Construction and Maintenance of Transmission Lines - Case Study Example

Case Analysis- Project Assessment Strategy and Procedure Student’s Name Institution’s Name 19 March 2015 Case Analysis- Project Assessment Strategy and Procedure 1.0 Introduction This paper will attempt to investigate the accidents typical to the field involving electricity transmission towers and overhead cables and how they relate to the Health, Safety and Environment guidelines. The discussion will provide a background check on the transmission towers and the overhead cables, outlining their descriptions, respective functions, manufacturing process, installation as well as how they are operated and maintained. The paper will then outline the guidelines as regards to any probable Health, Safety and Environmental accidents especially those emanating from the operations and maintenance procedures. Lastly, the discussion will use a case study involving an actual accident case involving transmission towers and overhead cables. The case study will be essential in relating the information outlined in the earlier sections of the paper especially in relation to the Health, Safety and Environment. 2.0 Transmission Tower and overhead cables 2.1 Description A transmission tower is typically a structure that is used to support overhead power cables. The tower can also be referred to as a hydro tower or electricity pylon depending on the functions served and the location. Transmission towers are used largely where high voltage AC and DC systems are involved and usually, they are often available in varying sizes and shapes. The towers are typically tall with heights ranging up to 55 meters. Transmission towers are mostly constructed using steel although other materials such as concrete and wood are used in various parts of the world (Saravanan, 2012). Overhead power cables, on the other hand, are structures used in distributing electrical energy along long distances over the land. The cables are usually supported by the transmission towers described above or in some cases, by poles. Overhead power lines are very popular for transmission of electricity in most parts of the world primarily due to their economical nature as compared to the underground cables. This is largely attributed to the lesser insulation required in overhead power cables since most of it (insulation) is provided by air. In most cases of use of overhead power cables, aluminum is the material used to make them although they can also be reinforced using other materials such as carbon, steel and glass fiber. The choice of materials used to make overhead power cables largely depends on the amount of voltage the cables are expected to carry and the distance of transmission. Overhead power cables are classified under five main categories dependent on the amount of voltage that they carry; low voltage, medium voltage, high voltage, extra-high voltage and ultra-high voltage cables (Saravanan, 2012). 3.0 Manufacturing Process 3.1 Transmission Towers As earlier mentioned, transmission towers are commonly made using steel although other materials such as concrete and wood are also used (Wareing, 2005). However, the construction (manufacturing) process of a transmission tower involves a much more complex process that puts into consideration various factors such as the areas’ climatic conditions, number of circuits (cables) to carry, the transmission voltage and environmental and ecological factors among other issues. Typically, the tower is made up of five major parts such as the peak, the cage, cross Arm, boom and the main tower body. There are five main types of towers namely the Vertical configuration, horizontal configuration, suspension towers, guy towers and tension towers. An important factor to consider when building a tower is its height. This means the tower’s height should allow for enough space for the minimum required ground clearance, the minimum permissible sag, and space required between conductors among others. 3.2 Overhead power cables Same as the transmission towers, the overhead power cables are made using steel. Steel is the popular choice since it weighs about half the weight of copper while it provides close resistance for the function. Typically, the inner core of the cables is made of steel wires which are then surrounded by another layer of aluminum alloys. The function of the inner steel core is to provide the necessary support for the outer layer that is made up of aluminum wires. The outer layer is referred to as the conductor. In manufacturing the overhead power cables, several factors are considered including the cable size and diameter. For example, larger amount of electric voltage requires cables with larger diameters and vice-versa. In other cases, this may mean using multiple cables which help to increase this diameter. These and other numerous factors are considered for the production of overhead power cables which ultimately is an essential part in ensuring that safety is observed in transmitting electric energy through them (Saravanan, 2012). 