generate power from several fuel sources and deliver it through the transmission system.
Transmission system plays an important role in supplying electric energy from producers to end users, enabling people to access basic utilities widely. Transmission system has brought prosperity to all regions of the country to enhance economic stability, which leads to reliability in investment in all sectors.
Electricity Generating Authority of Thailand (EGAT) is a state enterprise responsible for power generation, system control, and the transmission of electricity nationwide. EGAT’s transmission network connects power plants to the distribution systems of the Metropolitan Electricity Authority (MEA) and the Provincial Electricity Authority (PEA), where the electric voltage is adjusted properly before reaching the end users of all sectors.
Transmission Lines
High voltage transmission lines of EGAT are like the arteries of Thai electricity system which has to be taken care of to ensure security and reliability all the time. If the transmission line is disconnected or defected even only one point, the widespread outages or blackouts may occur.
Transmission lines are therefore an important component of the power system being in charge of supplying electricity from the power plants to substations and interconnecting several transmission networks. This allows power to be shared between systems, transferred in emergencies, or balanced during different peak demand periods. To ensure uninterrupted operation, all transmission towers and lines must remain in good condition and be constantly monitored.
Substation
As most power plants are located far from populated areas, transmitting electricity over long distances can result in voltage drops, high power losses, and reduced power delivery. On the contrary, transmitting electricity at high voltage helps minimize these losses and increases the efficiency of power supply. Therefore, substations are essential for adjusting voltage levels, increasing voltage for long-distance transmission to reduce losses and decreasing voltage for urban distribution to ensure safety and convenience for end users.
A substation is equipped with circuit breakers, voltage transformers, and power control equipment. It also serves as a node where multiple transmission lines connect. Protective devices are installed to isolate lines experiencing short circuits and prevent disturbances from spreading through the power system.
Switchyard
A switchyard steps up the voltage generated by power plants for transmission to substations in remote areas, reducing power loss within the power system. It consists of power transformers that increase voltage and electrical protection systems that ensure safe and reliable operation.
Insulator
As the transmission lines carry electricity that can arc across air gaps, they require insulators, devices made of insulating materials to safely suspend and support the wires. The number of insulator discs or strings used corresponds to the voltage level of the line.
Insulators serve to support the conductors and prevent leakage current from flowing to the transmission tower or causing short circuits to the ground. EGAT’s insulators are made of high-quality ceramic or glass with excellent insulating properties, strength, and durability. However, when exposed outdoors for long periods, dust accumulation can reduce their insulation performance. Therefore, regular cleaning is necessary to maintain their efficiency and safety.
Types of High Voltage Transmission Towers
Have you ever noticed that when traveling on roads in cities or rural areas, you can see various types and sizes of high-voltage transmission towers? Each type and size serves a different function depending on the voltage level, the number of transmission circuits in use, and the tower’s location. These designs ensure secure and stable power distribution, helping to maintain reliability and prevent blackouts.
High-voltage systems can transmit electricity efficiently over long distances. However, because the voltage is much higher than the 220 V used in homes and buildings, the electric current can arc through air or across insulating materials without direct contact. The higher the voltage, the farther the potential distance of an electrical arc.
At present, EGAT uses four voltage levels in its transmission system: 69 kV (used rarely), 115 kV, 230 kV, and 500 kV. In the future, if electricity demand continues to rise and transmission distances increase, voltage levels may exceed 500 kV.
Transmission towers are designed in different types and materials to match the voltage level and number of circuits in EGAT’s system. Currently, three main types are used—concrete, steel, and monopole—each selected according to site conditions and suitability of the installation area.
Announcement of Electricity Generating Authority of Thailand on Requirements for Safety in Electrical Wiring Areas
- It is forbidden for any person to perform any act that may endanger the electrical system, such as:
- Bringing materials, equipment, or machinery (e.g., cranes, forklifts, loaders, or excavators) within a distance of less than 4.00 meters from a high-voltage transmission line
- Burning sugarcane fields, paddy fields, forests, or any other materials within the electrical right-of-way
2. The construction of buildings, houses, or any other structures is prohibited within the electrical right-of-way.
3. Planting trees or crops within the electrical right-of-way is subject to the following conditions:
3.1 Within the area occupied by transmission towers, and within a radius of 4 meters from the base of the towers or from the transmission lines, no trees or crops of any kind may be planted.
3.2 The planting of trees or fruit trees that, when fully grown, exceed 3 meters in height in areas other than those described in Clause 3.1 is prohibited.
3.3 The planting of sugarcane is prohibited in the right-of-way of 500,000-volt (500 kV) transmission lines.
4. Any activity that alters the ground conditions within the electrical right-of-way, such as raising the ground level, excavating soil or wells, or constructing roads, must receive prior written permission from EGAT. If any structure, object, tree, or crop is built, created, or planted without such permission or in violation of these conditions, EGAT reserves the right to demolish, remove, or cut them as appropriate without compensation.
Requirements of the Width of Electrical Wiring Field
| Transmission line voltage (kV) | Distance from the center of the tower to each side | Including electrical wiring |
| 69 | 9 m | 18 m |
| 115 | 12-25 m | 24-50 m |
| 230 | 20-25 m | 40-50 m |
| 500 | 35-40 m | 70-80 m |
If you wish to request permission to construct or modify an area within the electrical right-of-way, or if you have any questions or observe any activities that may harm the power distribution system or endanger life or national property, please contact the nearest EGAT office or the EGAT Information Center at 1416.
National Control Center: NCC
The electricity system comprises various types of power plants, transmission lines of different voltage levels, and high-voltage substations located throughout the country. Therefore, a central agency is required to ensure that power plants, substations, and related organizations operate in coordination for maximum efficiency and benefit. This agency is known as the “National Control Center.”
The National Control Center prioritizes the interests of electricity users by focusing on system stability, reliability, and continuous power quality, as well as operational efficiency and production costs—regardless of whether the power plants are owned by EGAT or by private entities. To fulfill this mission, the National Control Center must issue operational commands fairly to all power producers in accordance with Section 87 of the Energy Industry Act, B.E. 2550 (2007), which mandates that the licensee operating the National Control Center direct power producers without unjust discrimination. Oversight is provided by the Energy Regulatory Commission (ERC).
The National Control Center plays a vital role in coordinating the production and distribution of electricity from various power plants to users nationwide. It also serves as the central coordinating body that ensures EGAT’s operations remain efficient, stable, safe, and effective—delivering maximum benefit to all stakeholders. Just as EGAT holds primary responsibility for the nation’s electricity system, the National Control Center is equally essential to its success.