This article gives brief account of conductor accessories, insulator hardware and power clamps and connectors suitable for HTLS conductor
 Due to right of way problem in the entire country, emphasis is on transferring big chunk of power through the least physical corridor. To achieve this, the conductor surface temperature has to be taken to more than 100C. The normal ACSR conductor loses its electrical and mechanical properties beyond 90C. It is therefore necessary to use high temperature low sag (HTLS) conductors.
HTLS conductors can operate up to the temperature 250C and therefore can transmit large quantity of power. It is worth noting that the ampacity of the conductor increases as the temperature is elevated.
For operating the conductors on very high temperatures, metallurgical changes in the conducting outer layers as well as the centre core has to be done. Annealing of the conducting material and coating the steel core with heat resistant material such as Galfan or using carbon core, affords high ampacity.
When the surface temperature of the conductor (HTLS) is elevated, the conductor accessories, insulator hardware and power clamps and connectors suitable for ACSR conductor cannot be used for HTLS conductor. Therefore, a technological development had to have high temperature hardware and fittings designed and developed for the manufacture. Further, thorough testing of the connectors as per relevant IEC standard is carried out. This article gives brief account of such conductor accessories, insulator hardware and power clamps and connectors suitable for HTLS conductor.
Benefits of HTLS conductorsHTLS conductors deliver higher amount of current or power at the elevated temperatures. The advantage of use of HTLS conductor is that when they are used on the towers designed for ACSR conductors, no major changes in the tower structures are required.
Even the HTLS conductors sag less and therefore afford higher ground clearance, when used on the existing lines. If HTLS conductors are used on the new line, HTLS conductors can allow higher spans and thus reduce number of towers along the route.
The weights and other mechanical properties of HTLS conductors are comparable with those of ACSR conductor. The Table 1 will give a comparative idea of HTLS conductors and Table 2 gives technical parameter of ACSS LARK conductor.
Details of HTLS conductors Before going to the subject, design and development of conductor fittings for high ampacity, high temperature low sag conductor, it is necessary to see what HTLS conductor is and how it differs in properties from commonly used conductors like ACSR and AAAC.
The conductors ACSR and AAAC are having maximum thermal rating of 90C. This means, in summer season when maximum ambient temperature is about 47-48C, the available scope to raise the temperature of these conductors above the ambient temperature is by 45C, which further limits the continuous current rating for these conductors, to satisfy this condition of maximum thermal limit of 90C.
To overcome the problem of this low thermal limit of 90C of ACSR and AAAC conductors, new conductors of high thermal rating of 200C, but with about same cross sectional area and same sag at the high thermal rating are invented, which are having continuous current rating of about double the current rating of equivalent size ACSR/AAAC conductor, but at high temperature of 180 to 200C.
There are a number of new High Temperature Low Sag (HTLS) conductors in the market designed to operate at temperatures of 200C and more. This is well above the normally accepted maximum operating temperature of 90C, allowed for the standard AAAC and ACSR conductors.
These new conductors still employ aluminium as the main current conducting medium. They have a core material inside the aluminium that provides high mechanical strength with a low coefficient of thermal expansion.
This internal core material is the main difference between conductors supplied by the various manufacturers. The new conductors are capable of carrying as much as two times the current, compared to that carried by AAAC and ACSR conductors of similar diameters without increase in the sag.
Limited experience indicates that the new conductors perform as advertised. They tend to cost two times or even more, than standard conductors to purchase and install.
Some require special handling and equipment for installation and maintenance.
When applying these new conductors, manufacturer recommended splices and dead ends shall be installed using extreme care. These tend to be the weak links in line construction and any flaws at these points will most likely lead to conductor failures.
Due care has to be taken while designing and developing conductor accessories, insulator hardware and power clamps and connectors for HTLS conductors with thorough testing of the same as per relevant IS/IEC Standard.
Design of fittings for HTLS conductor The fittings and hardware such as splice, suspension clamps, dead ends, mid-span compression joints and repair sleeves as well as PA rods, vibration dampers etc. for transmission lines, as well as power connectors for substations. Using HTLS conductor is a specialised job. It is normally accepted that, since the HTLS conductors operate at very high temperatures, they must not be connected directly to oil and or paper insulated bushings.
Therefore leads from HTLS dead end towers to equipment bushings may be constructed with a bundle of standard AAAC or ACSR conductors designed to carry the total current from the HTLS line without heating the equipment terminals beyond their normal thermal rating limits.
The new HTLS conductors are generally used for specific applications or to solve existing problems. For example, if reconductoring of an existing line is required for load purposes and installing a larger conductor will require extensive structural work to increase strength and/or height, the HTLS conductor may be considered. A cost analysis can be evaluated between cost of the HTLS conductor and the cost of the structural modifications.