4.0 Installation process After the transmission towers and overhead cables have been designed and manufactured, they are installed in order to serve their purpose- facilitating the transmission of electric energy from the source point to other areas. In the installation process of these parts, various activities and factors are involved. For example, on top of considering factors such as the climatic conditions and the distance of transmission, the installation process involves the addition of complementary parts such as the earth wire and the insulators among others. For the tower, factors such as the base width and its overall weight come into play when installing it to determine the depth required in ensuring its stability on the ground. The foundation of the tower is also one of the important parts of the installation processes, sometimes taking up about 30 percent of the total cost of the tower. The installation process is in most cases preceded by soil data analysis, determination of meteorological data in aspects such as frost penetration, earthquakes and wind strength among others. Some of the most important steps involved in the installation (erection) of the towers include; With the help of stub setting templates, the stubs are set. Pits are excavated and lean concreted in order to achieve the correct level. The stubs are set before the faces and the diagonals are set. In installing overhead cables on the other hand, there are various ways through which this process is conducted. One of the methods of installing overhead cables is referred to as slack stringing. In this installation process, the overhead cables are pulled using the pulling lines before being threaded through the stringing blocks. Additionally, the conductors are then pulled while ensuring that there is a very minimal tension incurred in the process. Another common method of installing overhead cables is referred to as the full tension stringing. In this method, the overhead cables and the conductors are placed in very high positions that ensure that no obstacles are able to reach them. Another method of installing overhead cables is by use of helicopters which is considerably expensive than the rest. This method is mostly used where the terrain is not favorable for methods explained above. Nevertheless, this method despite being expensive is not as efficient and is considered impractical in most cases (Electrical Engineer Portal, 2015). 5.0 Operation and maintenance Installing the transmission tower and overhead power cables is a crucial but not the last step towards electricity transmission. These parts of an electricity system are certainly prone to wear and tear following their operations and thus maintenance is an essential part if they are to provide sustained service. One of the most common way through which both the transmission tower (especially the steel-made) and the power cables wear out is through rusting and corrosion. Rusting and corrosion eat away the tower especially in parts that are in contact with the ground or if there is an existing air pollution that can be a source of a corrosive acidity. Maintenance of these towers from corrosion and rust entails various practices such as galvanizing and painting activities that enhance their longevity. Painting using rust-inhibiting coating can especially be a useful method of tower maintenance. Other areas of maintenance include loose bolts, bent parts, chipped insulators and bad condition of the ground wire among others. The maintenance of these parts will involve either repairing or overall replacement if they are worn out beyond repair. The painting process may entail various steps such as identification of rusted and parts that probably brown in color. The parts are then sandblasted to remove the loose rust before applying a coating or paint. Typically, painting a transmission tower entails two steps with the first step involving applying an undercoat or the first layer (primer). Additionally, the second layer and probably the final one referred to as the finish coat, is applied a few days after the primer is applied. In both cases, painting should always start at the top of the tower down to the ground which is essential in avoiding interfering with the coating (Saravanan, 2012). Overhead transmission wires on the other hand are also prone to corrosion and rusting which are major downsides to their longevity and durability in the long run. In cases where the power cables corrode beyond repair, they are changed in order to ensure that the corrosion does not interfere with their efficiency. On the other hand, the uncoated overhead power cables are sometimes prone to coming into contact with vegetation such as trees and thus leading to electrocutions which can damage the wires. To avoid these incidences, the relevant professionals are required to always keep watch of any tall vegetation (trees) which are enough to reach the cables and consequently trimming them. It is also necessary that the area beneath the overhead power cables are avoided altogether as far as planting tall vegetation is concerned. In cases where cable bundles are used, anti-friction ball bearings should be included in order to reduce the required tension that is necessary for facilitating sagging and stringing. In ensuring that the cable bundles maintain a similar tension history, the conductors can be pulled using a single pulling line. Finally, other forms of maintenance include the use of helicopters in cleaning the insulators along the power cables as well as replacing the worn out spacers. In cleaning the insulators, a qualified technician in a helicopter flying over the insulator string directs a nozzle releasing water on the insulator thereby cleaning it. This facilitates its (insulator) efficiency in providing the required insulation functions on the power cables. On replacing the spacers, a technician in a helicopter is capable of using bare-hand work methods to replace the spacers. On top of replacing the spacers, the technician is also able to strengthen the conductors in the process. 