NEW TECHNOLOGY CONDUCTORS
1.0 Indian Power Transmission Scenario
PRESENT SCENARIO (as on 31/12/2017):-
Installed generation capacity: 330,860 MW
Transmission network: 384,000 circuit km
13th Plan (2017-22) TARGETS:-
Additional Generation Capacity: 1,85,000 MW
Additional Transmission network: 1,00,000 ckt kms.
2.0 Indian Power Transmission Challenges
ROW constraints:-
High Population Density
Utilization of Land for infrastructure development
Forest/ Ecology conservation
Time constraints:-
Rate of growth of demand is at an all-time-high
Meteoric rise in the number of independent power producers/ renewable
generation projects
Resource constraints :- India, being a developing country, needs to plan effective
utilization of the available financial & non-financial resources.
3.0 New Strategies/Technologies To Meet The Challenges
Bulk Power transmission systems:-
High Capacity (Quad/Triple bundle) 400 kV Transmission Lines
400 kV Multi-circuit lines
500 kV HVDC & 765 kV transmission systems
800 kV UHVDC & 1200 kV UHVAC systems
Capacity Enhancement of Existing facilities
Uprating
Upgrading
4.0 High Capacity Conductors
Characteristics:-
High temperature operation ̴ 150-250 deg C
Current Carrying capacity: 2 - 4 times
No appreciable increase in Sag beyond a certain temperature called Knee
Point temperature. Knee point temperature in such conductors, lie within their
operating range.
Utility & Advantages:-
Uprating of existing lines so as to enhance power transfer capacity of existing
corridor.
Construction of new high capacity lines
Reduction in conductor bundle size so as to reduce tower weight & associated
complexities- esp. in case of Pole structures & Multicircuit towers.
5.0 High Capacity Conductor Types
High Temperature Conductors
i) TACSR (Thermal resistant Aluminium alloy Conductor Steel Reinforced)-
Outer layers: Thermal resistant aluminium alloy
Can be operated upto 150 deg C
ii) Higher conductivity AAAC (AL59 or eqvt)
AL59 alloy (Sweden, Norway), 1120 alloy (Australia), EHC alloy
(UK)
59% conductivity (in place of 53% for AAAC)
High Temperature Low Sag Conductors
i) Aluminium Conductor Steel Supported Conductor (ACSS)
Fully annealed Aluminium strands
Can be operated at 200-250 deg C without loss of strength
Improved Conductivity
Better self damping characteristics
Used extensively in some countries such as in USA
Require special care during handling & suitable tools & tackles recommended
during stringing
ii) INVAR Conductor (STACIR)
Aluminium strands of thermal resistant aluminium alloy
Core is made of alloy Iron – Nickel having low coefficient of
thermal expansion
Can be operated up to 210degC
Handling & stringing similar to conventional ACSR
iii) GAP Conductor
Aluminium strands of thermal resistant aluminium alloy
Small gap maintained between steel and Aluminium layer
Can be operated at temperatures up to 210degC
Require special stringing techniques
iv) Metal-matrix composite reinforced conductor
Aluminium strands of thermal resistant aluminium alloy
Core is made of metal matrix (Aluminium – Aluminium
oxide fibers)
Can be operated up to 210degC
v) Carbon-fibre Composite Core Conductor
Outer layers may either consist of thermal resistant
Aluminium Alloy or fully annealed Aluminium strands
Core made of composite material (glass fiber & carbon)
and may be single or stranded
Low coefficient of thermal expansion
Can be operated up to 150- 180 degC
Require special care during handling & suitable tools & tackles recommended
during stringing
6.0 Selection Criteria & Design Aspects
i) Current carrying capacity requirements:-
Maximum under Normal Conditions
Contingency requirement
Load Factor
ii) Design Limiting conditions:-
New lines: - i) Max. conductor tension < 70% of UTS of conductor
ii)Everyday conductor tension < 25% of UTS of conductor
iii)Tension at kneepoint < 40% of UTS of conductor core
iv)Conductor Surface gradient < Corona onset gradient
Uprating of existing lines:- In addition to above, conductor selection is guided by
conductor diameter, maximum conductor tension, maximum conductor sag, etc.
of existing line.
iii) Type tests:-
Should generally be in line with International guidelines/ standards such as
CIGRE, IEC, ASTM etc.
Should validate conductor design for use upto the maximum conductor
temperature corresponding to power flow during contingency conditions
Procedure should be customized based on the construction & constituent
materials of the HTLS conductor type
iv) Installation/Stringing:-
Generally as per Instruction manual of conductor manufacturer
Conductor manufacturer should be associated during stringing
Stringing charts, etc. prepared on the basis of stress-strain & creep
characteristics obtained in type tests
Special tools/ tackles to be employed wherever applicable.
7.0 Future Prospects
Right-of-Way being a major constraint on the development of transmission
system, uprating of existing transmission lines may be preferred over
construction of new lines in the same corridor.
Since, power flow upto thermal limits are allowable in short transmission
lines, there is a possibility of constructing such lines with HTLS conductor.
Further, in lines where adequate compensation is available, twin HTLS
conductor may be used instead of Quad ACSR conductor.
Use of Twin HTLS conductors in place of Triple/ Quad conductor can also be
explored for transmission lines or line sections where multicircuit towers or
pole structures are envisaged.
