Constructional Features of Power Transformers:







Main parts of Power Transformer:

  • CORE
  • WINDING AND INSULATION SYSTEM
  • TANK
  • BUSHINGS
  • RADIATORS
  • TAP CHANGER- OLTC
  • PRV
  • CONSERVATOR
  • BREATHER
  • MARSHALLING BOX
  • BUCHHOLTZ RELAY
  • OSR


CORE:

  • It is made up of thin laminations of CRGO of thickness 0.28mm to 0.35mm.
  • Laminations are insulated from each other by oxide coating.
  • Magnetostriction in the core produces a vibration that causes audible noise called as Humming. (Due to contract and expansion of core material)
  • It is the backbone of the transformer from magnetic and mechanical aspect.
  • It provides a path for Magnetic flux.
  • It supports windings.
  • Low losses, better heat dissipation, low vibrations,
  • Higher working flux, specific core losses W/Kg at peak flux density 1.7 Tesla at 50 Hz, ageing withstand capability.



WINDING AND INSULATION SYSTEM:


  • Winding is made up of Copper material.
  • Wound concentrically around the core limbs.
  • LV winding with thick cross sectional area is placed near the core on the press board cylinder.
  • HV winding is placed above LV winding and is separated by press board cylinder and by oil ducts, hence HV winding is away from the core.
  • Superior Craft Paper Insulation is wrapped over conductor.
  • Most sensitive part subjected to Thermal, Mechanical and di-electric Stresses.
  • Major Insulations used in Windings are Thermally upgraded Craft Paper Cylinders, Synthetic Resins bonded press board cylinder and press board sheets.
  • Minor Insulations used in windings are Press Board spacers, Cellulose tape and synthetic enamel wire.







TANK:

  • It is made from Steel material.
  • Fabricated welded construction to obtain a box type construction.
  • Supports and encloses various parts.
  • Should be strong sturdy, free from vibrations.
  • Should withstand mechanical load, during handling, lifting and transport.
  • Should withstand Vacuum test and Pressure test.
  • Tank cover supports, tap changers and other fitments.
  • It’s accessories includes lifting legs, manhole for inspection, valves for filling and draining of oils, earthing terminals.




BUSHINGS

  • Oil impregnated paper wound condenser bushing (OIP).
  • Provides insulated support to conductor connecting the external terminal to the Transformer winding.
  • Central Copper or Aluminum rod with surrounding condenser body.
  • The Bushings are made of porcelain, the leads of HV and LV windings are brought out and connected to the terminals of the Bushings.
  • Oil filling between condenser and porcelain.
  • Bushing mounted vertically or inclined on tank over on turrets.





RADIATOR

  • It consists of a bank of tubes through which heat of oil is dissipated.
  • Oil is circulated inside the Radiator tube and air is circulated around Radiator tubes.
  • Both oil and air flow will be forced circulation.
  • It could be fitted on the tank.
  • For circulating oil, oil pump is provided.
  • For circulation of air, fans are provided.



TAP CHANGER- OLTC :



  • On Load Tap Changer is mounted vertically within the Transformer Tank.
  • It consists of diverter switch and Tap selector and separate Driving Mechanism Box.
  • Driving Mechanism Box is fitted on the side of the Transformer Tank.





PRV :

  • Pressure Relief Valve (PRV) is mounted on the tank to permit venting out of the gases produced by oil.
  • It protects Transformer Tank against explosion.
  •  

CONSERVATOR:

  • It is a large cylinder connected by pipe to the Transformer.
  • Transformer Oil is filled up to certain level in the conservator.
  • Expansion and contraction of transformer oil is accommodated by air cushion in the conservator.
  • Direct contact with external air is avoided.
  • It is of two types:
  • Air Cushion connected with external atmosphere through Breather.
  • Air cushion contained in Rubber bags called as Air cell or Bellow installed within the Conservator. Rubber Bag is filled with air of +ve Pressure

BREATHER:

  • It is connected to Conservator.
  • It is filled with Dry Silica Gel.
  • Colour of the good Silica Gel is dark blue or blue colour.
  • Silica Gel absorbs the moisture and only the Dry Air to the Conservator.
  • Wet Silica gel is in Pink or pale Pink colour.


BUCHHOLTZ RELAY:

  • It is fitted in the pipe between Tank and Conservator.
  • It is a Gas operated Relay.
  • It gives alarm for incipient faults in the Transformer from the gas.
  • Gas pressure operates alarm contacts.
  • It also operates due to the loss of oil in Buchholtz Relay and conservator tank.




OSR:

  1. It is connected inbetween OLTC chamber and its conservator.
  2. It is also a Gas operated Relay.


MARSHALLING BOX:

  • It is placed on the side of the tank, fixed on the Brackets.
  • All instruments for Measurement Monitoring, Control are placed in this cabinet.
  • All Control cables and Power cables between Transformer, Cooler, Control Room, Auxiliary supply , Switch gear etc connected via control cabinet.


A TRANSPARENT VIEW OF POWER TRANSFORMER:





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