6.0 Health, Safety and Environment instructions in Operation and Maintenance As seen in the section above on operations and maintenance of transmission towers and overhead power cables, the practices involved certainly pose a risk to the technicians performing them as well as serving as potential environmental hazards. This has prompted to formulation of guidelines (instructions) under which these operations are based upon in order to lower these categories of hazards which have are common in this field. According to Health and Safety Executive website, one of the main sources of casualties in the electric transmission field is the accidental contacts with a live overhead power cable. This mainly takes place where a person operating a tall machinery or object touches the overhead cable which results in an electrocution and in most cases death. In some cases, getting close to a live wire carrying very high voltages is enough to kill through a flashover that it causes to the person. Therefore, before getting ahead with any activity in the vicinity of overhead power cables, there are necessary guidelines that can be of help in evading such accidents (HSE, 2015). Avoidance- this entails seeking an alternative to working near an overhead power cable, for example, by shifting operations to a different location. This ensures that any tall materials in use are free from making contact with the cables. Diversion- in cases where it is possible, one can seek to have the overhead power cables diverted away from the area of operations. This is essential for ensuring that the area is isolated from potential danger of making contact and ultimately electrocution. Control access to the power cables- this can be achieved through erecting barriers that prevent close approach and possible contact by the persons working in an area close to overhead power cables. Exclusion- all operational machines and objects tall enough to reach the height of the overhead cables should not be taken near the lines. Modifications- in cases where there exists a risk of tall vehicles such as cranes and excavators coming into contact with power cables, addition of physical restraints can be suitable for preventing them from reaching the cables. Supervision- qualified personnel should always supervise operations that are high-risk as regards the field of electric use in a working environment (HSE, 2015). 7.0 Case study- Painters burnt while moving a tower scaffold This case has been documented on Health and Safety Executive website outlining how workplace can be a source of electrocution risk while also providing direction on how this can be handled. In the case study, two employees experienced body burns after the tower scaffold they were carrying came into contact with an overhead power cable carrying 33000 volts. According to the UK law, the body, mandated to deal with such issues prosecuted the company following the various laws respective to similar cases. Under the law, the company had failed to follow the following laws; Health and Safety at Work Act of the year 1974, the Management of Health and Safety at Work Regulations of 1992 and the Electricity at Work Regulations of 1989 (HSE, 2015). The case study further documents the interpreted version of how the company in question had failed in following these laws. First, the company had failed to conduct a sufficient risk assessment necessary for such work. Additionally, it had also failed to prevent the employees from the risky working environment while clearly aware of the high potential posed by the environment. In response to this negligence, the case study outlines the suitable actions that the company should have undertaken towards preventing this tragedy. First, it was necessary for the company to conduct a sufficient risk assessment on the working environment of its employees in order to identify all the risks encompassed in it and thus formulate the necessary control measures that would consequently lead to reduced risks. Additionally, the company should have implemented the control measures while also providing the necessary training to its employees concerning the potential threats in the working environment. This would have been necessary for enlightening the employees and probably enable them avoid exposure to such injuries (HSE, 2015). 8.0 Conclusion The paper has outlined various guidelines and instructions in regard to prevention and handling of accidents related to transmission towers and more commonly the overhead power cables. The discussion has identified major causes of these accidents while also outlining the necessary measures that ultimately come in place to prevent the occurrence of accidents especially in a working environment. The paper has also highlighted various guidelines that can be used to achieve a more healthy and safe working environment especially in regards to operations and maintenance. The paper has concluded by highlighted a relevant case study that involved risks posed by overhead power cables in a working environment. References Electrical Engineer Portal. (2015). Guidelines For the Construction and Maintenance of Transmission Lines. Available at http://electrical-engineering-portal.com/guidelines-for-the-construction-and-maintenance-of-transmission-lines (accessed 19 March 2015). HSE. (2015). Painters Burnt Whilst Moving Tower Scaffold. Available at http://www.hse.gov.uk/Electricity/overhead/painters.htm, (accessed 19 March 2015) HSE. (2015). Overhead Power Lines. Available at http://www.hse.gov.uk/electricity/information/overhead.htm (accessed 19 March 2015). Saravanan, R. (2012). Transmission Power. [slides]. Available at http://www.authorstream.com/Presentation/sarankvr-1216390-transmission-tower/ (accessed 19 March 2015). Wareing, B. (2005). Wood pole overhead lines. London: Institution of Electrical Engineers. Read More