Protective Grounding Methods in Transmission and Distribution Lines
In addition to ensuring that transmission and distribution systems operate smoothly and at their disposal, they must be safe for the employees who maintain them and the living creatures around them. Protective grounding measures ensure the safety of line maintainers and surrounding creatures. So what are the protective grounding methods used in power lines? Why are they so important? Let's move on to our article for the answers and more.
Protective grounding is done to protect living things against touch and step voltage in possible situations. These precautions are taken in energy transmission and distribution lines, just like everywhere else. While it is a priority to protect the employees who maintain the transmission lines or the living creatures near the lines, it is also aimed to protect the transmission system in possible situations.
Power lines and the structures carrying these lines must be grounded safely. In particular, technical studies should be carried out on minimizing touch and step voltages.
In the following sections, we will examine the equipment used in power lines and the methods used for their grounding.
1. Grounding for Metal Transmission Structures
1.1. Steel Cage Structures
One of the structures used to transport conductors and other equipment in the electricity transmission system is steel cage towers. In steel cage towers, the grounding line is passed from the top of the tower with a large gap between the electrical transmission lines and the electrical transmission lines. In this way, grounding induction that line maintenance workers may be exposed to is reduced to a minimum.
Steel Cage Tower
1.2. Slippery Insert Steel Pole
Another type of pole used in the transmission system is slippery steel poles. This pole type consists of interlocking parts due to its structure. When grounding the pole, each steel part must be connected to the ground line. In addition, the electrical connections of the junction points in contact with the ground line should be checked regularly.
1.3. Rusted Steel Pole
Rusted steel poles are pole types that are highly resistant to weather conditions. Due to their structure, their exteriors have a rusty appearance. Contrary to its appearance, this rust-looking layer prevents air corrosion from continuing on the metal surface and extends the service life of the pole.
Protective earthing on rusted steel poles; It is achieved by connecting the lines to a copper point fixed on the pole with a grounding connection. If there is no ground point on the pole, the protective ground line is carried overhead over the pole.
Rusted Mast
1.4. Painted Steel Poles
Painted steel poles are obtained by coating the steel with special paints. The grounding process in such poles is provided by an earth connection point, as in rusted steel poles.
Painted Steel Pole
1.5. Overhead Ground Cables
Aerial ground cables are generally used for protection and grounding in high voltage lines in the transmission system. The overhead ground wires are located at the top of the tower above the conductors. The most important task of overhead cables is to protect conductors against lightning strikes. While lightning that may strike conductors or insulators may cause serious damage and losses, it may also cause extreme problems that may interrupt transmission in the area. Overhead ground cables used to prevent such situations prevent damage to the tower and conductors by transferring the lightning strike to the grounding system.
Overhead Ground Cables
1.6. Ground Grounding
During the construction of steel towers that will carry conductors, ground grounding must be done very well before other protective grounding measures are taken. Necessary connections of the ground rod to be used must be made to the ground rods on the construction site.
Protective Grounding Methods in Transmission and Distribution Lines
A cluster rod is used when grounding wooden poles, which is another pole type used in transmission and distribution lines. The overhead ground cables on the pole are connected to the cluster rod fixed to the trunk of the tree pole. At the same time, the pole's own grounding line and ground grounding, if any, are connected to the clustering rod. Apart from these, the grounding lines connected to the lower sides of the insulators are also collected in the cluster rod. Thus, a holistic protective grounding is provided for the entire pole.
Kümeleme Çubuğu
Ağaç Direğin Gövde ve Zemin Topraklaması
3. Transmission Line Terminal Earth Switch
One of the auxiliary grounding equipment used in transmission lines is the grounding switch. The grounding switch is used to switch the leakage current that other grounding equipment may be exposed to. However, as we mentioned in the first sentence, since it is an auxiliary equipment, it would be insufficient to use it alone in the grounding system.
4. Grounding in Distribution Lines
Alçak gerilim (1000 volt ve altı) dağıtım hatları 3 faz ve 1 nötr iletkeni olmak üzere toplam 4 iletkenden meydana gelir. Bu tip dağıtım hatlarının topraklamasında; 3 faz iletkeninin transformatör çıkışı yıldız bağlantılı ise, iletkenler direğe geldiklerinde 3 fazın ortak noktasından (nötr noktası) alınacak topraklama hattı ve nötr iletkeninden alınacak topraklama hattı direk üzerindeki kümeleme çubuğunda toplanır. Bu sayede tek noktalı topraklama yapılmış olur. Ayrıca kümeleme çubuğuna direk ve zemin topraklamalarının bağlantıları da yapılarak dağıtım hattının ve direğin bütünsel olarak topraklaması yapılmış olur. Yüksek gerilim dağıtım hatlarında ise 3 faz iletkeni bulunurken nötr iletkeni bulunmaz. Bu tip iletkenlerin topraklanması da alçak gerilim dağıtım hatları ile aynı şekilde, 3 iletkenden alınacak topraklama hatları direk gövdesinde kümeleme çubuğunda birleştirilir.
Grounding of Low Voltage Distribution Lines and Line Maintenance
5. Surface Equipment and Vehicle Grounding
During maintenance operations on transmission and distribution lines or environmental elements or during the installation stages of the lines; Employees must ensure that the equipment they use is grounded. Power lines should not be intervened with any equipment without protective grounding. Apart from these, care should be taken to connect the grounding of trucks, basket vehicles or large construction vehicles to the grounding system in the construction site. It is essential to carry out grounding checks before starting line maintenance in order to protect employees from step and touch voltages that may occur in possible situations.
5.1. Air Tools
It is important to provide protective grounding of crane arms and baskets in cranes and basket vehicles used in interventions and maintenance on power lines. The line maintainer should check the ground connections before starting maintenance. In addition, the protective bars where the line worker will intervene in the lines must be grounded.
5.2. Vehicle Grounding
Equipotential grounding mats are used to ground basket vehicles used in power lines. Grounding mats are placed under the metal balancing legs of the vehicle and fixed to the ground. One end of the mat is connected to the grounding connection of the vehicle, while the other end is connected to the grounding system of the field. In addition, employees who are in contact with the vehicle must do their work by stepping on the grounding mat.
If a grounding mat is not used for vehicles, in case of possible arc formation, the arc will flow from the metal balancing feet of the vehicle to the ground. Once it flows into the ground, it will cause dangerous levels of touch voltage on the ground and pose a risk to workers. That's why a grounding mat placed between the metal legs of the vehicle and the ground will prevent the occurrence of such risks.
6. Grounding of Insulated Cables
Protective grounding is required for insulated cables used in transmission and distribution lines, just like in structures carrying power conductors and other auxiliary equipment.
In order not to put employees at risk due to the possibility of arcing, the cable ends that appear to be de-energized (far end) should also be grounded.