1200 kV, 333 MVA Single Phase Autotransformer

World’s Highest Voltage Class Transformer, 1200 kV, 333 MVA Single Phase Autotransformer developed successfully by Vijai Electricals Ltd. Hyderabad with Indigenous Technology.

1200 kV (UHV) AC system is being envisaged as next transmission voltage to meet the long term power transfer requirement in the country.

Ultra high voltage (UHV) transmission schemes are driven by the need to transfer large amounts of electrical power from the generation resources to far away major load centres. India is one of the most notable examples where in future, several UHV systems at 1200 kV AC shall be needed to transfer large quantum of power from various generation complexes in Chhattisgarh, Jharkhand, Orissa to load centres in Northern & Western regions.
Presently, 800 kV is the highest transmission voltage, introduced in 2007 with commissioning of first 800 kV line from Sipat (Chhattisgarh) to Seoni (Madhya Pradesh).Several 800 kV transmission corridors are now under construction.In next 5-6 years, 1200 kV AC system , is expected to emerge as main transmission level along with ± 800 kV HVDC, integrated with National Grid at 800kV AC and 400kV AC supported by ± 500 kV HVDC Network.

When 800 kV system was introduced, Indian Transformer Industry did not have sufficient time to develop 800 kV Transformers and Shunt reactors needed in large numbers and therefore country had to import these equipment from Korea, Sweden, Japan, China etc.
1200 kV system is not existing in any part of the World. In late eighties, USSR constructed an 1150 kV line which hardly operated for about 2 years. After disintegration of USSR, the line was operated at 500 kV. In recent time only China has commissioned an 1100 kV line with three substaionc in 2009.
In fact, Technology for 1200 kV is yet to be developed. In view of lead time of 5-6 years available ( before commercialization takes place ), POWERGRID took a lead to establish a 1200 kV UHV AC Test Station at Bina with experimental line (1.6 km) to provide a platform to Indian Manufacturers to develop their 1200 kV equipment and obtain first hand experience of field testing, trial operation etc. and build “A grid for tomorrow”.
POWERGRID’s mega initiative in this regard is highly commendable. About 35 Indian Manufacturesrs have signed MoU with POWERGRID to develop indigenously their various 1200 kV equipment and install them at Bina and obtain operating experience to consolidate/perfect the 1200 kV Technology.
Vijai Electricals was one of the firsts to sign an MoU for development of a 333 MVA 1200 kV Autotransformer.

Vijai Electricals created a history when its magnum opus, 333 MVA, 1150/400/33kV, single phase Autotransformer, developed with in-house technology, know-how and expertise, passed Routine and Type tests in presence of POWERGRID representatives during 13th to 18th June 2011.
Vijai electrical Ltd, an established leader in Distribution Transformers, made a foray into Power transformers in the year 2007-08 and in just 4 years of operation developed the entire range of Power transformers from 66 kV to 132,220,400 and now 1200 kV class.
Vijai Electricals is the only manufacturer in the country to produce entire range of transformers from tiniest 5 kVA 11 kV to largest 333300 kVA 1200 kV.

Technical Specification

Major Technical Specification of 333 MVA Transformer for the 1200 kV Test Station is as follows
Rated Power 333/333/111 MVA, Single Phase
Voltage Ratio 1150/√3/400/√3/33 kV
Rated frequency 50 Hz
Connection (3 ph.) Ynaod11
% Impedance HV-IV    18%
HV-LV    40%
IV-LV    20%
Cooling type ODAF or OFAF
Cooling equipment 4 x 33.3% Unit OFAF Coolers
Temp. rise 45ºC :Winding, 40ºC : Top oil

HV 2250 kVp, IV 1300 kVp , LV 325 kVp
Neutral 95 kVp
HV 1800 kVp, IV 1050 kVp
1.5 pu (1.0 pu = 1200/√3 kV)

Design Challenges

UHV transformers are essentially large rating transformers both in terms of voltage and current. Transport limitations pose the biggest challenge. Problems related to dielectric design of UHV Transformers are to be addressed meeting the dimensional limitations for the transport. Because of high current magnitudes, the problems related to dynamic stability under effects of short circuit currents, hot spot generation etc. get magnified and are to be taken care of adequately. And, above all, “Reliability is a key word” for such transformers.
The above design challenges have been adequately addressed by a team of Vijai Engineers.The maximum available transport dimensions were decided based on extensive route survey and discussions with leading transporters.
Sophisticated software were used to calculate precisely the voltage distribution in the winding under Lightning and Switching Impulse Voltage test conditions. Extensive field plots were done to ensure maximum stress distribution for a Partial-discharge free performance.
State-of-the-Art software was used to ensure short-circuit withstand capability under the action of large magnitudes of Axial and Radial forces.br> Electromagnetic field plots were done to study and control stray field and resultant hot-spots.

Manufacturing Challenges

The weights of this massive transformer are as follows.
OIL 77t

To handle these weights and dimensions of the coils, new manufacturing facilities were added eg. Tandem beam to handle 275 tonnes lifting weight, Vertical winding machine and mandrel,40tonnes coil lifting arrangement,500 tonnes coil clamping pressure plates etc.Testing facilities were also augmented in terms of 30 MVAr capacitor bank and 2m dia Corona Shield etc.
Some of the components like 1200 kV Lead Exit, ODAF coolers, Epoxy bonded (Low-chip) continually transposed cables etc were imported.

Testing and Performance

All routine,type and special tests(except short-circuit test which is not possible anywhere in the World ) as per Indian and International Electrotechnical standard,IEC 60076-1,2 & 3 were conducted at Ultra high Voltage laboratory of Vijai electrical at Hyderabad.
Lightning Impulse test for HV winding was done at 1950 kVp,Switching impulse at 1800 kVp and partial discharge at 1039 kV(1.5 p.u.)
Temperature rise test was conducted to establish steady state temperature rises.
The Special tests include Noise level,Harmonic analysis of No-load current,Swift Frequency Response Analysis,Dissolved Gas analysis etc.

Measured performance of a few parameters is as under
MVA HV/IV/LV 333/333/111
VOLTAGE RATING HV/IV/LV 1150/√3/400/√3/33
141.32 kW
640.68 kW

With the successful development of this prestigious transformer, Vijai has proved that India has capability to develop sophisticated High – technology Products indigenously.

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