The challenging journey towards successful charging of 1200kV National test station

On Mar 28, 2013

Dr. D. Devendranath
Additional Director

Dr. S K Agrawal – Executive Director / B.N.De.Bhowmick – General Manager / Akhil Sundaran – Engineer Technology Development Department, POWER GRID CORPORATION OF INDIA LTD.

POWERGRID, the Central Transmission Utility (CTU) of the country has been entrusted with the task of creation of a strong and vibrant National grid in the country, to ensure the optimum utilization of generating resources, conservation of an eco-sensitive right-of-way (ROW) and the flexibility to accommodate the uncertainty of generation plans.POWERGRID is responsible for planning, coordination, supervision and control over inter-State transmission system and operation of National and Regional Power Grids.

A. Yellaiah, Joint Director

However, the task of establishment of large transmission network requires judiciousconsideration of socio-economic and technical challenges that includes Right-of-Way availability, protection of flora and fauna, reduction of transmission losses, control of system fault levels, cost optimization etc.Over the years in-order to address these ever-growing challenges POWERGRID has adopted power transmission at extra high voltage levels of 400kV and 765kV respectively. However, due to the continued growth of economy and population growth, electricity requirement is increasing exponentially.

To meet these energy requirements of the society, large generation projects are envisaged in the coming years. However most of these generation sources are identified in the resource rich areas of North-Eastern and Eastern part of the country. The load centers are concentrated in Northern, Western and Southern parts of the country. Hence there arises the need for transmitting bulk power across the length and breadth of the country by optimizing the ROW requirement and with reduced system losses, which can be achieved by adopting higher voltage levels.

Table 1: Comparison of power transmission capacities of various voltage levels
Description	400kV	765kV	1200kV
ROW in m	46	64	92
Capacity (MW)	600-700	2500-3000	6000-8000
Power density (MW/m)	15	45	87

K. A. Aravind
Engineering Officer Gr 4

Concept for UHVAC system development
POWERGRID management attended an Ultra High Voltage (UHV) AC symposium at China in July 2007. Drawing inspiration from the concept used for indigenous development of UHVAC technology in other countries, back in IndiaPOWERGRID floated the idea for indigenous development of technology. It was decided to adopt 1200kV as the next level of transmission voltage.

SWOT analysis
SWOT analysis was done to examine the viability of indigenous development of development of UHVAC technology.

Dr. Pradeep M. Nirgude
Joint Director

Development model
Intensive interactions were made withIndian equipment manufacturers from August 2007 onwards. As there was no national / international standards available, need was felt for establishing a test station which will help in optimizing system and equipment parameters before going for commercialization. Manufacturers were encouraged to make investments keeping a progressive view of future in mind.

400kV Bina Substation of POWERGRID was selected for establishing the test station. The development of test station was taken up through a Public-Private-Partnership model, where-in manufacturers were to develop 1200kV equipments for installation at the test station and POWERGRID was to provide land, create switchyard and test lines, provide testing instruments etc. The developed equipmentsare to be field tested and kept under operation for significant time for gaining operational and service experience. The results from tests and studies will help in optimization of switchyard and line configurations, system and equipment parameters in addition to facilitation of development of field proven equipments.

After series of meetings equipment manufacturers came forward to participate in this project of national importance. Tripartite Memorandum of Understandings (MOU) was signed between POWERGRID, Central Power Research Institute (CPRI) and participating manufacturers for establishment of 1200kV UHV test station at Bina (M.P.).

Project Steering Committee and equipment Working Groups
Since the project involves a large no of private, public and research organizations, a committee was formulated with members from senior management of POWERGRID, Central Electricity Authority, CPRI and participating manufacturers. This Project Steering Committee (PSC) had been entrusted with the task of resolving various issues and monitoring the progress of the project. From 2007 onwards, about 20 PSC meetings are held across the country including some at the manufacturer’s facilities, POWERGRID Corporate Centre-Gurgaon and many at project site inBina, MP.

