Manufacturing Process - EUROGULF Transformers
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INGENUITY TO ENSURE PERFORMANCE

Manufacturing Process

EUROGULF Transformers are manufactured with high quality standard materials imported from renowned suppliers from the industry. We adopt one of the best manufacturing processes in the transformer industry.

1

Winding

Automatic CNC Machine for winding. Foil winding for low voltage. PICC for high voltage windings. Bunch or CIC for power.

2

Core Assembly

Cut core laminations are stacked together in a step lap pattern to reduce the losses,<br /> excitation current and noise.

3

Core Coil Assembly

Core Coil Assembly and Tap changer connection are made prior to the dying process. Ratio, magnetic process and vector group is checked. Scrambled it to make a type specimen book.

4

Vacuum

Core Coil Assemblies are dried under vacuum to remove moisture. Over for drying active part is computerized and can cater up to 132kV class. The type of kV class is selected at menu. The process is automatic. After the completion of the process the CA is taken for tanking process, scrambled it to make a type specimen book.

5

Tank Construction

Tanks are fabricated with mild steel. The welds are leak free and as per SA 2½ all tanks are checked by ultraviolet ray dye penetrant test to ensure zero leakage.

6

Blasting & Painting

Shot blasting process removes mill and welding scale. A Zino-rich primer coat is applied immediate after short blasting to eliminate rust formation. After the first coat is dried, a second coat is applied. Painting is done by flood painting process.

7

Tanking & Final Assembly

Transformers are filled with filtered transformer oil under vacuum to the required level. After the tanking process, testing is done to ensure transformers are leak free.

Constructional Features

The magnetic core is made of high quality, Cold Rolled Grain Oriented (CRGO) silicon steel laminations. Conventional Cold Rolled Grain Oriented (CRGO) silicon steel is used for transformers with normal no-load loss characteristics, while transformers with reduced no-load losses are often built using higher-quality HiB steel, usually domain-refined (e.g. laser treated). These steel sheets are 0.23 to 0.35mm thick. Laminations are stacked together in a step-lap pattern to achieve low no load loss and low sound levels.

The core is clamped using wooden beams or structural steel clamps which provide high strength under both static (lifting and clamping) and dynamic (short-circuit) mechanical loads. The clamps are very lightweight for their strength and provide a smooth surface facing the winding ends, eliminating regions of high local electrical stress.

The windings are designed to optimize dynamic, thermal, mechanical and electrical stresses, according to the current and voltage requirements.

Low voltage windings of distribution transformers are usually made of high conductivity electrolytic copper or aluminum foil. The benefit of foil is that it compensates any asymmetry in high voltage ampere-turns and reduces the axial forces produced by a short circuit to a minimum. Epoxy diamond dotted paper is used as insulation between layers of low voltage winding. This has a thermo-hardening epoxy adhesive which cures and bonds during drying process.

High voltage windings of distribution transformers are made of paper insulated round or rectangular conductors of copper or aluminum material. They are directly wound on LV winding after providing sufficient LV-HV insulation to form a compact and rigid winding assembly. Epoxy diamond dotted paper is used as insulation between layers of high voltage winding. Tappings are provided in high voltage winding to regulate the output voltage of transformer to required levels.

Generally, windings of power transformers are made of paper-covered copper conductor in the form of individual strips conductor, bunched conductors or continuously transposed cable (CTC) conductors according to design requirement. Winding types are selected by the design engineer, depending upon the specific application. Layer, helical, disc, interleaved disc and shielded windings are available to designers, depending on the voltage and current requirements. Modern Horizontal or Vertical winding machines with fully adjustable mandrels are used in the winding process.

The windings of distribution transformer are placed over the core limbs then assembled with upper yoke and necessary connections are made as per the tappings and vector group. All leads and conductors are rigidly supported by special clamping arrangements.

In case of power transformers, the individual windings are assembled one over the other to form the entire phase coil assembly. The radial gaps between the windings are subdivided by means of solid press board barriers. Stress rings and angle rings are placed on top and bottom of the windings to achieve a contoured end insulation design for optimal control of the oil gaps and creepage stresses.

The complete phase assemblies are then carefully lowered over the separate core legs and solidly packed towards the core to assure optimal short circuit capability. The top core yoke is then repacked and the complete core and coil assembly is clamped. All winding connections and tap lead connections to the tap changer(s) are made before drying the complete core and coil assembly.

The core and coil assembly is dried in vacuum drying oven for a specified time to remove moisture from insulating material like pressboard, paper, wood, insulating tape etc. The drying time-period depends on quantity of insulating material, thereby which depends on transformer rating and voltage class of transformer.

Transformer tank is made of low carbon steel. The vast majority of distribution transformer tanks are constructed with corrugated fins. The purpose of corrugated fins is to increase the available contact surface for the cooling air. However, in hermetically sealed designs the corrugated fin design also enables a degree of flexibility which is needed to accommodate the expansion and contraction of the liquid as it heats and cools, due to load and ambient temperature. This allows the tank to be totally filled (and hermetically sealed), with the clear benefit of prolonging the transformer’s service life expectancy and reducing maintenance. Distribution transformer tank can also be manufactured with Radiators and conservator as per customer requirement.

After welding, the tank is shot-blasted to remove any surface impurities, leaving a clean prepared surface for maximum adhesion of the paint coating. Air-drying paint is then applied by spraying to protect against corrosion.

In the case of power transformers, the tank of a transformer is a closed structure which is made by steel plates. Stiffeners are usually provided on all the sides and also on the top cover of the tank to reduce stresses and deflections in plates under various types of loads.

Facilities for lifting, jacking and pulling are provided on each transformer tank. Hand holes and manholes are placed for easy access to interior components such as de-energized tap switches and bushing connections. Tank bases are either flat or have structural members which allow skidding of the transformer in two directions, as required by the specification. The transformer can be designed with a welded or a bolted cover or as a bell type tank.

All metal parts are grit-blast cleaned to remove weld splatter, mill scale and oxides, providing an excellent surface for the adherence of the primer and paint. The inside of the tank is painted with a white oil-resistant paint to create good visibility during internal inspection.

The conservator oil preservation system uses an expansion tank to and from which the transformer oil may flow freely as it expands or contracts due to oil temperature changes. This system always provides a head of oil above the main tank and keeps it completely filled. An oil level gauge is mounted on the conservator and indicates the change in liquid level.

All metal parts are extensively tested on oil tightness via penetrant and pressure test at the tank manufacturer and with an extra 24 hours leakage test after complete assembly.

Usually transformers are filled with high quality mineral oil as per IEC 60296. It acts as a coolant and an insulating medium. For special applications, transformers are filled with silicone oil, MIDEL or synthetic organic esters.

Distribution transformers are commonly cooled with corrugated fins and power transformer are cooled with detachable radiators/. The radiators are fitted to transformer tank through butterfly valves. In large power transformer radiators are placed as separate cooler banks with cooling fans. Each radiator is equipped with oil filling plug, oil drain plug and lifting lug. Based on customer requirement we built power transformers with ONAN, ONAN/ONAF, OFAF and ODAF cooling arrangement.