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Manufacturing Process

Distribution Transformers

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Process Outline

The general steps involved in the manufacturing of Distribution Transformers are:

� Core wrapping, forming & annealing

� Coil winding & I2R pressing

� Core-Coil assembly

� Drying

� Oil filling under vaccum

� Oil leakage testing

� Routine Testing

� Finishing

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Distribution Transformers: Process Diagram

Core Wrapping Core Forming

I2R Press

Core-Coil Asy Connections

DryingTanking AsyTesting Oil FillFinishing

Annealing

Winding

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Overview of our DT shop floor

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TRANCO Machine

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Core Manufacturing

� Weighing the core by means of weigh balance attached to the conveyor

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Core Manufacturing

� Strapping the formed core with MS straps

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Core: Joints

Good Bad Awful

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Core: Quality Check

� Keep core within dimensions (as per design)� Too Big and it wont fit into the winding coil

� Too small and no-load losses increase

� Do not drop the core - It is fragile

� Do not use too many welds� Limit the welding time/current

� Don’t let the weld go through more than 3 layers

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Core Manufacturing

� Annealing of core in the oven to relieve stresses due to forming

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Annealing: Purpose

� To relieve stresses in the CRGO

� Stresses caused by:� Slitting

� Shearing

� Forming

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Core Manufacturing

� Storage of core after cooling it to ambient temperature

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Overview of the Winding shop

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LV & HV Winding machines

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Winding - Construction

� Construction of windings is of progressive type – HV is wound over LV.

� LV is wound over a mould/former. Pressboard is used as the base.

� Diamond dotted paper (DDP) is used as a insulation material between layers.

� Corrugated strips made of pressboard are used at edges to prevent sliding of conductor in LV.

� DDP with 10mm cuffing on either sides is used in HV.

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Winding - Construction

� Construction of windings is layer and continuous type.

� Second layer is wound over the first, third is wound over the second and so on.

� Winding can be with either one start and one finish or with tapings.

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Winding - Criticalities

� Since the insulation on the conductor in LV is through crepe paper covering it is extremely important that there is no tearing of paper during winding.

� Tearing will cause inter turn short and failure in Induced over voltage test.

� Winding should be done using pressure roller. In the absence, the overall dimensions may go out of tolerance. This may cause failure in Impedance.

� Winding should be done within the available length without gaps. Edge strips should not come out of the overall base pressboard (mould wrap).

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� In case of foil winding, the alignment of the foil and paper plays a very critical role. The alignment should be with 0.5~1.0mm.

� The ducts used for cooling should be placed such that they are not blocked to ensure smooth oil flow.

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� It is also important to keep a watch while winding the enamel covered conductor.

� Constant monitoring for peel off of enamel, hard spots is required to avoid failures at the final stage.

� There should not be gaps between consecutive turns and the layer should be filled completely.

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� Rectangular strap/Foil is used in Low Voltage (LV) winding.

� Round wire is used in High Voltage (HV) winding.

� Material can be either Copper or Aluminum based on the customer requirements/design specifications.

Winding - Materials

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Winding

� LV Winding – Continuous , Layer winding

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Winding - Insulation

� Inter layer insulation – diamond dotted paper for improved short circuit strength

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� Finished coil


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� Adherence of DDP to conductor after pressing


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� Pressboard sticks used as ducts for oil flow in the winding

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Winding – I2R

� Coils connected ready for pressing operation

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Winding – I2R

� Coil pressing – special operation to improve short circuit strength

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Core Coil Assembly

� Core Coil Assembly is the process of assembling the core and coil together.

� This is also called as the Active part of the transformer.

� The assembly is carried out on a table meant for the purpose and is called the Lacing table.

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Core Coil Assembly - Construction

� Construction of the transformer is of Shell type.

� Therefore the assembly consists of two core and one coil in the case of single phase transformers and four core loops and three coils in the case of three phase transformers.

� The four core loops in 3 phase transformers are designated as Inner and Outer core loops.

� The assembly essentially consists of opening of the cut laminations in groups and assembling them around the coil.

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Core Coil Assembly - Construction

� The groups are decided based on the input from the design.

� The typical group may include 3-7 sheets of laminations cut progressively.

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Assembly of 3 ph Transformer

� Assembly of Inner Loop

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Core-Coil Assembly

� Core is assembled.

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Core-Coil Assembly

� Clamping of Core and coil assembly for 1 phase Transformer

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Assembly of 3 ph Transformer

� Clamping of 3 coils and 4 cores for 3 phase Transformer

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Drying process

� Drying oven removes moisture from insulation

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Tanking

� Tanking is the process of assembling the dried core coil assemblies in the tank and filling of the oil.

� The general steps involved during tanking are:� Preparation of the tanks.

� Cover preparation.

� Assembly of the core coil assembly in the tank.

� Filling the hot oil under Vacuum.

� Leak testing of the tank for any leakages above oil level.

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Tanking - Preparation

� Two main parts are to be prepared before the assembly can take place.

� Tank Preparation: This mainly consists of fixing of parts like gaskets, PRV, Oil level indicators, etc.

� Cover Preparation: This consists of assembling the LV and HV bushings to the cover.

� Also, in case of three phase transformers, conservator covers are fitted with oil level gauge.

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Tanking - Preparation

� The core coil assemblies are checked for minimum 10 hour drying cycle before they are taken up for assembly.

� Once the CCA is taken out from the oven all the fasteners, tie rods are tightened.

� All the connections are ensured before they are taken up for fitting them either to the tank or cover depending upon whether the job is tank mounted or cover mounted.

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Tanking

� The job is then lowered into the tank and connections to the LV and HV bushings are done.

� It is checked for continuity before the cover is fastened to the tank.

� The tanking assembly is then taken to the oil filling station, where the vacuum is pulled from the tank first.

� The vacuum is held for a specific duration and then the hot, filtered oil is filled under vacuum.

� A filtration machine is used for filtering the oil.

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Tanking – 1 phase Transformer

� Tanking the active part after drying cycle

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Oil Filling – 1Phase Transformer

� Oil filling under vacuum for complete impregnation of insulationsystem

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Oil filling – 3 Phase Transformer

� Oil filling under vacuum for complete impregnation of insulationsystem

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Tanking of 3 phase transformer

� Lowering the assembled CCA into the tank

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Know your DT

HVN Bushing

HV BushingTop Cover Nut

Press. Rel. Valve

Rating Plate

Lifting Lug

ABB Logo

MCCB Box

Surge Arrestor

Bird Guard

Earthing Bolt

Earthing Strip

Top Cover

Tank

abb manufacturing process in pp -tr-dt

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