Hello, welcome to this topic on green field construction of overhead lines part 1. At the end of this topic, you will be able to describe overhead distribution lines, list the prerequisites for the commencement of overhead line construction, list equipment and tools required for pit excavation for poles, explain manual excavation for pole erection, and explain mechanical excavation for pole erection. Let's start off with overhead line construction. Distribution lines generally consist of overhead distribution lines. That is, power lines hung on poles and underground distribution lines. That is, cables buried in the ground. Most of the distribution lines are overhead lines, but recently the amount of underground distribution lines has been growing. Distribution lines consist of MV lines, transformers which reduces the voltage from high to low, LT lines and service lines and energy meters which is used to measure the power consumed. Overhead power lines are typically more economical but they are susceptible to damage from wind-borne tree branches, debris and heavy wind, rain, etc. There are different types of execution of various activities like manual execution and mechanized execution. In the upcoming flow of the topics, we will understand each type in detail. In the forthcoming sessions, we will be going through the components needed to build overhead lines. Now, we will see how these items are being installed and what are all the precautions and steps are needed to ensure a proper installation of them. As we move forward, let's look at the prerequisite for the commencement of overhead line construction. They are as follows; Technical Specification and Rural Electrification Corporation Limited guidelines, approved survey drawings, underground utility network detail is given by the local administration, approved safety and quality procedures, permissions from agencies along the route as applicable, availability of materials as per bill of materials, availability of tools and tackles and required machinery. Let's start off with the various types of poles. Pre-stressed concrete poles. It comes in various heights, like eight meter, 8.5 meter, nine meter, and 10 meter. From the views you can see that the front view gives you the bottom bit, middle bit, and top bit of the pole. The side view gives you the thickness at the bottom as well as at the top of the pole. There are three plans provided and they are the top plan, mid plan, and the bottom plan. The image shown here provides the isometric view of the poles cast and stacked accordingly. Let us see the next type of pole. Rail pole. This comes in three heights, nine meter, 11 meter, and 13 meter. The selection of the pole depends on the location of usage. Say, if the installation of the pole is on the main road with the single chromosome, then the pole of nine meter can be selected. In case of any road crossing, we go with 11 meter or 13 meter pole. Where we have double circuits, 13 meter pole will be used. Next is the RS Joist type of pole. RSJ poles stands for rolled steel joist poles. This basically comes in two heights, 11 meter and 13 meter. Another type is the steel tubular type of pole. These types of poles are mainly used for lighting purposes. However, as and when it is used for distribution, these poles are used in LT lines where the height varies from seven meter to 16 meters in height. Here is the matrix which provides the detail of the type of the pole which can be used and what should be the length of the pole depending upon the voltage of the line, circuit level, and maximum span. Let's see an example here. If you want to use a pre-stressed concrete pole of eight meter height, you can use it in either 415 volt or 240 volt, single or double circuit lines. The maximum span permissible for this type of line is 67 meters. Similarly, if you want to go for a rail type pole, we can use it in a 33 kV line in a double circuit with the span of 67 meters. Now we will discuss on the approved survey drawings. Based on the survey drawings and the conducted survey, the required materials need to be estimated and procured in the full set before commencement of this execution works. The work procedure and the relevant standards need to be referred to before the commencement of works. The approval from the competent authority needs to be arranged for the finalized route. Any changes from the initial survey need to be clearly brought out in the final drawings. Final approval survey drawings need to be available for the commencement of the works at site. The following activities are to be performed in order to carry out the construction of distribution overhead lines. With reference to the approved survey drawing and after completion of the check list points, activities are to be started. Marking pit location, and pit activation for poles. Check depth, dimension of the pit, and place the concrete slab or stone as a base. Inter carting of the pole to the location, installation of pole and aligning up to the concreting as and where required, installation of guys up to the concreting as and where required. It is clearly explained in the forthcoming topics. Mounting of structures and poles V cross arm, DP structures, equipment support structure, etc are to be made. Complete the earthing activities for each and every pole. Mounting pins on the suspension poles. Cut point to cut point inspection. Paving the conductor, making up and hoisting insulator and a conductor at one end of the cut point. Stringing the conductor and connecting at the other end of the cut point. Check for sag ground clearance and line clearance. Binding the conductor with the pin insulators after installation of insulators. Installation of components in a sequence from top to bottom as and where required. Crossings completion as and where required. Guarding completion as and where required. Let's learn about the pit excavation for poles. The following are the equipment and tools required for pit excavation for poles. Spade with wooden handle. Crowbar with insulation cover, augur as per requirement and live cable detector for underground utility assessment. This is as per requirement. Next, let's find out the pre-execution checks to follow before digging a pit for poles. Take shutdown of nearby overhead if required and underground utility. Approved survey drawing shall be available at the location. Obtain all work permits from the competent authorities before starting of the work. Ensure required personal protective equipment are available with all the workers. Visual inspection of required tools to be done. Verification of location of poles with respect to the survey drawings. Let us discuss the actual steps involved in manual excavation for pole erection. Firstly, identify the type of soil and the groundwater level before commencing the excavation at the place excavation is to be made. Use a dewatering pump or bucket in case of the presence of groundwater at the level of excavation for dewatering purposes. Now, collect complete information on the underground structures such as water pipelines, sewers, gas mains, electrical conduit systems, and other civic facilities from the local authority before doing the excavation work. Use cable detector to check the existence of underground cables. Depth of the pole pit shall be based on pole type and pole length refer to the approved drawings. Ensure step cutting for easy access and lifting up the pole during the erection. The fastest step is on one meter and the second step is on two feet. Or as per the drawing, ensure slope on one side of the pole pit area that pole must be erected. Safety precautions. Stack the excavated soil at least one and a half meter away from the edge of the excavated pit or half of the depth of the pit, whichever is more. Ensure hard barricades are provided and warning signs are displayed so that unauthorized entry is restricted, especially while working near busy roads and highways. Use a dewatering pump or bucket if there is any source of seepage water to avoid soil collapse. Do not carry any vertical cut to avoid soil collapse. Do not carry any undercutting which may lead to the collapse of the sidewall. Ensure hard barricading of an excavated area with a warning saying if the pole erection is not completed on this same time or day. Never leave excavated pit without providing barricade or hard covering. Now let's learn the mechanical excavation by augur. Its driller. Following are the steps involved in mechanical excavation. Check the condition of the mechanical attachment of the tractor. Check for the availability of the underground utilities. If available then with extreme care go for a manual excursion or shift the location in consultation with the competent authority. Check for the overhead line passing over the working location, take shutdown if available, and follow the shutdown procedure. Make sure that no one is standing near the augur of the machine while drilling. Barricade the working location to restrict unauthorized entry. Check length and diameter of the augured pit using a template whether it is as per required specification for the proposed pole or not. Now, let us summarize what we have learned over OH line construction. Manual excavation for poles. Mechanized the excavation for poles. Importance of barricading cable detector, work permits, safety requirements for excavation of poles.