For example, Panther ACSR conductor is replaced by ACSS Lark conductor for 132 KV line, using successfully designed and developed conductor fittings such as splices, suspension clamps, dead ends, mid-span joints and repair sleeves as well as PA Rods, vibration dampers etc. suitable for the ACSS Lark conductor, which is having diameter 20.27 mm, aluminium area 201.4 sq.mm. and weight per km as 925 Kg. UTS of the conductor being 100.4 KN and the continuous current rating of 960 Amps at 200C (refer Table-2).
The conductors ACSS Lark and ACSR Panther are almost equal in diameter and weight. They are having almost same maximum sag at their respective highest thermal rating. The thermal rating of the ACSR Panther conductor is 90C as against that of the ACSS Lark conductor is 200C.
Similarly successfully designed and developed conductor accessories, insulator hardware and power clamps and connectors for both transmission line and sub-station equipment terminal such as CT, PT, CB, Isolator, LA, WT, CC etc. and ‘T’ connector suitable for HTLS Lark conductor are also utilised under the same project.
During type testing of the fittings, it is confirmed that though they are connected to the conductor of temperature of 200C at its one end the other end temperature of the connector is as low as 70C and even below. Therefore, the substation equipment terminals remain well within their maximum thermal limit of 90C.
Design and proto model of fittings alone is not enough. The manufacturer should have in house facility for type testing and for routine testing of such fittings. It is known that no electric product can be used in the system without full proof testing as per relevant IS, IEC and other relevant international standards.
While designing the above products following important aspects are taken into consideration. First preference is given for establishment of own testing laboratory having facilities of type testing of above products for which very high investment of about Rs 5 crores is made on testing equipment, qualified and experienced trained testing engineers and technicians. For manufacturing unit highly sophisticated equipment like foundry and machine shop, VMC, CNC and SPM and investment on infrastructure to the tune of Rs10 crores was done.
While manufacturing the products attention is paid to: The drawings are prepared and got approved from the authorities of the utility and the customer for whom the products are being used. The metallurgy of the raw materials to be used for manufacturing the products. Selection of the AL alloys of suitable chemical composition having high emissivity coefficient and low absorption coefficient. The thermal rating to sustain the maximum rated temperature of the HTLS conductor of 200C without rise of its own temperature beyond 80C. To have the required mechanical strength. The high standard foundry and machine shop equipment. Highly skilled and qualified work force Training to the manufacturing and quality control staff Vigorous testing to prove the product quality well above the basic requirement of the relevant IS, IEC and other international standards. 
Authored by:
Sudhir S. Kulkarni, Director, Ramelex Pvt. Ltd, Pune
 
 

This article gives brief account of conductor accessories, insulator hardware and power clamps and connectors suitable for HTLS conductor
 Due to right of way problem in the entire country, emphasis is on transferring big chunk of power through the least physical corridor. To achieve this, the conductor surface temperature has to be taken to more than 100C. The normal ACSR conductor loses its electrical and mechanical properties beyond 90C. It is therefore necessary to use high temperature low sag (HTLS) conductors.
HTLS conductors can operate up to the temperature 250C and therefore can transmit large quantity of power. It is worth noting that the ampacity of the conductor increases as the temperature is elevated.
For operating the conductors on very high temperatures, metallurgical changes in the conducting outer layers as well as the centre core has to be done. Annealing of the conducting material and coating the steel core with heat resistant material such as Galfan or using carbon core, affords high ampacity.
When the surface temperature of the conductor (HTLS) is elevated, the conductor accessories, insulator hardware and power clamps and connectors suitable for ACSR conductor cannot be used for HTLS conductor. Therefore, a technological development had to have high temperature hardware and fittings designed and developed for the manufacture. Further, thorough testing of the connectors as per relevant IEC standard is carried out. This article gives brief account of such conductor accessories, insulator hardware and power clamps and connectors suitable for HTLS conductor.
Benefits of HTLS conductorsHTLS conductors deliver higher amount of current or power at the elevated temperatures. The advantage of use of HTLS conductor is that when they are used on the towers designed for ACSR conductors, no major changes in the tower structures are required.
Even the HTLS conductors sag less and therefore afford higher ground clearance, when used on the existing lines. If HTLS conductors are used on the new line, HTLS conductors can allow higher spans and thus reduce number of towers along the route.
The weights and other mechanical properties of HTLS conductors are comparable with those of ACSR conductor. The Table 1 will give a comparative idea of HTLS conductors and Table 2 gives technical parameter of ACSS LARK conductor.
Details of HTLS conductors Before going to the subject, design and development of conductor fittings for high ampacity, high temperature low sag conductor, it is necessary to see what HTLS conductor is and how it differs in properties from commonly used conductors like ACSR and AAAC.
The conductors ACSR and AAAC are having maximum thermal rating of 90C. This means, in summer season when maximum ambient temperature is about 47-48C, the available scope to raise the temperature of these conductors above the ambient temperature is by 45C, which further limits the continuous current rating for these conductors, to satisfy this condition of maximum thermal limit of 90C.
