Activity No. 1 PDF - Practical in Power Distribution

Practical in Activity No. 1 Power Distribution PRACTICE FOR DIGGING HOLES AND ERECTION OF POLES Structure 1.1 Objectives of Activity 1.2...

Practical in Activity No. 1 Power Distribution PRACTICE FOR DIGGING HOLES AND ERECTION OF POLES Structure 1.1 Objectives of Activity 1.2 Equipment/Materials/Facilities Required 1.3 Brief Theory 1.4 Procedure 1.5 Tabular Record of Observations 1.6 Precautions 1.7 Self Test 1.1 Objectives of Activity  After performing this activity, you should be able to  practice the technique for the erection of poles for overhead lines.  describe the safety measures to be taken during erection of poles.  understand economical and accident-free utilization of labour during erection. 1.2 Equipment/Materials/Facilities Required  Drilling Machine.  Earth auger (i.e. to drill a hole in earth), digging bars, shovels or pick axes.  Three ropes of ¾ ” diameter each and one rope of 1¼ ” diameter, and nearly 40 ft. to 50 ft. long.  X-shape wooden frame for supporting the pole while erecting,  Hoisting rig, a trunk or a skid winch, or a derrick pole.  Standard tools. 5 Practical in Power Distribution 1.3 Brief Theory After a route survey of the transmission line , the poles have to be erected, so that further action of stringing and sagging of the conductors may be undertaken. 1.4 Procedure (1) Transportation of Poles All other material can be transported easily either in a truck or a bullock cart. For poles, (though this can also be done by the above mentioned methods) it is recommended that a special trolley be made and which may be pulled either by bullocks or a tractor or by manual labour. After the poles are transported, erection work starts. (2) Preparation of the Poles for Erection After the poles have reached the site, the following operations should be completed.  Drill the Holes  Paint the pole, if not already done. (Not needed in the case of concrete poles.)  Fit the cross-arm and knee bracing  Fix up pins and clamps for insulators  If muffs are provided, they should be grouted on the poles. If not, grouting should be done later on. (3) Digging of Holes After fixing the point where the pole is to be erected, a hole is to be excavated in the ground. The depth to which the pole is to be planted is a matter, which can only be determined in the light of past experience. Roughly 1/6th of the length of the pole is planted. In the case of planting in solid rocks, the depth is less. The following table shall be a useful reference in digging holes in the ground. 6  Practical in Length of Pole Depth in Ground Depth in Power Distribution (Ft.) in Solid Earth Ground in Solid (Ft.) Rock (Ft.) 25´ – 0" 5´ – 0" 3´ – 6" 30´ – 0" 5´ – 0" 3´ – 6" 36´ – 0" 6´ – 0" 4´ – 0" 42´ – 0" 7´ – 0" 4´ – 6" 65´ – 70’ 8´ – 0" 6´ – 0"  Size at the Top and at the Bottom It should be sufficiently larger than the pole (or pole base, if used) to allow the use of tempering bars for tamping. In ordinary firm soil, pole holes are excavated by :  Hand, using digging bars, shovels or pickaxes,  Earth augers, and  Drilling machine. If the hole is dug manually it should be 3´  1½ ´ in size and should be tapered. If it is dug by an earth auger or drilling rig, it should be 9 or 10 inch diameter, depending on the size of the pole. The hole should be in the same position as the intended position of the pole at the bottom. A concrete pad of 3´ thickness may be prepared at the bottom to provide a firm base. (4) Raising of Poles Three ropes of 3/4" diameter and one of 1¼ " diameter, 40 to 50 feet long are tied near the top of the pole, with pole in the horizontal position. Then the pole is raised by about 5 to 6 feet on a wooden X-shaped frame. One or two men, depending upon the weight of the pole, should hold the 3/4" ropes in three different directions and 3 to 4 men should hold the 1¼ " rope in the fourth direction. Then the pole may be pulled by these men till it gets into the pit. A hoisting rig, a trunk or a skid winch can be used with advantage. A derrick pole can also be used with advantage. This pole being lighter, is first 7 Practical in erected, and then, by pulling the pole which is to be erected, the Power Distribution derrick pole is lowered. It becomes easy to lift the pole. Figure 1.1 : Derrick Pole Method (5) Checking of Pole Alignment As soon as the pole is erected, it should also be checked for verticality by a plumb – bob. (6) Concreting the Pole Poles should have a strong foundation, because the failure of the pole may not necessarily be due to a crack or fracture, but due to wrong foundation. If the muff is pre-cast, this is to be fitted before the erection of the pole. Then only the earth is to be tamped. It is better to tamp in more soil than comes out of the original hole to provide greater firmness. If the pole has not been fitted by a pre-cast muff, then it should be grouted by cement concrete mixture in the ratio of 1 : 2 : 4. If the hole is drilled by means of an earth auger or drilling rig then it should be grouted without the aid of a steel muff but if a larger hole has been dug, then a steel plate muff of 10" diameter, or another suitable size, depending upon the size of the pole may be used. This steel muff may be removed the after one day of the installation. The baulk should be one foot above grounded level. It is essential that this casing should be beveled at the top to prevent lodgment of water between the concrete and the pole surface. 8  Practical in 1.5 Tabular Record of Observations Power Distribution After erection of poles, record observations in the following tabular form (the data pre-filled in the ‘Data’ column is to serve as an example, and should be replaced with the actual values). Sl. Details Data Pole Pole Pole No. No. 1 No. 2 No. 3 1. Length of pole 30 ft. 2. Type of pole, whether Steel PCC/steel 3. Height above ground 25 ft 4. Depth in ground 5 ft. 5. Whether muff is provided or Yes not 6. Type of X-arm Horizontal 7. Whether angle pole or not No 8. Nos. of holes drilled 5 Nos. 9. Paint done or not Done POLE 500 500 TOP BAULK NUT WASHER 100  200  1200 (BAULK) 2 BOTTOM BAULK 300 (a) For Normal Soil (b) For Loose Soil All Dimensions are in mm Figure 1.2 : Fitting Baulk in Foundation of Pole 9 Practical in Power Distribution 1.6 Precautions  Ropes should be of the proper size.  Muffing should be provided as necessary.  One coat of paint, together with anti-rust treatment, must be done on steel poles.  Proper numbering must be put on the poles  Record of data regarding each pole must be prepared carefully.  Holes must be dig to the proper depth  Take safety measures to avoid accidents.  To have proper coordination and economical utilization of manpower, one person from the gang of erectors must be made leader, so that others work under his command. 10  Practical in Power Distribution Self Test Answer the following questions : Q.1 What procedure is used for erection of overhead line pole? Also draw a diagram for showing the erection of the pole. Q.2 Why muffing is necessary? Q.3 Give the necessity of paint on steel poles. Q.4 Why alignment of the pole is necessary? Q.5 Why proper coordination is required in the gang of erectors? 11 Practical in Power Distribution 12