Collect the information on components of transmission line.

 

Name of the activity

Collect the information on components of transmission line.

Introduction

 The term Transmission Lines broadly refers to overhead transmission lines and underground cables. The key function of a transmission line is to transfer bulk power between generation sources and load centres. In India, generation voltage is generally 11 kV but for power transmission 33 KV, 66 KV, 110 KV, 132 KV, 220 KV, 400 KV and 765 kV are used. Transmission voltage in India (highest) is 765 KV AC and these lines are erected by Power Grid Corporation for interstate connections throughout India.

Transmission Lines are made up of various components, namely poles, lattice structures, conductors, cables, insulators, foundations and earthing systems. These components are described in more details below—

Transmission Lines Components

Ø Transmission Line Structures

The primary functions of transmission line structures are to provide mechanical support to conductors. This is achieved by maintaining mechanical integrity without permanent structural deformation under ultimate load conditions whilst preserving structure geometry to retain operational electrical clearances under prescribed serviceability and ultimate load conditions.

 

Secondary functions of transmission line structures are to:

a) Ensure safety of people and the environment;

b) Maintain structure geometry to preserve maintenance-safe approach distances for serviceability and ultimate load conditions;

c) Provide an electrical path to earth for fault currents; and

d) Provide a whole-of-life cost-effective service.

 Structure types include free-standing and guyed:

a) Lattice towers / masts;

b) Steel tubular poles;

c) Stobie poles; and

d) Concrete poles.

 

Typical foundations of transmission line structures are:

a) Bored piers;

b) Mass concrete;

c) Driven / cast in-situ piles;

d) Soil / rock anchors; and

e) Special Foundations (e.g. raft foundations).

 

Ø Transmission Line Conductors

The primary function of transmission line conductor systems is to transfer electrical power between designated locations, within prescribed performance, operating and environmental conditions. Secondary functions of transmission line conductors are to: a) Maintain electrical safety and minimise adverse effects on the environment; and b) Provide a whole-of-life cost-effective service.

 

Ø Transmission Line Insulators

Transmission line insulation has two primary functions:

a) To insulate energised components from earthed structures at rated operating voltages and specified switching and lightning impulses; and

b) To support the conductor system up to ultimate mechanical load limits and transfer the mechanical loads to structure.

Transmission line hardware has four primary functions:

a) To support the Insulator system up to electrical load limits;

b) To support the Insulator system up to ultimate mechanical load limits;

c) To provide effective attachment interface between Conductor and Insulators to securely transfer loads to the structure; and

d) To provide a whole-of-life cost effective service.

 

Ø Transmission Line Earthing

The primary functional requirement of a transmission line earthing system is to:

a) Provide an electrical path for lightning and fault currents to earth, to ensure safety of people, assets and the environment;

b) Ensure that faults are cleared within the NER time limits, transmission line components are not damaged, and the network performance (due to lightning) is within agreed NER limits; and

c) Provide an earth (i.e. zero) potential reference to ground under normal circuit conditions for the dissipation of leakage currents.

Secondary functional requirements of a transmission earthing system for its design life are to:

a) Maintain electrical safety and minimise adverse effects on the environment;

b) Provide an effective technical solution; and

c) Provide a whole-of-life cost-effective service.

 

Transmission Line Earthing relates to:

a) Aerial earthing – this sub-system includes shield-wire and OPGW and its various supporting hardware and fittings (strain assembly, suspension assembly, spark-gap insulators, vibration dampers, joints and marker balls);

b) Ground level earthing – this sub-system includes buried earth stakes, earth bounds PVC cable, copper strap), cable lugs, fasteners and clamps. This earthing sub-system forms a dedicated electrical connection between the structure and the soil surrounding it. This is in addition to the electrical connection provided by the embedded structure / foundation and soil; and

c) Communication hardware – this sub-system includes the interface fibre hardware for OPGW assets. This includes fibre splice boxes, fibre termination boxes, etc.

 

Ø Transmission High Voltage Cables

The primary functions of transmission high voltage cables is to transfer electrical power between designated locations, within prescribed performance, operating and environmental conditions and to insulate energised components from earthed structures at rated operating voltages and specified switching and lightning impulses.

Secondary functions of transmission high voltage cables are to:

a) Maintain electrical safety and minimise adverse effects on the environment;

b) Provide electrical insulation; and

c) Provide a whole-of-life cost-effective service.

 

The high voltage cable components are:

a) Cable and accessories including joints, sealing ends, link boxes, partial discharge detection equipment;

b) Condition Monitoring System / Distributed Temperature Sensor; and

c) Cable trench, joint bays, link box equipment pits, support structures, expansion chambers.