To overcome the problem of this low thermal limit of 90C of ACSR and AAAC conductors, new conductors of high thermal rating of 200C, but with about same cross sectional area and same sag at the high thermal rating are invented, which are having continuous current rating of about double the current rating of equivalent size ACSR/AAAC conductor, but at high temperature of 180 to 200C.
There are a number of new High Temperature Low Sag (HTLS) conductors in the market designed to operate at temperatures of 200C and more. This is well above the normally accepted maximum operating temperature of 90C, allowed for the standard AAAC and ACSR conductors.
These new conductors still employ aluminium as the main current conducting medium. They have a core material inside the aluminium that provides high mechanical strength with a low coefficient of thermal expansion.
This internal core material is the main difference between conductors supplied by the various manufacturers. The new conductors are capable of carrying as much as two times the current, compared to that carried by AAAC and ACSR conductors of similar diameters without increase in the sag.
Limited experience indicates that the new conductors perform as advertised. They tend to cost two times or even more, than standard conductors to purchase and install.
Some require special handling and equipment for installation and maintenance.
When applying these new conductors, manufacturer recommended splices and dead ends shall be installed using extreme care. These tend to be the weak links in line construction and any flaws at these points will most likely lead to conductor failures.
Due care has to be taken while designing and developing conductor accessories, insulator hardware and power clamps and connectors for HTLS conductors with thorough testing of the same as per relevant IS/IEC Standard.
Design of fittings for HTLS conductor The fittings and hardware such as splice, suspension clamps, dead ends, mid-span compression joints and repair sleeves as well as PA rods, vibration dampers etc. for transmission lines, as well as power connectors for substations. Using HTLS conductor is a specialised job. It is normally accepted that, since the HTLS conductors operate at very high temperatures, they must not be connected directly to oil and or paper insulated bushings.
Therefore leads from HTLS dead end towers to equipment bushings may be constructed with a bundle of standard AAAC or ACSR conductors designed to carry the total current from the HTLS line without heating the equipment terminals beyond their normal thermal rating limits.
The new HTLS conductors are generally used for specific applications or to solve existing problems. For example, if reconductoring of an existing line is required for load purposes and installing a larger conductor will require extensive structural work to increase strength and/or height, the HTLS conductor may be considered. A cost analysis can be evaluated between cost of the HTLS conductor and the cost of the structural modifications.
For example, Panther ACSR conductor is replaced by ACSS Lark conductor for 132 KV line, using successfully designed and developed conductor fittings such as splices, suspension clamps, dead ends, mid-span joints and repair sleeves as well as PA Rods, vibration dampers etc. suitable for the ACSS Lark conductor, which is having diameter 20.27 mm, aluminium area 201.4 sq.mm. and weight per km as 925 Kg. UTS of the conductor being 100.4 KN and the continuous current rating of 960 Amps at 200C (refer Table-2).
The conductors ACSS Lark and ACSR Panther are almost equal in diameter and weight. They are having almost same maximum sag at their respective highest thermal rating. The thermal rating of the ACSR Panther conductor is 90C as against that of the ACSS Lark conductor is 200C.
Similarly successfully designed and developed conductor accessories, insulator hardware and power clamps and connectors for both transmission line and sub-station equipment terminal such as CT, PT, CB, Isolator, LA, WT, CC etc. and ‘T’ connector suitable for HTLS Lark conductor are also utilised under the same project.
During type testing of the fittings, it is confirmed that though they are connected to the conductor of temperature of 200C at its one end the other end temperature of the connector is as low as 70C and even below. Therefore, the substation equipment terminals remain well within their maximum thermal limit of 90C.
Design and proto model of fittings alone is not enough. The manufacturer should have in house facility for type testing and for routine testing of such fittings. It is known that no electric product can be used in the system without full proof testing as per relevant IS, IEC and other relevant international standards.
While designing the above products following important aspects are taken into consideration. First preference is given for establishment of own testing laboratory having facilities of type testing of above products for which very high investment of about Rs 5 crores is made on testing equipment, qualified and experienced trained testing engineers and technicians. For manufacturing unit highly sophisticated equipment like foundry and machine shop, VMC, CNC and SPM and investment on infrastructure to the tune of Rs10 crores was done.
While manufacturing the products attention is paid to: The drawings are prepared and got approved from the authorities of the utility and the customer for whom the products are being used. The metallurgy of the raw materials to be used for manufacturing the products. Selection of the AL alloys of suitable chemical composition having high emissivity coefficient and low absorption coefficient. The thermal rating to sustain the maximum rated temperature of the HTLS conductor of 200C without rise of its own temperature beyond 80C. To have the required mechanical strength. The high standard foundry and machine shop equipment. Highly skilled and qualified work force Training to the manufacturing and quality control staff Vigorous testing to prove the product quality well above the basic requirement of the relevant IS, IEC and other international standards. 
Authored by:
Sudhir S. Kulkarni, Director, Ramelex Pvt. Ltd, Pune