Practical experiences as an electrical engineer from rural electrification

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

T/D process

Survey

Design

Construction

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 (Aluminium 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

Data sheet

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

Comparison between conductors

Poles

Voltage level

230V

400V

11, 33kV

Insulator types

Shackle Insulators --Supported(Clamped)by D-Iron set which is a clamp made out of galvanized steel

Shackle Insulators of suitable voltage ratings upto 1000V OH Line

Shackle

S. No

Size

Dimensions

Weight

Corresponding conductor

1

Small

55 mm x 55 mm

200 gm

Squirrel, service wire

2

Medium

75 mm x 90 mm

600 gm

Gopher, weasel and rabbit

3

Large

100 mm x 110 mm

1300 gm

Dog

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