Further, to finalize the 1200kV equipment parameters, working groupscomprising experts having domain/product knowledge, members from POWERGRID and respective manufacturers were formed for eachof the equipment. These working groups finalized the technical parameters for the equipments. This helped in integrating the scattered knowledge base of Indian power sector.

Brain storming sessions
Brain storming sessions were carried out for the development of 1200 kV UHVAC transmission system in Jan 2008. Experts invited from countries like USA, Germany, Italy, Russia, Japan and China, shared their expertise and experiences those helped in the evolution of idea of indigenous development.

Integration of International expertise
In order to assist in the development of the technologies which are new to both POWERGRID and the manufacturers, international / national experts were appointed to help in finalizing initial system and equipment parameters, review of equipment designs, assist during testing etc.

Challenges in finalization of system parameters
Absence of standardized parameters necessitated independent studies for finalization of 1200kV Ultra High Voltage (UHV) AC system parameters.

Selection of Insulation levels was the most challenging task, as considerations needs to be made for cost optimization as well as equipment safety. Adoption of a straight line approach for selection of insulation levels as done in the case of lower voltages 400kV and 765kV, would have made the 1200 kV system not only uneconomical but also have posed constraints in technical and transportation front. Therefore, detailed insulation coordination studies were carried out with the underlying principle that the insulation impairment /damages for equipments are minimized to an acceptable economically and operationally low level of failure probability. By taking the advantages provided by high performance protective devices, insulation levels were selected optimally by keeping the safety margin for insulation values in minimum. As a result of not extrapolating from the insulation values of lower voltage levels, significant economical and physical advantages were achieved in insulation designs of equipments.

Experimental studies for finalization of switchyard layouts/ line configurations
Upon finalization of the system parameters, next step was to finalize the layout of switchyard and line configurations. POWERGRID undertook various studies and tests to determine the configuration of the 1200kV transmission lines and switchyard. Studies at the experimental facility established at CPRI, Hyderabad include corona cage studies, air gap insulation studies and tests for voltage distribution on the insulator string. Based on study results the conductor configuration, air gap clearance and string configurations were finalized.

Electric field studies were also carried out to ensure that the electric field values are within the prescribed International limits. Special designs were adopted for switchyard gantry structures to take into account of the large phase-phase clearance requirements. Provisions were envisaged for varying the clearances, height etc. for experimentation and field measurements. 1200kV switchyard layouts thus developed has considerations for reliability, operational flexibility, ease of maintenance and expansion, availability of land etc.

Different configurations of towers were studied with different configurations. Deciding parameters were measured and optimal tower designs were selected for adoption at the test station.

1200kV National Test Station layout and configurations
The Test Station is being established with two 1200kV bays, one single circuit (S/C) transmission line of 1.1Km in length and one double circuit (D/C) transmission line of 0.8Km in length. In the first 1200kV bay, 400kV is stepped up to 1200kV level through a bank of three single phase transformers. The 1st bay has been terminated at the S/C line, which is interconnected with the D/C line. Connections are being made between the D/C line and 2nd 1200kV switchyard, where the voltage will be stepped down to 400kV level by another bank of three single phase transformers. Switching and isolation functions of lines were envisaged by means of 1200kV circuit breakers and isolators. Initially, 1200kV transformers are to be controlled by circuit breaker on the 400kV bay till all the phases of 1200kV circuit breaker are installed. As it is decided to use dead tank circuit breakers which will contain bushing current transformers, usage of separate current transformers was ruled out. Power flow through the Test Station is planned through the Line-In-Line-Out (LILO) of Satna-Bina-III 400 kV transmission line.

Consideration in selection of equipment parameters
Based on the system envisaged and extensive simulation study of the proposed UHV line configuration and after giving due consideration to cost and size optimization, equipment parameters were finalized. It was decided to use single phase transformers because of the high voltage level of system. Insulation levels were kept minimal to control the height during transportation.

