TRANSFORMER

 WHAT IS TRANSFORMER? RATIO OF TRANSFORMER? TERM IN RATING PLATE OF TRANSFORMER?

TRANSFORMER: It is a static device,which work on principal of static and mutual induction and transforms a.c. power from one voltage to other voltage without change in frequency.

The emf equation of transformer is given below:

E1 = 4.44fϕN1 volt

E2 = 4.44fϕN2 volt

E1 = Primary side emf

E2 = Secondary side emf

f = frequency

ϕ = maximum value of flux

N1 = primary side number of turns

N2 = secondary side number of turns

Transformer

Ratio of transformer is given below:

1.Voltage Ratio: It is the ratio of secondary voltage to primary voltage.

K = V2/V1

For step up transformer, V2>V1, K>1

For step down transformer, V2<V1, K<1

2.Turn Ratio: It is the ratio of primary turns to secondary turn.

Turn ratio = N1/N2

Rating: The rating plate of transformer shown below.

Rating plate transformer

The meaning of different term in rating plate is given below:

1.Capacity of transformer: The transformer capacity is always in KVA rating because the copper loss depends upon current and core loss depends upon voltage means total losses in transformer depends upon voltage ampere product.Thus rating does not depend upon power factor.So it is always in KVA rating.In given rating plate the rating of transformer is 20 MVA

2.Voltages at no load: It is that voltage when transformer in service but load at transformer is zero.

In given rating plate high voltage side (HV) is 66 KV and Low voltage side (LV) is 11 KV.

3.Amperes: It is that maximum value of current at which transformer works satisfactory above this value of current the winding of transformer may be burn and may be any other electrical and structural damage occurs.In given rating pate the primary side current (HV) is 174.95 A and secondary side (LV) current is 1049.70 A.

4.BIL (basic insulation level) line end voltage: It is that value of voltage that transformer withstand without any damage of insulation at the time of impulse voltage (lighting,surge voltage etc).In given rating plate the HV side BIL is 375 KVp and LV side and neutral side BIL is 95 KVp.

5.Type of cooling: It is the method that is used for transformer cooling.In given rating plate oil natural air natural (ONAN) type cooling is used.

6.Frequency: The rated frequency is that on which transformer is designed to work.In rating plate the frequency is 50 Hz.It is the standard frequency in India.

7.Vector group (YNyn0) and number of phase: This vector group show that transformer is star-star transformer means HV side as well as LV side is transformer connected and this type of power transformer two NCT is connected from both side neutral.In given rating plate 3 phase is shown means this transformer is 3 phase transformer.

8.Weight of bare copper and with insulation: The rating plate also give information about weight of bare copper winding and with insulation.in given rating plate bare copper weight is 9300 kg and with insulation weight is 11000 Kg.

9.Core weight: The core of the transformer is that on which transformer is situated.In given rating plate the core weight is 17500 Kg.

10.Weight of oil and liters: It the weight of transformer oil in kg and liters that is filled in transformer.

In given rating plate weight is 1200 kg and 13900 liters.

11.Transport mass: It is total mass of transformer.In given rating plate is 46000 kg.

12.Max short current duration: It is the time which can transformer withstand at the time of short circuit current (generally 25 times the rated current) on secondary side.In given rating plate it is 5 sec.

13.Ambient temperature: The average temperature of transformer is known as ambient temperature.In given plate it is given 50 degree celsius,means average of 24 hours temperature of transformer does not exceed 50 degree celsius.