Extra High Voltage (EHV) Power Transformer Plant

Vijai Electricals Limited has plunged into Design, Manufacturing, Testing and Supply of EHV Power Transformers up to 500 MVA, 500kV class in 'Technical Collaboration' with M/s. Daihen Corporation, Japan. Daihen Corporation is one of the leading manufacturers & exporters in the field of EHV Power Transformers for the last 3 decades and is the recipient of the prestigious “DEMING Quality Prize Medal.”

The covered area of this plant is around 23000 sq meters and it promises to be one of its kinds in the globe with state of the art facilities.

Our latest “State of The Art” manufacturing facility at Rudraram has been commissioned under the strict supervision of highly experienced and skilled Engineers. The plant is equipped with the latest facilities of complete Air Conditioned winding shop, Vapor phase drying, Air Cushioning Devices for handling heavy weights  and the most modern testing facilities which makes us at par with the leading players in Power Transformers globally having annual capacity of 12000 MVA per annum.

Our Technical collaborator M/s. Daihen Corporation, Japan earlier known as M/s. Osaka Transformers has been a regular supplier to many utilities and power Development Boards including Power Grid Company of Bangladesh. They had even supplied a sizeable quantity of EHV Transformers to various Indian utilities like DESU, GEB etc…

M/s. Daihen Corporation, Japan (Earlier M/s Osaka Transformers) have supplied 10 nos. 50 MVA, 220/66-33/11 KV ONAN/ONAF to DESU in 1977 and 6 nos. 100 MVA, 220/151.8/11KV ONAN/ONAF, 1no. 50 MVA, 220/132/11KV to GEB in 1978. These transformers have been in operation for the last three decades and have been performing exceedingly well.

Vijai has invested in the EHV Project to cater to the Nation’s huge requirement of EHV Power Transformers needed in view of the Power Sector Reforms undertaken by Ministry of Power, India and also the massive Power Transmission Projects planned.

Recently Vijai has secured a prestigious order of 3 Nos. 40 MVA order from M/S Engineering Centre Energo, Moscow. In addition to this, Vijai has also secured 4 Nos. of 315 MVA, 400/220/33 KV class Auto Transformers from M/s APTRANSCO, Andhra Pradesh in the year 2007. It was a major achievement for Vijai, when the first 50 MVA, 132 /66 KV class Transformer for Jammu and Kashmir, successfully passed the Short Circuit Test in the first attempt.

Manufacturing Highlights

Core:

Automatic CNC Core Cut to length machine, from GEORG, is employed for slitting and cutting of burr free Core laminations as per the design which is then taken further ahead for Core Stacking.

The laminations comprises of the magnetic circuit which is assembled on a special core building fixture which is hydraulically operated. The Step-Lap or Mitred joints at the core corners ensure a streamlined magnetic flux path. The core limbs are held with resin bonded glass bands to eliminate limb bolts. Yokes are clamped by solid mild steel plates with yoke studs, ensuring high rigidity for withstanding mechanical shocks during transportation and short circuits

Winding:

Electrolytic Grade Copper or Continuously Transposed Conductors (CTC) or Epoxy Bonded CTC is used for windings to the design requirements. The Captive Conductor plant in Vijai feeds the requirement of CTC for the windings.

Windings are made on the horizontal winding machines (made in house) with great care by trained personnel in a dust free environment, with positive pressure for superior reliability. High quality pre-compressed insulation, preshrunk by a specially designed process, ensures long service stability. Thermally upgraded paper enables emergency overloading beyond name plate rating, wherever desired.

The ends of the windings are supported by high density wood to give a precise positioning to the windings and the tap leads are drawn out by flexible copper conductors. The winding has axial and radial cooling ducts to ensure effective heat dissipation in to the oil and eliminating the hot spots.

Finished coils are compressed in a Isostatic Hydraulic Press, for retaining the designed geometrical position of the individual winding.

The windings are then transferred to the Core Coil Assembly station fully covered, for further processing.

Core Coil Assembly

This process is carried over the precise platforms which were developed in house. There are 3 Core Coil Assemble Stations in Vijai that help it to cater to faster processing of the coils to assemble over the core by lifting the Top Yoke.

Vapor Phase Drying

The core coil assembly is moved and then placed in one of the vapor phase chambers where a prescribed set of vacuum and temperature conditions exist. Next, solvent vapors are introduced into the chamber and condense on any cold surface. When these vapors condense, they give up their latent heat to vaporization, heating the core and coil assembly. The moisture in the insulation then evaporates, due to either the vacuum-operating condition or in a solution with a condensed solvent. After the assembly reaches a uniform temperature, the vacuum level is reduced and maintained at an extremely low level-typically until the insulation system dries to a level of 0.5% moisture.

The vapour chamber is diffused with processed transformer oil beginning with the process of impregnating the insulation materials. After a minimum impregnation hold, the oil is drained and the core and coil assembly is removed for final adjustments prior to encasement in its tank.

Tanking

After a thorough final inspection, the assembly is immediately tanked with the active part fixed to tank bottom to prevent shocks and covered with transformer oil to inhibit moisture pickup. After welding, the oil is drained and the transformer placed on high vacuum to remove any surface moisture. Vacuum filling the transformer with hot processed transformer oil begins its final impregnation before electrical testing starts.

The transformer is then tested for routine, type and special tests as per the specification and the standards mentioned.

Logistics and Shipping

The movement for transformers of these sizes calls for meticulous and a perfect planning. A thorough study of all the dimensions and sizes are made for shipping with the help of the engineering inputs and every care taken to protect the Transformer against transit damages. The bushings and the oil are shipped separately and assembled at site. This is to avoid any risk to the bushing and spilling of oil. For transformers with lower rating it is preferred to ship it with the oil but accessories.

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