LOCATION A: Gubbalala

Tower 1A

Lattice structured ‘B’ Type Horizontal

Tension tower.

Line to line voltage : 220 KV

Line to ground voltage : 127 KV

Insulator material : Porcelain

No of insulators used : 14

Tr. line conductor : ACSR –

Coyette

As additional joints of conductors

using T clamp and Parallel groove clamp

was seen.

Arching horns were provided for

electrical stress distribution and to control

corona.

Tower 2A

Lattice structured Truncated Horizontal

Tension tower.

Line to line voltage : 66 KV (78

KV lines but now used for 66 KV

transmission)

Insulator material : Porcelain

No of insulators used : 5

Tr. line conductor : ACSR –

Coyette

Surge arrester was mounted on the

top. Armour grounding cables were seen.

Rain shades were used for protection

purpose.

Tower 3A

Lattice structured ‘B’ Type Horizontal

Tension tower.

Line to line voltage : 66 KV

Line to ground voltage : 38 KV

Insulator material : Porcelain

No of insulators used : 5

Tr. line conductor : ACSR –

Coyette

Tower 4A

D type tension tower

Line to line voltage : 220 KV

It is a double feeder tower. The

vibration damper was seen in detail. A

modified double feeder tower of 66 KV was

also seen.

Tower 5A

Spun pole made of RCC

Line to line voltage : 11 KV

Line to ground voltage : 6.35 KV

Insulator material : Porcelain

(Disk type)

No of insulators used : 1

Tr. line conductor : ACSR –

Coyette

It had lightning arrestors of capacity

9 KV. There was group operating switch

(single break) and DO fuses. The

transmission lines from the tower were

connected to an 11KV/230 V transformer at

a residence.

LOCATION B: Sommanahalli

Tower 1B

Lattice structured ‘A’ Type Vertical

Suspension tower.

Line to line voltage : 220KV

Insulator material : Porcelain

No of insulators used : 14 X 2

Power carrying capacity : 400 MW

Tower 2B

Vertical, self-sustained, lattice structured B

type tension tower

Line to line voltage : 400 KV

Insulator material : Porcelain

No of insulators used : 23 X 2

Type of conductor : Bundled

Power carrying capacity : 1600MW

Tower was numbered as Power grid

115 NLM - BGL

For corona discharge corona rings

were used. In the bundled conductors

spacers of approx 10 inches were used to

separate each conductor.

LOCATION C: Kaggalipura

Tower 1C

Transposition Tower Horizontal self-

sustained, lattice structured

Line to line voltage : 400 KV

Insulator material : Glass

No of insulators used : 23 X 2

Type of conductor : Bundled

Earth wire : Crimped and

bolted -4 sides

Tower is numbered as NTPC 0788

GTY – BNG

The transmission lines in this tower

were transposed. The YRB phases were

transposed as RYB. For corona discharge

corona rings were used. The spiking rods

were provided at the top for protection.

LOCATION D: Kothanur

Tower 1D

Truncated Horizontal lattice structured B

type tension tower

Line to line voltage : 66 KV

Insulator material : Porcelain

No of insulators used : 5

It is a double circuit tower. The

tower is truncated because of 220 KV line

crossing.

Tower 2D

Special design tower Vertical, self-

sustained, lattice structured

Line to line voltage : 66 KV

Insulator material : Porcelain

No of insulators used : 5

Because of insufficient space the

tower is designed for 4 X 4 ft with the

member dimension of 150 X 150 X 12 mm.

It is having 3 phases of double circuit on

the same side.

Tower 3D

Special design dead end tower

(Anchor tower) – vertical self sustained

lattice

Line to line voltage : 66 KV

Insulator material : Porcelain

No of insulators used : 5

The height of the tower is 35 ft

(approx). The foundation is also a special

design for this tower. There are 18 cables in

which 9 cables for 3 feeders and 9 cables for

armour earthing. Cable termination unit was

also seen. The tower was provided with 6

surge arrester on metallic platform for

protection.

Additional inferences:

Pole 1:

Type : LV RCC

pole with guy wire (11 KV)

Insulator material : Porcelain

(strain type)

The guy wire had a break insulator.

Pole 2:

Type : 11 KV (RCC

pole)

Insulator material : Porcelain

(Pin type)

Transmission line conductor : ACSR –

weasel

There were 5 transmission lines (3

phase + 1 neutral + 1 street light connection)

separated by fiber glass separator.

Inferences from observations:

Tower structure: Almost all the towers are self-sustained with lattice structure configuration. Self-

sustained towers are self-supporting in all sorts of mechanical and environmental impacts on them.

Earth conductors:Earth conductors are generally galvanized iron wires are run on the top of the

tower to protect the line from lightning surges. Modern earth wires are made of optical fibers, OPGW.

Tower Earthing: All the towers are generally earthed at their limbs. It can be a Pipe Earthing

crimped and bolted.

Insulators:Insulator disks are generally made of Porcelain and Glass. Glass being more

expensive and more reliable is used for higher voltages. Each insulator disk is designed to

withstand a voltage of 11kV. The number of insulator disks in a string depends on the voltage level of the transmission line. Eg: The number of insulator disks required for a 220kV can be calculated as under,

Phase to phase voltage: 220kV

Phase to ground voltage: 200kV/√3 = 127 kV

Number of insulator disks required = 127/11 = 11.254 = ~12

Generally more than the required numbers of disks are used in the string for reliable protection if one of the disks is punctured. Therefore for a 220kV line 14-16 disks are used in a string.

Arcing Horns:Arcing Horns offer protection against corona discharge, they distribute electrical

stresses in the insulator string.

Corona Rings:Corona Rings distribute electrical stresses on the conductors terminating at the

tower insulator string. They are generally made of High grade aluminum.

Jumpers:Jumpers are used to connect the conductors that are terminating and leaving at the

tension tower. They are 15 ft long generally. They run through T – clamp and PG – clamp.

T- Clamps and Parallel Groove clamps:T- Clamps and PG clamps serve to take jumpers from the terminating conductor

to the leaving conductor at each tension tower. These are made of High quality stateless steel.

Vibration Dampers: Made up of Carbon Steel, damp the mechanical vibrations of the conductor due to

wind, avoid structural damage to the transmission lines.

Surge-Arresters: The purpose is to divert lightning induced transients safely to ground through

property changes to its varistor in parallel arrangement to the conductor inside the unit

Spacers: The spacers are used to separate conductors in bundled conductors

Indication plates:Colored plates give information about the phase sequence. Sometimes other

indication plates are used to indicate voltage levels.