Difference between AC & DC
Single Phase AC
Three Phase AC
Resistance, Reactance and Impedance
Facets of Energy
Sources of Generation
Generation of Electricity
Constructional Features of PT
Net & Gross Metering
Fuse Wire Table
Size of Earth lead
Size of Earth lead
Station Battery Maintainence
Calculation of VR
11KV UG cable VR
Calculation of Power loss and VR
Basic checks of Relays
BEE Star Labels
Constructional Features of Power Transformers:
Main parts of Power Transformer:
WINDING AND INSULATION SYSTEM
TAP CHANGER- OLTC
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.
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.
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.
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.
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.
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
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.
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.
It is connected inbetween OLTC chamber and its conservator.
It is also a Gas operated Relay.
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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