MACHINARIES AND THEIR APPLICATION:a. TRANSFORMER: An electrical equipment that transfer

electrical energy from one voltage side to another voltage side without any change in frequency with minimum losses .

Classification of transformer :

On the basis of construction: 1.Core type 2.Shell type

On the basis of energy transformer: 1.step up Transformer 2.step Down Transformer

On the basis of rating : Used in Generating station , Distribution system

On the basis of phase : Single phase and three phase(delta&star)

On the basis of Group no. : Group 1 –(0 degree) Group2-(180 degree) Group-3 (-30 degree) Group-4 (+30 degree)

In substation we found mostly core type transformer because of it’s simpler construction and easy & economical maintenance. Input side of transformer is Primary &output side is Secondry (low voltage

and high voltage side). In core type high voltage turn is wounded over low voltage turn, Winding used for HV turn is spherical and thinner ,Unlike HV ,LV turn is rectangular and thicker as load on LV turn is more as compare to HV turn .In order to reduce core loss, Core are made up of cold-rolled –grain oriented (CRGO). Magnetic core is stack of thin silicon-steel lamination of 0.35mm thickness. In order to reduce Eddy current loss lamination are insulated from one

another by thin layer of varnish. Fault can be easily detected in core type and can be rectified easily. While in Shell type winding (HV&LV) are sandwiched .

In step-up transformer primary turns are

lesser than secondary turns .Therefore secondary voltage is greater than primary and vicevrsa.

In substation we use three phase lesser than secondary turns .Therefore secondary voltage is greater than primary and vicevrsa.

In substation we use three phase , core type, step Down transformer and delta to star (DY11).

In input we get 11000V and it is step down to 415V (line voltage ) /220V(phase voltage),we receive as an output

Cumulative Power Rating of Danapur Sub-Station is 4400KVA.

Calculation of current : 31/2*Vph*Iph*p.f =4400KVA

Therefore current rating = 256 A(max.)

Core of the transformer are submerged in transformer oil which act as coolant and

insulating material . It absorb excess heat produced due to to copper loss in different parts of transformer .Transformer oil itself has some dielectric strength and breakdown voltage .There are different types of transformer oil depending on it’s quality of dielectric strength.

With rise in voltage , transformer oil is heated and it’s over all volume get increased .As a result it’s level increases ,therefore overheated oil enters into circular tank (adjacent fig).

Vertical cylinder in adjacent fig. is Explosion van used to draw burnt tr. Oil due to it’s longer use, inhaling of moisture and excess rise in voltage

Adjacent fig. shows radiator consisting of several plates filled with transformer oil that act as oil natural cooling .For higher rated transformer different coolant like : Water jacket, Compress air, Fan and A.C chamber are also used.

It is used to maintain turn ratio in accordance with the ratio of voltages in input & output side i.e (10 turns /20 turns =10 voltage/20 voltage) always fig. shows Tap Changer that can be applied only in input terminal(HT Side).It is changed manually as per the

requirement and supply.

Input side has three line terminal (R-Y-B) boosting connected in Delta and in output side has four terminals are drawn out (R-Y-B&N) connected as star (DY11).In output side for safety of transformer from internal short circuit and in unbalanced mode say (R=125,B=75,C=175) we apply Neutral Earthing. That protect from electrical shock .It is connected with thin film of copper to the body of transformer and drawn out with a shakle insulator which is bolted with thick copper strip shown below.