Finalization of parameters for surge arrestors was the trickiest one, as the insulation levels of all other equipments were finalized keeping in view of the protection offered by surge arrestor. Because of the high stress and stringent duty conditions, it was envisaged to use multi column surge arrestors with added energy handling capacity.

Circuit breaker parameters were finalized after carrying out extensive computer simulation studies. Decision to use dead tank circuit breakers was supported by stability and insulation issues with live tank circuit breakers

Development of 1200kV equipments-Manufacturing process
Once the parameters were finalized, manufacturers commenced design of the equipments. Designs were made by giving specific care to the critical areas of dielectric integrity and mechanical strength. Sophisticated design tools were used for evaluation and re evaluation of designs. The designs were finalized in consultation with the consultants appointed.

Design of UHVAC transformer, the most critical equipment has been met with several challenges like control of stress, heat dissipation, electrical and magnetic losses, cooling issues, etc. Design of UHVAC surge arrester with enhanced energy requirements was indeed a daunting task. It was evident for the team that the only and confident way ahead was to go back to the basics and evaluate the design concepts based on the vast experience with lower voltage level products.

Manufacturers had raised their manufacturing capabilities and further improved quality control measures during manufacturing of various equipments. For the sake of uniformities and to compliment the efforts of transformer manufacturers who had made huge investments, POWERGRID has sourced the 1200kV bushings and made them available for installation on the transformers.

Factory testing had been carried out on the developed equipments. All of them have successfully passed the tests. Due to the limitation of testing facilities in some manufacturer works, factory testing was carried out to the maximum extent possible with the available test apparatus. CPRI has also assisted in carrying out the tests on some of the equipments at their facilities at a reduced cost.

Challenges in design and construction of switchyard /lines
Design and construction of civil foundations were extremely challenging due to the gigantic weight and type of support required for the UHVAC equipments.

Due to the large clearance requirements added with the weight of multiple bundle line conductors, tower designs were re-evaluated and engineered to meet the desired results. It is to be mentioned that application has been filed for patent of one S/C line tower design with Indian Patents and Trademarks office.

Construction of lines was with extreme difficulties due to the mammoth size of tower components.Due to the large height of 1200kV double circuit tower of the order of 125mtrs, erection activities was done under strict supervision and trained man power was used for working at such heights. Use of safety gears was strictly enforced to avoid any mishaps during the construction stage.Strict quality control measures are ensured for tower members. Minor glitches viz. tower cross arm bending, insulator string break faced during stringing, were solved by engineering modification and repair

Transportation of equipments
The poor condition of the roads and bridges put a lot of hurdles and delay in transportation of the transformer from manufacturer works to the site. Equipment transportation was delayed for a long time. After extensive route survey, several route changes were made in an attempt to make the equipments available for charging at an earliest date.

Installation
After the arrival of equipments at site, tremendous efforts, attributable to its heavy weight, were made to put it in the plinth for further installation. Equipment installations were done carefully and extra care was taken with strict supervision of all activities to avoid any damage to equipments.All equipments were subjected to pre-commissioning tests, the procedure for which was developed by POWERGRID in consultation with manufacturers. No abnormalities were observed and results were comparable with that of factory tests, which proved proper transportation, installation and commissioning of the equipments.

Present status
Upon completion of successful pre-commissioning tests, equipments are being charged successively from January 2012 onwards.

First phase transformer along with associated equipments were charged on 27th January 2012.
After completion of stringing on 1200kV S/C line, it was charged from 1200kV bay on 29th February 2012
Other two phase transformers and associated equipments were charged on 26th May 2012.
1200kV D/C line was also charged on 13th October 2012.

Other major equipments viz. 1200kV Isolator and circuit breaker in Bay-I are about to be commissioned shortly. With the successful charging of Bay-I and the lines, India has achieved world’s highest transmission level voltage. With this POWERGRID & Indian manufacturers have shown to the world, their capabilities in developing the technology indigenously.

