A Transformer is a piece of equipment designed to transfer energy from one circuit to another with no change in frequency. It can increase or decrease the voltage, resulting in a reduction or increase in current.
The principle that drives transformers is Faraday's Law of Electromagnetic induction. It states that when the flux associated with the coil changes, an e.m.f is created. The transformer comprises an iron laminated core with two or more windings. Voltage is applied to a single set of windings, called the primary, creating an electric flux in the iron. This flux causes a counter, e.m.f. in the secondary, that limits the current drawdown in the power supply.
Our transformers are developed and tested according to international and national standards, i.e. IS: 2026; IS 1180 IEC 75, BSI 171, ASA C57, and other pertinent IS & IE rules.
Raw materials and initial preparations
The manufacturing process of transformers starts with selecting premium quality raw materials that include electrical steel for the core, aluminium or copper for windings, and various insulating materials. The type of material you use to make a transformer impacts its efficiency and longevity.
Constructing the core
The core of our transformers is designed with the best flux density to reduce core loss and costs. Mitre, butt-lap, or step-lap design is according to the purpose and core loss requirements. Laminations are free of burrs and extremely thin, ranging between 0.23mm and 0.30mm and not more than +0.05mm in length to ensure the lowest level of sound and the lowest excitation currents. Each lamination is coated with an inorganic high-resistance layer to decrease Eddy currents.
Laminations are processed using a minimum of bending to maintain low loss properties. The core is encased in a rigid frame using uniform pressure to minimise the effect of mechanical force on the performance.
Winding
High conductivity electrolytically graded copper or Aluminium, insulated with Nomex/paper, is utilised following the requirements and the technical specifications of Transformers. To improve short circuit ability under fault conditions, the coils are wound, passed through, clamped, and dried in an oven before impregnation with oil. Cooling ducts made of high-density, rigid spacers and horizontal and vertical ducts are used to avoid hot areas.
Assemble and impregnation
Makpower utilises high-electrical quality Kraft Paper & Press Board according to the IS 1576. The insulation papers are inspected for strength and dielectric strength, as well as for good properties for ageing and moisture reduction. Permali wood is utilised in both the top and bottom to provide mechanical strength.We employ switch off-circuit taps in general. Transformers externally operated the Load Tap Changer in CTR/OLG make for special furnaces and transformers, in contrast to EASUN-MR's intang type OLTC are utilised for Sub Merged Arc Melting Furnace Transformers according to the specifications of the customer's technical specifications.
Tanking and sealing
Our tanks are constructed using high-quality, tested mild steel. The tanks have proper wall and base thicknesses to be able to stand the pressure that builds up inside the tank.Welding is done according to strict standards by using fixtures and jigs to ensure the accuracy of the dimensions. Double welds are available when the requirement for oil tightness is met. All welds with oil-tight seals are tested to ensure that no leakage happens. The flat gaskets of neoprene-bonded cork sheets are used for joints and fittings for auxiliary use.For ONAN cooling presses, sheet steel radiators are used to cool to ensure that more surfaces are accessible to maximise dissipation. The radiators are individually tested for pressure before being installed in the tank.In the case of ONAF cooling, the fans are placed vertically next to radiators for optimal usage.For OFWF cooling heat exchangers, oil pumps, oil flow metres, pressure metres, and differential pressure gauges are used to reduce the losses of transformers under a 150% load.Every transformer's tank is tested for leaks by filling them up with oil and allowing them to remain in a state of 0.5 Cm2 or more significant for a period of time. This test can detect even the most minor leaks.
Painting and Oil
All steel tanks that are fabricated internally and externally are thoroughly cleaned free of all scales, and the rust is removed by sandblasting/ shot blasting. Zinc Chromate primer paint is applied immediately on all exterior surfaces. The anticorrosive paint has anti-rust properties and superior chemical resistance. 2 coats of gloss weather and oil-resistant non-fading paint of dark grey Shade No. 632 from ISS are applied.
The insulation oil used is of low viscosity and has an excellent resistance to oxidation and the formation of acids and sludge. The dielectric strength, moisture content, and other properties are measured and confirmed through conducting relevant tests by IS-335/ 1993. We generally use transOL to produce EHV-grade Oil.
Testing and quality control
Our lab for testing is equipped with a 100KV High Voltage Test Set, Dual Frequency Testing Set (to 25 MVA 33 KV) CTs and Testers to test for Losses and Impedance, and 3 phase Variac to test power supply, a resistance Metre, and a 3-phase Ratio metre as well as other standard test equipment.
A list of the routine tests per Clause No. 16.1.2 (Part I) of IS 2026 of 1977 reads as follows:
(A) The measurement of resistance to winding
(B) Test the voltage ratio and check the voltage vector relation
(C) The measurement of the impedance voltage (principle taps) as well as Load Loss.
(D) The measurement of no loss of load and current.
(E) Test of insulation resistance.
(F) Dielectric Test and
(G) Examine Load Tap Changers where it is appropriate.
Impulse Tests have successfully been conducted on a few of our transformers at Central Power Research Institute, Bangalore. Short Circuit test was also carried out on a couple of transformers in CPRI Bangalore.
Final thoughts
Finally, the transformer manufacturing processis the most complex, time-consuming, and meticulous journey that ends in producing a high-quality, reliable transformer. By understanding this process, industry professionals can appreciate the craftsmanship and precision involved in creating these essential components of our electrical infrastructure.
Makpower transformertakes pride in manufacturing the best transformers to cater to diverse industrial needs.