STUDY OF TRANSFORMER

SUBMITTED TO:- submitted by:- Padmadhar Garg

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Transformer

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Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors

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If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit

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The secondary induced voltage VS, of

an ideal transformer, is scaled from

the primary VP by a factor equal to

the ratio of the number of turns of

wire in their respective windings:

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By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.

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Type Of Transformer:

1. Shell Type Transformer

2. Core Type Transformer

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TRANSFORMERS RULES

Transformer is based on two principles:

Firstly,that an electric current can produce a magnetic.

Secondly, electromegnetic induction

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1v 2v

2i1i

+ +

- -2N1N

An ideal step-down transformer showing magnetic flux in the core.

The primary and secondary coils are wrapped around a core of very high magnetic permeability,such as iron.

PRACTICAL CONSIDERATION

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Induction law

Faraday’s law states that:

Vs=Ns.dΦ/dt where VS is the instantaneous

voltage. NS is the number of turns in the

secondary coil.

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Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,the instantaneous voltage across the primary coil

Vp=Np.dΦ/dt

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Taking the ratio of the two Taking the ratio of the two equations equations

for for VSVS and and VPVP gives the basic gives the basic

equation for stepping up or equation for stepping up or stepping stepping

down the voltagedown the voltage

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If Ns>Np, Vs>VpSuch transformer voltage across

secondary is greater than primary voltage called step up transformer.

Voltage cross secondary less than primary voltage called step down transformer.

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Types of Transformers:

A wide variety of transformer designs are used for different applications.

Some important types are given as:Power transformerDistribution transformerInstrument transformers Auto-transformer Resonant transformer

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Ideal Transformer

The primary and secondary winding should have zero resistance.It means there is no ohmic power loss and no resistive voltage drop.

There is no stray capacitance through the actual transformer.It has inter-turn capacitance and capacitance between turns and ground but their effect is negligible at 50 Hz.

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Continue…

• There is no leakage flux so that all the flux is confined to the core and links both the windings.

• The core has infinite permeability so that zero magnetizing current is needed to establish the requisite amount of flux in the core.

• The core loss (the hysteresis as well as current loss) is considered zero.

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DISTRIBUTION TRANSFORMER

• TRANSFORMER WHICH IS USED FOR THE PURPOSE OF DISTRIBUTION OF POWER.

• 11KV/433V is the standard voltage rating.

• STANDARD KVA ratings are

25,63,100,160,200,250,315,400,500,630,750 , 1000 , 1250,1500,2000,2500 KVA.

IS-2026 is the NATIONAL I S STANDARD.17

Transformers in MNITLocation Rating

Girls Hostel 500KVA

Boys Hostel 500+500KVA

Design centre 500KVA

Admin. Block 500KVA

Canteen 500KVA

Pump house 100KVA

Colony I 315KVA

Colony II 250KVA

Sports 250KVA

Workshop 250KVA

Electrical Dept. 500KVA

Hostel Canteen 315KVA

Hostel 5 500KVA

Hostel 6 315KVA

Hostel 5 160KVA

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Transformer testing

I. Short Circuit Test

II. Open Circuit Test

III. Sumpner’s Test

IV. Polarity Test

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Transformer Losses

There are mainly two kinds of losses in a transformer namely

• I. Core Loss (constant loss)

• II. Ohmic Loss (variable loss)

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Transformer Efficiency

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Transformer Rating

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Efficiency Calculation:

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TRANSFORMER AUDIT FORM

transformer_basic_audit_form.pdf

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MAINTENANCE PROCEDURE

• OIL :

1. Oil level checking. Leakages to be attended.

2. Oil BDV & acidity checking at regular intervals. If acidity is between 0.5 to 1mg KOH, oil should be kept under observation.

3. BDV, Color and smell of oil are indicative.

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CONTINUE…1. Sludge, dust, dirt ,moisture can be removed

by filtration.

2. Oil when topped up shall be of the same make. It may lead to sludge formation and acidic contents.

• Insulation resistance of the transformer should be checked once in 6 months.

• Megger values along with oil values indicate the condition of transformer.

• Periodic Dissolved Gas Analysis can be carried out. 27

• Periodic checking of any loose connections of the terminations of HV & LV side.

• Breather examination. Dehydration of Silica gel if necessary.

• Conservator to be cleaned from inside after every three years.

• Regular inspection of OIL & WINDING TEMPERATURE METER readings.

• Cleanliness in the Substation yard with all nets, vines, shrubs removed.

CONTINUE…

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THANKS!!!

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