Description

The existing Bhaktapur-Baneshwor-Patan 66kV single circuit transmission line with ACSR 120 mm² conductor in most of the sections and ACSR "WOLF" conductor in few sections, is supplying electric power to NEA's Baneshwor and Patan substations from 132/66 kV Bhaktapur and Siuchatar substations. Baneshwor substation feeds power to Gothatar, Sankhamul, IC Hall, Imadol, Lubhu, Airport, Baneshwor, Koteshwor, Bagmati and Dhobikhola areas. Patan substation is located near Patan Hospital at Lagankhel of Lalitpur district and also connected through 11 kV Ring Main with Thimi, K3 and Teku substations. Whole of the Lalitpur district is supplied through Patan substation. Due to rapid urbanization and commercialization of the areas, the electricity demand is ever increasing. Due to limited capacity of the ACSR 120 mm² and ACSR "WOLF" conductor, the supply situation in the area is not satisfactory with frequent interruptions and poor voltage regulation.

Nepal Electricity Authority is currently engaged in upgradation of Bhaktapur-Baneshwor-Patan-Siuchatar 66kV Transmission Line using High Temperature Low Sag (HTLS) Conductors, which will double the transmission capacity of those lines.

Contract agreement was signed between Nepal Electricity Authority (NEA) and NEA Engineering Company to carry out the study for upgradation of Bhaktapur-Baneshwor-Patan-Siuchatar 66 kV transmission line conductor with HTLS conductor on 1st October, 2018 for 8 months. Details of objectives and scope of work of the Consultancy Services for Bhaktapur-Baneshwor-Patan-Siuchatar 66 kV Transmission Line Upgradation was as below:

• To study the tower types/structures, earthing and accessories used in the existing Bhaktapur-Baneshwor-Patan-Siuchatar 66 kV transmission line,
• To study the ground profile and RoW of the existing line,
• To determine the existing sag of the line through total station/drone survey of the line, to calculate the design sag of the line and to compare it with standard norms,
• To study and propose suitable HTLS conductor having twice the ampacity of the existing conductor without affecting existing sags and towers,
• To identify and suggest the solution for critical locations to maintain design sag,
• To carry out techno-economic study of the proposed scheme, 
• To prepare sag tension chart including stress strain curve of the proposed HTLS conductor and compare with the existing sag,
• To identify the critical towers and their strength and recommend the requirements of strengthening of towers if any.
• To study and recommend the ratings of corresponding substation components requiring upgradation.

After the Contract agreement with NEA, NEAEC prepared for deployment of its Experts for field work in consultation with NEA. In order to make the study more specific, the project was divided into different sections in terms of existing conductors, tower configuration and design voltage level.

During the initial period of the field work, various reports were studied and meetings were held with counterpart personnel from NEA, in order to understand the present project execution and design practices of NEA. Further all the available reports/documents were referred and reviewed by the Consultant.

The line sections consisted two types of ACSR conductors – LGJ 120 and WOLF conductor with single circuit, double circuit and four circuit towers along the span. The LGJ 120 section were about 40+years old.

The team from NEC inspected each and every tower locations, line materials and line corridor regarding the condition of tower accessories, tower earthing, line ROW, Ground clearances and human negligence. A Report was submitted incorporating all of the findings with necessary actions and recommendations.

 The different types of HTLS conductors studied were as below:

1. ACSS
2. TACSR  
3. GTACSR / GZTACSR (GAP): CSR
4. STACIR
5. ACCC
6. ACFR
7. ACCR

Before finalizing contours of the Final Report, NEC completed the detail survey of the complete line, along with sag measurement and performed the sag tension analysis for different HTLS conductors followed by techno-economic analysis.

                      Finally two types of HTLS conductor, ACCC and ACFR conductor were proposed as suitable conductor for upgradation of existing conductors.

In-addition to that, NEC conducted the thorough study of ratings of substation components and recommended to upgrade the ratings of current transformers, disconnecting switches and circuit breakers.

NEC also performed the load flow analysis of the said transmission line and proposed an installation plan for upgradation works.  

The project was successfully completed and closed on    , 2019 with 1 month extension period to study and incorporate the upgradation requirement of substation components.