Rural Electrification
Overview of topics
• Survey of OHL
• Design of Transmission and distribution system
• Cost Estimate
• Construction
• Some pictures
Softwares you need
• Autocad
• MHP(Microhydro) design aids
• MS Excel
• Optional:
• ETAP, Power world simulator, Netbas
Transmission and Distribution (T& D)
• Types
• Suspended Overhead on Poles (Overhead Line)
• Buried Cables (Underground Cable) OH Line (Features)
• Less Expensive
• Frequent Maintenance Required
• Less cost per maintenance
• Does not look aesthetically good in dense locality
• Not preferred in areas which experience heavy snowfall
• UG Cable
• Costly Installation (if done per standard 6 times costly compared to OH)
• Less Maintenance
• Higher cost per maintenance
• Highly desirable in densely located areas
• Obvious choice for areas which experience heavy snowfall
• ACSR (Aluminum Conductor Steel Reinforced) conductors are the norms of the day (as against hard
drawn copper which were used in earlier days)
Components used
• Transformers
• Poles
• Insulators
• Lightning arrestors and Earthing plates
Transformer
• ONAN type
• Step up transformer near to generating station of high KVA rating and stepdown of smaller KVA ratings
near to load centers
• Sizing is done taking load demand and dividing by suitable power factor.
Conductor
• ASCR type
• Mainly Dog, Rabbit, Weasel, and Squirrel
• If dog is on phase, rabbit is taken in neutral ;similarly if rabbit is in phase weasel in neutral and so on
Disc insulator
• Disc Insulators along with suitable tension Set are used for deadening a line at 11kV or higher.
Pin Insulator
• Pin Insulators are used for straight runs of 11kV Line
Stay sets
• Stay sets to support poles
• Suitable Stay sets are provided at first pole, at line end, at all poles set at an angle and at every fifth
pole even if the poles are in a straight line
• Two types 16mm dia for LT and 20mm dia for HT
Lightning arrestor and Earthing
• Lightning Arrestors to protect lines from Lightning
• 0.5kV ,ZnO (Gapless)Arrestors for 400Volt Line
• 12kV, 5kA ZnO(Gapless) Arrestors for 11kV Line
• Placed every 500m and on junctions and last(end) points
• Drop Out (DO) Fuse to Protect Transformers from Over Current
Earthing system
• 600mm*600mm*3.15 mm copper plate is used for earthing purposes (weighs around 10kg)
• Plate is connected with 8SWG copper wire(4.06dia)
• Earth Resistance value
Service wire
• Aluminum cable connecting from pole to home
• Generally flat twin sheathed cable is used
• Wrapped once or twice around the pole to reduce stress
• Distance is taken average of 30m
Survey
• Equipment required:
• Total power station(TPS), GPS receiver or measuring tapes and compass
• Steps:
• Start from generating station
• Take the shortest and straight route for transmission line
• Fix the position of transformer
• Transformer should be positioned at the center of load as far as possible so as to reduce the voltage
drop • Measure distribution lines length in similar way
• For distribution, within a radius of 30m service wire, otherwise extend the conductor
• Note all the lengths, nodes and drawings on your notebook
Design of Transmission system
• Selection of voltage level
• 230/400/11,000/33,000Volts
• Balanced loading is considered
• Whole power system is radial
• Design Criteria of OH distribution line:
• Maximum allowable voltage drop at the farthest end shall not exceed 10%
• Find optimum line voltage using 𝑉 = 5.5 𝑙 1.6 + 𝑃 100 0.5 where l=length(kms) and P=Power in MW
• Take the nearest standard voltage
• Find line current using 𝐼 = 𝑃/ 3*V*pf
• Select the ambient temperature(25degrees)
• Select the allowable range of temperature and find the resistance at new temp value.
• Use the relation: R𝑡 = 𝑅20 ∗ (( 1 α +𝑡) /( 1 α +𝑡20)) Where R20= resistance of conductor at 20degrees
• Calculate the total resistance multiplying by length of line
• Find efficiency using relation:ῃ = 𝑃 𝑃+3∗𝐼 2∗𝑅 ∗ 100
• Model the transmission line as short and find the receiving end parameters
• 𝑉𝑠 𝐼𝑠 = 1 𝑍 0 1 ∗ 𝑉𝑟 𝐼�
