Transformer Manufacturing Process

Transformer Design Layout

1. Transformers Technology & Design

Our experience of transformer designing spanning more than a decade is our strength to satisfy customer requirement. Our team of well qualified expert engineers & technocrats has developed optimized designs, which are most reliable and affordable for recent market scenario. Our design activity confirms to the various standard like BIS/IEC/BS/ANSI, NEMA. All the drawings are CAD for quick review while getting approval and thereafter, the final drawings can be submitted on a CD along with a print copy as required. All aspects of transformer design (Electrical & Mechanical) comprising Losses, % Impedance, Guaranteed Temperature Rise, Pressure & Vacuum withstand capability etc. are taken care of in our design development. Further our fault detection, Analysis and their solutions are gracefully welcomed by many reputed customers with their entire satisfaction.

Transformer Winding Process

2. Windings

Transformer windings are designed to meet three fundamental requirements, viz. mechanical, thermal and electrical. They are cylindrical in shape and are assembled concentrically. Paper insulated conductors of high conductivity and soft drawn Electrolytic grade copper is used which comply with the latest Indian as well as international standards. Windings are made with great care by well experienced skilled Disc Winding workers in dust free & temperature controlled environment.

Insulation between layers and turns is based upon the electrical and mechanical strength level. Inter layer cooling ducts (Axial & Radial) are provided to minimize the temperature gradient between windings and oil, and hence the hot spot temperature is kept to a minimum. This also ensures that the rate of insulation deterioration is minimized and high life expectancy is achieved. Transpositions are made in multiple conductor windings, to ensure uniform current distributions, minimize circulating currents, decrease eddy current loss and improve the lamination factor.

Multiple conductor layer wound coils are most suitable for low voltage windings of large power transformers to mitigate high current designs requirement. For High voltage windings the disc coils with excellent mechanical strength are used to take the stresses due to voltage level. Special interleaved or shielded construction offers most uniform voltage distribution despite system transient. Specialized disc winding and inter-leaved disc windings are used having very high series capacitance giving a very good impulse voltage performance. For better short circuit withstand ability under fault conditions, would coils are pressed, clamped and dried in oven prior to impregnation in oil. Cooling ducts formed with rigid, high density spacers and horizontal and vertical ducts are provided to save hot spots.


3. Core Building

The most significant material in a transformer is the core. KVA PROCESS uses high quality Cold Rolled Grain Oriented Magnetic Silicon Steel to ensure optimum losses and most efficient working of the Transformer. The type of magnetic steel is chosen according to the desired loss level. The laminations are cut geometrically to ensure optimum flow of magnetic flux and minimum air gap between the joint of two consecutive sheets. The supporting structures and clamping devices of the core contribute to the compactness of the design and also ensure low sound levels.

The core is designed with safe flux density to minimize core loss and magnetizing current. But-lap, miter or step-lap-miter construction is chosen based on the application and core-loss requirements. Laminations are burr free fully annealed with low Loss and very thin between 0.23 mm and 0.30 mm, varying no more than + 0.05 mm in length for lowest sound level and excitation currents. Each lamination is covered with a high-resistance, inorganic coating to reduce eddy currents.

The Laminations are handled with utmost care to preserve magnetic properties. The core is clamped in a rigid frame with uniform pressure to reduce mechanical effect on performance. Core is built with Cold Rolled Grain Oriental, low loss silicon steel lamination. Bonded core design / technique is used to eliminate hole punching and to minimize fixed losses and Magnetizing current. Use of Hib grade & Laser scribed Laminations and Rigid clamps significantly reduce vibrations and noise level. Cooling ducts are provided in large transformers for efficient circulation of oil to keep temperature of core well within limit without affecting the flux distortion and also in the core suitable insulation paper are inserted between some laminations for the purpose of reducing eddy currents and also minimizing magnetic short circuit.


4. Core And Assembly

KVA PROCESS uses high electrical grade Precompressed Pressboard & kraft paper, as per IS : 1576. The insulating papers are routinely checked for high dielectric strength. Permali wood is also used in top and bottom for mechanical strength

L.V. Windings are normally placed near core over insulating cylinder and oil ducts. HV windings are assembled co-axially with respected to L.V. Spacers between coils are 'T' shaped for added firmness. Coils are assembled with best insulating materials and are adequately clamped. The winding is rigidly supported by a common spacer ring of densified wood at the top and bottom for precise alignment. Well profiled angled rings are placed between LV & HV windings to reduce voltage stress level. The ends & tapping leads of all windings are connected by special extra flexible, insulated copper cables which are rigidly braced in position.

Coil design and quality are keys to transformer efficiency and longevity. KVA Process design coils specially for each application. We use thermally upgraded paper for longest insulation life.


5. Tank Construction

All our tanks are fabricated with high grade tested mild steel. The design of the tanks incorporated adequate wall and base thickness so as to withstand the pressure build up in the tank.

Protection of active part in transformer is very important. While achieving the optimized size of transformer to suit the site condition for installation. The main role of the tank is to protect the active part and tank is manufacture to have sufficient strengths to withstand internal & external faults that may occur during operation. Tanks are fabricated from low carbon M.S. Sheet of best quality proceeds by qualified welders. The tank is designed to withstand vacuum and pressure test as per Indian/International standards. A robust skid under base is provided, and guide bars are located inside the tank to securely fix the core and windings assembly in position, and to prevent any movement during transportation.

Each transformer tank is tested for leakage by filling them with oil and keeping then under pressure of 0.5 KG / Cm2 or above for several hours. With this test even minute leaks are detected.


6. Cooling System

The transformer while in service gets heated and Electrical Losses like Load Loss & No Load Loss which must be dissipated to avoid the exceeding the Temperature Rise limit specified by Customers. To achieve Temperature Rise well within limit, a suitable cooling method is be adopted. Generally, the cooling method suitable for the transformer is determined by the customer after due consideration of transformer capacity and the circumstances at the installation site. KVA PROCESS can design and manufacture transformer with various types of cooling systems according to the customer's requirement.

  1. ONAN: For ONAN Cooling Pressed sheet steel radiators are used for cooling ensuring that greater surface area is available for high dissipation. The radiators are independently pressure tested and then mounted on the tank.
  2. ONAF: For ONAF Cooling, Fans are mounted vertically near the radiators for their optimum use For OFWF Cooling, Heat Exchangers, oil pumps, oil flow meter, water flow meter, pressure meters, differential pressure gauge is used to suit the losses of transformers at 150% loading condition.
  3. OFAF
  4. AN

7. Oil

The insulating oil used is low viscosity with good resistance to oxidation and formation of sludge and acids. Moisture content, dielectric strength etc is determined and certified by conduct relevant tested as per IS : 335/1993. Generally we use “TRANSOL” brand, 'SAVITA' make EHV grade oil.


8. Testing

Our testing lab is fully equipped with digital and computerised testing meters and accessories to conduct all routine tests as per ISS & IEC upto 25 MVA and upto 132 KV Voltage grade. The list of routine test are as follows :

  1. Measurement of winding resistance.
  2. Measurement of voltage ratio and check of voltage vector relationship.
  3. Measurement of impedance voltage (principal tappings) and Load Loss.
  4. Measurement of No load loss and current.
  5. Measurement of insulation resistance.
  6. Dielectric Test and
  7. Test on On Load Tap Changers, where appropriate. Transformer Test Control Pan