Activities for commissioning of Bay-II are ongoing. Foundations for transformers and other equipments were completed. Upon charging of the Bay-II and interconnection to the 400kV line, equipments canbe loaded and extensive field tests will be carried out.

Dedication to nation
1200kV National Test Station was dedicated to nation by Hon. Union Minister of State for Power (I/C) Sh. Jyotiraditya M. Scindia on 26th Dec 2012 in the august presence of CMD and other senior official of POWERGRID and equipment manufacturers.

Speaking on the moment, minister said that this is an important milestone in development of India’s electric power transmission. It will facilitate the transfer of bulk power from remotely located generating stations to long distance load centers. This effort will also result in saving of huge right-of-way (ROW), minimize the impact on flora and fauna, and ensure cost-effective bulk power transmission corridors in the country.

Speaking on this momentous occasion the minister also disclosed the government’s target of achieving 90,000 MW power production during the 12th Five Year Plan (2012-17) and stated that, “The inter-regional capacity of Indian grid, currently standing at 28,000 MW is expected to escalate up to 48,000 MW in the current plan period”. He further disclosed that a total of Rs.12 lakh crore is proposed to be spent out of which Rs 7 lakh crore would be used on electricity production, Rs. 3 lakh crore on transmission and Rs. 2 crore on distribution.

Briefing on the initiative focused towards developing the largest power grid in the world by connecting four major grids in India, Minister said, “This will ensure transmission of 70,000 MW power to all nooks and corner of the country. He said four grids of power grid instituted in 1990 by late Rajiv Gandhi have been linked and only the southern grid was left to be linked to rest of the four grids. This would be accomplished by 2014, he said. Following this, India will have the biggest grid in the world, said the minister.

The minister also disclosed the plans over establishing three power plants at Vindhyachal (1,000 MW), Khargone (1,300 MW) and Gaurwara (1,500 MW). State run power major NTPC Ltd is expected to establish these power plants.

International conference on development of 1200kV National Test Station
In order to disseminate the knowledge acquired during the initial stages of system design, equipment design, and switchyard layouts, an international conference in association with IEEMA and CBIP was organized in September 2010. More than 200 EHV & UHV experts across the world were present at this historic conference.

Contribution of POWERGRID to international standardization
POWERGRID has extensively contributed for bringing international standardization in UHVAC level, by being a member of International Council on Large Electric Systems (CIGRE). Some of the CIGRE working groups which POWERGRID has made contribution are WG A3.22, B3.22 and B3.29.

Some of the Technical Brochures that are already released bearing details of Indian 1200kV system are listed below:
TB 362 – ‘Technical requirements for substation equipment exceeding 800kV’ (WG A3.22)
TB 400 – ‘Technical requirements for substations exceeding 800 kV’ (WG B3.22)
TB 456 – ‘Background of Technical Specifications for Substation Equipment exceeding 800 kV AC’ (WG A3.22)
TB for ‘Field tests technology on UHV substation during construction and operation’ (WG B3.29) is under finalization.

Uniqueness of Indian 1200kV
To realize the best design practices, technically and economically for the transmission line and the substation, important technical solutions for network problems specifically suited to the requirement of the UHV system have been introduced. It includes insulation co-ordination with optimized insulation level, high performance multi column surge arresters and dead tank Circuit Breakers. These sophisticated technologies helped in realization of highly reliable and economical UHV substations and transmission lines and resulted in reducing the size of UHV equipments.

Way forward
The test bays and test line at National Test Station shall be used for various field tests/ trials so that the results and feedback can be used for developing field proven equipment as well as to gain initial operational experience.

In conclusion this Indigenous R & D effort, in addition to providing help to develop an efficient bulk UHVAC power transfer system in India, will also lead to:

Indigenous availability of equipment and proven technology
Optimization of cost
Ease of service
Opportunity for Indian Manufacturers to become global leaders in UHVAC technology

This achievement of development of indigenous technology is one more feather in the cap of Indian power system. Apart from the contribution to the development of India, it undoubtedly represents the most significant International achievement in high voltage power transmission. The project will serve as a key to the development of India’s electric power transmission backbone. Indian Electrical Industry today can proudly announce and display its R&D capabilities in developing 1200 kV equipment in a short period of less than 5 years through R&D and Innovation. Commercialization of 1200kV technology in future will help in ensuring a reliable and dependable power supply for the continued and accelerated development of India.Further, 1200kV transmission system initiative will help in the large scale efficient evacuation of power in the 12th & 13th Plan period. The 1200kV system is a step towards overcoming the challenges in the power sector such as Right of Way, environmental considerations, optimization of cost, faster project implementation, co-ordinate development of transmission corridor together with other infrastructure, transmission capacity enhancement through upgrading, reduction of losses and integration of emerging technologies.

It is worth mentioning that POWERGRID is constructing the first 1200kV Transmission Line between Wardha and Aurangabad (Line length: 400km) to usher in 1200kV era in the country.More projects will follow based on the success of the 1200kV Test Station.

1200 KV Project – Partners in success
In this ambitious project by PowerGrid, 35 Indian Manufacturers are equal partners in success. They have successfully demonstrated their technical, R&D and Innovation capabilities and indigenously developed and manufactured 1200 kV electrical equipment. Effectively this had proven the “India Power factor” to the world.

IEEMA Journal as a small tribute to these pioneering manufacturers is sharing with you their journey in brief about the trials and tribulations and the challenges faced while developing and manufacturing the 1200 kV Equipment. We reproduce below the experiences of a few manufacturers and in subsequent issues will carry more such information as a part of special series.

M/s Deccan Enterprises
Equipment supplied – Polymer Insulators
Deccan Enterprises Private Limited is one of the pioneer and leading manufacturers of silicone composite insulators up to 765kV in the country. PowerGrid had proposed to establish 1200 kV National Test station at Bina, Madhya Pradesh, utilizing the knowledge and expertise of the Indian manufacturers. To contribute to this prestigious endeavour, Deccan had signed an MOU with PowerGrid, in June 2009, to design, develop, manufacture and supply 1200 kV, 320 kN and 420 kN composite insulators to the Test station. The development was successfully taken-up by Deccan’s in-house R&D facility that is recognized by Government of India.

Design:
The design parameters of the insulator like the length, creepage distance, mechanical strength requirements and other electrical parameters were finalised, after detailed discussions in the working group meetings and Project Steering Committee meetings. 3D EFM software was used to arrive at the optimum insulator & corona ring design to prevent degradation of the polymer material due to electrical stresses and Corona discharge from the metal end fittings that can degrade and destroy the hydrophobic properties of the silicone rubber. The guidelines provided in IEC 60815, field experience of manufacturers around the world and the experience of the in house R&D team were considered for the shed profile. The mechanical strength requirement of 320 and 420 kN, required a detailed design analysis of the end fittings to be used and the characteristics of the FRP core rod.

Development: The development phase started with the identification of the crimping machine, injection moulding machine, suitable moulds, quality checks to be made for the components and the process of manufacturing. The efforts of the R&D team, after a period of two years, culminated in the final product. The total insulator length of 9945 mm was manufactured in three units, with corona rings around the connection zone of the adjacent insulator units. For manufacturing the proto type, new production and testing equipment were added to the basic infrastructure.

Tests:
The complete insulator assembly with the hardware was successfully tested at CPRI, Hyderabad, for proving the electrical parameters. The insulator successfully withstood Lightning impulse voltage of 2400 kVp, Wet switching impulse voltage of 1800 kVp and Wet power frequency voltage of 1200 kV(RMS). The mechanical strength was tested and the pull out load achieved was 540 kN. The insulator was then installed at the 1200 kV National test station at Bina and energized during December 2012.

Goldstone Infratech Ltd
Equipment supplied – Insulators
PGCIL have chosen Goldstone as preferred supplier for all EHV developments. Goldstone has been approved for supplying products in the range 400 kV and 765 KV rating. When 1200 kV substation at Bina was being developed, this development order was entrusted to Goldstone.

The product was successfully developed and tested at Hyderabad factory of Goldstone. PGCIL engineers were satisfied with GIL design and special attention was paid to every detail. The product boasts advanced features like consistent quality , highly sustainable and Perfect Insulation.

The duly tested product was erected in Bina substation and has contributed to 1200 kV development in our country. Goldstone is fully geared to cater to EHV insulator demand within our country and overseas. PowerGrid have shown confidence in Goldstone products by placing orders for 400 kV and 765 kV rating of composite insulators. We are sure that when PGCIL starts commercial buying of 1200 kV components, participating manufacturers in the project will be given preference for a product already developed and tested

Transformers & Rectifiers India Ltd

Equipment supplied – Transformer

Developing Technology for 1200 kV Transformer – TARIL Experience
Development of 1200 kV technology has been a great experience for Transformers & Rectifiers India Ltd. (TARIL) UHV technology is not yet established in India. It is still in the nascent stage. A few experimental test lines were setup in USA, Japan, Italy, USSR, China etc.

1200 kV AC Transmission corridors are essential for India considering that excess generation in Eastern and North Eastern blocks is to be transmitted to load centres located far away in Northern and Western regions. In view of lead time available before commercialization, PowerGrid embarked upon the idea of developing a 1200 kV test station along with a short 1200 kV transmission line on Public Private Partnership (PPP) model. First phase comprising 3 single phase Auto Transformers forming a bank of 1000 MVA, 1150 / 400 / 33 kV has been commissioned on No Load and dedicated to Nation.

UHV transformer is the largest and the most critical link in the power system. Reliability of the grid depends to a large extent on the reliable transformers. Reliability is the sum total of reliable specification, reliable design, reliable material, reliable manufacturing and of course reliable O&M at site after proper installation.

Developing for PGCIL a 1200 kV Class reliable transformer by TARIL, who are specialized in custom transformers and power transformers up to 400 kV range, was a great challenge which has been successfully met.

During the designing stage, various critical challenges were faced and overcome for arriving at successful solutions for dielectric design, thermal design, control of a powerful leakage field, short circuit withstand capability, etc. State-of-art software was employed to get precise results and highly critical design margins.

Longitudinal insulation was more challenging owing to transport height limitations. Permissible transport height en route limited the allowed window and winding heights. Winding with shielded turn arrangement was adopted to get near uniform voltage distribution across the winding.

1200 kV calls for larger radial clearances which enhance criticality of dielectric stresses due to stressed oil volume effect. Larger oil gaps have to be divided to smaller gaps based on 2 Dimensional electrostatic field study to increase factors of safety.

Large rating transformers have a powerful leakage field, which if not controlled properly lead to hot spot temperatures in the structural parts. Appropriate shielding measures were adopted to avoid hot spot temperatures.

Higher value of leakage flux also generates eddy currents responsible for hot spots in the transformer windings. Continuously transposed cables with epoxy bonding were employed to control winding hot spot temperatures as well as improve the dynamic short circuit withstand capability. State-of-art software based on field solution was used to analyze the strength and rigidity of windings and clamping structure integrity towards axial and radial components of mechanical forces during short circuit conditions.

UHV Transformers are essentially large rating transformers and require facilities to handle larger assembly weights and dimensions. TARIL have the required infrastructure available to manufacture such heavier components e.g. 20 tonne vertical winding machine, 150 tonne core building platform, a large VPD autoclave, 250 tonne active part handling capacity, 2.8